diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 0000000..b687be7
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,120 @@
+linters:
+  disable-all: true
+  enable:
+    # Re-enable the default linters
+    - errcheck
+    - gosimple
+    - govet
+    - ineffassign
+    - staticcheck
+    - typecheck
+    - unused
+
+    # Enable the "always useful" linters as of 1.53.3
+    - asasalint
+    - asciicheck
+    - bidichk
+    - decorder
+    - dogsled
+    - dupl
+    - dupword
+    - errchkjson
+    - errname
+    - errorlint
+    - exhaustive
+    - exportloopref
+    - forbidigo
+    - forcetypeassert
+    - gci
+    - gocheckcompilerdirectives
+    - gochecknoinits
+    - goconst
+    - gocritic
+    - godot
+    - godox
+    - gofumpt
+    - gomoddirectives
+    - goprintffuncname
+    - gosec
+    - gosmopolitan
+    - importas
+    - interfacebloat
+    - makezero
+    - mirror
+    - misspell
+    - musttag
+    - nakedret
+    - nestif
+    - nilerr
+    - nilnil
+    - nolintlint
+    - nonamedreturns
+    - prealloc
+    - predeclared
+    - reassign
+    - revive
+    - tagalign
+    - tenv
+    - testableexamples
+    - unconvert
+    - unparam
+    - usestdlibvars
+    - wastedassign
+    - whitespace
+
+    # Disabled: Run periodically, but too many places to annotate
+    # - gomnd
+
+    # Disabled: Not how I do things
+    # - exhaustruct      # Zero value is fine.
+    # - funlen           # I'm not breaking up my math.
+    # - gochecknoglobals # How else am I supposed to declare constants.
+    # - lll              # The 70s called and wants their ttys back.
+    # - paralleltest
+    # - varnamelen       # The papers use short variable names.
+    # - tagliatelle      # I want my tags to match the files.
+    # - thelper
+    # - tparallel
+    # - testpackage
+    # - wsl              # Nice idea, not how I like to write code.
+    # - goerr113         # Nice idea, this package has too much legacy bs.
+    # - ireturn          # By virtue of the PT API we are interface heavy.
+
+    # Disabled: Annoying/Useless
+    # - cyclop
+    # - gocognit
+    # - gocyclo
+    # - maintidx
+    # - wrapcheck
+
+    # Disabled: Irrelevant/redundant
+    # - bodyclose
+    # - containedctx
+    # - contextcheck
+    # - depguard
+    # - durationcheck
+    # - execinquery
+    # - ginkgolinter
+    # - gofmt
+    # - goheader
+    # - goimports
+    # - gomodguard
+    # - grouper
+    # - loggercheck
+    # - nlreturn
+    # - noctx
+    # - nosprintfhostport
+    # - promlinter
+    # - rowserrcheck
+    # - sqlclosecheck
+    # - stylecheck
+    # - zerologlint
+
+linters-settings:
+  gci:
+    sections:
+      - standard
+      - default
+      - prefix(gitlab.com/yawning/obfs4.git)
+    skip-generated: true
+    custom-order: true
diff --git a/common/csrand/csrand.go b/common/csrand/csrand.go
index ddf14e8..e22c184 100644
--- a/common/csrand/csrand.go
+++ b/common/csrand/csrand.go
@@ -45,7 +45,7 @@ var (
 	csRandSourceInstance csRandSource
 
 	// Rand is a math/rand instance backed by crypto/rand CSPRNG.
-	Rand = rand.New(csRandSourceInstance)
+	Rand = rand.New(csRandSourceInstance) //nolint:gosec
 )
 
 type csRandSource struct {
@@ -63,7 +63,7 @@ func (r csRandSource) Int63() int64 {
 	return int64(val)
 }
 
-func (r csRandSource) Seed(seed int64) {
+func (r csRandSource) Seed(_ int64) {
 	// No-op.
 }
 
diff --git a/common/drbg/hash_drbg.go b/common/drbg/hash_drbg.go
index 5a9cc7f..543345e 100644
--- a/common/drbg/hash_drbg.go
+++ b/common/drbg/hash_drbg.go
@@ -30,12 +30,14 @@
 package drbg // import "gitlab.com/yawning/obfs4.git/common/drbg"
 
 import (
+	"bytes"
 	"encoding/binary"
 	"encoding/hex"
 	"fmt"
 	"hash"
 
 	"github.com/dchest/siphash"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 )
 
@@ -60,33 +62,33 @@ func (seed *Seed) Hex() string {
 }
 
 // NewSeed returns a Seed initialized with the runtime CSPRNG.
-func NewSeed() (seed *Seed, err error) {
-	seed = new(Seed)
-	if err = csrand.Bytes(seed.Bytes()[:]); err != nil {
+func NewSeed() (*Seed, error) {
+	seed := new(Seed)
+	if err := csrand.Bytes(seed.Bytes()[:]); err != nil {
 		return nil, err
 	}
 
-	return
+	return seed, nil
 }
 
 // SeedFromBytes creates a Seed from the raw bytes, truncating to SeedLength as
 // appropriate.
-func SeedFromBytes(src []byte) (seed *Seed, err error) {
+func SeedFromBytes(src []byte) (*Seed, error) {
 	if len(src) < SeedLength {
 		return nil, InvalidSeedLengthError(len(src))
 	}
 
-	seed = new(Seed)
+	seed := new(Seed)
 	copy(seed.Bytes()[:], src)
 
-	return
+	return seed, nil
 }
 
 // SeedFromHex creates a Seed from the hexdecimal representation, truncating to
 // SeedLength as appropriate.
-func SeedFromHex(encoded string) (seed *Seed, err error) {
-	var raw []byte
-	if raw, err = hex.DecodeString(encoded); err != nil {
+func SeedFromHex(encoded string) (*Seed, error) {
+	raw, err := hex.DecodeString(encoded)
+	if err != nil {
 		return nil, err
 	}
 
@@ -133,7 +135,7 @@ func (drbg *HashDrbg) Int63() int64 {
 }
 
 // Seed does nothing, call NewHashDrbg if you want to reseed.
-func (drbg *HashDrbg) Seed(seed int64) {
+func (drbg *HashDrbg) Seed(_ int64) {
 	// No-op.
 }
 
@@ -142,7 +144,5 @@ func (drbg *HashDrbg) NextBlock() []byte {
 	_, _ = drbg.sip.Write(drbg.ofb[:])
 	copy(drbg.ofb[:], drbg.sip.Sum(nil))
 
-	ret := make([]byte, Size)
-	copy(ret, drbg.ofb[:])
-	return ret
+	return bytes.Clone(drbg.ofb[:])
 }
diff --git a/common/log/log.go b/common/log/log.go
index 5e08c64..b8a5eaa 100644
--- a/common/log/log.go
+++ b/common/log/log.go
@@ -30,8 +30,9 @@
 package log // import "gitlab.com/yawning/obfs4.git/common/log"
 
 import (
+	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"net"
 	"os"
@@ -54,20 +55,22 @@ const (
 	LevelDebug
 )
 
-var logLevel = LevelInfo
-var enableLogging bool
-var unsafeLogging bool
+var (
+	logLevel      = LevelInfo
+	enableLogging bool
+	unsafeLogging bool
+)
 
 // Init initializes logging with the given path, and log safety options.
 func Init(enable bool, logFilePath string, unsafe bool) error {
 	if enable {
-		f, err := os.OpenFile(logFilePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)
+		f, err := os.OpenFile(logFilePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o600)
 		if err != nil {
 			return err
 		}
 		log.SetOutput(f)
 	} else {
-		log.SetOutput(ioutil.Discard)
+		log.SetOutput(io.Discard)
 	}
 	enableLogging = enable
 	unsafeLogging = unsafe
@@ -163,8 +166,8 @@ func ElideError(err error) string {
 
 	// If err is not a net.Error, just return the string representation,
 	// presumably transport authors know what they are doing.
-	netErr, ok := err.(net.Error)
-	if !ok {
+	var netErr net.Error
+	if !errors.As(err, &netErr) {
 		return err.Error()
 	}
 
diff --git a/common/ntor/ntor.go b/common/ntor/ntor.go
index 17a9ff7..346507a 100644
--- a/common/ntor/ntor.go
+++ b/common/ntor/ntor.go
@@ -70,15 +70,17 @@ const (
 	// KeySeedLength is the length of the derived KEY_SEED.
 	KeySeedLength = sha256.Size
 
-	// AuthLength is the lenght of the derived AUTH.
+	// AuthLength is the length of the derived AUTH.
 	AuthLength = sha256.Size
 )
 
-var protoID = []byte("ntor-curve25519-sha256-1")
-var tMac = append(protoID, []byte(":mac")...)
-var tKey = append(protoID, []byte(":key_extract")...)
-var tVerify = append(protoID, []byte(":key_verify")...)
-var mExpand = append(protoID, []byte(":key_expand")...)
+var (
+	protoID = []byte("ntor-curve25519-sha256-1")
+	tMac    = append(protoID, []byte(":mac")...)
+	tKey    = append(protoID, []byte(":key_extract")...)
+	tVerify = append(protoID, []byte(":key_verify")...)
+	mExpand = append(protoID, []byte(":key_expand")...)
+)
 
 // PublicKeyLengthError is the error returned when the public key being
 // imported is an invalid length.
@@ -320,48 +322,43 @@ func KeypairFromHex(encoded string) (*Keypair, error) {
 
 // ServerHandshake does the server side of a ntor handshake and returns status,
 // KEY_SEED, and AUTH.  If status is not true, the handshake MUST be aborted.
-func ServerHandshake(clientPublic *PublicKey, serverKeypair *Keypair, idKeypair *Keypair, id *NodeID) (ok bool, keySeed *KeySeed, auth *Auth) {
+func ServerHandshake(clientPublic *PublicKey, serverKeypair *Keypair, idKeypair *Keypair, id *NodeID) (bool, *KeySeed, *Auth) {
 	var notOk int
 	var secretInput bytes.Buffer
 
 	// Server side uses EXP(X,y) | EXP(X,b)
 	var exp [SharedSecretLength]byte
-	curve25519.ScalarMult(&exp, serverKeypair.private.Bytes(),
-		clientPublic.Bytes())
+	curve25519.ScalarMult(&exp, serverKeypair.private.Bytes(), clientPublic.Bytes()) //nolint:staticcheck
 	notOk |= constantTimeIsZero(exp[:])
 	secretInput.Write(exp[:])
 
-	curve25519.ScalarMult(&exp, idKeypair.private.Bytes(),
-		clientPublic.Bytes())
+	curve25519.ScalarMult(&exp, idKeypair.private.Bytes(), clientPublic.Bytes()) //nolint:staticcheck
 	notOk |= constantTimeIsZero(exp[:])
 	secretInput.Write(exp[:])
 
-	keySeed, auth = ntorCommon(secretInput, id, idKeypair.public,
+	keySeed, auth := ntorCommon(secretInput, id, idKeypair.public,
 		clientPublic, serverKeypair.public)
 	return notOk == 0, keySeed, auth
 }
 
 // ClientHandshake does the client side of a ntor handshake and returnes
 // status, KEY_SEED, and AUTH.  If status is not true or AUTH does not match
-// the value recieved from the server, the handshake MUST be aborted.
-func ClientHandshake(clientKeypair *Keypair, serverPublic *PublicKey, idPublic *PublicKey, id *NodeID) (ok bool, keySeed *KeySeed, auth *Auth) {
+// the value received from the server, the handshake MUST be aborted.
+func ClientHandshake(clientKeypair *Keypair, serverPublic *PublicKey, idPublic *PublicKey, id *NodeID) (bool, *KeySeed, *Auth) {
 	var notOk int
 	var secretInput bytes.Buffer
 
 	// Client side uses EXP(Y,x) | EXP(B,x)
 	var exp [SharedSecretLength]byte
-	curve25519.ScalarMult(&exp, clientKeypair.private.Bytes(),
-		serverPublic.Bytes())
+	curve25519.ScalarMult(&exp, clientKeypair.private.Bytes(), serverPublic.Bytes()) //nolint:staticcheck
 	notOk |= constantTimeIsZero(exp[:])
 	secretInput.Write(exp[:])
 
-	curve25519.ScalarMult(&exp, clientKeypair.private.Bytes(),
-		idPublic.Bytes())
+	curve25519.ScalarMult(&exp, clientKeypair.private.Bytes(), idPublic.Bytes()) //nolint:staticcheck
 	notOk |= constantTimeIsZero(exp[:])
 	secretInput.Write(exp[:])
 
-	keySeed, auth = ntorCommon(secretInput, id, idPublic,
-		clientKeypair.public, serverPublic)
+	keySeed, auth := ntorCommon(secretInput, id, idPublic, clientKeypair.public, serverPublic)
 	return notOk == 0, keySeed, auth
 }
 
@@ -402,7 +399,7 @@ func ntorCommon(secretInput bytes.Buffer, id *NodeID, b *PublicKey, x *PublicKey
 	// auth_input = verify | ID | B | Y | X | PROTOID | "Server"
 	authInput := bytes.NewBuffer(verify)
 	_, _ = authInput.Write(suffix.Bytes())
-	_, _ = authInput.Write([]byte("Server"))
+	_, _ = authInput.WriteString("Server")
 	h = hmac.New(sha256.New, tMac)
 	_, _ = h.Write(authInput.Bytes())
 	tmp = h.Sum(nil)
diff --git a/common/probdist/weighted_dist.go b/common/probdist/weighted_dist.go
index d0d380c..72f1e22 100644
--- a/common/probdist/weighted_dist.go
+++ b/common/probdist/weighted_dist.go
@@ -64,8 +64,8 @@ type WeightedDist struct {
 // based on a HashDrbg initialized with seed.  Optionally, bias the weight
 // generation to match the ScrambleSuit non-uniform distribution from
 // obfsproxy.
-func New(seed *drbg.Seed, min, max int, biased bool) (w *WeightedDist) {
-	w = &WeightedDist{minValue: min, maxValue: max, biased: biased}
+func New(seed *drbg.Seed, min, max int, biased bool) *WeightedDist {
+	w := &WeightedDist{minValue: min, maxValue: max, biased: biased}
 
 	if max <= min {
 		panic(fmt.Sprintf("wDist.Reset(): min >= max (%d, %d)", min, max))
@@ -73,7 +73,7 @@ func New(seed *drbg.Seed, min, max int, biased bool) (w *WeightedDist) {
 
 	w.Reset(seed)
 
-	return
+	return w
 }
 
 // genValues creates a slice containing a random number of random values
@@ -132,7 +132,7 @@ func (w *WeightedDist) genTables() {
 	scaled := make([]float64, n)
 	for i, weight := range w.weights {
 		// Multiply each probability by $n$.
-		p_i := weight * float64(n) / sum
+		p_i := weight * float64(n) / sum //nolint:revive
 		scaled[i] = p_i
 
 		// For each scaled probability $p_i$:
@@ -148,9 +148,9 @@ func (w *WeightedDist) genTables() {
 	// While $Small$ and $Large$ are not empty: ($Large$ might be emptied first)
 	for small.Len() > 0 && large.Len() > 0 {
 		// Remove the first element from $Small$; call it $l$.
-		l := small.Remove(small.Front()).(int)
+		l, _ := small.Remove(small.Front()).(int)
 		// Remove the first element from $Large$; call it $g$.
-		g := large.Remove(large.Front()).(int)
+		g, _ := large.Remove(large.Front()).(int)
 
 		// Set $Prob[l] = p_l$.
 		prob[l] = scaled[l]
@@ -172,7 +172,7 @@ func (w *WeightedDist) genTables() {
 	// While $Large$ is not empty:
 	for large.Len() > 0 {
 		// Remove the first element from $Large$; call it $g$.
-		g := large.Remove(large.Front()).(int)
+		g, _ := large.Remove(large.Front()).(int)
 		// Set $Prob[g] = 1$.
 		prob[g] = 1.0
 	}
@@ -180,7 +180,7 @@ func (w *WeightedDist) genTables() {
 	// While $Small$ is not empty: This is only possible due to numerical instability.
 	for small.Len() > 0 {
 		// Remove the first element from $Small$; call it $l$.
-		l := small.Remove(small.Front()).(int)
+		l, _ := small.Remove(small.Front()).(int)
 		// Set $Prob[l] = 1$.
 		prob[l] = 1.0
 	}
@@ -194,7 +194,7 @@ func (w *WeightedDist) genTables() {
 func (w *WeightedDist) Reset(seed *drbg.Seed) {
 	// Initialize the deterministic random number generator.
 	drbg, _ := drbg.NewHashDrbg(seed)
-	rng := rand.New(drbg)
+	rng := rand.New(drbg) //nolint:gosec
 
 	w.Lock()
 	defer w.Unlock()
diff --git a/common/probdist/weighted_dist_test.go b/common/probdist/weighted_dist_test.go
index 4619212..883485c 100644
--- a/common/probdist/weighted_dist_test.go
+++ b/common/probdist/weighted_dist_test.go
@@ -28,7 +28,6 @@
 package probdist
 
 import (
-	"fmt"
 	"testing"
 
 	"gitlab.com/yawning/obfs4.git/common/drbg"
@@ -49,7 +48,7 @@ func TestWeightedDist(t *testing.T) {
 	w := New(seed, 0, 999, true)
 	if debug {
 		// Dump a string representation of the probability table.
-		fmt.Println("Table:")
+		t.Logf("Table:")
 		var sum float64
 		for _, weight := range w.weights {
 			sum += weight
@@ -57,10 +56,9 @@ func TestWeightedDist(t *testing.T) {
 		for i, weight := range w.weights {
 			p := weight / sum
 			if p > 0.000001 { // Filter out tiny values.
-				fmt.Printf(" [%d]: %f\n", w.minValue+w.values[i], p)
+				t.Logf(" [%d]: %f", w.minValue+w.values[i], p)
 			}
 		}
-		fmt.Println()
 	}
 
 	for i := 0; i < nrTrials; i++ {
@@ -69,11 +67,11 @@ func TestWeightedDist(t *testing.T) {
 	}
 
 	if debug {
-		fmt.Println("Generated:")
+		t.Logf("Generated:")
 		for value, count := range hist {
 			if count != 0 {
 				p := float64(count) / float64(nrTrials)
-				fmt.Printf(" [%d]: %f (%d)\n", value, p, count)
+				t.Logf(" [%d]: %f (%d)", value, p, count)
 			}
 		}
 	}
diff --git a/common/replayfilter/replay_filter.go b/common/replayfilter/replay_filter.go
index 00ee3e9..3823d9b 100644
--- a/common/replayfilter/replay_filter.go
+++ b/common/replayfilter/replay_filter.go
@@ -39,6 +39,7 @@ import (
 	"time"
 
 	"github.com/dchest/siphash"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 )
 
@@ -67,21 +68,21 @@ type ReplayFilter struct {
 }
 
 // New creates a new ReplayFilter instance.
-func New(ttl time.Duration) (filter *ReplayFilter, err error) {
+func New(ttl time.Duration) (*ReplayFilter, error) {
 	// Initialize the SipHash-2-4 instance with a random key.
 	var key [16]byte
-	if err = csrand.Bytes(key[:]); err != nil {
-		return
+	if err := csrand.Bytes(key[:]); err != nil {
+		return nil, err
 	}
 
-	filter = new(ReplayFilter)
+	filter := new(ReplayFilter)
 	filter.filter = make(map[uint64]*entry)
 	filter.fifo = list.New()
 	filter.key[0] = binary.BigEndian.Uint64(key[0:8])
 	filter.key[1] = binary.BigEndian.Uint64(key[8:16])
 	filter.ttl = ttl
 
-	return
+	return filter, nil
 }
 
 // TestAndSet queries the filter for a given byte sequence, inserts the
diff --git a/common/socks5/args.go b/common/socks5/args.go
index a5efb43..479d710 100644
--- a/common/socks5/args.go
+++ b/common/socks5/args.go
@@ -29,7 +29,8 @@ package socks5
 
 import (
 	"fmt"
-	"git.torproject.org/pluggable-transports/goptlib.git"
+
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
 )
 
 // parseClientParameters takes a client parameter string formatted according to
@@ -37,14 +38,14 @@ import (
 // specification, and returns it as a goptlib Args structure.
 //
 // This is functionally identical to the equivalently named goptlib routine.
-func parseClientParameters(argStr string) (args pt.Args, err error) {
-	args = make(pt.Args)
+func parseClientParameters(argStr string) (pt.Args, error) {
+	args := make(pt.Args)
 	if len(argStr) == 0 {
-		return
+		return args, nil
 	}
 
 	var key string
-	var acc []byte
+	acc := make([]byte, 0, len(argStr))
 	prevIsEscape := false
 	for idx, ch := range []byte(argStr) {
 		switch ch {
diff --git a/common/socks5/args_test.go b/common/socks5/args_test.go
index d9d3f22..8683e8c 100644
--- a/common/socks5/args_test.go
+++ b/common/socks5/args_test.go
@@ -5,7 +5,7 @@ package socks5
 import (
 	"testing"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
 )
 
 func stringSlicesEqual(a, b []string) bool {
diff --git a/common/socks5/rfc1929.go b/common/socks5/rfc1929.go
index 93a2c16..42162e1 100644
--- a/common/socks5/rfc1929.go
+++ b/common/socks5/rfc1929.go
@@ -35,12 +35,12 @@ const (
 	authRFC1929Fail    = 0x01
 )
 
-func (req *Request) authRFC1929() (err error) {
-	sendErrResp := func() {
+func (req *Request) authRFC1929() error {
+	sendErrResp := func(err error) error {
 		// Swallow write/flush errors, the auth failure is the relevant error.
-		resp := []byte{authRFC1929Ver, authRFC1929Fail}
-		_, _ = req.rw.Write(resp[:])
+		_, _ = req.rw.Write([]byte{authRFC1929Ver, authRFC1929Fail})
 		_ = req.flushBuffers()
+		return err // Pass this through from the arg.
 	}
 
 	// The client sends a Username/Password request.
@@ -50,39 +50,35 @@ func (req *Request) authRFC1929() (err error) {
 	//  uint8_t plen (>= 1)
 	//  uint8_t passwd[plen]
 
-	if err = req.readByteVerify("auth version", authRFC1929Ver); err != nil {
-		sendErrResp()
-		return
+	if err := req.readByteVerify("auth version", authRFC1929Ver); err != nil {
+		return sendErrResp(err)
 	}
 
 	// Read the username.
-	var ulen byte
+	var (
+		ulen byte
+		err  error
+	)
 	if ulen, err = req.readByte(); err != nil {
-		sendErrResp()
-		return
+		return sendErrResp(err)
 	} else if ulen < 1 {
-		sendErrResp()
-		return fmt.Errorf("username with 0 length")
+		return sendErrResp(fmt.Errorf("username with 0 length"))
 	}
 	var uname []byte
 	if uname, err = req.readBytes(int(ulen)); err != nil {
-		sendErrResp()
-		return
+		return sendErrResp(err)
 	}
 
 	// Read the password.
 	var plen byte
 	if plen, err = req.readByte(); err != nil {
-		sendErrResp()
-		return
+		return sendErrResp(err)
 	} else if plen < 1 {
-		sendErrResp()
-		return fmt.Errorf("password with 0 length")
+		return sendErrResp(fmt.Errorf("password with 0 length"))
 	}
 	var passwd []byte
 	if passwd, err = req.readBytes(int(plen)); err != nil {
-		sendErrResp()
-		return
+		return sendErrResp(err)
 	}
 
 	// Pluggable transports use the username/password field to pass
@@ -95,11 +91,10 @@ func (req *Request) authRFC1929() (err error) {
 		argStr += string(passwd)
 	}
 	if req.Args, err = parseClientParameters(argStr); err != nil {
-		sendErrResp()
-		return
+		return sendErrResp(err)
 	}
 
 	resp := []byte{authRFC1929Ver, authRFC1929Success}
-	_, err = req.rw.Write(resp[:])
-	return
+	_, err = req.rw.Write(resp)
+	return err
 }
diff --git a/common/socks5/socks5.go b/common/socks5/socks5.go
index 7630d3d..28976a1 100644
--- a/common/socks5/socks5.go
+++ b/common/socks5/socks5.go
@@ -30,23 +30,24 @@
 // 1929.
 //
 // Notes:
-//  * GSSAPI authentication, is NOT supported.
-//  * Only the CONNECT command is supported.
-//  * The authentication provided by the client is always accepted as it is
-//    used as a channel to pass information rather than for authentication for
-//    pluggable transports.
+//   - GSSAPI authentication, is NOT supported.
+//   - Only the CONNECT command is supported.
+//   - The authentication provided by the client is always accepted as it is
+//     used as a channel to pass information rather than for authentication for
+//     pluggable transports.
 package socks5 // import "gitlab.com/yawning/obfs4.git/common/socks5"
 
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"net"
 	"syscall"
 	"time"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
 )
 
 const (
@@ -89,16 +90,16 @@ func Version() string {
 
 // ErrorToReplyCode converts an error to the "best" reply code.
 func ErrorToReplyCode(err error) ReplyCode {
-	opErr, ok := err.(*net.OpError)
-	if !ok {
+	var opErr *net.OpError
+	if !errors.As(err, &opErr) {
 		return ReplyGeneralFailure
 	}
 
-	errno, ok := opErr.Err.(syscall.Errno)
-	if !ok {
+	var errno syscall.Errno
+	if !errors.As(opErr.Err, &errno) {
 		return ReplyGeneralFailure
 	}
-	switch errno {
+	switch errno { //nolint:exhaustive
 	case syscall.EADDRNOTAVAIL:
 		return ReplyAddressNotSupported
 	case syscall.ETIMEDOUT:
@@ -307,7 +308,7 @@ func (req *Request) readCommand() error {
 			return err
 		}
 		addr := make(net.IP, net.IPv6len)
-		copy(addr[:], rawAddr[:])
+		copy(addr[:], rawAddr)
 		host = fmt.Sprintf("[%s]", addr.String())
 	default:
 		_ = req.Reply(ReplyAddressNotSupported)
diff --git a/common/socks5/socks_test.go b/common/socks5/socks_test.go
index ace7fd3..433904e 100644
--- a/common/socks5/socks_test.go
+++ b/common/socks5/socks_test.go
@@ -48,11 +48,11 @@ type testReadWriter struct {
 	writeBuf bytes.Buffer
 }
 
-func (c *testReadWriter) Read(buf []byte) (n int, err error) {
+func (c *testReadWriter) Read(buf []byte) (int, error) {
 	return c.readBuf.Read(buf)
 }
 
-func (c *testReadWriter) Write(buf []byte) (n int, err error) {
+func (c *testReadWriter) Write(buf []byte) (int, error) {
 	return c.writeBuf.Write(buf)
 }
 
@@ -96,11 +96,11 @@ func TestAuthInvalidVersion(t *testing.T) {
 	// VER = 03, NMETHODS = 01, METHODS = [00]
 	c.writeHex("030100")
 	if _, err := req.negotiateAuth(); err == nil {
-		t.Error("negotiateAuth(InvalidVersion) succeded")
+		t.Error("negotiateAuth(InvalidVersion) succeeded")
 	}
 }
 
-// TestAuthInvalidNMethods tests auth negotiaton with no methods.
+// TestAuthInvalidNMethods tests auth negotiation with no methods.
 func TestAuthInvalidNMethods(t *testing.T) {
 	c := new(testReadWriter)
 	req := c.toRequest()
@@ -120,7 +120,7 @@ func TestAuthInvalidNMethods(t *testing.T) {
 	}
 }
 
-// TestAuthNoneRequired tests auth negotiaton with NO AUTHENTICATION REQUIRED.
+// TestAuthNoneRequired tests auth negotiation with NO AUTHENTICATION REQUIRED.
 func TestAuthNoneRequired(t *testing.T) {
 	c := new(testReadWriter)
 	req := c.toRequest()
@@ -230,7 +230,7 @@ func TestRFC1929InvalidVersion(t *testing.T) {
 	// VER = 03, ULEN = 5, UNAME = "ABCDE", PLEN = 5, PASSWD = "abcde"
 	c.writeHex("03054142434445056162636465")
 	if err := req.authenticate(authUsernamePassword); err == nil {
-		t.Error("authenticate(InvalidVersion) succeded")
+		t.Error("authenticate(InvalidVersion) succeeded")
 	}
 	if msg := c.readHex(); msg != "0101" {
 		t.Error("authenticate(InvalidVersion) invalid response:", msg)
@@ -245,7 +245,7 @@ func TestRFC1929InvalidUlen(t *testing.T) {
 	// VER = 01, ULEN = 0, UNAME = "", PLEN = 5, PASSWD = "abcde"
 	c.writeHex("0100056162636465")
 	if err := req.authenticate(authUsernamePassword); err == nil {
-		t.Error("authenticate(InvalidUlen) succeded")
+		t.Error("authenticate(InvalidUlen) succeeded")
 	}
 	if msg := c.readHex(); msg != "0101" {
 		t.Error("authenticate(InvalidUlen) invalid response:", msg)
@@ -260,7 +260,7 @@ func TestRFC1929InvalidPlen(t *testing.T) {
 	// VER = 01, ULEN = 5, UNAME = "ABCDE", PLEN = 0, PASSWD = ""
 	c.writeHex("0105414243444500")
 	if err := req.authenticate(authUsernamePassword); err == nil {
-		t.Error("authenticate(InvalidPlen) succeded")
+		t.Error("authenticate(InvalidPlen) succeeded")
 	}
 	if msg := c.readHex(); msg != "0101" {
 		t.Error("authenticate(InvalidPlen) invalid response:", msg)
@@ -275,7 +275,7 @@ func TestRFC1929InvalidPTArgs(t *testing.T) {
 	// VER = 01, ULEN = 5, UNAME = "ABCDE", PLEN = 5, PASSWD = "abcde"
 	c.writeHex("01054142434445056162636465")
 	if err := req.authenticate(authUsernamePassword); err == nil {
-		t.Error("authenticate(InvalidArgs) succeded")
+		t.Error("authenticate(InvalidArgs) succeeded")
 	}
 	if msg := c.readHex(); msg != "0101" {
 		t.Error("authenticate(InvalidArgs) invalid response:", msg)
@@ -301,7 +301,7 @@ func TestRFC1929Success(t *testing.T) {
 	}
 }
 
-// TestRequestInvalidHdr tests SOCKS5 requests with invalid VER/CMD/RSV/ATYPE
+// TestRequestInvalidHdr tests SOCKS5 requests with invalid VER/CMD/RSV/ATYPE.
 func TestRequestInvalidHdr(t *testing.T) {
 	c := new(testReadWriter)
 	req := c.toRequest()
@@ -309,7 +309,7 @@ func TestRequestInvalidHdr(t *testing.T) {
 	// VER = 03, CMD = 01, RSV = 00, ATYPE = 01, DST.ADDR = 127.0.0.1, DST.PORT = 9050
 	c.writeHex("030100017f000001235a")
 	if err := req.readCommand(); err == nil {
-		t.Error("readCommand(InvalidVer) succeded")
+		t.Error("readCommand(InvalidVer) succeeded")
 	}
 	if msg := c.readHex(); msg != "05010001000000000000" {
 		t.Error("readCommand(InvalidVer) invalid response:", msg)
@@ -319,7 +319,7 @@ func TestRequestInvalidHdr(t *testing.T) {
 	// VER = 05, CMD = 05, RSV = 00, ATYPE = 01, DST.ADDR = 127.0.0.1, DST.PORT = 9050
 	c.writeHex("050500017f000001235a")
 	if err := req.readCommand(); err == nil {
-		t.Error("readCommand(InvalidCmd) succeded")
+		t.Error("readCommand(InvalidCmd) succeeded")
 	}
 	if msg := c.readHex(); msg != "05070001000000000000" {
 		t.Error("readCommand(InvalidCmd) invalid response:", msg)
@@ -329,7 +329,7 @@ func TestRequestInvalidHdr(t *testing.T) {
 	// VER = 05, CMD = 01, RSV = 30, ATYPE = 01, DST.ADDR = 127.0.0.1, DST.PORT = 9050
 	c.writeHex("050130017f000001235a")
 	if err := req.readCommand(); err == nil {
-		t.Error("readCommand(InvalidRsv) succeded")
+		t.Error("readCommand(InvalidRsv) succeeded")
 	}
 	if msg := c.readHex(); msg != "05010001000000000000" {
 		t.Error("readCommand(InvalidRsv) invalid response:", msg)
@@ -339,7 +339,7 @@ func TestRequestInvalidHdr(t *testing.T) {
 	// VER = 05, CMD = 01, RSV = 01, ATYPE = 05, DST.ADDR = 127.0.0.1, DST.PORT = 9050
 	c.writeHex("050100057f000001235a")
 	if err := req.readCommand(); err == nil {
-		t.Error("readCommand(InvalidAtype) succeded")
+		t.Error("readCommand(InvalidAtype) succeeded")
 	}
 	if msg := c.readHex(); msg != "05080001000000000000" {
 		t.Error("readCommand(InvalidAtype) invalid response:", msg)
diff --git a/common/uniformdh/uniformdh.go b/common/uniformdh/uniformdh.go
index 1d500a3..47109b6 100644
--- a/common/uniformdh/uniformdh.go
+++ b/common/uniformdh/uniformdh.go
@@ -32,6 +32,7 @@
 package uniformdh // import "gitlab.com/yawning/obfs4.git/common/uniformdh"
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"math/big"
@@ -54,8 +55,16 @@ const (
 	g = 2
 )
 
-var modpGroup *big.Int
-var gen *big.Int
+var (
+	modpGroup = func() *big.Int {
+		n, ok := new(big.Int).SetString(modpStr, 16)
+		if !ok {
+			panic("Failed to load the RFC3526 MODP Group")
+		}
+		return n
+	}()
+	gen = big.NewInt(g)
+)
 
 // A PrivateKey represents a UniformDH private key.
 type PrivateKey struct {
@@ -70,14 +79,11 @@ type PublicKey struct {
 }
 
 // Bytes returns the byte representation of a PublicKey.
-func (pub *PublicKey) Bytes() (pubBytes []byte, err error) {
+func (pub *PublicKey) Bytes() ([]byte, error) {
 	if len(pub.bytes) != Size || pub.bytes == nil {
 		return nil, fmt.Errorf("public key is not initialized")
 	}
-	pubBytes = make([]byte, Size)
-	copy(pubBytes, pub.bytes)
-
-	return
+	return bytes.Clone(pub.bytes), nil
 }
 
 // SetBytes sets the PublicKey from a byte slice.
@@ -85,25 +91,22 @@ func (pub *PublicKey) SetBytes(pubBytes []byte) error {
 	if len(pubBytes) != Size {
 		return fmt.Errorf("public key length %d is not %d", len(pubBytes), Size)
 	}
-	pub.bytes = make([]byte, Size)
-	copy(pub.bytes, pubBytes)
+	pub.bytes = bytes.Clone(pubBytes)
 	pub.publicKey = new(big.Int).SetBytes(pub.bytes)
 
 	return nil
 }
 
 // GenerateKey generates a UniformDH keypair using the random source random.
-func GenerateKey(random io.Reader) (priv *PrivateKey, err error) {
-	privBytes := make([]byte, Size)
-	if _, err = io.ReadFull(random, privBytes); err != nil {
-		return
+func GenerateKey(random io.Reader) (*PrivateKey, error) {
+	var privBytes [Size]byte
+	if _, err := io.ReadFull(random, privBytes[:]); err != nil {
+		return nil, err
 	}
-	priv, err = generateKey(privBytes)
-
-	return
+	return generateKey(privBytes[:])
 }
 
-func generateKey(privBytes []byte) (priv *PrivateKey, err error) {
+func generateKey(privBytes []byte) (*PrivateKey, error) {
 	// This function does all of the actual heavy lifting of creating a public
 	// key from a raw 192 byte private key.  It is split so that the KAT tests
 	// can be written easily, and not exposed since non-ephemeral keys are a
@@ -132,52 +135,26 @@ func generateKey(privBytes []byte) (priv *PrivateKey, err error) {
 	// to the key so that it is always exactly Size bytes.
 	pubBytes := make([]byte, Size)
 	if wasEven {
-		err = prependZeroBytes(pubBytes, pubBn.Bytes())
+		pubBn.FillBytes(pubBytes)
 	} else {
-		err = prependZeroBytes(pubBytes, pubAlt.Bytes())
-	}
-	if err != nil {
-		return
+		pubAlt.FillBytes(pubBytes)
 	}
 
-	priv = new(PrivateKey)
+	priv := new(PrivateKey)
 	priv.PublicKey.bytes = pubBytes
 	priv.PublicKey.publicKey = pubBn
 	priv.privateKey = privBn
 
-	return
+	return priv, nil
 }
 
 // Handshake generates a shared secret given a PrivateKey and PublicKey.
-func Handshake(privateKey *PrivateKey, publicKey *PublicKey) (sharedSecret []byte, err error) {
+func Handshake(privateKey *PrivateKey, publicKey *PublicKey) ([]byte, error) {
 	// When a party wants to calculate the shared secret, she raises the
 	// foreign public key to her private key.
 	secretBn := new(big.Int).Exp(publicKey.publicKey, privateKey.privateKey, modpGroup)
-	sharedSecret = make([]byte, Size)
-	err = prependZeroBytes(sharedSecret, secretBn.Bytes())
-
-	return
-}
+	sharedSecret := make([]byte, Size)
+	secretBn.FillBytes(sharedSecret)
 
-func prependZeroBytes(dst, src []byte) error {
-	zeros := len(dst) - len(src)
-	if zeros < 0 {
-		return fmt.Errorf("src length is greater than destination: %d", zeros)
-	}
-	for i := 0; i < zeros; i++ {
-		dst[i] = 0
-	}
-	copy(dst[zeros:], src)
-
-	return nil
-}
-
-func init() {
-	// Load the MODP group and the generator.
-	var ok bool
-	modpGroup, ok = new(big.Int).SetString(modpStr, 16)
-	if !ok {
-		panic("Failed to load the RFC3526 MODP Group")
-	}
-	gen = big.NewInt(g)
+	return sharedSecret, nil
 }
diff --git a/common/uniformdh/uniformdh_test.go b/common/uniformdh/uniformdh_test.go
index 326293b..ab09a8e 100644
--- a/common/uniformdh/uniformdh_test.go
+++ b/common/uniformdh/uniformdh_test.go
@@ -101,7 +101,14 @@ const (
 		"a81359543e77e4a4cfa7598a4152e4c0"
 )
 
-var xPriv, xPub, yPriv, yPub, ss []byte
+var (
+	// Load the test vectors into byte slices.
+	xPriv, _ = hex.DecodeString(xPrivStr)
+	xPub, _  = hex.DecodeString(xPubStr)
+	yPriv, _ = hex.DecodeString(yPrivStr)
+	yPub, _  = hex.DecodeString(yPubStr)
+	ss, _    = hex.DecodeString(ssStr)
+)
 
 // TestGenerateKeyOdd tests creating a UniformDH keypair with a odd private
 // key.
@@ -137,7 +144,7 @@ func TestGenerateKeyEven(t *testing.T) {
 	}
 }
 
-// TestHandshake tests conductiong a UniformDH handshake with know values.
+// TestHandshake tests conducting a UniformDH handshake with know values.
 func TestHandshake(t *testing.T) {
 	xX, err := generateKey(xPriv)
 	if err != nil {
@@ -193,28 +200,3 @@ func BenchmarkHandshake(b *testing.B) {
 		_ = yX
 	}
 }
-
-func init() {
-	// Load the test vectors into byte slices.
-	var err error
-	xPriv, err = hex.DecodeString(xPrivStr)
-	if err != nil {
-		panic("hex.DecodeString(xPrivStr) failed")
-	}
-	xPub, err = hex.DecodeString(xPubStr)
-	if err != nil {
-		panic("hex.DecodeString(xPubStr) failed")
-	}
-	yPriv, err = hex.DecodeString(yPrivStr)
-	if err != nil {
-		panic("hex.DecodeString(yPrivStr) failed")
-	}
-	yPub, err = hex.DecodeString(yPubStr)
-	if err != nil {
-		panic("hex.DecodeString(yPubStr) failed")
-	}
-	ss, err = hex.DecodeString(ssStr)
-	if err != nil {
-		panic("hex.DecodeString(ssStr) failed")
-	}
-}
diff --git a/go.mod b/go.mod
index 96e5cee..3f24c77 100644
--- a/go.mod
+++ b/go.mod
@@ -2,11 +2,13 @@ module gitlab.com/yawning/obfs4.git
 
 require (
 	filippo.io/edwards25519 v1.0.0
-	git.torproject.org/pluggable-transports/goptlib.git v1.3.0
 	github.com/dchest/siphash v1.2.3
-	gitlab.com/yawning/edwards25519-extra.git v0.0.0-20211229043746-2f91fcc9fbdb
-	golang.org/x/crypto v0.9.0
-	golang.org/x/net v0.10.0
+	gitlab.com/yawning/edwards25519-extra.git v0.0.0-20220726154925-def713fd18e4
+	gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib v1.4.0
+	golang.org/x/crypto v0.11.0
+	golang.org/x/net v0.12.0
 )
 
+require golang.org/x/sys v0.10.0 // indirect
+
 go 1.20
diff --git a/go.sum b/go.sum
index c67246b..e6623c8 100644
--- a/go.sum
+++ b/go.sum
@@ -1,48 +1,22 @@
 filippo.io/edwards25519 v1.0.0-rc.1.0.20210721174708-390f27c3be20/go.mod h1:N1IkdkCkiLB6tki+MYJoSx2JTY9NUlxZE7eHn5EwJns=
 filippo.io/edwards25519 v1.0.0 h1:0wAIcmJUqRdI8IJ/3eGi5/HwXZWPujYXXlkrQogz0Ek=
 filippo.io/edwards25519 v1.0.0/go.mod h1:N1IkdkCkiLB6tki+MYJoSx2JTY9NUlxZE7eHn5EwJns=
-git.torproject.org/pluggable-transports/goptlib.git v1.3.0 h1:G+iuRUblCCC2xnO+0ag1/4+aaM98D5mjWP1M0v9s8a0=
-git.torproject.org/pluggable-transports/goptlib.git v1.3.0/go.mod h1:4PBMl1dg7/3vMWSoWb46eGWlrxkUyn/CAJmxhDLAlDs=
 github.com/dchest/siphash v1.2.3 h1:QXwFc8cFOR2dSa/gE6o/HokBMWtLUaNDVd+22aKHeEA=
 github.com/dchest/siphash v1.2.3/go.mod h1:0NvQU092bT0ipiFN++/rXm69QG9tVxLAlQHIXMPAkHc=
-github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
-gitlab.com/yawning/edwards25519-extra.git v0.0.0-20211229043746-2f91fcc9fbdb h1:qRSZHsODmAP5qDvb3YsO7Qnf3TRiVbGxNG/WYnlM4/o=
-gitlab.com/yawning/edwards25519-extra.git v0.0.0-20211229043746-2f91fcc9fbdb/go.mod h1:gvdJuZuO/tPZyhEV8K3Hmoxv/DWud5L4qEQxfYjEUTo=
-golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+gitlab.com/yawning/edwards25519-extra.git v0.0.0-20220726154925-def713fd18e4 h1:LeXiZggivkDGgmkl7+r+m/2xj3rd+K/30/0obRKayAU=
+gitlab.com/yawning/edwards25519-extra.git v0.0.0-20220726154925-def713fd18e4/go.mod h1:gvdJuZuO/tPZyhEV8K3Hmoxv/DWud5L4qEQxfYjEUTo=
+gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib v1.4.0 h1:Y7fHDMy11yyjM+YlHfcM3svaujdL+m5DqS444wbj8o4=
+gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib v1.4.0/go.mod h1:70bhd4JKW/+1HLfm+TMrgHJsUHG4coelMWwiVEJ2gAg=
 golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
-golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
-golang.org/x/crypto v0.9.0 h1:LF6fAI+IutBocDJ2OT0Q1g8plpYljMZ4+lty+dsqw3g=
-golang.org/x/crypto v0.9.0/go.mod h1:yrmDGqONDYtNj3tH8X9dzUun2m2lzPa9ngI6/RUPGR0=
-golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
-golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
-golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/crypto v0.11.0 h1:6Ewdq3tDic1mg5xRO4milcWCfMVQhI4NkqWWvqejpuA=
+golang.org/x/crypto v0.11.0/go.mod h1:xgJhtzW8F9jGdVFWZESrid1U1bjeNy4zgy5cRr/CIio=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
-golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
-golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
-golang.org/x/net v0.10.0 h1:X2//UzNDwYmtCLn7To6G58Wr6f5ahEAQgKNzv9Y951M=
-golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
-golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/net v0.12.0 h1:cfawfvKITfUsFCeJIHJrbSxpeu/E81khclypR0GVT50=
+golang.org/x/net v0.12.0/go.mod h1:zEVYFnQC7m/vmpQFELhcD1EWkZlX69l4oqgmer6hfKA=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.8.0 h1:EBmGv8NaZBZTWvrbjNoL6HVt+IVy3QDQpJs7VRIw3tU=
-golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.10.0 h1:SqMFp9UcQJZa+pmYuAKjd9xq1f0j5rLcDIk0mj4qAsA=
+golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
-golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
-golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
-golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
-golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
-golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
-golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
-golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
-golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/internal/x25519ell2/x25519ell2.go b/internal/x25519ell2/x25519ell2.go
index eb2b1dd..8d02141 100644
--- a/internal/x25519ell2/x25519ell2.go
+++ b/internal/x25519ell2/x25519ell2.go
@@ -22,7 +22,6 @@ import (
 
 	"filippo.io/edwards25519"
 	"filippo.io/edwards25519/field"
-
 	"gitlab.com/yawning/edwards25519-extra.git/elligator2"
 )
 
@@ -52,7 +51,7 @@ var (
 		0xbb, 0x4a, 0xde, 0x38, 0x32, 0x99, 0x33, 0xe9, 0x28, 0x4a, 0x39, 0x06, 0xa0, 0xb9, 0xd5, 0x1f,
 	})
 
-	// Low order point Edwards y-coordinate `-lop_x * sqrtm1`
+	// Low order point Edwards y-coordinate `-lop_x * sqrtm1`.
 	feLopY = mustFeFromBytes([]byte{
 		0x26, 0xe8, 0x95, 0x8f, 0xc2, 0xb2, 0x27, 0xb0, 0x45, 0xc3, 0xf4, 0x89, 0xf2, 0xef, 0x98, 0xf0,
 		0xd5, 0xdf, 0xac, 0x05, 0xd3, 0xc6, 0x33, 0x39, 0xb1, 0x38, 0x02, 0x88, 0x6d, 0x53, 0xfc, 0x05,
diff --git a/obfs4proxy/obfs4proxy.go b/obfs4proxy/obfs4proxy.go
index 32359d0..a695514 100644
--- a/obfs4proxy/obfs4proxy.go
+++ b/obfs4proxy/obfs4proxy.go
@@ -41,12 +41,13 @@ import (
 	"sync"
 	"syscall"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+	"golang.org/x/net/proxy"
+
 	"gitlab.com/yawning/obfs4.git/common/log"
 	"gitlab.com/yawning/obfs4.git/common/socks5"
 	"gitlab.com/yawning/obfs4.git/transports"
 	"gitlab.com/yawning/obfs4.git/transports/base"
-	"golang.org/x/net/proxy"
 )
 
 const (
@@ -55,23 +56,27 @@ const (
 	socksAddr         = "127.0.0.1:0"
 )
 
-var stateDir string
-var termMon *termMonitor
+var (
+	stateDir string
+	termMon  *termMonitor
+)
 
-func clientSetup() (launched bool, listeners []net.Listener) {
+func clientSetup() (bool, []net.Listener) {
 	ptClientInfo, err := pt.ClientSetup(transports.Transports())
 	if err != nil {
 		golog.Fatal(err)
 	}
 
-	ptClientProxy, err := ptGetProxy()
+	ptClientProxy, err := ptGetProxy(&ptClientInfo)
 	if err != nil {
 		golog.Fatal(err)
 	} else if ptClientProxy != nil {
-		ptProxyDone()
+		pt.ProxyDone()
 	}
 
 	// Launch each of the client listeners.
+	var launched bool
+	listeners := make([]net.Listener, 0, len(ptClientInfo.MethodNames))
 	for _, name := range ptClientInfo.MethodNames {
 		t := transports.Get(name)
 		if t == nil {
@@ -103,7 +108,7 @@ func clientSetup() (launched bool, listeners []net.Listener) {
 	}
 	pt.CmethodsDone()
 
-	return
+	return launched, listeners
 }
 
 func clientAcceptLoop(f base.ClientFactory, ln net.Listener, proxyURI *url.URL) error {
@@ -111,10 +116,7 @@ func clientAcceptLoop(f base.ClientFactory, ln net.Listener, proxyURI *url.URL)
 	for {
 		conn, err := ln.Accept()
 		if err != nil {
-			if e, ok := err.(net.Error); ok && !e.Temporary() {
-				return err
-			}
-			continue
+			return err
 		}
 		go clientHandler(f, conn, proxyURI)
 	}
@@ -176,12 +178,14 @@ func clientHandler(f base.ClientFactory, conn net.Conn, proxyURI *url.URL) {
 	}
 }
 
-func serverSetup() (launched bool, listeners []net.Listener) {
+func serverSetup() (bool, []net.Listener) {
 	ptServerInfo, err := pt.ServerSetup(transports.Transports())
 	if err != nil {
 		golog.Fatal(err)
 	}
 
+	var launched bool
+	listeners := make([]net.Listener, 0, len(ptServerInfo.Bindaddrs))
 	for _, bindaddr := range ptServerInfo.Bindaddrs {
 		name := bindaddr.MethodName
 		t := transports.Get(name)
@@ -218,7 +222,7 @@ func serverSetup() (launched bool, listeners []net.Listener) {
 	}
 	pt.SmethodsDone()
 
-	return
+	return launched, listeners
 }
 
 func serverAcceptLoop(f base.ServerFactory, ln net.Listener, info *pt.ServerInfo) error {
@@ -226,10 +230,7 @@ func serverAcceptLoop(f base.ServerFactory, ln net.Listener, info *pt.ServerInfo
 	for {
 		conn, err := ln.Accept()
 		if err != nil {
-			if e, ok := err.(net.Error); ok && !e.Temporary() {
-				return err
-			}
-			continue
+			return err
 		}
 		go serverHandler(f, conn, info)
 	}
@@ -317,7 +318,7 @@ func main() {
 	flag.Parse()
 
 	if *showVer {
-		fmt.Printf("%s\n", getVersion())
+		fmt.Printf("%s\n", getVersion()) //nolint:forbidigo
 		os.Exit(0)
 	}
 	if err := log.SetLogLevel(*logLevelStr); err != nil {
diff --git a/obfs4proxy/proxy_http.go b/obfs4proxy/proxy_http.go
index 1adadf8..e263935 100644
--- a/obfs4proxy/proxy_http.go
+++ b/obfs4proxy/proxy_http.go
@@ -30,6 +30,7 @@ package main
 import (
 	"bufio"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -69,14 +70,14 @@ func (s *httpProxy) Dial(network, addr string) (net.Conn, error) {
 		return nil, err
 	}
 	conn := new(httpConn)
-	conn.httpConn = httputil.NewClientConn(c, nil) // nolint: staticcheck
+	conn.httpConn = httputil.NewClientConn(c, nil) //nolint:staticcheck
 	conn.remoteAddr, err = net.ResolveTCPAddr(network, addr)
 	if err != nil {
 		conn.httpConn.Close()
 		return nil, err
 	}
 
-	// HACK HACK HACK HACK.  http.ReadRequest also does this.
+	// HACK: http.ReadRequest also does this.
 	reqURL, err := url.Parse("http://" + addr)
 	if err != nil {
 		conn.httpConn.Close()
@@ -84,7 +85,7 @@ func (s *httpProxy) Dial(network, addr string) (net.Conn, error) {
 	}
 	reqURL.Scheme = ""
 
-	req, err := http.NewRequest("CONNECT", reqURL.String(), nil)
+	req, err := http.NewRequest(http.MethodConnect, reqURL.String(), nil)
 	if err != nil {
 		conn.httpConn.Close()
 		return nil, err
@@ -93,16 +94,16 @@ func (s *httpProxy) Dial(network, addr string) (net.Conn, error) {
 	if s.haveAuth {
 		// SetBasicAuth doesn't quite do what is appropriate, because
 		// the correct header is `Proxy-Authorization`.
-		req.Header.Set("Proxy-Authorization", "Basic " + base64.StdEncoding.EncodeToString([]byte(s.username+":"+s.password)))
+		req.Header.Set("Proxy-Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(s.username+":"+s.password)))
 	}
 	req.Header.Set("User-Agent", "")
 
 	resp, err := conn.httpConn.Do(req)
-	if err != nil && err != httputil.ErrPersistEOF { // nolint: staticcheck
+	if err != nil && !errors.Is(err, httputil.ErrPersistEOF) { //nolint:staticcheck
 		conn.httpConn.Close()
 		return nil, err
 	}
-	if resp.StatusCode != 200 {
+	if resp.StatusCode != http.StatusOK {
 		conn.httpConn.Close()
 		return nil, fmt.Errorf("proxy error: %s", resp.Status)
 	}
@@ -113,7 +114,7 @@ func (s *httpProxy) Dial(network, addr string) (net.Conn, error) {
 
 type httpConn struct {
 	remoteAddr   *net.TCPAddr
-	httpConn     *httputil.ClientConn // nolint: staticcheck
+	httpConn     *httputil.ClientConn //nolint:staticcheck
 	hijackedConn net.Conn
 	staleReader  *bufio.Reader
 }
@@ -156,6 +157,6 @@ func (c *httpConn) SetWriteDeadline(t time.Time) error {
 	return c.hijackedConn.SetWriteDeadline(t)
 }
 
-func init() {
+func init() { //nolint:gochecknoinits
 	proxy.RegisterDialerType("http", newHTTP)
 }
diff --git a/obfs4proxy/proxy_socks4.go b/obfs4proxy/proxy_socks4.go
index ac8be9e..2e623f6 100644
--- a/obfs4proxy/proxy_socks4.go
+++ b/obfs4proxy/proxy_socks4.go
@@ -150,7 +150,7 @@ func socks4ErrorToString(code byte) string {
 	case socks4Rejected:
 		return "request rejected or failed"
 	case socks4RejectedIdentdFailed:
-		return "request rejected becasue SOCKS server cannot connect to identd on the client"
+		return "request rejected because SOCKS server cannot connect to identd on the client"
 	case socks4RejectedIdentdMismatch:
 		return "request rejected because the client program and identd report different user-ids"
 	default:
@@ -158,7 +158,7 @@ func socks4ErrorToString(code byte) string {
 	}
 }
 
-func init() {
+func init() { //nolint:gochecknoinits
 	// Despite the scheme name, this really is SOCKS4.
 	proxy.RegisterDialerType("socks4a", newSOCKS4)
 }
diff --git a/obfs4proxy/pt_extras.go b/obfs4proxy/pt_extras.go
index 18bc2df..5f10f14 100644
--- a/obfs4proxy/pt_extras.go
+++ b/obfs4proxy/pt_extras.go
@@ -35,11 +35,11 @@ import (
 	"os"
 	"strconv"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
 )
 
 // This file contains things that probably should be in goptlib but are not
-// yet or are not finalized.
+// yet or not exposed.
 
 func ptEnvError(msg string) error {
 	line := []byte(fmt.Sprintf("ENV-ERROR %s\n", msg))
@@ -47,89 +47,61 @@ func ptEnvError(msg string) error {
 	return errors.New(msg)
 }
 
-func ptProxyError(msg string) error {
-	line := []byte(fmt.Sprintf("PROXY-ERROR %s\n", msg))
-	_, _ = pt.Stdout.Write(line)
-	return errors.New(msg)
-}
-
-func ptProxyDone() {
-	line := []byte("PROXY DONE\n")
-	_, _ = pt.Stdout.Write(line)
-}
-
 func ptIsClient() (bool, error) {
 	clientEnv := os.Getenv("TOR_PT_CLIENT_TRANSPORTS")
 	serverEnv := os.Getenv("TOR_PT_SERVER_TRANSPORTS")
-	if clientEnv != "" && serverEnv != "" {
+	switch {
+	case clientEnv != "" && serverEnv != "":
 		return false, ptEnvError("TOR_PT_[CLIENT,SERVER]_TRANSPORTS both set")
-	} else if clientEnv != "" {
+	case clientEnv != "":
 		return true, nil
-	} else if serverEnv != "" {
+	case serverEnv != "":
 		return false, nil
 	}
 	return false, errors.New("not launched as a managed transport")
 }
 
-func ptGetProxy() (*url.URL, error) {
-	specString := os.Getenv("TOR_PT_PROXY")
-	if specString == "" {
-		return nil, nil
-	}
-	spec, err := url.Parse(specString)
-	if err != nil {
-		return nil, ptProxyError(fmt.Sprintf("failed to parse proxy config: %s", err))
+func ptGetProxy(info *pt.ClientInfo) (*url.URL, error) {
+	proxyURL := info.ProxyURL
+	if proxyURL == nil {
+		return nil, nil //nolint:nilnil
 	}
 
-	// Validate the TOR_PT_PROXY uri.
-	if !spec.IsAbs() {
-		return nil, ptProxyError("proxy URI is relative, must be absolute")
-	}
-	if spec.Path != "" {
-		return nil, ptProxyError("proxy URI has a path defined")
-	}
-	if spec.RawQuery != "" {
-		return nil, ptProxyError("proxy URI has a query defined")
-	}
-	if spec.Fragment != "" {
-		return nil, ptProxyError("proxy URI has a fragment defined")
-	}
-
-	switch spec.Scheme {
+	// Validate the arguments.
+	switch proxyURL.Scheme {
 	case "http":
 		// The most forgiving of proxies.
 
 	case "socks4a":
-		if spec.User != nil {
-			_, isSet := spec.User.Password()
+		if proxyURL.User != nil {
+			_, isSet := proxyURL.User.Password()
 			if isSet {
-				return nil, ptProxyError("proxy URI specified SOCKS4a and a password")
+				return nil, pt.ProxyError("proxy URI proxyURLified SOCKS4a and a password")
 			}
 		}
 
 	case "socks5":
-		if spec.User != nil {
+		if proxyURL.User != nil {
 			// UNAME/PASSWD both must be between 1 and 255 bytes long. (RFC1929)
-			user := spec.User.Username()
-			passwd, isSet := spec.User.Password()
+			user := proxyURL.User.Username()
+			passwd, isSet := proxyURL.User.Password()
 			if len(user) < 1 || len(user) > 255 {
-				return nil, ptProxyError("proxy URI specified a invalid SOCKS5 username")
+				return nil, pt.ProxyError("proxy URI proxyURLified a invalid SOCKS5 username")
 			}
 			if !isSet || len(passwd) < 1 || len(passwd) > 255 {
-				return nil, ptProxyError("proxy URI specified a invalid SOCKS5 password")
+				return nil, pt.ProxyError("proxy URI proxyURLified a invalid SOCKS5 password")
 			}
 		}
 
 	default:
-		return nil, ptProxyError(fmt.Sprintf("proxy URI has invalid scheme: %s", spec.Scheme))
+		return nil, pt.ProxyError(fmt.Sprintf("proxy URI has invalid scheme: %s", proxyURL.Scheme))
 	}
 
-	_, err = resolveAddrStr(spec.Host)
-	if err != nil {
-		return nil, ptProxyError(fmt.Sprintf("proxy URI has invalid host: %s", err))
+	if _, err := resolveAddrStr(proxyURL.Host); err != nil {
+		return nil, pt.ProxyError(fmt.Sprintf("proxy URI has invalid host: %s", err))
 	}
 
-	return spec, nil
+	return proxyURL, nil
 }
 
 // Sigh, pt.resolveAddr() isn't exported.  Include our own getto version that
diff --git a/obfs4proxy/termmon.go b/obfs4proxy/termmon.go
index 59304c9..aa89b82 100644
--- a/obfs4proxy/termmon.go
+++ b/obfs4proxy/termmon.go
@@ -29,7 +29,6 @@ package main
 
 import (
 	"io"
-	"io/ioutil"
 	"os"
 	"os/signal"
 	"runtime"
@@ -73,7 +72,7 @@ func (m *termMonitor) wait(termOnNoHandlers bool) os.Signal {
 }
 
 func (m *termMonitor) termOnStdinClose() {
-	_, err := io.Copy(ioutil.Discard, os.Stdin)
+	_, err := io.Copy(io.Discard, os.Stdin)
 
 	// io.Copy() will return a nil on EOF, since reaching EOF is
 	// expected behavior.  No matter what, if this unblocks, assume
@@ -103,9 +102,9 @@ func (m *termMonitor) termOnPPIDChange(ppid int) {
 	m.sigChan <- syscall.SIGTERM
 }
 
-func newTermMonitor() (m *termMonitor) {
+func newTermMonitor() *termMonitor {
 	ppid := os.Getppid()
-	m = new(termMonitor)
+	m := new(termMonitor)
 	m.sigChan = make(chan os.Signal)
 	m.handlerChan = make(chan int)
 	signal.Notify(m.sigChan, syscall.SIGINT, syscall.SIGTERM)
@@ -113,7 +112,7 @@ func newTermMonitor() (m *termMonitor) {
 	// If tor supports feature #15435, we can use Stdin being closed as an
 	// indication that tor has died, or wants the PT to shutdown for any
 	// reason.
-	if ptShouldExitOnStdinClose() {
+	if ptShouldExitOnStdinClose() { //nolint:nestif
 		go m.termOnStdinClose()
 	} else {
 		// Instead of feature #15435, use various kludges and hacks:
@@ -124,12 +123,12 @@ func newTermMonitor() (m *termMonitor) {
 			// Errors here are non-fatal, since it might still be
 			// possible to fall back to a generic implementation.
 			if err := termMonitorOSInit(m); err == nil {
-				return
+				return m
 			}
 		}
 		if runtime.GOOS != "windows" {
 			go m.termOnPPIDChange(ppid)
 		}
 	}
-	return
+	return m
 }
diff --git a/obfs4proxy/termmon_linux.go b/obfs4proxy/termmon_linux.go
index 926e630..13f8c54 100644
--- a/obfs4proxy/termmon_linux.go
+++ b/obfs4proxy/termmon_linux.go
@@ -32,18 +32,18 @@ import (
 	"syscall"
 )
 
-func termMonitorInitLinux(m *termMonitor) error {
+func termMonitorInitLinux(_ *termMonitor) error {
 	// Use prctl() to have the kernel deliver a SIGTERM if the parent
 	// process dies.  This beats anything else that can be done before
 	// #15435 is implemented.
 	_, _, errno := syscall.Syscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGTERM), 0)
 	if errno != 0 {
 		var err error = errno
-		return fmt.Errorf("prctl(PR_SET_PDEATHSIG, SIGTERM) returned: %s", err)
+		return fmt.Errorf("prctl(PR_SET_PDEATHSIG, SIGTERM) returned: %w", err)
 	}
 	return nil
 }
 
-func init() {
+func init() { //nolint:gochecknoinits
 	termMonitorOSInit = termMonitorInitLinux
 }
diff --git a/transports/base/base.go b/transports/base/base.go
index bc6e025..ab7bdbc 100644
--- a/transports/base/base.go
+++ b/transports/base/base.go
@@ -32,7 +32,7 @@ package base // import "gitlab.com/yawning/obfs4.git/transports/base"
 import (
 	"net"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
 )
 
 type DialFunc func(string, string) (net.Conn, error)
@@ -48,12 +48,12 @@ type ClientFactory interface {
 	// for use with WrapConn.  This routine is called before the outgoing
 	// TCP/IP connection is created to allow doing things (like keypair
 	// generation) to be hidden from third parties.
-	ParseArgs(args *pt.Args) (interface{}, error)
+	ParseArgs(args *pt.Args) (any, error)
 
 	// Dial creates an outbound net.Conn, and does whatever is required
 	// (eg: handshaking) to get the connection to the point where it is
 	// ready to relay data.
-	Dial(network, address string, dialFn DialFunc, args interface{}) (net.Conn, error)
+	Dial(network, address string, dialFn DialFunc, args any) (net.Conn, error)
 }
 
 // ServerFactory is the interface that defines the factory for creating
diff --git a/transports/meeklite/base.go b/transports/meeklite/base.go
index e9d8ca1..b8f3732 100644
--- a/transports/meeklite/base.go
+++ b/transports/meeklite/base.go
@@ -36,7 +36,8 @@ import (
 	"fmt"
 	"net"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/transports/base"
 )
 
@@ -51,15 +52,13 @@ func (t *Transport) Name() string {
 }
 
 // ClientFactory returns a new meekClientFactory instance.
-func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) {
+func (t *Transport) ClientFactory(_ string) (base.ClientFactory, error) {
 	cf := &meekClientFactory{transport: t}
 	return cf, nil
 }
 
 // ServerFactory will one day return a new meekServerFactory instance.
-func (t *Transport) ServerFactory(stateDir string, args *pt.Args) (base.ServerFactory, error) {
-	// TODO: Fill this in eventually, though for servers people should
-	// just use the real thing.
+func (t *Transport) ServerFactory(_ string, _ *pt.Args) (base.ServerFactory, error) {
 	return nil, fmt.Errorf("server not supported")
 }
 
@@ -71,18 +70,18 @@ func (cf *meekClientFactory) Transport() base.Transport {
 	return cf.transport
 }
 
-func (cf *meekClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
+func (cf *meekClientFactory) ParseArgs(args *pt.Args) (any, error) {
 	return newClientArgs(args)
 }
 
-func (cf *meekClientFactory) Dial(network, addr string, dialFn base.DialFunc, args interface{}) (net.Conn, error) {
+func (cf *meekClientFactory) Dial(_, _ string, dialFn base.DialFunc, args any) (net.Conn, error) {
 	// Validate args before opening outgoing connection.
 	ca, ok := args.(*meekClientArgs)
 	if !ok {
 		return nil, fmt.Errorf("invalid argument type for args")
 	}
 
-	return newMeekConn(network, addr, dialFn, ca)
+	return newMeekConn(dialFn, ca)
 }
 
 var (
diff --git a/transports/meeklite/meek.go b/transports/meeklite/meek.go
index 17c7a67..3407f9b 100644
--- a/transports/meeklite/meek.go
+++ b/transports/meeklite/meek.go
@@ -35,7 +35,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net"
 	"net/http"
 	gourl "net/url"
@@ -44,7 +43,8 @@ import (
 	"sync"
 	"time"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/transports/base"
 )
 
@@ -83,8 +83,11 @@ func (ca *meekClientArgs) String() string {
 	return transportName + ":" + ca.front + ":" + ca.url.String()
 }
 
-func newClientArgs(args *pt.Args) (ca *meekClientArgs, err error) {
-	ca = &meekClientArgs{}
+func newClientArgs(args *pt.Args) (*meekClientArgs, error) {
+	var (
+		ca  meekClientArgs
+		err error
+	)
 
 	// Parse the URL argument.
 	str, ok := args.Get(urlArg)
@@ -104,7 +107,7 @@ func newClientArgs(args *pt.Args) (ca *meekClientArgs, err error) {
 	// Parse the (optional) front argument.
 	ca.front, _ = args.Get(frontArg)
 
-	return ca, nil
+	return &ca, nil
 }
 
 type meekConn struct {
@@ -119,18 +122,18 @@ type meekConn struct {
 	rdBuf           *bytes.Buffer
 }
 
-func (c *meekConn) Read(p []byte) (n int, err error) {
+func (c *meekConn) Read(p []byte) (int, error) {
 	// If there is data left over from the previous read,
 	// service the request using the buffered data.
 	if c.rdBuf != nil {
 		if c.rdBuf.Len() == 0 {
 			panic("empty read buffer")
 		}
-		n, err = c.rdBuf.Read(p)
+		n, err := c.rdBuf.Read(p)
 		if c.rdBuf.Len() == 0 {
 			c.rdBuf = nil
 		}
-		return
+		return n, err
 	}
 
 	// Wait for the worker to enqueue more incoming data.
@@ -142,16 +145,16 @@ func (c *meekConn) Read(p []byte) (n int, err error) {
 
 	// Ew, an extra copy, but who am I kidding, it's meek.
 	buf := bytes.NewBuffer(b)
-	n, err = buf.Read(p)
+	n, err := buf.Read(p)
 	if buf.Len() > 0 {
 		// If there's data pending, stash the buffer so the next
 		// Read() call will use it to fulfuill the Read().
 		c.rdBuf = buf
 	}
-	return
+	return n, err
 }
 
-func (c *meekConn) Write(b []byte) (n int, err error) {
+func (c *meekConn) Write(b []byte) (int, error) {
 	// Check to see if the connection is actually open.
 	select {
 	case <-c.workerCloseChan:
@@ -196,19 +199,19 @@ func (c *meekConn) RemoteAddr() net.Addr {
 	return c.args
 }
 
-func (c *meekConn) SetDeadline(t time.Time) error {
+func (c *meekConn) SetDeadline(_ time.Time) error {
 	return ErrNotSupported
 }
 
-func (c *meekConn) SetReadDeadline(t time.Time) error {
+func (c *meekConn) SetReadDeadline(_ time.Time) error {
 	return ErrNotSupported
 }
 
-func (c *meekConn) SetWriteDeadline(t time.Time) error {
+func (c *meekConn) SetWriteDeadline(_ time.Time) error {
 	return ErrNotSupported
 }
 
-func (c *meekConn) enqueueWrite(b []byte) (ok bool) {
+func (c *meekConn) enqueueWrite(b []byte) (ok bool) { //nolint:nonamedreturns
 	defer func() {
 		if err := recover(); err != nil {
 			ok = false
@@ -218,21 +221,26 @@ func (c *meekConn) enqueueWrite(b []byte) (ok bool) {
 	return true
 }
 
-func (c *meekConn) roundTrip(sndBuf []byte) (recvBuf []byte, err error) {
-	var req *http.Request
-	var resp *http.Response
+func (c *meekConn) roundTrip(sndBuf []byte) ([]byte, error) {
+	var (
+		req  *http.Request
+		resp *http.Response
+		err  error
+	)
+
+	url := *c.args.url
+	host := url.Host
+	if c.args.front != "" {
+		url.Host = c.args.front
+	}
+	urlStr := url.String()
 
 	for retries := 0; retries < maxRetries; retries++ {
-		url := *c.args.url
-		host := url.Host
-		if c.args.front != "" {
-			url.Host = c.args.front
-		}
 		var body io.Reader
 		if len(sndBuf) > 0 {
 			body = bytes.NewReader(sndBuf)
 		}
-		req, err = http.NewRequest("POST", url.String(), body)
+		req, err = http.NewRequest(http.MethodPost, urlStr, body)
 		if err != nil {
 			return nil, err
 		}
@@ -248,16 +256,17 @@ func (c *meekConn) roundTrip(sndBuf []byte) (recvBuf []byte, err error) {
 		}
 
 		if resp.StatusCode == http.StatusOK {
-			recvBuf, err = ioutil.ReadAll(io.LimitReader(resp.Body, maxPayloadLength))
+			var recvBuf []byte
+			recvBuf, err = io.ReadAll(io.LimitReader(resp.Body, maxPayloadLength))
 			resp.Body.Close()
-			return
+			return recvBuf, err
 		}
 
 		resp.Body.Close()
 		err = fmt.Errorf("status code was %d, not %d", resp.StatusCode, http.StatusOK)
 		time.Sleep(retryDelay)
 	}
-	return
+	return nil, err
 }
 
 func (c *meekConn) ioWorker() {
@@ -305,19 +314,20 @@ loop:
 		}
 
 		// Determine the next poll interval.
-		if len(rdBuf) > 0 {
+		switch {
+		case len(rdBuf) > 0:
 			// Received data, enqueue the read.
 			c.workerRdChan <- rdBuf
 
 			// And poll immediately.
 			interval = 0
-		} else if wrSz > 0 {
+		case wrSz > 0:
 			// Sent data, poll immediately.
 			interval = 0
-		} else if interval == 0 {
+		case interval == 0:
 			// Neither sent nor received data after a poll, re-initialize the delay.
 			interval = initPollInterval
-		} else {
+		default:
 			// Apply a multiplicative backoff.
 			interval = time.Duration(float64(interval) * pollIntervalMultiplier)
 			if interval > maxPollInterval {
@@ -337,7 +347,7 @@ loop:
 	_ = c.Close()
 }
 
-func newMeekConn(network, addr string, dialFn base.DialFunc, ca *meekClientArgs) (net.Conn, error) {
+func newMeekConn(dialFn base.DialFunc, ca *meekClientArgs) (net.Conn, error) {
 	id, err := newSessionID()
 	if err != nil {
 		return nil, err
diff --git a/transports/obfs2/obfs2.go b/transports/obfs2/obfs2.go
index 531bcd4..ff0e4f6 100644
--- a/transports/obfs2/obfs2.go
+++ b/transports/obfs2/obfs2.go
@@ -40,7 +40,8 @@ import (
 	"net"
 	"time"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 	"gitlab.com/yawning/obfs4.git/transports/base"
 )
@@ -81,13 +82,13 @@ func (t *Transport) Name() string {
 }
 
 // ClientFactory returns a new obfs2ClientFactory instance.
-func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) {
+func (t *Transport) ClientFactory(_ string) (base.ClientFactory, error) {
 	cf := &obfs2ClientFactory{transport: t}
 	return cf, nil
 }
 
 // ServerFactory returns a new obfs2ServerFactory instance.
-func (t *Transport) ServerFactory(stateDir string, args *pt.Args) (base.ServerFactory, error) {
+func (t *Transport) ServerFactory(_ string, args *pt.Args) (base.ServerFactory, error) {
 	if err := validateArgs(args); err != nil {
 		return nil, err
 	}
@@ -104,11 +105,11 @@ func (cf *obfs2ClientFactory) Transport() base.Transport {
 	return cf.transport
 }
 
-func (cf *obfs2ClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
+func (cf *obfs2ClientFactory) ParseArgs(args *pt.Args) (any, error) {
 	return nil, validateArgs(args)
 }
 
-func (cf *obfs2ClientFactory) Dial(network, addr string, dialFn base.DialFunc, args interface{}) (net.Conn, error) {
+func (cf *obfs2ClientFactory) Dial(network, addr string, dialFn base.DialFunc, _ any) (net.Conn, error) {
 	conn, err := dialFn(network, addr)
 	if err != nil {
 		return nil, err
@@ -154,46 +155,46 @@ func (conn *obfs2Conn) Write(b []byte) (int, error) {
 	return conn.tx.Write(b)
 }
 
-func newObfs2ClientConn(conn net.Conn) (c *obfs2Conn, err error) {
+func newObfs2ClientConn(conn net.Conn) (*obfs2Conn, error) {
 	// Initialize a client connection, and start the handshake timeout.
-	c = &obfs2Conn{conn, true, nil, nil}
+	c := &obfs2Conn{conn, true, nil, nil}
 	deadline := time.Now().Add(clientHandshakeTimeout)
-	if err = c.SetDeadline(deadline); err != nil {
+	if err := c.SetDeadline(deadline); err != nil {
 		return nil, err
 	}
 
 	// Handshake.
-	if err = c.handshake(); err != nil {
+	if err := c.handshake(); err != nil {
 		return nil, err
 	}
 
 	// Disarm the handshake timer.
-	if err = c.SetDeadline(time.Time{}); err != nil {
+	if err := c.SetDeadline(time.Time{}); err != nil {
 		return nil, err
 	}
 
-	return
+	return c, nil
 }
 
-func newObfs2ServerConn(conn net.Conn) (c *obfs2Conn, err error) {
+func newObfs2ServerConn(conn net.Conn) (*obfs2Conn, error) {
 	// Initialize a server connection, and start the handshake timeout.
-	c = &obfs2Conn{conn, false, nil, nil}
+	c := &obfs2Conn{conn, false, nil, nil}
 	deadline := time.Now().Add(serverHandshakeTimeout)
-	if err = c.SetDeadline(deadline); err != nil {
+	if err := c.SetDeadline(deadline); err != nil {
 		return nil, err
 	}
 
 	// Handshake.
-	if err = c.handshake(); err != nil {
+	if err := c.handshake(); err != nil {
 		return nil, err
 	}
 
 	// Disarm the handshake timer.
-	if err = c.SetDeadline(time.Time{}); err != nil {
+	if err := c.SetDeadline(time.Time{}); err != nil {
 		return nil, err
 	}
 
-	return
+	return c, nil
 }
 
 func (conn *obfs2Conn) handshake() error {
@@ -220,7 +221,7 @@ func (conn *obfs2Conn) handshake() error {
 	} else {
 		padMagic = []byte(responderPadString)
 	}
-	padKey, padIV := hsKdf(padMagic, seed[:], conn.isInitiator)
+	padKey, padIV := hsKdf(padMagic, seed[:])
 	padLen := uint32(csrand.IntRange(0, maxPadding))
 
 	hsBlob := make([]byte, hsLen+padLen)
@@ -265,7 +266,7 @@ func (conn *obfs2Conn) handshake() error {
 	} else {
 		peerPadMagic = []byte(initiatorPadString)
 	}
-	peerKey, peerIV := hsKdf(peerPadMagic, peerSeed[:], !conn.isInitiator)
+	peerKey, peerIV := hsKdf(peerPadMagic, peerSeed[:])
 	rxBlock, err := aes.NewCipher(peerKey)
 	if err != nil {
 		return err
@@ -273,7 +274,7 @@ func (conn *obfs2Conn) handshake() error {
 	rxStream := cipher.NewCTR(rxBlock, peerIV)
 	conn.rx = &cipher.StreamReader{S: rxStream, R: conn.Conn}
 	hsHdr := make([]byte, hsLen)
-	if _, err := io.ReadFull(conn, hsHdr[:]); err != nil {
+	if _, err := io.ReadFull(conn, hsHdr); err != nil {
 		return err
 	}
 
@@ -296,11 +297,7 @@ func (conn *obfs2Conn) handshake() error {
 	}
 
 	// Derive the actual keys.
-	if err := conn.kdf(seed[:], peerSeed[:]); err != nil {
-		return err
-	}
-
-	return nil
+	return conn.kdf(seed[:], peerSeed[:])
 }
 
 func (conn *obfs2Conn) kdf(seed, peerSeed []byte) error {
@@ -321,14 +318,14 @@ func (conn *obfs2Conn) kdf(seed, peerSeed []byte) error {
 		combSeed = append(combSeed, seed...)
 	}
 
-	initKey, initIV := hsKdf([]byte(initiatorKdfString), combSeed, true)
+	initKey, initIV := hsKdf([]byte(initiatorKdfString), combSeed)
 	initBlock, err := aes.NewCipher(initKey)
 	if err != nil {
 		return err
 	}
 	initStream := cipher.NewCTR(initBlock, initIV)
 
-	respKey, respIV := hsKdf([]byte(responderKdfString), combSeed, false)
+	respKey, respIV := hsKdf([]byte(responderKdfString), combSeed)
 	respBlock, err := aes.NewCipher(respKey)
 	if err != nil {
 		return err
@@ -346,16 +343,16 @@ func (conn *obfs2Conn) kdf(seed, peerSeed []byte) error {
 	return nil
 }
 
-func hsKdf(magic, seed []byte, isInitiator bool) (padKey, padIV []byte) {
+func hsKdf(magic, seed []byte) ([]byte, []byte) {
 	// The actual key/IV is derived in the form of:
 	// m = MAC(magic, seed)
 	// KEY = m[:KEYLEN]
 	// IV = m[KEYLEN:]
 	m := mac(magic, seed)
-	padKey = m[:keyLen]
-	padIV = m[keyLen:]
+	padKey := m[:keyLen]
+	padIV := m[keyLen:]
 
-	return
+	return padKey, padIV
 }
 
 func mac(s, x []byte) []byte {
@@ -368,7 +365,9 @@ func mac(s, x []byte) []byte {
 	return h.Sum(nil)
 }
 
-var _ base.ClientFactory = (*obfs2ClientFactory)(nil)
-var _ base.ServerFactory = (*obfs2ServerFactory)(nil)
-var _ base.Transport = (*Transport)(nil)
-var _ net.Conn = (*obfs2Conn)(nil)
+var (
+	_ base.ClientFactory = (*obfs2ClientFactory)(nil)
+	_ base.ServerFactory = (*obfs2ServerFactory)(nil)
+	_ base.Transport     = (*Transport)(nil)
+	_ net.Conn           = (*obfs2Conn)(nil)
+)
diff --git a/transports/obfs3/obfs3.go b/transports/obfs3/obfs3.go
index 42bdd90..fb5d99a 100644
--- a/transports/obfs3/obfs3.go
+++ b/transports/obfs3/obfs3.go
@@ -40,7 +40,8 @@ import (
 	"net"
 	"time"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 	"gitlab.com/yawning/obfs4.git/common/uniformdh"
 	"gitlab.com/yawning/obfs4.git/transports/base"
@@ -69,13 +70,13 @@ func (t *Transport) Name() string {
 }
 
 // ClientFactory returns a new obfs3ClientFactory instance.
-func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) {
+func (t *Transport) ClientFactory(_ string) (base.ClientFactory, error) {
 	cf := &obfs3ClientFactory{transport: t}
 	return cf, nil
 }
 
 // ServerFactory returns a new obfs3ServerFactory instance.
-func (t *Transport) ServerFactory(stateDir string, args *pt.Args) (base.ServerFactory, error) {
+func (t *Transport) ServerFactory(_ string, _ *pt.Args) (base.ServerFactory, error) {
 	sf := &obfs3ServerFactory{transport: t}
 	return sf, nil
 }
@@ -88,11 +89,11 @@ func (cf *obfs3ClientFactory) Transport() base.Transport {
 	return cf.transport
 }
 
-func (cf *obfs3ClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
-	return nil, nil
+func (cf *obfs3ClientFactory) ParseArgs(_ *pt.Args) (any, error) {
+	return nil, nil //nolint:nilnil
 }
 
-func (cf *obfs3ClientFactory) Dial(network, addr string, dialFn base.DialFunc, args interface{}) (net.Conn, error) {
+func (cf *obfs3ClientFactory) Dial(network, addr string, dialFn base.DialFunc, _ any) (net.Conn, error) {
 	conn, err := dialFn(network, addr)
 	if err != nil {
 		return nil, err
@@ -133,46 +134,46 @@ type obfs3Conn struct {
 	tx *cipher.StreamWriter
 }
 
-func newObfs3ClientConn(conn net.Conn) (c *obfs3Conn, err error) {
+func newObfs3ClientConn(conn net.Conn) (*obfs3Conn, error) {
 	// Initialize a client connection, and start the handshake timeout.
-	c = &obfs3Conn{conn, true, nil, nil, new(bytes.Buffer), nil, nil}
+	c := &obfs3Conn{conn, true, nil, nil, new(bytes.Buffer), nil, nil}
 	deadline := time.Now().Add(clientHandshakeTimeout)
-	if err = c.SetDeadline(deadline); err != nil {
+	if err := c.SetDeadline(deadline); err != nil {
 		return nil, err
 	}
 
 	// Handshake.
-	if err = c.handshake(); err != nil {
+	if err := c.handshake(); err != nil {
 		return nil, err
 	}
 
 	// Disarm the handshake timer.
-	if err = c.SetDeadline(time.Time{}); err != nil {
+	if err := c.SetDeadline(time.Time{}); err != nil {
 		return nil, err
 	}
 
-	return
+	return c, nil
 }
 
-func newObfs3ServerConn(conn net.Conn) (c *obfs3Conn, err error) {
+func newObfs3ServerConn(conn net.Conn) (*obfs3Conn, error) {
 	// Initialize a server connection, and start the handshake timeout.
-	c = &obfs3Conn{conn, false, nil, nil, new(bytes.Buffer), nil, nil}
+	c := &obfs3Conn{conn, false, nil, nil, new(bytes.Buffer), nil, nil}
 	deadline := time.Now().Add(serverHandshakeTimeout)
-	if err = c.SetDeadline(deadline); err != nil {
+	if err := c.SetDeadline(deadline); err != nil {
 		return nil, err
 	}
 
 	// Handshake.
-	if err = c.handshake(); err != nil {
+	if err := c.handshake(); err != nil {
 		return nil, err
 	}
 
 	// Disarm the handshake timer.
-	if err = c.SetDeadline(time.Time{}); err != nil {
+	if err := c.SetDeadline(time.Time{}); err != nil {
 		return nil, err
 	}
 
-	return
+	return c, nil
 }
 
 func (conn *obfs3Conn) handshake() error {
@@ -217,11 +218,7 @@ func (conn *obfs3Conn) handshake() error {
 	if err != nil {
 		return err
 	}
-	if err := conn.kdf(sharedSecret); err != nil {
-		return err
-	}
-
-	return nil
+	return conn.kdf(sharedSecret)
 }
 
 func (conn *obfs3Conn) kdf(sharedSecret []byte) error {
@@ -313,13 +310,13 @@ func (conn *obfs3Conn) findPeerMagic() error {
 	}
 }
 
-func (conn *obfs3Conn) Read(b []byte) (n int, err error) {
+func (conn *obfs3Conn) Read(b []byte) (int, error) {
 	// If this is the first time we read data post handshake, scan for the
 	// magic value.
 	if conn.rxMagic != nil {
-		if err = conn.findPeerMagic(); err != nil {
+		if err := conn.findPeerMagic(); err != nil {
 			conn.Close()
-			return
+			return 0, err
 		}
 		conn.rxMagic = nil
 	}
@@ -339,20 +336,20 @@ func (conn *obfs3Conn) Read(b []byte) (n int, err error) {
 	return conn.rx.Read(b)
 }
 
-func (conn *obfs3Conn) Write(b []byte) (n int, err error) {
+func (conn *obfs3Conn) Write(b []byte) (int, error) {
 	// If this is the first time we write data post handshake, send the
 	// padding/magic value.
 	if conn.txMagic != nil {
 		padLen := csrand.IntRange(0, maxPadding/2)
 		blob := make([]byte, padLen+len(conn.txMagic))
-		if err = csrand.Bytes(blob[:padLen]); err != nil {
+		if err := csrand.Bytes(blob[:padLen]); err != nil {
 			conn.Close()
-			return
+			return 0, err
 		}
 		copy(blob[padLen:], conn.txMagic)
-		if _, err = conn.Conn.Write(blob); err != nil {
+		if _, err := conn.Conn.Write(blob); err != nil {
 			conn.Close()
-			return
+			return 0, err
 		}
 		conn.txMagic = nil
 	}
@@ -360,7 +357,9 @@ func (conn *obfs3Conn) Write(b []byte) (n int, err error) {
 	return conn.tx.Write(b)
 }
 
-var _ base.ClientFactory = (*obfs3ClientFactory)(nil)
-var _ base.ServerFactory = (*obfs3ServerFactory)(nil)
-var _ base.Transport = (*Transport)(nil)
-var _ net.Conn = (*obfs3Conn)(nil)
+var (
+	_ base.ClientFactory = (*obfs3ClientFactory)(nil)
+	_ base.ServerFactory = (*obfs3ServerFactory)(nil)
+	_ base.Transport     = (*Transport)(nil)
+	_ net.Conn           = (*obfs3Conn)(nil)
+)
diff --git a/transports/obfs4/framing/framing.go b/transports/obfs4/framing/framing.go
index 10604a9..679348b 100644
--- a/transports/obfs4/framing/framing.go
+++ b/transports/obfs4/framing/framing.go
@@ -25,39 +25,40 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-//
 // Package framing implements the obfs4 link framing and cryptography.
 //
 // The Encoder/Decoder shared secret format is:
-//    uint8_t[32] NaCl secretbox key
-//    uint8_t[16] NaCl Nonce prefix
-//    uint8_t[16] SipHash-2-4 key (used to obfsucate length)
-//    uint8_t[8]  SipHash-2-4 IV
+//
+//	uint8_t[32] NaCl secretbox key
+//	uint8_t[16] NaCl Nonce prefix
+//	uint8_t[16] SipHash-2-4 key (used to obfsucate length)
+//	uint8_t[8]  SipHash-2-4 IV
 //
 // The frame format is:
-//   uint16_t length (obfsucated, big endian)
-//   NaCl secretbox (Poly1305/XSalsa20) containing:
-//     uint8_t[16] tag (Part of the secretbox construct)
-//     uint8_t[]   payload
+//
+//	uint16_t length (obfsucated, big endian)
+//	NaCl secretbox (Poly1305/XSalsa20) containing:
+//	  uint8_t[16] tag (Part of the secretbox construct)
+//	  uint8_t[]   payload
 //
 // The length field is length of the NaCl secretbox XORed with the truncated
 // SipHash-2-4 digest ran in OFB mode.
 //
-//     Initialize K, IV[0] with values from the shared secret.
-//     On each packet, IV[n] = H(K, IV[n - 1])
-//     mask[n] = IV[n][0:2]
-//     obfsLen = length ^ mask[n]
+//	Initialize K, IV[0] with values from the shared secret.
+//	On each packet, IV[n] = H(K, IV[n - 1])
+//	mask[n] = IV[n][0:2]
+//	obfsLen = length ^ mask[n]
 //
 // The NaCl secretbox (Poly1305/XSalsa20) nonce format is:
-//     uint8_t[24] prefix (Fixed)
-//     uint64_t    counter (Big endian)
+//
+//	uint8_t[24] prefix (Fixed)
+//	uint64_t    counter (Big endian)
 //
 // The counter is initialized to 1, and is incremented on each frame.  Since
 // the protocol is designed to be used over a reliable medium, the nonce is not
 // transmitted over the wire as both sides of the conversation know the prefix
 // and the initial counter value.  It is imperative that the counter does not
 // wrap, and sessions MUST terminate before 2^64 frames are sent.
-//
 package framing // import "gitlab.com/yawning/obfs4.git/transports/obfs4/framing"
 
 import (
@@ -67,9 +68,10 @@ import (
 	"fmt"
 	"io"
 
+	"golang.org/x/crypto/nacl/secretbox"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 	"gitlab.com/yawning/obfs4.git/common/drbg"
-	"golang.org/x/crypto/nacl/secretbox"
 )
 
 const (
@@ -175,7 +177,7 @@ func NewEncoder(key []byte) *Encoder {
 // Encode encodes a single frame worth of payload and returns the encoded
 // length.  InvalidPayloadLengthError is recoverable, all other errors MUST be
 // treated as fatal and the session aborted.
-func (encoder *Encoder) Encode(frame, payload []byte) (n int, err error) {
+func (encoder *Encoder) Encode(frame, payload []byte) (int, error) {
 	payloadLen := len(payload)
 	if MaximumFramePayloadLength < payloadLen {
 		return 0, InvalidPayloadLengthError(payloadLen)
@@ -186,7 +188,7 @@ func (encoder *Encoder) Encode(frame, payload []byte) (n int, err error) {
 
 	// Generate a new nonce.
 	var nonce [nonceLength]byte
-	if err = encoder.nonce.bytes(&nonce); err != nil {
+	if err := encoder.nonce.bytes(&nonce); err != nil {
 		return 0, err
 	}
 	encoder.nonce.counter++
diff --git a/transports/obfs4/framing/framing_test.go b/transports/obfs4/framing/framing_test.go
index d830625..585f6ed 100644
--- a/transports/obfs4/framing/framing_test.go
+++ b/transports/obfs4/framing/framing_test.go
@@ -30,6 +30,7 @@ package framing
 import (
 	"bytes"
 	"crypto/rand"
+	"errors"
 	"testing"
 )
 
@@ -89,7 +90,9 @@ func TestEncoder_Encode_Oversize(t *testing.T) {
 	var buf [MaximumFramePayloadLength + 1]byte
 	_, _ = rand.Read(buf[:]) // YOLO
 	_, err := encoder.Encode(frame[:], buf[:])
-	if _, ok := err.(InvalidPayloadLengthError); !ok {
+
+	var payloadErr InvalidPayloadLengthError
+	if !errors.As(err, &payloadErr) {
 		t.Error("Encoder.encode() returned unexpected error:", err)
 	}
 }
@@ -150,7 +153,7 @@ func BenchmarkEncoder_Encode(b *testing.B) {
 	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
-		transfered := 0
+		var xfered int
 		buffer := bytes.NewBuffer(payload)
 		for 0 < buffer.Len() {
 			n, err := buffer.Read(chopBuf[:])
@@ -159,11 +162,10 @@ func BenchmarkEncoder_Encode(b *testing.B) {
 			}
 
 			n, _ = encoder.Encode(frame[:], chopBuf[:n])
-			transfered += n - FrameOverhead
+			xfered += n - FrameOverhead
 		}
-		if transfered != len(payload) {
-			b.Fatalf("Transfered length mismatch: %d != %d", transfered,
-				len(payload))
+		if xfered != len(payload) {
+			b.Fatalf("Xfered length mismatch: %d != %d", xfered, len(payload))
 		}
 	}
 }
diff --git a/transports/obfs4/handshake_ntor.go b/transports/obfs4/handshake_ntor.go
index c5d0e6c..c39a116 100644
--- a/transports/obfs4/handshake_ntor.go
+++ b/transports/obfs4/handshake_ntor.go
@@ -280,7 +280,7 @@ func (hs *serverHandshake) parseClientHandshake(filter *replayfilter.ReplayFilte
 	macFound := false
 	for _, off := range []int64{0, -1, 1} {
 		// Allow epoch to be off by up to a hour in either direction.
-		epochHour := []byte(strconv.FormatInt(getEpochHour()+int64(off), 10))
+		epochHour := []byte(strconv.FormatInt(getEpochHour()+off, 10))
 		hs.mac.Reset()
 		_, _ = hs.mac.Write(resp[:pos+markLength])
 		_, _ = hs.mac.Write(epochHour)
@@ -367,7 +367,7 @@ func getEpochHour() int64 {
 	return time.Now().Unix() / 3600
 }
 
-func findMarkMac(mark, buf []byte, startPos, maxPos int, fromTail bool) (pos int) {
+func findMarkMac(mark, buf []byte, startPos, maxPos int, fromTail bool) int {
 	if len(mark) != markLength {
 		panic(fmt.Sprintf("BUG: Invalid mark length: %d", len(mark)))
 	}
@@ -387,19 +387,19 @@ func findMarkMac(mark, buf []byte, startPos, maxPos int, fromTail bool) (pos int
 		// The server can optimize the search process by only examining the
 		// tail of the buffer.  The client can't send valid data past M_C |
 		// MAC_C as it does not have the server's public key yet.
-		pos = endPos - (markLength + macLength)
+		pos := endPos - (markLength + macLength)
 		if !hmac.Equal(buf[pos:pos+markLength], mark) {
 			return -1
 		}
 
-		return
+		return pos
 	}
 
 	// The client has to actually do a substring search since the server can
 	// and will send payload trailing the response.
 	//
 	// XXX: bytes.Index() uses a naive search, which kind of sucks.
-	pos = bytes.Index(buf[startPos:endPos], mark)
+	pos := bytes.Index(buf[startPos:endPos], mark)
 	if pos == -1 {
 		return -1
 	}
@@ -411,7 +411,7 @@ func findMarkMac(mark, buf []byte, startPos, maxPos int, fromTail bool) (pos int
 
 	// Return the index relative to the start of the slice.
 	pos += startPos
-	return
+	return pos
 }
 
 func makePad(padLen int) ([]byte, error) {
diff --git a/transports/obfs4/handshake_ntor_test.go b/transports/obfs4/handshake_ntor_test.go
index 701c610..3d26d74 100644
--- a/transports/obfs4/handshake_ntor_test.go
+++ b/transports/obfs4/handshake_ntor_test.go
@@ -115,7 +115,7 @@ func TestHandshakeNtorClient(t *testing.T) {
 	serverHs := newServerHandshake(nodeID, idKeypair, serverKeypair)
 	_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
 	if err == nil {
-		t.Fatalf("serverHandshake.parseClientHandshake() succeded (oversized)")
+		t.Fatalf("serverHandshake.parseClientHandshake() succeeded (oversized)")
 	}
 
 	// Test undersized client padding.
@@ -127,7 +127,7 @@ func TestHandshakeNtorClient(t *testing.T) {
 	serverHs = newServerHandshake(nodeID, idKeypair, serverKeypair)
 	_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
 	if err == nil {
-		t.Fatalf("serverHandshake.parseClientHandshake() succeded (undersized)")
+		t.Fatalf("serverHandshake.parseClientHandshake() succeeded (undersized)")
 	}
 }
 
@@ -204,7 +204,7 @@ func TestHandshakeNtorServer(t *testing.T) {
 	serverHs := newServerHandshake(nodeID, idKeypair, serverKeypair)
 	_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
 	if err == nil {
-		t.Fatalf("serverHandshake.parseClientHandshake() succeded (oversized)")
+		t.Fatalf("serverHandshake.parseClientHandshake() succeeded (oversized)")
 	}
 
 	// Test undersized client padding.
@@ -216,7 +216,7 @@ func TestHandshakeNtorServer(t *testing.T) {
 	serverHs = newServerHandshake(nodeID, idKeypair, serverKeypair)
 	_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
 	if err == nil {
-		t.Fatalf("serverHandshake.parseClientHandshake() succeded (undersized)")
+		t.Fatalf("serverHandshake.parseClientHandshake() succeeded (undersized)")
 	}
 
 	// Test oversized server padding.
@@ -243,6 +243,6 @@ func TestHandshakeNtorServer(t *testing.T) {
 	}
 	_, _, err = clientHs.parseServerHandshake(serverBlob)
 	if err == nil {
-		t.Fatalf("clientHandshake.parseServerHandshake() succeded (oversized)")
+		t.Fatalf("clientHandshake.parseServerHandshake() succeeded (oversized)")
 	}
 }
diff --git a/transports/obfs4/obfs4.go b/transports/obfs4/obfs4.go
index 9723735..e053ddc 100644
--- a/transports/obfs4/obfs4.go
+++ b/transports/obfs4/obfs4.go
@@ -32,17 +32,18 @@ package obfs4 // import "gitlab.com/yawning/obfs4.git/transports/obfs4"
 import (
 	"bytes"
 	"crypto/sha256"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math/rand"
 	"net"
 	"strconv"
 	"syscall"
 	"time"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/common/drbg"
 	"gitlab.com/yawning/obfs4.git/common/ntor"
 	"gitlab.com/yawning/obfs4.git/common/probdist"
@@ -81,7 +82,7 @@ const (
 
 // biasedDist controls if the probability table will be ScrambleSuit style or
 // uniformly distributed.
-var biasedDist bool
+var biasedDist = flag.Bool(biasCmdArg, false, "Enable obfs4 using ScrambleSuit style table generation")
 
 type obfs4ClientArgs struct {
 	nodeID     *ntor.NodeID
@@ -99,7 +100,7 @@ func (t *Transport) Name() string {
 }
 
 // ClientFactory returns a new obfs4ClientFactory instance.
-func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) {
+func (t *Transport) ClientFactory(_ string) (base.ClientFactory, error) {
 	cf := &obfs4ClientFactory{transport: t}
 	return cf, nil
 }
@@ -137,7 +138,7 @@ func (t *Transport) ServerFactory(stateDir string, args *pt.Args) (base.ServerFa
 	if err != nil {
 		return nil, err
 	}
-	rng := rand.New(drbg)
+	rng := rand.New(drbg) //nolint:gosec
 
 	sf := &obfs4ServerFactory{t, &ptArgs, st.nodeID, st.identityKey, st.drbgSeed, iatSeed, st.iatMode, filter, rng.Intn(maxCloseDelay)}
 	return sf, nil
@@ -151,14 +152,14 @@ func (cf *obfs4ClientFactory) Transport() base.Transport {
 	return cf.transport
 }
 
-func (cf *obfs4ClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
+func (cf *obfs4ClientFactory) ParseArgs(args *pt.Args) (any, error) {
 	var nodeID *ntor.NodeID
 	var publicKey *ntor.PublicKey
 
 	// The "new" (version >= 0.0.3) bridge lines use a unified "cert" argument
 	// for the Node ID and Public Key.
 	certStr, ok := args.Get(certArg)
-	if ok {
+	if ok { //nolint:nestif
 		cert, err := serverCertFromString(certStr)
 		if err != nil {
 			return nil, err
@@ -195,7 +196,7 @@ func (cf *obfs4ClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
 		return nil, fmt.Errorf("invalid iat-mode '%d'", iatMode)
 	}
 
-	// Generate the session key pair before connectiong to hide the Elligator2
+	// Generate the session key pair before connecting to hide the Elligator2
 	// rejection sampling from network observers.
 	sessionKey, err := ntor.NewKeypair(true)
 	if err != nil {
@@ -205,7 +206,7 @@ func (cf *obfs4ClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
 	return &obfs4ClientArgs{nodeID, publicKey, sessionKey, iatMode}, nil
 }
 
-func (cf *obfs4ClientFactory) Dial(network, addr string, dialFn base.DialFunc, args interface{}) (net.Conn, error) {
+func (cf *obfs4ClientFactory) Dial(network, addr string, dialFn base.DialFunc, args any) (net.Conn, error) {
 	// Validate args before bothering to open connection.
 	ca, ok := args.(*obfs4ClientArgs)
 	if !ok {
@@ -259,10 +260,10 @@ func (sf *obfs4ServerFactory) WrapConn(conn net.Conn) (net.Conn, error) {
 		return nil, err
 	}
 
-	lenDist := probdist.New(sf.lenSeed, 0, framing.MaximumSegmentLength, biasedDist)
+	lenDist := probdist.New(sf.lenSeed, 0, framing.MaximumSegmentLength, *biasedDist)
 	var iatDist *probdist.WeightedDist
 	if sf.iatSeed != nil {
-		iatDist = probdist.New(sf.iatSeed, 0, maxIATDelay, biasedDist)
+		iatDist = probdist.New(sf.iatSeed, 0, maxIATDelay, *biasedDist)
 	}
 
 	c := &obfs4Conn{conn, true, lenDist, iatDist, sf.iatMode, bytes.NewBuffer(nil), bytes.NewBuffer(nil), make([]byte, consumeReadSize), nil, nil}
@@ -294,25 +295,28 @@ type obfs4Conn struct {
 	decoder *framing.Decoder
 }
 
-func newObfs4ClientConn(conn net.Conn, args *obfs4ClientArgs) (c *obfs4Conn, err error) {
+func newObfs4ClientConn(conn net.Conn, args *obfs4ClientArgs) (*obfs4Conn, error) {
 	// Generate the initial protocol polymorphism distribution(s).
-	var seed *drbg.Seed
+	var (
+		seed *drbg.Seed
+		err  error
+	)
 	if seed, err = drbg.NewSeed(); err != nil {
-		return
+		return nil, err
 	}
-	lenDist := probdist.New(seed, 0, framing.MaximumSegmentLength, biasedDist)
+	lenDist := probdist.New(seed, 0, framing.MaximumSegmentLength, *biasedDist)
 	var iatDist *probdist.WeightedDist
 	if args.iatMode != iatNone {
 		var iatSeed *drbg.Seed
 		iatSeedSrc := sha256.Sum256(seed.Bytes()[:])
 		if iatSeed, err = drbg.SeedFromBytes(iatSeedSrc[:]); err != nil {
-			return
+			return nil, err
 		}
-		iatDist = probdist.New(iatSeed, 0, maxIATDelay, biasedDist)
+		iatDist = probdist.New(iatSeed, 0, maxIATDelay, *biasedDist)
 	}
 
 	// Allocate the client structure.
-	c = &obfs4Conn{conn, false, lenDist, iatDist, args.iatMode, bytes.NewBuffer(nil), bytes.NewBuffer(nil), make([]byte, consumeReadSize), nil, nil}
+	c := &obfs4Conn{conn, false, lenDist, iatDist, args.iatMode, bytes.NewBuffer(nil), bytes.NewBuffer(nil), make([]byte, consumeReadSize), nil, nil}
 
 	// Start the handshake timeout.
 	deadline := time.Now().Add(clientHandshakeTimeout)
@@ -329,7 +333,7 @@ func newObfs4ClientConn(conn net.Conn, args *obfs4ClientArgs) (c *obfs4Conn, err
 		return nil, err
 	}
 
-	return
+	return c, nil
 }
 
 func (conn *obfs4Conn) clientHandshake(nodeID *ntor.NodeID, peerIdentityKey *ntor.PublicKey, sessionKey *ntor.Keypair) error {
@@ -359,14 +363,14 @@ func (conn *obfs4Conn) clientHandshake(nodeID *ntor.NodeID, peerIdentityKey *nto
 		conn.receiveBuffer.Write(hsBuf[:n])
 
 		n, seed, err := hs.parseServerHandshake(conn.receiveBuffer.Bytes())
-		if err == ErrMarkNotFoundYet {
+		if errors.Is(err, ErrMarkNotFoundYet) {
 			continue
 		} else if err != nil {
 			return err
 		}
 		_ = conn.receiveBuffer.Next(n)
 
-		// Use the derived key material to intialize the link crypto.
+		// Use the derived key material to initialize the link crypto.
 		okm := ntor.Kdf(seed, framing.KeyLength*2)
 		conn.encoder = framing.NewEncoder(okm[:framing.KeyLength])
 		conn.decoder = framing.NewDecoder(okm[framing.KeyLength:])
@@ -398,7 +402,7 @@ func (conn *obfs4Conn) serverHandshake(sf *obfs4ServerFactory, sessionKey *ntor.
 		conn.receiveBuffer.Write(hsBuf[:n])
 
 		seed, err := hs.parseClientHandshake(sf.replayFilter, conn.receiveBuffer.Bytes())
-		if err == ErrMarkNotFoundYet {
+		if errors.Is(err, ErrMarkNotFoundYet) {
 			continue
 		} else if err != nil {
 			return err
@@ -406,10 +410,10 @@ func (conn *obfs4Conn) serverHandshake(sf *obfs4ServerFactory, sessionKey *ntor.
 		conn.receiveBuffer.Reset()
 
 		if err := conn.Conn.SetDeadline(time.Time{}); err != nil {
-			return nil
+			return err
 		}
 
-		// Use the derived key material to intialize the link crypto.
+		// Use the derived key material to initialize the link crypto.
 		okm := ntor.Kdf(seed, framing.KeyLength*2)
 		conn.encoder = framing.NewEncoder(okm[framing.KeyLength:])
 		conn.decoder = framing.NewDecoder(okm[:framing.KeyLength])
@@ -421,7 +425,7 @@ func (conn *obfs4Conn) serverHandshake(sf *obfs4ServerFactory, sessionKey *ntor.
 	// the length obfuscation, this makes the amount of data received from the
 	// server inconsistent with the length sent from the client.
 	//
-	// Rebalance this by tweaking the client mimimum padding/server maximum
+	// Rebalance this by tweaking the client minimum padding/server maximum
 	// padding, and sending the PRNG seed unpadded (As in, treat the PRNG seed
 	// as part of the server response).  See inlineSeedFrameLength in
 	// handshake_ntor.go.
@@ -447,13 +451,14 @@ func (conn *obfs4Conn) serverHandshake(sf *obfs4ServerFactory, sessionKey *ntor.
 	return nil
 }
 
-func (conn *obfs4Conn) Read(b []byte) (n int, err error) {
+func (conn *obfs4Conn) Read(b []byte) (int, error) {
 	// If there is no payload from the previous Read() calls, consume data off
 	// the network.  Not all data received is guaranteed to be usable payload,
 	// so do this in a loop till data is present or an error occurs.
+	var err error
 	for conn.receiveDecodedBuffer.Len() == 0 {
 		err = conn.readPackets()
-		if err == framing.ErrAgain {
+		if errors.Is(err, framing.ErrAgain) {
 			// Don't proagate this back up the call stack if we happen to break
 			// out of the loop.
 			err = nil
@@ -465,6 +470,7 @@ func (conn *obfs4Conn) Read(b []byte) (n int, err error) {
 
 	// Even if err is set, attempt to do the read anyway so that all decoded
 	// data gets relayed before the connection is torn down.
+	var n int
 	if conn.receiveDecodedBuffer.Len() > 0 {
 		var berr error
 		n, berr = conn.receiveDecodedBuffer.Read(b)
@@ -475,28 +481,29 @@ func (conn *obfs4Conn) Read(b []byte) (n int, err error) {
 		}
 	}
 
-	return
+	return n, err
 }
 
-func (conn *obfs4Conn) Write(b []byte) (n int, err error) {
+func (conn *obfs4Conn) Write(b []byte) (int, error) {
 	chopBuf := bytes.NewBuffer(b)
-	var payload [maxPacketPayloadLength]byte
-	var frameBuf bytes.Buffer
+	var (
+		payload  [maxPacketPayloadLength]byte
+		frameBuf bytes.Buffer
+		n        int
+	)
 
 	// Chop the pending data into payload frames.
 	for chopBuf.Len() > 0 {
 		// Send maximum sized frames.
-		rdLen := 0
-		rdLen, err = chopBuf.Read(payload[:])
+		rdLen, err := chopBuf.Read(payload[:])
 		if err != nil {
 			return 0, err
 		} else if rdLen == 0 {
-			panic(fmt.Sprintf("BUG: Write(), chopping length was 0"))
+			panic("BUG: Write(), chopping length was 0")
 		}
 		n += rdLen
 
-		err = conn.makePacket(&frameBuf, packetTypePayload, payload[:rdLen], 0)
-		if err != nil {
+		if err = conn.makePacket(&frameBuf, packetTypePayload, payload[:rdLen], 0); err != nil {
 			return 0, err
 		}
 	}
@@ -504,7 +511,7 @@ func (conn *obfs4Conn) Write(b []byte) (n int, err error) {
 	if conn.iatMode != iatParanoid {
 		// For non-paranoid IAT, pad once per burst.  Paranoid IAT handles
 		// things differently.
-		if err = conn.padBurst(&frameBuf, conn.lenDist.Sample()); err != nil {
+		if err := conn.padBurst(&frameBuf, conn.lenDist.Sample()); err != nil {
 			return 0, err
 		}
 	}
@@ -513,10 +520,11 @@ func (conn *obfs4Conn) Write(b []byte) (n int, err error) {
 	// because the frame encoder state is advanced, and the code doesn't keep
 	// frameBuf around.  In theory, write timeouts and whatnot could be
 	// supported if this wasn't the case, but that complicates the code.
-	if conn.iatMode != iatNone {
+	var err error
+	if conn.iatMode != iatNone { //nolint:nestif
 		var iatFrame [framing.MaximumSegmentLength]byte
 		for frameBuf.Len() > 0 {
-			iatWrLen := 0
+			var iatWrLen int
 
 			switch conn.iatMode {
 			case iatEnabled:
@@ -549,7 +557,7 @@ func (conn *obfs4Conn) Write(b []byte) (n int, err error) {
 			if err != nil {
 				return 0, err
 			} else if iatWrLen == 0 {
-				panic(fmt.Sprintf("BUG: Write(), iat length was 0"))
+				panic("BUG: Write(), iat length was 0")
 			}
 
 			// Calculate the delay.  The delay resolution is 100 usec, leading
@@ -557,8 +565,7 @@ func (conn *obfs4Conn) Write(b []byte) (n int, err error) {
 			iatDelta := time.Duration(conn.iatDist.Sample() * 100)
 
 			// Write then sleep.
-			_, err = conn.Conn.Write(iatFrame[:iatWrLen])
-			if err != nil {
+			if _, err = conn.Conn.Write(iatFrame[:iatWrLen]); err != nil {
 				return 0, err
 			}
 			time.Sleep(iatDelta * time.Microsecond)
@@ -567,14 +574,14 @@ func (conn *obfs4Conn) Write(b []byte) (n int, err error) {
 		_, err = conn.Conn.Write(frameBuf.Bytes())
 	}
 
-	return
+	return n, err
 }
 
-func (conn *obfs4Conn) SetDeadline(t time.Time) error {
+func (conn *obfs4Conn) SetDeadline(_ time.Time) error {
 	return syscall.ENOTSUP
 }
 
-func (conn *obfs4Conn) SetWriteDeadline(t time.Time) error {
+func (conn *obfs4Conn) SetWriteDeadline(_ time.Time) error {
 	return syscall.ENOTSUP
 }
 
@@ -594,13 +601,13 @@ func (conn *obfs4Conn) closeAfterDelay(sf *obfs4ServerFactory, startTime time.Ti
 
 	// Consume and discard data on this connection until the specified interval
 	// passes.
-	_, _ = io.Copy(ioutil.Discard, conn.Conn)
+	_, _ = io.Copy(io.Discard, conn.Conn)
 }
 
-func (conn *obfs4Conn) padBurst(burst *bytes.Buffer, toPadTo int) (err error) {
+func (conn *obfs4Conn) padBurst(burst *bytes.Buffer, toPadTo int) error {
 	tailLen := burst.Len() % framing.MaximumSegmentLength
 
-	padLen := 0
+	var padLen int
 	if toPadTo >= tailLen {
 		padLen = toPadTo - tailLen
 	} else {
@@ -608,32 +615,24 @@ func (conn *obfs4Conn) padBurst(burst *bytes.Buffer, toPadTo int) (err error) {
 	}
 
 	if padLen > headerLength {
-		err = conn.makePacket(burst, packetTypePayload, []byte{},
-			uint16(padLen-headerLength))
-		if err != nil {
-			return
+		if err := conn.makePacket(burst, packetTypePayload, []byte{}, uint16(padLen-headerLength)); err != nil {
+			return err
 		}
 	} else if padLen > 0 {
-		err = conn.makePacket(burst, packetTypePayload, []byte{},
-			maxPacketPayloadLength)
-		if err != nil {
-			return
+		if err := conn.makePacket(burst, packetTypePayload, []byte{}, maxPacketPayloadLength); err != nil {
+			return err
 		}
-		err = conn.makePacket(burst, packetTypePayload, []byte{},
-			uint16(padLen))
-		if err != nil {
-			return
+		if err := conn.makePacket(burst, packetTypePayload, []byte{}, uint16(padLen)); err != nil {
+			return err
 		}
 	}
 
-	return
-}
-
-func init() {
-	flag.BoolVar(&biasedDist, biasCmdArg, false, "Enable obfs4 using ScrambleSuit style table generation")
+	return nil
 }
 
-var _ base.ClientFactory = (*obfs4ClientFactory)(nil)
-var _ base.ServerFactory = (*obfs4ServerFactory)(nil)
-var _ base.Transport = (*Transport)(nil)
-var _ net.Conn = (*obfs4Conn)(nil)
+var (
+	_ base.ClientFactory = (*obfs4ClientFactory)(nil)
+	_ base.ServerFactory = (*obfs4ServerFactory)(nil)
+	_ base.Transport     = (*Transport)(nil)
+	_ net.Conn           = (*obfs4Conn)(nil)
+)
diff --git a/transports/obfs4/packet.go b/transports/obfs4/packet.go
index 8d47af9..9b19190 100644
--- a/transports/obfs4/packet.go
+++ b/transports/obfs4/packet.go
@@ -30,6 +30,7 @@ package obfs4
 import (
 	"crypto/sha256"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
 
@@ -52,7 +53,7 @@ const (
 )
 
 // InvalidPacketLengthError is the error returned when decodePacket detects a
-// invalid packet length/
+// invalid packet length.
 type InvalidPacketLengthError int
 
 func (e InvalidPacketLengthError) Error() string {
@@ -85,7 +86,7 @@ func (conn *obfs4Conn) makePacket(w io.Writer, pktType uint8, data []byte, padLe
 	pkt[0] = pktType
 	binary.BigEndian.PutUint16(pkt[1:], uint16(len(data)))
 	if len(data) > 0 {
-		copy(pkt[3:], data[:])
+		copy(pkt[3:], data)
 	}
 	copy(pkt[3+len(data):], zeroPadBytes[:padLen])
 
@@ -108,23 +109,28 @@ func (conn *obfs4Conn) makePacket(w io.Writer, pktType uint8, data []byte, padLe
 	return nil
 }
 
-func (conn *obfs4Conn) readPackets() (err error) {
+func (conn *obfs4Conn) readPackets() error {
 	// Attempt to read off the network.
 	rdLen, rdErr := conn.Conn.Read(conn.readBuffer)
 	conn.receiveBuffer.Write(conn.readBuffer[:rdLen])
 
-	var decoded [framing.MaximumFramePayloadLength]byte
+	var (
+		decoded [framing.MaximumFramePayloadLength]byte
+		err     error
+	)
+bufferLoop:
 	for conn.receiveBuffer.Len() > 0 {
 		// Decrypt an AEAD frame.
-		decLen := 0
+		var decLen int
 		decLen, err = conn.decoder.Decode(decoded[:], conn.receiveBuffer)
-		if err == framing.ErrAgain {
-			break
-		} else if err != nil {
-			break
-		} else if decLen < packetOverhead {
+		switch {
+		case errors.Is(err, framing.ErrAgain):
+			break bufferLoop
+		case err != nil:
+			break bufferLoop
+		case decLen < packetOverhead:
 			err = InvalidPacketLengthError(decLen)
-			break
+			break bufferLoop
 		}
 
 		// Decode the packet.
@@ -171,5 +177,5 @@ func (conn *obfs4Conn) readPackets() (err error) {
 		return rdErr
 	}
 
-	return
+	return err
 }
diff --git a/transports/obfs4/statefile.go b/transports/obfs4/statefile.go
index cbf1d6e..20fc5bd 100644
--- a/transports/obfs4/statefile.go
+++ b/transports/obfs4/statefile.go
@@ -28,16 +28,17 @@
 package obfs4
 
 import (
+	"bytes"
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path"
 	"strconv"
 	"strings"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 	"gitlab.com/yawning/obfs4.git/common/drbg"
 	"gitlab.com/yawning/obfs4.git/common/ntor"
@@ -81,7 +82,7 @@ func (cert *obfs4ServerCert) unpack() (*ntor.NodeID, *ntor.PublicKey) {
 func serverCertFromString(encoded string) (*obfs4ServerCert, error) {
 	decoded, err := base64.StdEncoding.DecodeString(encoded + certSuffix)
 	if err != nil {
-		return nil, fmt.Errorf("failed to decode cert: %s", err)
+		return nil, fmt.Errorf("failed to decode cert: %w", err)
 	}
 
 	if len(decoded) != certLength {
@@ -93,7 +94,10 @@ func serverCertFromString(encoded string) (*obfs4ServerCert, error) {
 
 func serverCertFromState(st *obfs4ServerState) *obfs4ServerCert {
 	cert := new(obfs4ServerCert)
-	cert.raw = append(st.nodeID.Bytes()[:], st.identityKey.Public().Bytes()[:]...)
+
+	cert.raw = bytes.Clone(st.nodeID.Bytes()[:])
+	cert.raw = append(cert.raw, st.identityKey.Public().Bytes()[:]...)
+
 	return cert
 }
 
@@ -121,15 +125,16 @@ func serverStateFromArgs(stateDir string, args *pt.Args) (*obfs4ServerState, err
 
 	// Either a private key, node id, and seed are ALL specified, or
 	// they should be loaded from the state file.
-	if !privKeyOk && !nodeIDOk && !seedOk {
+	switch {
+	case !privKeyOk && !nodeIDOk && !seedOk:
 		if err := jsonServerStateFromFile(stateDir, &js); err != nil {
 			return nil, err
 		}
-	} else if !privKeyOk {
+	case !privKeyOk:
 		return nil, fmt.Errorf("missing argument '%s'", privateKeyArg)
-	} else if !nodeIDOk {
+	case !nodeIDOk:
 		return nil, fmt.Errorf("missing argument '%s'", nodeIDArg)
-	} else if !seedOk {
+	case !seedOk:
 		return nil, fmt.Errorf("missing argument '%s'", seedArg)
 	}
 
@@ -177,7 +182,7 @@ func serverStateFromJSONServerState(stateDir string, js *jsonServerState) (*obfs
 
 func jsonServerStateFromFile(stateDir string, js *jsonServerState) error {
 	fPath := path.Join(stateDir, stateFile)
-	f, err := ioutil.ReadFile(fPath)
+	f, err := os.ReadFile(fPath)
 	if err != nil {
 		if os.IsNotExist(err) {
 			if err = newJSONServerState(stateDir, js); err == nil {
@@ -188,27 +193,29 @@ func jsonServerStateFromFile(stateDir string, js *jsonServerState) error {
 	}
 
 	if err := json.Unmarshal(f, js); err != nil {
-		return fmt.Errorf("failed to load statefile '%s': %s", fPath, err)
+		return fmt.Errorf("failed to load statefile '%s': %w", fPath, err)
 	}
 
 	return nil
 }
 
-func newJSONServerState(stateDir string, js *jsonServerState) (err error) {
+func newJSONServerState(stateDir string, js *jsonServerState) error {
 	// Generate everything a server needs, using the cryptographic PRNG.
 	var st obfs4ServerState
 	rawID := make([]byte, ntor.NodeIDLength)
-	if err = csrand.Bytes(rawID); err != nil {
-		return
+	if err := csrand.Bytes(rawID); err != nil {
+		return err
 	}
+
+	var err error
 	if st.nodeID, err = ntor.NewNodeID(rawID); err != nil {
-		return
+		return err
 	}
 	if st.identityKey, err = ntor.NewKeypair(false); err != nil {
-		return
+		return err
 	}
 	if st.drbgSeed, err = drbg.NewSeed(); err != nil {
-		return
+		return err
 	}
 	st.iatMode = iatNone
 
@@ -228,11 +235,7 @@ func writeJSONServerState(stateDir string, js *jsonServerState) error {
 	if encoded, err = json.Marshal(js); err != nil {
 		return err
 	}
-	if err = ioutil.WriteFile(path.Join(stateDir, stateFile), encoded, 0600); err != nil {
-		return err
-	}
-
-	return nil
+	return os.WriteFile(path.Join(stateDir, stateFile), encoded, 0o600)
 }
 
 func newBridgeFile(stateDir string, st *obfs4ServerState) error {
@@ -252,9 +255,5 @@ func newBridgeFile(stateDir string, st *obfs4ServerState) error {
 		st.clientString())
 
 	tmp := []byte(prefix + bridgeLine)
-	if err := ioutil.WriteFile(path.Join(stateDir, bridgeFile), tmp, 0600); err != nil {
-		return err
-	}
-
-	return nil
+	return os.WriteFile(path.Join(stateDir, bridgeFile), tmp, 0o600)
 }
diff --git a/transports/scramblesuit/base.go b/transports/scramblesuit/base.go
index 655ad7a..9947573 100644
--- a/transports/scramblesuit/base.go
+++ b/transports/scramblesuit/base.go
@@ -33,7 +33,8 @@ import (
 	"fmt"
 	"net"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+
 	"gitlab.com/yawning/obfs4.git/transports/base"
 )
 
@@ -58,8 +59,7 @@ func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) {
 }
 
 // ServerFactory will one day return a new ssServerFactory instance.
-func (t *Transport) ServerFactory(stateDir string, args *pt.Args) (base.ServerFactory, error) {
-	// TODO: Fill this in eventually, though obfs4 is better.
+func (t *Transport) ServerFactory(_ string, _ *pt.Args) (base.ServerFactory, error) {
 	return nil, fmt.Errorf("server not supported")
 }
 
@@ -72,11 +72,11 @@ func (cf *ssClientFactory) Transport() base.Transport {
 	return cf.transport
 }
 
-func (cf *ssClientFactory) ParseArgs(args *pt.Args) (interface{}, error) {
+func (cf *ssClientFactory) ParseArgs(args *pt.Args) (any, error) {
 	return newClientArgs(args)
 }
 
-func (cf *ssClientFactory) Dial(network, addr string, dialFn base.DialFunc, args interface{}) (net.Conn, error) {
+func (cf *ssClientFactory) Dial(network, addr string, dialFn base.DialFunc, args any) (net.Conn, error) {
 	// Validate args before opening outgoing connection.
 	ca, ok := args.(*ssClientArgs)
 	if !ok {
@@ -95,5 +95,7 @@ func (cf *ssClientFactory) Dial(network, addr string, dialFn base.DialFunc, args
 	return conn, nil
 }
 
-var _ base.ClientFactory = (*ssClientFactory)(nil)
-var _ base.Transport = (*Transport)(nil)
+var (
+	_ base.ClientFactory = (*ssClientFactory)(nil)
+	_ base.Transport     = (*Transport)(nil)
+)
diff --git a/transports/scramblesuit/conn.go b/transports/scramblesuit/conn.go
index cc18e18..7b0f66c 100644
--- a/transports/scramblesuit/conn.go
+++ b/transports/scramblesuit/conn.go
@@ -42,7 +42,9 @@ import (
 	"net"
 	"time"
 
-	"git.torproject.org/pluggable-transports/goptlib.git"
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib"
+	"golang.org/x/crypto/hkdf"
+
 	"gitlab.com/yawning/obfs4.git/common/csrand"
 	"gitlab.com/yawning/obfs4.git/common/drbg"
 	"gitlab.com/yawning/obfs4.git/common/probdist"
@@ -87,8 +89,11 @@ type ssClientArgs struct {
 	sessionKey *uniformdh.PrivateKey
 }
 
-func newClientArgs(args *pt.Args) (ca *ssClientArgs, err error) {
-	ca = &ssClientArgs{}
+func newClientArgs(args *pt.Args) (*ssClientArgs, error) {
+	var (
+		ca  ssClientArgs
+		err error
+	)
 	if ca.kB, err = parsePasswordArg(args); err != nil {
 		return nil, err
 	}
@@ -99,7 +104,7 @@ func newClientArgs(args *pt.Args) (ca *ssClientArgs, err error) {
 	if ca.sessionKey, err = uniformdh.GenerateKey(csrand.Reader); err != nil {
 		return nil, err
 	}
-	return
+	return &ca, nil
 }
 
 func parsePasswordArg(args *pt.Args) (*ssSharedSecret, error) {
@@ -112,7 +117,7 @@ func parsePasswordArg(args *pt.Args) (*ssSharedSecret, error) {
 	// shared secret (k_B) used for handshaking.
 	decoded, err := base32.StdEncoding.DecodeString(str)
 	if err != nil {
-		return nil, fmt.Errorf("failed to decode password: %s", err)
+		return nil, fmt.Errorf("failed to decode password: %w", err)
 	}
 	if len(decoded) != sharedSecretLength {
 		return nil, fmt.Errorf("password length %d is invalid", len(decoded))
@@ -131,7 +136,7 @@ func newCryptoState(aesKey []byte, ivPrefix []byte, macKey []byte) (*ssCryptoSta
 	// The ScrambleSuit CTR-AES256 link crypto uses an 8 byte prefix from the
 	// KDF, and a 64 bit counter initialized to 1 as the IV.  The initial value
 	// of the counter isn't documented in the spec either.
-	var initialCtr = []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}
+	initialCtr := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}
 	iv := make([]byte, 0, aes.BlockSize)
 	iv = append(iv, ivPrefix...)
 	iv = append(iv, initialCtr...)
@@ -168,7 +173,8 @@ type ssRxState struct {
 	payloadLen int
 }
 
-func (conn *ssConn) Read(b []byte) (n int, err error) {
+func (conn *ssConn) Read(b []byte) (int, error) {
+	var err error
 	// If the receive payload buffer is empty, consume data off the network.
 	for conn.receiveDecodedBuffer.Len() == 0 {
 		if err = conn.readPackets(); err != nil {
@@ -177,17 +183,19 @@ func (conn *ssConn) Read(b []byte) (n int, err error) {
 	}
 
 	// Service the read request using buffered payload.
+	var n int
 	if conn.receiveDecodedBuffer.Len() > 0 {
 		n, _ = conn.receiveDecodedBuffer.Read(b)
 	}
-	return
+	return n, err
 }
 
-func (conn *ssConn) Write(b []byte) (n int, err error) {
+func (conn *ssConn) Write(b []byte) (int, error) {
 	var frameBuf bytes.Buffer
 	p := b
 	toSend := len(p)
 
+	var n int
 	for toSend > 0 {
 		// Send as much payload as will fit into each frame as possible.
 		wrLen := len(p)
@@ -195,7 +203,7 @@ func (conn *ssConn) Write(b []byte) (n int, err error) {
 			wrLen = maxPayloadLength
 		}
 		payload := p[:wrLen]
-		if err = conn.makePacket(&frameBuf, pktPayload, payload, 0); err != nil {
+		if err := conn.makePayloadPacket(&frameBuf, payload, 0); err != nil {
 			return 0, err
 		}
 
@@ -205,28 +213,28 @@ func (conn *ssConn) Write(b []byte) (n int, err error) {
 	}
 
 	// Pad out the burst as appropriate.
-	if err = conn.padBurst(&frameBuf, conn.lenDist.Sample()); err != nil {
+	if err := conn.padBurst(&frameBuf, conn.lenDist.Sample()); err != nil {
 		return 0, err
 	}
 
 	// Write and return.
-	_, err = conn.Conn.Write(frameBuf.Bytes())
-	return
+	_, err := conn.Conn.Write(frameBuf.Bytes())
+	return n, err
 }
 
-func (conn *ssConn) SetDeadline(t time.Time) error {
+func (conn *ssConn) SetDeadline(_ time.Time) error {
 	return ErrNotSupported
 }
 
-func (conn *ssConn) SetReadDeadline(t time.Time) error {
+func (conn *ssConn) SetReadDeadline(_ time.Time) error {
 	return ErrNotSupported
 }
 
-func (conn *ssConn) SetWriteDeadline(t time.Time) error {
+func (conn *ssConn) SetWriteDeadline(_ time.Time) error {
 	return ErrNotSupported
 }
 
-func (conn *ssConn) makePacket(w io.Writer, pktType byte, data []byte, padLen int) error {
+func (conn *ssConn) makePayloadPacket(w io.Writer, data []byte, padLen int) error {
 	payloadLen := len(data)
 	totalLen := payloadLen + padLen
 	if totalLen > maxPayloadLength {
@@ -238,7 +246,7 @@ func (conn *ssConn) makePacket(w io.Writer, pktType byte, data []byte, padLen in
 	pkt := make([]byte, pktHdrLength, pktHdrLength+payloadLen+padLen)
 	binary.BigEndian.PutUint16(pkt[0:], uint16(totalLen))
 	binary.BigEndian.PutUint16(pkt[2:], uint16(payloadLen))
-	pkt[4] = pktType
+	pkt[4] = pktPayload
 	pkt = append(pkt, data...)
 	pkt = append(pkt, zeroPadBytes[:padLen]...)
 
@@ -319,7 +327,7 @@ func (conn *ssConn) readPackets() error {
 		// Authenticate the packet, by comparing the received MAC with the one
 		// calculated over the ciphertext consumed off the network.
 		cmpMAC := conn.rxCrypto.mac.Sum(nil)[:macLength]
-		if !hmac.Equal(cmpMAC, conn.receiveState.mac[:]) {
+		if !hmac.Equal(cmpMAC, conn.receiveState.mac) {
 			return ErrInvalidPacket
 		}
 
@@ -426,7 +434,7 @@ handshakeUDH:
 		// Attempt to process all the data seen so far as a response.
 		var seed []byte
 		n, seed, err = hs.parseServerHandshake(conn.receiveBuffer.Bytes())
-		if err == errMarkNotFoundYet {
+		if errors.Is(err, errMarkNotFoundYet) {
 			// No response found yet, keep trying.
 			continue
 		} else if err != nil {
@@ -444,7 +452,12 @@ handshakeUDH:
 func (conn *ssConn) initCrypto(seed []byte) error {
 	// Use HKDF-SHA256 (Expand only, no Extract) to generate session keys from
 	// initial keying material.
-	okm := hkdfExpand(sha256.New, seed, nil, kdfSecretLength)
+	rd := hkdf.Expand(sha256.New, seed, nil)
+	okm := make([]byte, kdfSecretLength)
+	if _, err := io.ReadFull(rd, okm); err != nil {
+		return err
+	}
+
 	var err error
 	conn.txCrypto, err = newCryptoState(okm[0:32], okm[32:40], okm[80:112])
 	if err != nil {
@@ -463,7 +476,7 @@ func (conn *ssConn) padBurst(burst *bytes.Buffer, sampleLen int) error {
 	// the ScrambleSuit MTU) is sampleLen bytes.
 
 	dataLen := burst.Len() % maxSegmentLength
-	padLen := 0
+	var padLen int
 	if sampleLen >= dataLen {
 		padLen = sampleLen - dataLen
 	} else {
@@ -481,12 +494,12 @@ func (conn *ssConn) padBurst(burst *bytes.Buffer, sampleLen int) error {
 	if padLen > maxSegmentLength {
 		// Note: packetmorpher.py: getPadding is slightly wrong and only
 		// accounts for one of the two packet headers.
-		if err := conn.makePacket(burst, pktPayload, nil, 700-pktOverhead); err != nil {
+		if err := conn.makePayloadPacket(burst, nil, 700-pktOverhead); err != nil {
 			return err
 		}
-		return conn.makePacket(burst, pktPayload, nil, padLen-(700+2*pktOverhead))
+		return conn.makePayloadPacket(burst, nil, padLen-(700+2*pktOverhead))
 	}
-	return conn.makePacket(burst, pktPayload, nil, padLen-pktOverhead)
+	return conn.makePayloadPacket(burst, nil, padLen-pktOverhead)
 }
 
 func newScrambleSuitClientConn(conn net.Conn, tStore *ssTicketStore, ca *ssClientArgs) (net.Conn, error) {
diff --git a/transports/scramblesuit/handshake_ticket.go b/transports/scramblesuit/handshake_ticket.go
index f415be0..a850dcd 100644
--- a/transports/scramblesuit/handshake_ticket.go
+++ b/transports/scramblesuit/handshake_ticket.go
@@ -34,7 +34,6 @@ import (
 	"errors"
 	"fmt"
 	"hash"
-	"io/ioutil"
 	"net"
 	"os"
 	"path"
@@ -56,9 +55,7 @@ const (
 	ticketMaxPadLength = 1388
 )
 
-var (
-	errInvalidTicket = errors.New("scramblesuit: invalid serialized ticket")
-)
+var errInvalidTicket = errors.New("scramblesuit: invalid serialized ticket")
 
 type ssTicketStore struct {
 	sync.Mutex
@@ -129,7 +126,7 @@ func (s *ssTicketStore) getTicket(addr net.Addr) (*ssTicket, error) {
 	}
 
 	// No ticket was found, that's fine.
-	return nil, nil
+	return nil, nil //nolint:nilnil
 }
 
 func (s *ssTicketStore) serialize() error {
@@ -146,7 +143,7 @@ func (s *ssTicketStore) serialize() error {
 	if err != nil {
 		return err
 	}
-	return ioutil.WriteFile(s.filePath, jsonStr, 0600)
+	return os.WriteFile(s.filePath, jsonStr, 0o600)
 }
 
 func loadTicketStore(stateDir string) (*ssTicketStore, error) {
@@ -154,7 +151,7 @@ func loadTicketStore(stateDir string) (*ssTicketStore, error) {
 	s := &ssTicketStore{filePath: fPath}
 	s.store = make(map[string]*ssTicket)
 
-	f, err := ioutil.ReadFile(fPath)
+	f, err := os.ReadFile(fPath)
 	if err != nil {
 		// No ticket store is fine.
 		if os.IsNotExist(err) {
@@ -167,7 +164,7 @@ func loadTicketStore(stateDir string) (*ssTicketStore, error) {
 
 	encMap := make(map[string]*ssTicketJSON)
 	if err = json.Unmarshal(f, &encMap); err != nil {
-		return nil, fmt.Errorf("failed to load ticket store '%s': '%s'", fPath, err)
+		return nil, fmt.Errorf("failed to load ticket store '%s': %w", fPath, err)
 	}
 	for k, v := range encMap {
 		raw, err := base32.StdEncoding.DecodeString(v.KeyTicket)
diff --git a/transports/scramblesuit/hkdf_expand.go b/transports/scramblesuit/hkdf_expand.go
deleted file mode 100644
index cbdcbb3..0000000
--- a/transports/scramblesuit/hkdf_expand.go
+++ /dev/null
@@ -1,67 +0,0 @@
-/*
- * Copyright (c) 2015, Yawning Angel <yawning at schwanenlied dot me>
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are met:
- *
- *  * Redistributions of source code must retain the above copyright notice,
- *    this list of conditions and the following disclaimer.
- *
- *  * Redistributions in binary form must reproduce the above copyright notice,
- *    this list of conditions and the following disclaimer in the documentation
- *    and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
- * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGE.
- */
-
-package scramblesuit
-
-import (
-	"crypto/hmac"
-	"hash"
-)
-
-func hkdfExpand(hashFn func() hash.Hash, prk []byte, info []byte, l int) []byte {
-	// Why, yes.  golang.org/x/crypto/hkdf exists, and is a fine
-	// implementation of HKDF.  However it does both the extract
-	// and expand, while ScrambleSuit only does extract, with no
-	// way to separate the two steps.
-
-	h := hmac.New(hashFn, prk)
-	digestSz := h.Size()
-	if l > 255*digestSz {
-		panic("hkdf: requested OKM length > 255*HashLen")
-	}
-
-	var t []byte
-	okm := make([]byte, 0, l)
-	toAppend := l
-	ctr := byte(1)
-	for toAppend > 0 {
-		h.Reset()
-		_, _ = h.Write(t)
-		_, _ = h.Write(info)
-		_, _ = h.Write([]byte{ctr})
-		t = h.Sum(nil)
-		ctr++
-
-		aLen := digestSz
-		if toAppend < digestSz {
-			aLen = toAppend
-		}
-		okm = append(okm, t[:aLen]...)
-		toAppend -= aLen
-	}
-	return okm
-}
diff --git a/transports/transports.go b/transports/transports.go
index 2e83688..b4e6377 100644
--- a/transports/transports.go
+++ b/transports/transports.go
@@ -41,8 +41,10 @@ import (
 	"gitlab.com/yawning/obfs4.git/transports/scramblesuit"
 )
 
-var transportMapLock sync.Mutex
-var transportMap map[string]base.Transport = make(map[string]base.Transport)
+var (
+	transportMapLock sync.Mutex
+	transportMap     map[string]base.Transport = make(map[string]base.Transport)
+)
 
 // Register registers a transport protocol.
 func Register(transport base.Transport) error {
@@ -64,7 +66,7 @@ func Transports() []string {
 	transportMapLock.Lock()
 	defer transportMapLock.Unlock()
 
-	var ret []string
+	ret := make([]string, 0, len(transportMap))
 	for name := range transportMap {
 		ret = append(ret, name)
 	}