diff --git a/csrand/csrand.go b/csrand/csrand.go
index 721fb1e..a3299aa 100644
--- a/csrand/csrand.go
+++ b/csrand/csrand.go
@@ -68,7 +68,12 @@ func (r csRandSource) Seed(seed int64) {
 	// No-op.
 }
 
-// Float64 returns, as a float 64, a pesudo random number in [0.0,1.0).
+// Int63n returns, as a int64, a pseudo random number in [0, n).
+func Int63n(n int64) int64 {
+	return CsRand.Int63n(n)
+}
+
+// Float64 returns, as a float64, a pesudo random number in [0.0,1.0).
 func Float64() float64 {
 	return CsRand.Float64()
 }
diff --git a/framing/framing.go b/framing/framing.go
index 66eeff5..48d12c3 100644
--- a/framing/framing.go
+++ b/framing/framing.go
@@ -287,7 +287,7 @@ func (decoder *Decoder) Decode(data []byte, frames *bytes.Buffer) (int, error) {
 	}
 	out, ok := secretbox.Open(data[:0], box[:n], &decoder.nextNonce, &decoder.key)
 	if !ok || decoder.nextLengthInvalid {
-		// When a random lenght is used (on length error) the tag should always
+		// When a random length is used (on length error) the tag should always
 		// mismatch, but be paranoid.
 		return 0, ErrTagMismatch
 	}
diff --git a/obfs4.go b/obfs4.go
index e4c22f8..c780e0c 100644
--- a/obfs4.go
+++ b/obfs4.go
@@ -33,6 +33,7 @@ package obfs4
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"fmt"
 	"io"
 	"math/rand"
@@ -568,7 +569,12 @@ func DialObfs4DialFn(dialFn DialFn, network, address, nodeID, publicKey string,
 	c := new(Obfs4Conn)
 	c.lenProbDist = newWDist(seed, 0, framing.MaximumSegmentLength)
 	if iatObfuscation {
-		c.iatProbDist = newWDist(seed, 0, maxIatDelay)
+		iatSeedSrc := sha256.Sum256(seed.Bytes()[:])
+		iatSeed, err := DrbgSeedFromBytes(iatSeedSrc[:])
+		if err != nil {
+			return nil, err
+		}
+		c.iatProbDist = newWDist(iatSeed, 0, maxIatDelay)
 	}
 	c.conn, err = dialFn(network, address)
 	if err != nil {
@@ -596,6 +602,7 @@ type Obfs4Listener struct {
 	nodeID  *ntor.NodeID
 
 	seed           *DrbgSeed
+	iatSeed        *DrbgSeed
 	iatObfuscation bool
 
 	closeDelayBytes int
@@ -631,7 +638,7 @@ func (l *Obfs4Listener) AcceptObfs4() (*Obfs4Conn, error) {
 	cObfs.listener = l
 	cObfs.lenProbDist = newWDist(l.seed, 0, framing.MaximumSegmentLength)
 	if l.iatObfuscation {
-		cObfs.iatProbDist = newWDist(l.seed, 0, maxIatDelay)
+		cObfs.iatProbDist = newWDist(l.iatSeed, 0, maxIatDelay)
 	}
 	if err != nil {
 		c.Close()
@@ -692,6 +699,14 @@ func ListenObfs4(network, laddr, nodeID, privateKey, seed string, iatObfuscation
 	if err != nil {
 		return nil, err
 	}
+	l.iatObfuscation = iatObfuscation
+	if l.iatObfuscation {
+		iatSeedSrc := sha256.Sum256(l.seed.Bytes()[:])
+		l.iatSeed, err = DrbgSeedFromBytes(iatSeedSrc[:])
+		if err != nil {
+			return nil, err
+		}
+	}
 
 	l.filter, err = newReplayFilter()
 	if err != nil {
@@ -701,7 +716,6 @@ func ListenObfs4(network, laddr, nodeID, privateKey, seed string, iatObfuscation
 	rng := rand.New(newHashDrbg(l.seed))
 	l.closeDelayBytes = rng.Intn(maxCloseDelayBytes)
 	l.closeDelay = rng.Intn(maxCloseDelay)
-	l.iatObfuscation = iatObfuscation
 
 	// Start up the listener.
 	l.listener, err = net.Listen(network, laddr)
diff --git a/packet.go b/packet.go
index 78f6697..61ed981 100644
--- a/packet.go
+++ b/packet.go
@@ -28,6 +28,7 @@
 package obfs4
 
 import (
+	"crypto/sha256"
 	"encoding/binary"
 	"fmt"
 	"io"
@@ -182,7 +183,12 @@ func (c *Obfs4Conn) consumeFramedPackets(w io.Writer) (n int, err error) {
 				}
 				c.lenProbDist.reset(seed)
 				if c.iatProbDist != nil {
-					c.iatProbDist.reset(seed)
+					iatSeedSrc := sha256.Sum256(seed.Bytes()[:])
+					iatSeed, err := DrbgSeedFromBytes(iatSeedSrc[:])
+					if err != nil {
+						break
+					}
+					c.iatProbDist.reset(iatSeed)
 				}
 			}
 		default:
diff --git a/weighted_dist.go b/weighted_dist.go
index 04b0d2d..55432b2 100644
--- a/weighted_dist.go
+++ b/weighted_dist.go
@@ -39,6 +39,11 @@ import (
 	"github.com/yawning/obfs4/csrand"
 )
 
+const (
+	minBuckets = 1
+	maxBuckets = 100
+)
+
 // DrbgSeedLength is the length of the hashDrbg seed.
 const DrbgSeedLength = 32
 
@@ -133,10 +138,11 @@ func (drbg *hashDrbg) Seed(seed int64) {
 
 // wDist is a weighted distribution.
 type wDist struct {
-	minValue int
-	maxValue int
-	values   []int
-	buckets  []float64
+	minValue    int
+	maxValue    int
+	values      []int
+	buckets     []int64
+	totalWeight int64
 
 	rng *rand.Rand
 }
@@ -160,11 +166,11 @@ func newWDist(seed *DrbgSeed, min, max int) (w *wDist) {
 // sample generates a random value according to the distribution.
 func (w *wDist) sample() int {
 	retIdx := 0
-	totalProb := 0.0
-	prob := csrand.Float64()
-	for i, bucketProb := range w.buckets {
-		totalProb += bucketProb
-		if prob <= totalProb {
+	var totalWeight int64
+	weight := csrand.Int63n(w.totalWeight)
+	for i, bucketWeight := range w.buckets {
+		totalWeight += bucketWeight
+		if weight <= totalWeight {
 			retIdx = i
 			break
 		}
@@ -181,15 +187,22 @@ func (w *wDist) reset(seed *DrbgSeed) {
 
 	nBuckets := (w.maxValue + 1) - w.minValue
 	w.values = w.rng.Perm(nBuckets)
+	if nBuckets < minBuckets {
+		nBuckets = minBuckets
+	}
+	if nBuckets > maxBuckets {
+		nBuckets = maxBuckets
+	}
+	nBuckets = w.rng.Intn(nBuckets) + 1
 
-	w.buckets = make([]float64, nBuckets)
-	var totalProb float64
+	w.totalWeight = 0
+	w.buckets = make([]int64, nBuckets)
 	for i, _ := range w.buckets {
-		prob := w.rng.Float64() * (1.0 - totalProb)
+		prob := w.rng.Int63n(1000)
 		w.buckets[i] = prob
-		totalProb += prob
+		w.totalWeight += prob
 	}
-	w.buckets[len(w.buckets)-1] = 1.0
+	w.buckets[len(w.buckets)-1] = w.totalWeight
 }
 
 /* vim :set ts=4 sw=4 sts=4 noet : */