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Move the server keypair generation to right after Accept().

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Instead of threading the code, move the keypair generation to right
after Accept() is called.  This should mask the timing differential due
to the rejection sampling with the noise from the variablity in how
long it takes for the server to get around to pulling a connection out
of the backlog, and the time taken for the client to send it's portion
of the handshake.

The downside is that anyone connecting to the obfs4 port does force us
to do a bunch of math, but the obfs4 math is relatively cheap compared
to it's precursors.

Fixes #9.
merge-requests/3/head
Yawning Angel 10 years ago
parent 2001f0b698
commit 36228437c4
3 changed files with 38 additions and 31 deletions
Show Stats Download Patch File Download Diff File

15
handshake_ntor.go
Unescape Escape View File

@ -121,7 +121,7 @@ type clientHandshake struct {
serverMark []byte
}
func newClientHandshake(nodeID *ntor.NodeID, serverIdentity *ntor.PublicKey, sessionKey *ntor.Keypair) (*clientHandshake, error) {
func newClientHandshake(nodeID *ntor.NodeID, serverIdentity *ntor.PublicKey, sessionKey *ntor.Keypair) *clientHandshake {
hs := new(clientHandshake)
hs.keypair = sessionKey
hs.nodeID = nodeID
@ -129,7 +129,7 @@ func newClientHandshake(nodeID *ntor.NodeID, serverIdentity *ntor.PublicKey, ses
hs.padLen = csrand.IntRange(clientMinPadLength, clientMaxPadLength)
hs.mac = hmac.New(sha256.New, append(hs.serverIdentity.Bytes()[:], hs.nodeID.Bytes()[:]...))
return hs, nil
return hs
}
func (hs *clientHandshake) generateHandshake() ([]byte, error) {
@ -236,8 +236,9 @@ type serverHandshake struct {
clientMark []byte
}
func newServerHandshake(nodeID *ntor.NodeID, serverIdentity *ntor.Keypair) *serverHandshake {
func newServerHandshake(nodeID *ntor.NodeID, serverIdentity *ntor.Keypair, sessionKey *ntor.Keypair) *serverHandshake {
hs := new(serverHandshake)
hs.keypair = sessionKey
hs.nodeID = nodeID
hs.serverIdentity = serverIdentity
hs.padLen = csrand.IntRange(serverMinPadLength, serverMaxPadLength)
@ -312,14 +313,6 @@ func (hs *serverHandshake) parseClientHandshake(filter *replayFilter, resp []byt
return nil, ErrInvalidHandshake
}
// At this point the client knows that we exist, so do the keypair
// generation and complete our side of the handshake.
var err error
hs.keypair, err = ntor.NewKeypair(true)
if err != nil {
return nil, err
}
clientPublic := hs.clientRepresentative.ToPublic()
ok, seed, auth := ntor.ServerHandshake(clientPublic, hs.keypair,
hs.serverIdentity, hs.nodeID)

34
handshake_ntor_test.go
Unescape Escape View File

@ -47,10 +47,7 @@ func TestHandshakeNtor(t *testing.T) {
if err != nil {
t.Fatalf("[%d:0] ntor.NewKeypair failed: %s", l, err)
}
clientHs, err := newClientHandshake(nodeID, idKeypair.Public(), clientKeypair)
if err != nil {
t.Fatalf("[%d:0] newClientHandshake failed: %s", l, err)
}
clientHs := newClientHandshake(nodeID, idKeypair.Public(), clientKeypair)
clientHs.padLen = l
// Generate what the client will send to the server.
@ -69,7 +66,11 @@ func TestHandshakeNtor(t *testing.T) {
}
// Generate the server state and override the pad length.
serverHs := newServerHandshake(nodeID, idKeypair)
serverKeypair, err := ntor.NewKeypair(true)
if err != nil {
t.Fatalf("[%d:0] ntor.NewKeypair failed: %s", l, err)
}
serverHs := newServerHandshake(nodeID, idKeypair, serverKeypair)
serverHs.padLen = serverMinPadLength
// Parse the client handshake message.
@ -107,10 +108,7 @@ func TestHandshakeNtor(t *testing.T) {
if err != nil {
t.Fatalf("[%d:0] ntor.NewKeypair failed: %s", l, err)
}
clientHs, err := newClientHandshake(nodeID, idKeypair.Public(), clientKeypair)
if err != nil {
t.Fatalf("[%d:0] newClientHandshake failed: %s", l, err)
}
clientHs := newClientHandshake(nodeID, idKeypair.Public(), clientKeypair)
clientHs.padLen = clientMinPadLength
// Generate what the client will send to the server.
@ -123,7 +121,11 @@ func TestHandshakeNtor(t *testing.T) {
}
// Generate the server state and override the pad length.
serverHs := newServerHandshake(nodeID, idKeypair)
serverKeypair, err := ntor.NewKeypair(true)
if err != nil {
t.Fatalf("[%d:0] ntor.NewKeypair failed: %s", l, err)
}
serverHs := newServerHandshake(nodeID, idKeypair, serverKeypair)
serverHs.padLen = l
// Parse the client handshake message.
@ -158,7 +160,7 @@ func TestHandshakeNtor(t *testing.T) {
if err != nil {
t.Fatalf("ntor.NewKeypair failed: %s", err)
}
clientHs, err := newClientHandshake(nodeID, idKeypair.Public(), clientKeypair)
clientHs := newClientHandshake(nodeID, idKeypair.Public(), clientKeypair)
if err != nil {
t.Fatalf("newClientHandshake failed: %s", err)
}
@ -168,7 +170,11 @@ func TestHandshakeNtor(t *testing.T) {
if err != nil {
t.Fatalf("clientHandshake.generateHandshake() (forced oversize) failed: %s", err)
}
serverHs := newServerHandshake(nodeID, idKeypair)
serverKeypair, err := ntor.NewKeypair(true)
if err != nil {
t.Fatalf("ntor.NewKeypair failed: %s", err)
}
serverHs := newServerHandshake(nodeID, idKeypair, serverKeypair)
_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
if err == nil {
t.Fatalf("serverHandshake.parseClientHandshake() succeded (oversized)")
@ -180,7 +186,7 @@ func TestHandshakeNtor(t *testing.T) {
if err != nil {
t.Fatalf("clientHandshake.generateHandshake() (forced undersize) failed: %s", err)
}
serverHs = newServerHandshake(nodeID, idKeypair)
serverHs = newServerHandshake(nodeID, idKeypair, serverKeypair)
_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
if err == nil {
t.Fatalf("serverHandshake.parseClientHandshake() succeded (undersized)")
@ -198,7 +204,7 @@ func TestHandshakeNtor(t *testing.T) {
if err != nil {
t.Fatalf("clientHandshake.generateHandshake() failed: %s", err)
}
serverHs = newServerHandshake(nodeID, idKeypair)
serverHs = newServerHandshake(nodeID, idKeypair, serverKeypair)
serverHs.padLen = serverMaxPadLength + inlineSeedFrameLength + 1
_, err = serverHs.parseClientHandshake(serverFilter, clientBlob)
if err != nil {

20
obfs4.go
Unescape Escape View File

@ -159,7 +159,6 @@ func (c *Obfs4Conn) clientHandshake(nodeID *ntor.NodeID, publicKey *ntor.PublicK
}
defer func() {
// The session key is not needed past returning from this routine.
c.sessionKey = nil
if err != nil {
c.setBroken()
@ -169,10 +168,7 @@ func (c *Obfs4Conn) clientHandshake(nodeID *ntor.NodeID, publicKey *ntor.PublicK
// Generate/send the client handshake.
var hs *clientHandshake
var blob []byte
hs, err = newClientHandshake(nodeID, publicKey, c.sessionKey)
if err != nil {
return
}
hs = newClientHandshake(nodeID, publicKey, c.sessionKey)
blob, err = hs.generateHandshake()
if err != nil {
return
@ -231,12 +227,13 @@ func (c *Obfs4Conn) serverHandshake(nodeID *ntor.NodeID, keypair *ntor.Keypair)
}
defer func() {
c.sessionKey = nil
if err != nil {
c.setBroken()
}
}()
hs := newServerHandshake(nodeID, keypair)
hs := newServerHandshake(nodeID, keypair, c.sessionKey)
err = c.conn.SetDeadline(time.Now().Add(connectionTimeout))
if err != nil {
return
@ -645,6 +642,17 @@ func (l *Obfs4Listener) AcceptObfs4() (*Obfs4Conn, error) {
// Allocate the obfs4 connection state.
cObfs := new(Obfs4Conn)
// Generate the session keypair *before* consuming data from the peer, to
// add more noise to the keypair generation time. The idea is that jitter
// here is masked by network latency (the time it takes for a server to
// accept a socket out of the backlog should not be fixed, and the client
// needs to send the public key).
cObfs.sessionKey, err = ntor.NewKeypair(true)
if err != nil {
return nil, err
}
cObfs.conn = c
cObfs.isServer = true
cObfs.listener = l

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