diff --git a/obfs4.go b/obfs4.go
index 429ba95f655c9ae2e762e4df38449bc2ffcf8bc3..d3dfc3854ef4a26a52fa1bd1ce43ddb1cb80cd85 100644
--- a/obfs4.go
+++ b/obfs4.go
@@ -467,12 +467,15 @@ func Dial(network, address, nodeID, publicKey string) (net.Conn, error) {
return nil, err
}
- // Connect to the peer.
- c := new(Obfs4Conn)
- c.lenProbDist, err = newWDist(nil, 0, framing.MaximumSegmentLength)
+ // Generate the initial length obfuscation distribution.
+ seed, err := newRandomDrbgSeed()
if err != nil {
return nil, err
}
+
+ // Connect to the peer.
+ c := new(Obfs4Conn)
+ c.lenProbDist = newWDist(seed, 0, framing.MaximumSegmentLength)
c.conn, err = net.Dial(network, address)
if err != nil {
return nil, err
@@ -495,6 +498,7 @@ type Obfs4Listener struct {
keyPair *ntor.Keypair
nodeID *ntor.NodeID
+ seed *drbgSeed
}
func (l *Obfs4Listener) Accept() (net.Conn, error) {
@@ -509,7 +513,7 @@ func (l *Obfs4Listener) Accept() (net.Conn, error) {
cObfs.conn = c
cObfs.isServer = true
cObfs.listener = l
- cObfs.lenProbDist, err = newWDist(nil, 0, framing.MaximumSegmentLength)
+ cObfs.lenProbDist = newWDist(l.seed, 0, framing.MaximumSegmentLength)
if err != nil {
c.Close()
return nil, err
@@ -548,6 +552,13 @@ func Listen(network, laddr, nodeID, privateKey string) (net.Listener, error) {
return nil, err
}
+ // Generate the initial length obfuscation distribution.
+ // XXX: Load this from args.
+ l.seed, err = newRandomDrbgSeed()
+ if err != nil {
+ return nil, err
+ }
+
// Start up the listener.
l.listener, err = net.Listen(network, laddr)
if err != nil {
diff --git a/packet.go b/packet.go
index 75179cbe17e769e00b30691df2d2f5ddb7b78286..2528a53be9f70e725e629e3f16db71ed694438d4 100644
--- a/packet.go
+++ b/packet.go
@@ -173,8 +173,13 @@ func (c *Obfs4Conn) consumeFramedPackets(w io.Writer) (n int, err error) {
}
case packetTypePrngSeed:
// Only regenerate the distribution if we are the client.
- if len(payload) >= distSeedLength && !c.isServer {
- c.lenProbDist.reset(payload[:distSeedLength])
+ if len(payload) >= drbgSeedLength && !c.isServer {
+ var seed *drbgSeed
+ seed, err = drbgSeedFromBytes(payload[:drbgSeedLength])
+ if err != nil {
+ break
+ }
+ c.lenProbDist.reset(seed)
}
default:
// Ignore unrecognised packet types.
diff --git a/weighted_dist.go b/weighted_dist.go
index b1658692636cd0f07c4ee6727600f0c7d8c8fffb..56128ae6c1dca3db0e7e842e6497fe3b1e93f2a7 100644
--- a/weighted_dist.go
+++ b/weighted_dist.go
@@ -29,6 +29,7 @@ package obfs4
import (
csrand "crypto/rand"
+ "encoding/base64"
"encoding/binary"
"fmt"
"hash"
@@ -37,7 +38,51 @@ import (
"github.com/dchest/siphash"
)
-const distSeedLength = 16
+const drbgSeedLength = 32
+
+// drbgSeed is the initial state for a hashDrbg. It consists of a SipHash-2-4
+// key, and 16 bytes of initial data.
+type drbgSeed [drbgSeedLength]byte
+
+// bytes returns a pointer to the raw hashDrbg seed.
+func (seed *drbgSeed) bytes() *[drbgSeedLength]byte {
+ return (*[drbgSeedLength]byte)(seed)
+}
+
+// base64 returns the Base64 representation of the seed.
+func (seed *drbgSeed) base64() string {
+ return base64.StdEncoding.EncodeToString(seed.bytes()[:])
+}
+
+// newRandomDrbgSeed returns a drbgSeed initialized with the runtime CSPRNG.
+func newRandomDrbgSeed() (seed *drbgSeed, err error) {
+ seed = new(drbgSeed)
+ _, err = csrand.Read(seed.bytes()[:])
+ if err != nil {
+ return nil, err
+ }
+
+ return
+}
+
+// drbgSeedFromBytes returns a drbg seed initialized with the caller provided
+// slice.
+func drbgSeedFromBytes(src []byte) (seed *drbgSeed, err error) {
+ if len(src) != drbgSeedLength {
+ return nil, InvalidSeedLengthError(len(src))
+ }
+
+ seed = new(drbgSeed)
+ copy(seed.bytes()[:], src)
+
+ return
+}
+
+/*
+func drbgSeedFromBse64(encoded string) (seed *drbgSeed, err error) {
+ return
+}
+*/
// InvalidSeedLengthError is the error returned when the seed provided to the
// DRBG is an invalid length.
@@ -54,10 +99,11 @@ type hashDrbg struct {
}
// newHashDrbg makes a hashDrbg instance based off an optional seed. The seed
-// is truncated to distSeedLength.
-func newHashDrbg(seed []byte) *hashDrbg {
+// is truncated to drbgSeedLength.
+func newHashDrbg(seed *drbgSeed) *hashDrbg {
drbg := new(hashDrbg)
- drbg.sip = siphash.New(seed)
+ drbg.sip = siphash.New(seed.bytes()[:16])
+ copy(drbg.ofb[:], seed.bytes()[16:])
return drbg
}
@@ -88,9 +134,9 @@ type wDist struct {
}
// newWDist creates a weighted distribution of values ranging from min to max
-// based on a CSDRBG initialized with the optional 128 bit seed.
-func newWDist(seed []byte, min, max int) (*wDist, error) {
- w := new(wDist)
+// based on a hashDrbg initialized with seed.
+func newWDist(seed *drbgSeed, min, max int) (w *wDist) {
+ w = new(wDist)
w.minValue = min
w.maxValue = max
@@ -98,12 +144,9 @@ func newWDist(seed []byte, min, max int) (*wDist, error) {
panic(fmt.Sprintf("wDist.Reset(): min >= max (%d, %d)", min, max))
}
- err := w.reset(seed)
- if err != nil {
- return nil, err
- }
+ w.reset(seed)
- return w, nil
+ return
}
// sample generates a random value according to the distribution.
@@ -123,18 +166,7 @@ func (w *wDist) sample() int {
}
// reset generates a new distribution with the same min/max based on a new seed.
-func (w *wDist) reset(seed []byte) error {
- if seed == nil {
- seed = make([]byte, distSeedLength)
- _, err := csrand.Read(seed)
- if err != nil {
- return err
- }
- }
- if len(seed) != distSeedLength {
- return InvalidSeedLengthError(len(seed))
- }
-
+func (w *wDist) reset(seed *drbgSeed) {
// Initialize the deterministic random number generator.
drbg := newHashDrbg(seed)
dRng := rand.New(drbg)
@@ -150,8 +182,6 @@ func (w *wDist) reset(seed []byte) error {
totalProb += prob
}
w.buckets[len(w.buckets)-1] = 1.0
-
- return nil
}
/* vim :set ts=4 sw=4 sts=4 noet : */