commit 0066cfc3932c50323fa596981f18ef5b0e862742 Author: Yawning Angel yawning@torproject.org Date: Tue Feb 17 11:33:29 2015 +0000
Add support for acting as a ScrambleSuit client.
This allows obfs4proxy to be used as a ScrambleSuit client that is wire compatible with the obfs4proxy implementation, including session ticket support, and length obfuscation.
The current implementation has the following limitations: * IAT obfuscation is not supported (and is disabled in all other ScrambleSuit implementations by default). * The length distribution and probabilites are different from those generated by obfsproxy and obfsclient due to a different DRBG. * Server support is missing and is unlikely to be implemented. --- ChangeLog | 1 + README.md | 3 + common/probdist/weighted_dist.go | 25 ++ doc/obfs4proxy.1 | 5 +- transports/scramblesuit/base.go | 88 ++++ transports/scramblesuit/conn.go | 521 ++++++++++++++++++++++++ transports/scramblesuit/handshake_ticket.go | 228 +++++++++++ transports/scramblesuit/handshake_uniformdh.go | 174 ++++++++ transports/scramblesuit/hkdf_expand.go | 67 +++ transports/transports.go | 2 + 10 files changed, 1112 insertions(+), 2 deletions(-)
diff --git a/ChangeLog b/ChangeLog index b2387e1..85fc60f 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,6 +1,7 @@ Changes in version 0.0.4 - UNRELEASED - Improve the runtime performance of the obfs4 handshake tests. - Changed the go.crypto import path to the new location (golang.org/x/crypto). + - Added client only support for ScrambleSuit.
Changes in version 0.0.3 - 2014-10-01 - Change the obfs4 bridge line format to use a "cert" argument instead of the diff --git a/README.md b/README.md index e4d4595..31c9e2b 100644 --- a/README.md +++ b/README.md @@ -81,6 +81,9 @@ ServerTransportPlugin obfs4 exec /usr/local/bin/obfs4proxy `ClientTransportPlugin` and `ServerTransportPlugin` lines in the torrc as appropriate.
+ * obfs4proxy can also act as a ScrambleSuit client. Adjust the + `ClientTransportPlugin` line in the torrc as appropriate. + * The autogenerated obfs4 bridge parameters are placed in `DataDir/pt_state/obfs4_state.json`. To ease deployment, the client side bridge line is written to `DataDir/pt_state/obfs4_bridgeline.txt`. diff --git a/common/probdist/weighted_dist.go b/common/probdist/weighted_dist.go index 2386bbe..811a8a0 100644 --- a/common/probdist/weighted_dist.go +++ b/common/probdist/weighted_dist.go @@ -31,9 +31,11 @@ package probdist
import ( + "bytes" "container/list" "fmt" "math/rand" + "sync"
"git.torproject.org/pluggable-transports/obfs4.git/common/csrand" "git.torproject.org/pluggable-transports/obfs4.git/common/drbg" @@ -46,6 +48,8 @@ const (
// WeightedDist is a weighted distribution. type WeightedDist struct { + sync.Mutex + minValue int maxValue int biased bool @@ -192,6 +196,9 @@ func (w *WeightedDist) Reset(seed *drbg.Seed) { drbg, _ := drbg.NewHashDrbg(seed) rng := rand.New(drbg)
+ w.Lock() + defer w.Unlock() + w.genValues(rng) if w.biased { w.genBiasedWeights(rng) @@ -205,6 +212,9 @@ func (w *WeightedDist) Reset(seed *drbg.Seed) { func (w *WeightedDist) Sample() int { var idx int
+ w.Lock() + defer w.Unlock() + // Generate a fair die roll from an $n$-sided die; call the side $i$. i := csrand.Intn(len(w.values)) // Flip a biased coin that comes up heads with probability $Prob[i]$. @@ -218,3 +228,18 @@ func (w *WeightedDist) Sample() int {
return w.minValue + w.values[idx] } + +// String returns a dump of the distribution table. +func (w *WeightedDist) String() string { + var buf bytes.Buffer + + buf.WriteString("[ ") + for i, v := range w.values { + p := w.weights[i] + if p > 0.01 { // Squelch tiny probabilities. + buf.WriteString(fmt.Sprintf("%d: %f ", v, p)) + } + } + buf.WriteString("]") + return buf.String() +} diff --git a/doc/obfs4proxy.1 b/doc/obfs4proxy.1 index e442946..a9c6257 100644 --- a/doc/obfs4proxy.1 +++ b/doc/obfs4proxy.1 @@ -1,4 +1,4 @@ -.TH OBFS4PROXY 1 "2014-09-24" +.TH OBFS4PROXY 1 "2015-01-20" .SH NAME obfs4proxy - pluggable transport proxy for Tor, implementing obfs4 .SH SYNOPSIS @@ -11,7 +11,8 @@ censors, who usually monitor traffic between the client and the bridge, will see innocent-looking transformed traffic instead of the actual Tor traffic. .PP -obfs4proxy implements the obfuscation protocols obfs2, obfs3 and obfs4. +obfs4proxy implements the obfuscation protocols obfs2, obfs3, +ScrambleSuit (client only) and obfs4. .PP obfs4proxy is currently only supported as a managed pluggable transport spawned as a helper process via the \fBtor\fR daemon. diff --git a/transports/scramblesuit/base.go b/transports/scramblesuit/base.go new file mode 100644 index 0000000..711c046 --- /dev/null +++ b/transports/scramblesuit/base.go @@ -0,0 +1,88 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * 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 provides an implementation of the ScrambleSuit +// obfuscation protocol. The implementation is client only. +package scramblesuit + +import ( + "fmt" + "net" + + "git.torproject.org/pluggable-transports/goptlib.git" + "git.torproject.org/pluggable-transports/obfs4.git/transports/base" +) + +const transportName = "scramblesuit" + +// Transport is the ScrambleSuit implementation of the base.Transport interface. +type Transport struct{} + +// Name returns the name of the ScrambleSuit transport protocol. +func (t *Transport) Name() string { + return transportName +} + +// ClientFactory returns a new ssClientFactory instance. +func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) { + tStore, err := loadTicketStore(stateDir) + if err != nil { + return nil, err + } + cf := &ssClientFactory{transport: t, ticketStore: tStore} + return cf, nil +} + +// 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. + return nil, fmt.Errorf("server not supported") +} + +type ssClientFactory struct { + transport base.Transport + ticketStore *ssTicketStore +} + +func (cf *ssClientFactory) Transport() base.Transport { + return cf.transport +} + +func (cf *ssClientFactory) ParseArgs(args *pt.Args) (interface{}, error) { + return newClientArgs(args) +} + +func (cf *ssClientFactory) WrapConn(conn net.Conn, args interface{}) (net.Conn, error) { + ca, ok := args.(*ssClientArgs) + if !ok { + return nil, fmt.Errorf("invalid argument type for args") + } + return newScrambleSuitClientConn(conn, cf.ticketStore, ca) +} + +var _ base.ClientFactory = (*ssClientFactory)(nil) +var _ base.Transport = (*Transport)(nil) diff --git a/transports/scramblesuit/conn.go b/transports/scramblesuit/conn.go new file mode 100644 index 0000000..b77bc5f --- /dev/null +++ b/transports/scramblesuit/conn.go @@ -0,0 +1,521 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * 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 ( + "bytes" + "crypto/aes" + "crypto/cipher" + "crypto/hmac" + "crypto/sha256" + "encoding/base32" + "encoding/binary" + "errors" + "fmt" + "hash" + "io" + "net" + "time" + + "git.torproject.org/pluggable-transports/goptlib.git" + "git.torproject.org/pluggable-transports/obfs4.git/common/csrand" + "git.torproject.org/pluggable-transports/obfs4.git/common/drbg" + "git.torproject.org/pluggable-transports/obfs4.git/common/probdist" + "git.torproject.org/pluggable-transports/obfs4.git/common/uniformdh" +) + +const ( + passwordArg = "password" + + maxSegmentLength = 1448 + maxPayloadLength = 1427 + sharedSecretLength = 160 / 8 // k_B + clientHandshakeTimeout = time.Duration(60) * time.Second + + minLenDistLength = 21 + maxLenDistLength = maxSegmentLength + + keyLength = 32 + 8 + 32 + + pktPrngSeedLength = 32 + pktOverhead = macLength + pktHdrLength + pktHdrLength = 2 + 2 + 1 + pktPayload = 1 + pktNewTicket = 1 << 1 + pktPrngSeed = 1 << 2 +) + +var ( + // ErrNotSupported is the error returned for a unsupported operation. + ErrNotSupported = errors.New("scramblesuit: operation not supported") + + // ErrInvalidPacket is the error returned when a invalid packet is received. + ErrInvalidPacket = errors.New("scramblesuit: invalid packet") + + zeroPadBytes [maxPayloadLength]byte +) + +type ssSharedSecret [sharedSecretLength]byte + +type ssClientArgs struct { + kB *ssSharedSecret + sessionKey *uniformdh.PrivateKey +} + +func newClientArgs(args *pt.Args) (ca *ssClientArgs, err error) { + ca = &ssClientArgs{} + if ca.kB, err = parsePasswordArg(args); err != nil { + return nil, err + } + + // Generate the client keypair before opening a connection since the time + // taken is visible to an adversary. This key might not end up being used + // if a session ticket is present, but this doesn't take that long. + if ca.sessionKey, err = uniformdh.GenerateKey(csrand.Reader); err != nil { + return nil, err + } + return +} + +func parsePasswordArg(args *pt.Args) (*ssSharedSecret, error) { + str, ok := args.Get(passwordArg) + if !ok { + return nil, fmt.Errorf("missing argument '%s'", passwordArg) + } + + // To match the obfsproxy behavior, 'str' should contain a Base32 encoded + // 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) + } + if len(decoded) != sharedSecretLength { + return nil, fmt.Errorf("password length %d is invalid", len(decoded)) + } + ss := new(ssSharedSecret) + copy(ss[:], decoded) + return ss, nil +} + +type ssCryptoState struct { + s cipher.Stream + mac hash.Hash +} + +func newCryptoState(aesKey []byte, ivPrefix []byte, macKey []byte) (*ssCryptoState, error) { + // 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} + iv := make([]byte, 0, aes.BlockSize) + iv = append(iv, ivPrefix...) + iv = append(iv, initialCtr...) + b, err := aes.NewCipher(aesKey) + if err != nil { + return nil, err + } + s := cipher.NewCTR(b, iv) + mac := hmac.New(sha256.New, macKey) + return &ssCryptoState{s: s, mac: mac}, nil +} + +type ssConn struct { + net.Conn + + isServer bool + + lenDist *probdist.WeightedDist + receiveBuffer *bytes.Buffer + receiveDecodedBuffer *bytes.Buffer + receiveState ssRxState + + txCrypto *ssCryptoState + rxCrypto *ssCryptoState + + ticketStore *ssTicketStore +} + +type ssRxState struct { + mac []byte + hdr []byte + + totalLen int + payloadLen int +} + +func (conn *ssConn) Read(b []byte) (n int, 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 { + break + } + } + + // Service the read request using buffered payload. + if conn.receiveDecodedBuffer.Len() > 0 { + n, _ = conn.receiveDecodedBuffer.Read(b) + } + return +} + +func (conn *ssConn) Write(b []byte) (n int, err error) { + var frameBuf bytes.Buffer + p := b + toSend := len(p) + + for toSend > 0 { + // Send as much payload as will fit into each frame as possible. + wrLen := len(p) + if wrLen > maxPayloadLength { + wrLen = maxPayloadLength + } + payload := p[:wrLen] + if err = conn.makePacket(&frameBuf, pktPayload, payload, 0); err != nil { + return 0, err + } + + toSend -= wrLen + p = p[wrLen:] + n += wrLen + } + + // Pad out the burst as appropriate. + if err = conn.padBurst(&frameBuf, conn.lenDist.Sample()); err != nil { + return 0, err + } + + // Write and return. + _, err = conn.Conn.Write(frameBuf.Bytes()) + return +} + +func (conn *ssConn) SetDeadline(t time.Time) error { + return ErrNotSupported +} + +func (conn *ssConn) SetReadDeadline(t time.Time) error { + return ErrNotSupported +} + +func (conn *ssConn) SetWriteDeadline(t time.Time) error { + return ErrNotSupported +} + +func (conn *ssConn) makePacket(w io.Writer, pktType byte, data []byte, padLen int) error { + payloadLen := len(data) + totalLen := payloadLen + padLen + if totalLen > maxPayloadLength { + panic(fmt.Sprintf("BUG: makePacket() len(data) + padLen > maxPayloadLength: %d + %d > %d", len(data), padLen, maxPayloadLength)) + } + + // Build the packet header (total length, payload length, flags), + // and append the payload and padding. + 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 = append(pkt, data...) + pkt = append(pkt, zeroPadBytes[:padLen]...) + + // Encrypt the packet, and calculate the MAC. + conn.txCrypto.s.XORKeyStream(pkt, pkt) + conn.txCrypto.mac.Reset() + conn.txCrypto.mac.Write(pkt) + mac := conn.txCrypto.mac.Sum(nil)[:macLength] + + // Write out MAC | Packet. Note that this does not go onto the network + // yet, as w is a byte.Buffer (This is done so each call to conn.Write() + // gets padding added). + if _, err := w.Write(mac); err != nil { + return err + } + _, err := w.Write(pkt) + return err +} + +func (conn *ssConn) readPackets() error { + // Consume and buffer up to 1 MSS worth of data. + var buf [maxSegmentLength]byte + rdLen, rdErr := conn.Conn.Read(buf[:]) + conn.receiveBuffer.Write(buf[:rdLen]) + + // Process incoming packets incrementally. conn.receiveState stores + // the results of partial processing. + for conn.receiveBuffer.Len() > 0 { + if conn.receiveState.mac == nil { + // Read and store the packet MAC. + if conn.receiveBuffer.Len() < macLength { + break + } + mac := make([]byte, macLength) + conn.receiveBuffer.Read(mac) + conn.receiveState.mac = mac + } + + if conn.receiveState.hdr == nil { + // Read and store the packet header. + if conn.receiveBuffer.Len() < pktHdrLength { + break + } + hdr := make([]byte, pktHdrLength) + conn.receiveBuffer.Read(hdr) + + // Add the encrypted packet header to the HMAC instance, and then + // decrypt it so that the length of the packet can be determined. + conn.rxCrypto.mac.Reset() + conn.rxCrypto.mac.Write(hdr) + conn.rxCrypto.s.XORKeyStream(hdr, hdr) + + // Store the plaintext packet header, and host byte order length + // values. + totalLen := int(binary.BigEndian.Uint16(hdr[0:])) + payloadLen := int(binary.BigEndian.Uint16(hdr[2:])) + if payloadLen > totalLen || totalLen > maxPayloadLength { + return ErrInvalidPacket + } + conn.receiveState.hdr = hdr + conn.receiveState.totalLen = totalLen + conn.receiveState.payloadLen = payloadLen + } + + var data []byte + if conn.receiveState.totalLen > 0 { + // If the packet actually has payload (including padding), read, + // digest and decrypt it. + if conn.receiveBuffer.Len() < conn.receiveState.totalLen { + break + } + data = make([]byte, conn.receiveState.totalLen) + conn.receiveBuffer.Read(data) + conn.rxCrypto.mac.Write(data) + conn.rxCrypto.s.XORKeyStream(data, data) + } + + // 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[:]) { + return ErrInvalidPacket + } + + // Based on the packet flags, do something useful with the payload. + data = data[:conn.receiveState.payloadLen] + switch conn.receiveState.hdr[4] { + case pktPayload: + // User data, write it into the decoded payload buffer so that Read + // calls can be serviced. + conn.receiveDecodedBuffer.Write(data) + case pktNewTicket: + // New Session Ticket to be used for future handshakes, store it in + // the Session Ticket store. + if conn.isServer || len(data) != ticketKeyLength+ticketLength { + return ErrInvalidPacket + } + conn.ticketStore.storeTicket(conn.RemoteAddr(), data) + case pktPrngSeed: + // New PRNG_SEED for the protocol polymorphism. Regenerate the + // length obfuscation probability distribution. + if conn.isServer || len(data) != pktPrngSeedLength { + return ErrInvalidPacket + } + seed, err := drbg.SeedFromBytes(data) + if err != nil { + return ErrInvalidPacket + } + conn.lenDist.Reset(seed) + default: + return ErrInvalidPacket + } + + // Done processing a packet, clear the partial state. + conn.receiveState.mac = nil + conn.receiveState.hdr = nil + conn.receiveState.totalLen = 0 + conn.receiveState.payloadLen = 0 + } + return rdErr +} + +func (conn *ssConn) clientHandshake(kB *ssSharedSecret, sessionKey *uniformdh.PrivateKey) error { + if conn.isServer { + return fmt.Errorf("clientHandshake called on server connection") + } + + // Query the Session Ticket store to see if there is a stored session + // ticket. + ticket, err := conn.ticketStore.getTicket(conn.RemoteAddr()) + if err != nil { + return err + } else if ticket != nil { + // Ok, there is an existing ticket, so attempt to do a Session Ticket + // handshake. Until we write to the network, failures are non-fatal as + // we can transition gracefully into doing a UniformDH handshake. + + // Derive the keys from the prestored master key received with the + // ticket. This is done before the actual handshake since the + // handshake uses the outgoing HMAC-SHA256-128 key for authentication. + if err = conn.initCrypto(ticket.key[:]); err != nil { + goto handshakeUDH + } + + // Generate and send the ticket handshake. There is no response, since + // both sides have the keying material. + hs := newTicketClientHandshake(conn.txCrypto.mac, ticket) + blob, err := hs.generateHandshake() + if err != nil { + goto handshakeUDH + } + if _, err = conn.Conn.Write(blob); err != nil { + return err + } + return nil + } + +handshakeUDH: + // No session ticket, so take the slow path and do a UniformDH based + // handshake. + + // Generate and send the client handshake. + hs := newDHClientHandshake(kB, sessionKey) + blob, err := hs.generateHandshake() + if err != nil { + return err + } + if _, err = conn.Conn.Write(blob); err != nil { + return err + } + + // Consume the server handshake. Since we don't actually know the length + // of the respose, we need to consume data off the network till we either + // find the tail marker + MAC digest indicating that a handshake response + // has been received, or the maximum handshake size passes without a valid + // response. + var hsBuf [maxHandshakeLength]byte + for { + var n int + if n, err = conn.Conn.Read(hsBuf[:]); err != nil { + return err + } + conn.receiveBuffer.Write(hsBuf[:n]) + + // 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 { + // No response found yet, keep trying. + continue + } else if err != nil { + return err + } + + // Ok, done processing the handshake, discard the response, and do the + // key derivation based off the calculated shared secret. + _ = conn.receiveBuffer.Next(n) + err = conn.initCrypto(seed) + return err + } +} + +func (conn *ssConn) initCrypto(seed []byte) (err error) { + // Use HKDF-SHA256 (Expand only, no Extract) to generate session keys from + // initial keying material. + okm := hkdfExpand(sha256.New, seed, nil, kdfSecretLength) + if conn.txCrypto, err = newCryptoState(okm[0:32], okm[32:40], okm[80:112]); err != nil { + return + } + if conn.rxCrypto, err = newCryptoState(okm[40:72], okm[72:80], okm[112:144]); err != nil { + return + } + return +} + +func (conn *ssConn) padBurst(burst *bytes.Buffer, sampleLen int) (err error) { + // Burst contains the fully encrypted+MACed outgoing payload that will be + // written to the network. Pad it out so that the last segment (based on + // the ScrambleSuit MTU) is sampleLen bytes. + + dataLen := burst.Len() % maxSegmentLength + padLen := 0 + if sampleLen >= dataLen { + padLen = sampleLen - dataLen + } else { + padLen = (maxSegmentLength - dataLen) + sampleLen + } + if padLen < pktOverhead { + // The padLen is less than the MAC + packet header in length, so + // two packets are required. + padLen += maxSegmentLength + } + + if padLen == 0 { + return + } else 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 { + return + } + err = conn.makePacket(burst, pktPayload, nil, padLen-(700+2*pktOverhead)) + } else { + err = conn.makePacket(burst, pktPayload, nil, padLen-pktOverhead) + } + return +} + +func newScrambleSuitClientConn(conn net.Conn, tStore *ssTicketStore, ca *ssClientArgs) (net.Conn, error) { + // At this point we have kB and our session key, so we can directly + // start handshaking and seeing what happens. + + // Seed the initial polymorphism distribution. + seed, err := drbg.NewSeed() + if err != nil { + return nil, err + } + dist := probdist.New(seed, minLenDistLength, maxLenDistLength, true) + + // Allocate the client structure. + c := &ssConn{conn, false, dist, bytes.NewBuffer(nil), bytes.NewBuffer(nil), ssRxState{}, nil, nil, tStore} + + // Start the handshake timeout. + deadline := time.Now().Add(clientHandshakeTimeout) + if err := conn.SetDeadline(deadline); err != nil { + return nil, err + } + + // Attempt to handshake. + if err := c.clientHandshake(ca.kB, ca.sessionKey); err != nil { + return nil, err + } + + // Stop the handshake timeout. + if err := conn.SetDeadline(time.Time{}); err != nil { + return nil, err + } + + return c, nil +} diff --git a/transports/scramblesuit/handshake_ticket.go b/transports/scramblesuit/handshake_ticket.go new file mode 100644 index 0000000..ad9b4d4 --- /dev/null +++ b/transports/scramblesuit/handshake_ticket.go @@ -0,0 +1,228 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * 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 ( + "bytes" + "encoding/base32" + "encoding/json" + "errors" + "fmt" + "hash" + "io/ioutil" + "net" + "os" + "path" + "strconv" + "sync" + "time" + + "git.torproject.org/pluggable-transports/obfs4.git/common/csrand" +) + +const ( + ticketFile = "scramblesuit_tickets.json" + + ticketKeyLength = 32 + ticketLength = 112 + ticketLifetime = 60 * 60 * 24 * 7 + + ticketMinPadLength = 0 + ticketMaxPadLength = 1388 +) + +var ( + errInvalidTicket = errors.New("scramblesuit: invalid serialized ticket") +) + +type ssTicketStore struct { + sync.Mutex + + filePath string + store map[string]*ssTicket +} + +type ssTicket struct { + key [ticketKeyLength]byte + ticket [ticketLength]byte + issuedAt int64 +} + +type ssTicketJSON struct { + KeyTicket string `json:"key-ticket"` + IssuedAt int64 `json:"issuedAt"` +} + +func (t *ssTicket) isValid() bool { + return t.issuedAt+ticketLifetime > time.Now().Unix() +} + +func newTicket(raw []byte) (*ssTicket, error) { + if len(raw) != ticketKeyLength+ticketLength { + return nil, errInvalidTicket + } + t := &ssTicket{issuedAt: time.Now().Unix()} + copy(t.key[:], raw[0:]) + copy(t.ticket[:], raw[ticketKeyLength:]) + return t, nil +} + +func (s *ssTicketStore) storeTicket(addr net.Addr, rawT []byte) { + t, err := newTicket(rawT) + if err != nil { + // Silently ignore ticket store failures. + return + } + + s.Lock() + defer s.Unlock() + + // Add the ticket to the map, and checkpoint to disk. Serialization errors + // are ignored because the handshake code will just use UniformDH if a + // ticket is not available. + s.store[addr.String()] = t + s.serialize() +} + +func (s *ssTicketStore) getTicket(addr net.Addr) (*ssTicket, error) { + aStr := addr.String() + + s.Lock() + defer s.Unlock() + + t, ok := s.store[aStr] + if ok && t != nil { + // Tickets are one use only, so remove tickets from the map, and + // checkpoint the map to disk. + delete(s.store, aStr) + err := s.serialize() + if !t.isValid() { + // Expired ticket, ignore it. + return nil, err + } + return t, err + } + + // No ticket was found, that's fine. + return nil, nil +} + +func (s *ssTicketStore) serialize() error { + encMap := make(map[string]*ssTicketJSON) + for k, v := range s.store { + kt := make([]byte, 0, ticketKeyLength+ticketLength) + kt = append(kt, v.key[:]...) + kt = append(kt, v.ticket[:]...) + ktStr := base32.StdEncoding.EncodeToString(kt) + jsonObj := &ssTicketJSON{KeyTicket: ktStr, IssuedAt: v.issuedAt} + encMap[k] = jsonObj + } + jsonStr, err := json.Marshal(encMap) + if err != nil { + return err + } + return ioutil.WriteFile(s.filePath, jsonStr, 0600) +} + +func loadTicketStore(stateDir string) (*ssTicketStore, error) { + fPath := path.Join(stateDir, ticketFile) + s := &ssTicketStore{filePath: fPath} + s.store = make(map[string]*ssTicket) + + f, err := ioutil.ReadFile(fPath) + if err != nil { + // No ticket store is fine. + if os.IsNotExist(err) { + return s, nil + } + + // But a file read error is not. + return nil, err + } + + 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) + } + for k, v := range encMap { + raw, err := base32.StdEncoding.DecodeString(v.KeyTicket) + if err != nil || len(raw) != ticketKeyLength+ticketLength { + // Just silently skip corrupted tickets. + continue + } + t := &ssTicket{issuedAt: v.IssuedAt} + if !t.isValid() { + // Just ignore expired tickets. + continue + } + copy(t.key[:], raw[0:]) + copy(t.ticket[:], raw[ticketKeyLength:]) + s.store[k] = t + } + return s, nil +} + +type ssTicketClientHandshake struct { + mac hash.Hash + ticket *ssTicket + padLen int +} + +func (hs *ssTicketClientHandshake) generateHandshake() ([]byte, error) { + var buf bytes.Buffer + hs.mac.Reset() + + // The client handshake is T | P | M | MAC(T | P | M | E) + hs.mac.Write(hs.ticket.ticket[:]) + m := hs.mac.Sum(nil)[:macLength] + p, err := makePad(hs.padLen) + if err != nil { + return nil, err + } + + // Write T, P, M. + buf.Write(hs.ticket.ticket[:]) + buf.Write(p) + buf.Write(m) + + // Calculate and write the MAC. + e := []byte(strconv.FormatInt(getEpochHour(), 10)) + hs.mac.Write(p) + hs.mac.Write(m) + hs.mac.Write(e) + buf.Write(hs.mac.Sum(nil)[:macLength]) + + hs.mac.Reset() + return buf.Bytes(), nil +} + +func newTicketClientHandshake(mac hash.Hash, ticket *ssTicket) *ssTicketClientHandshake { + hs := &ssTicketClientHandshake{mac: mac, ticket: ticket} + hs.padLen = csrand.IntRange(ticketMinPadLength, ticketMaxPadLength) + return hs +} diff --git a/transports/scramblesuit/handshake_uniformdh.go b/transports/scramblesuit/handshake_uniformdh.go new file mode 100644 index 0000000..4345d65 --- /dev/null +++ b/transports/scramblesuit/handshake_uniformdh.go @@ -0,0 +1,174 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * 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 ( + "bytes" + "crypto/hmac" + "crypto/sha256" + "errors" + "hash" + "strconv" + "time" + + "git.torproject.org/pluggable-transports/obfs4.git/common/csrand" + "git.torproject.org/pluggable-transports/obfs4.git/common/uniformdh" +) + +const ( + minHandshakeLength = uniformdh.Size + macLength*2 + maxHandshakeLength = 1532 + dhMinPadLength = 0 + dhMaxPadLength = 1308 + macLength = 128 / 8 // HMAC-SHA256-128() + + kdfSecretLength = keyLength * 2 +) + +var ( + errMarkNotFoundYet = errors.New("mark not found yet") + + // ErrInvalidHandshake is the error returned when the handshake fails. + ErrInvalidHandshake = errors.New("invalid handshake") +) + +type ssDHClientHandshake struct { + mac hash.Hash + keypair *uniformdh.PrivateKey + epochHour []byte + padLen int + + serverPublicKey *uniformdh.PublicKey + serverMark []byte +} + +func (hs *ssDHClientHandshake) generateHandshake() ([]byte, error) { + var buf bytes.Buffer + hs.mac.Reset() + + // The client handshake is X | P_C | M_C | MAC(X | P_C | M_C | E) + x, err := hs.keypair.PublicKey.Bytes() + if err != nil { + return nil, err + } + hs.mac.Write(x) + mC := hs.mac.Sum(nil)[:macLength] + pC, err := makePad(hs.padLen) + if err != nil { + return nil, err + } + + // Write X, P_C, M_C. + buf.Write(x) + buf.Write(pC) + buf.Write(mC) + + // Calculate and write the MAC. + hs.epochHour = []byte(strconv.FormatInt(getEpochHour(), 10)) + hs.mac.Write(pC) + hs.mac.Write(mC) + hs.mac.Write(hs.epochHour) + buf.Write(hs.mac.Sum(nil)[:macLength]) + + return buf.Bytes(), nil +} + +func (hs *ssDHClientHandshake) parseServerHandshake(resp []byte) (int, []byte, error) { + if len(resp) < minHandshakeLength { + return 0, nil, errMarkNotFoundYet + } + + // The server response is Y | P_S | M_S | MAC(Y | P_S | M_S | E). + if hs.serverPublicKey == nil { + y := resp[:uniformdh.Size] + + // Pull out the public key, and derive the server mark. + hs.serverPublicKey = &uniformdh.PublicKey{} + err := hs.serverPublicKey.SetBytes(y) + if err != nil { + return 0, nil, err + } + hs.mac.Reset() + hs.mac.Write(y) + hs.serverMark = hs.mac.Sum(nil)[:macLength] + } + + // Find the mark+MAC, if it exits. + endPos := len(resp) + if endPos > maxHandshakeLength-macLength { + endPos = maxHandshakeLength - macLength + } + pos := bytes.Index(resp[uniformdh.Size:endPos], hs.serverMark) + if pos == -1 { + if len(resp) >= maxHandshakeLength { + // Couldn't find the mark in a maximum length response. + return 0, nil, ErrInvalidHandshake + } + return 0, nil, errMarkNotFoundYet + } else if len(resp) < pos+2*macLength { + // Didn't receive the full M_S. + return 0, nil, errMarkNotFoundYet + } + pos += uniformdh.Size + + // Validate the MAC. + hs.mac.Write(resp[uniformdh.Size : pos+macLength]) + hs.mac.Write(hs.epochHour) + macCmp := hs.mac.Sum(nil)[:macLength] + macRx := resp[pos+macLength : pos+2*macLength] + if !hmac.Equal(macCmp, macRx) { + return 0, nil, ErrInvalidHandshake + } + + // Derive the shared secret. + ss, err := uniformdh.Handshake(hs.keypair, hs.serverPublicKey) + if err != nil { + return 0, nil, err + } + seed := sha256.Sum256(ss) + return pos + 2*macLength, seed[:], nil +} + +func newDHClientHandshake(kB *ssSharedSecret, sessionKey *uniformdh.PrivateKey) *ssDHClientHandshake { + hs := &ssDHClientHandshake{keypair: sessionKey} + hs.mac = hmac.New(sha256.New, kB[:]) + hs.padLen = csrand.IntRange(dhMinPadLength, dhMaxPadLength) + return hs +} + +func getEpochHour() int64 { + return time.Now().Unix() / 3600 +} + +func makePad(padLen int) ([]byte, error) { + pad := make([]byte, padLen) + if err := csrand.Bytes(pad); err != nil { + return nil, err + } + return pad, nil +} diff --git a/transports/scramblesuit/hkdf_expand.go b/transports/scramblesuit/hkdf_expand.go new file mode 100644 index 0000000..9626b38 --- /dev/null +++ b/transports/scramblesuit/hkdf_expand.go @@ -0,0 +1,67 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * 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 6b80bdc..ba4e099 100644 --- a/transports/transports.go +++ b/transports/transports.go @@ -37,6 +37,7 @@ import ( "git.torproject.org/pluggable-transports/obfs4.git/transports/obfs2" "git.torproject.org/pluggable-transports/obfs4.git/transports/obfs3" "git.torproject.org/pluggable-transports/obfs4.git/transports/obfs4" + "git.torproject.org/pluggable-transports/obfs4.git/transports/scramblesuit" )
var transportMapLock sync.Mutex @@ -88,4 +89,5 @@ func init() { Register(new(obfs2.Transport)) Register(new(obfs3.Transport)) Register(new(obfs4.Transport)) + Register(new(scramblesuit.Transport)) }