diff options
Diffstat (limited to 'vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/otr/otr.go')
| -rw-r--r-- | vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/otr/otr.go | 1415 |
1 files changed, 1415 insertions, 0 deletions
diff --git a/vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/otr/otr.go b/vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/otr/otr.go new file mode 100644 index 000000000..173b753db --- /dev/null +++ b/vendor/github.com/miekg/dns/vendor/golang.org/x/crypto/otr/otr.go @@ -0,0 +1,1415 @@ +// Copyright 2012 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Package otr implements the Off The Record protocol as specified in +// http://www.cypherpunks.ca/otr/Protocol-v2-3.1.0.html +package otr // import "golang.org/x/crypto/otr" + +import ( + "bytes" + "crypto/aes" + "crypto/cipher" + "crypto/dsa" + "crypto/hmac" + "crypto/rand" + "crypto/sha1" + "crypto/sha256" + "crypto/subtle" + "encoding/base64" + "encoding/hex" + "errors" + "hash" + "io" + "math/big" + "strconv" +) + +// SecurityChange describes a change in the security state of a Conversation. +type SecurityChange int + +const ( + NoChange SecurityChange = iota + // NewKeys indicates that a key exchange has completed. This occurs + // when a conversation first becomes encrypted, and when the keys are + // renegotiated within an encrypted conversation. + NewKeys + // SMPSecretNeeded indicates that the peer has started an + // authentication and that we need to supply a secret. Call SMPQuestion + // to get the optional, human readable challenge and then Authenticate + // to supply the matching secret. + SMPSecretNeeded + // SMPComplete indicates that an authentication completed. The identity + // of the peer has now been confirmed. + SMPComplete + // SMPFailed indicates that an authentication failed. + SMPFailed + // ConversationEnded indicates that the peer ended the secure + // conversation. + ConversationEnded +) + +// QueryMessage can be sent to a peer to start an OTR conversation. +var QueryMessage = "?OTRv2?" + +// ErrorPrefix can be used to make an OTR error by appending an error message +// to it. +var ErrorPrefix = "?OTR Error:" + +var ( + fragmentPartSeparator = []byte(",") + fragmentPrefix = []byte("?OTR,") + msgPrefix = []byte("?OTR:") + queryMarker = []byte("?OTR") +) + +// isQuery attempts to parse an OTR query from msg and returns the greatest +// common version, or 0 if msg is not an OTR query. +func isQuery(msg []byte) (greatestCommonVersion int) { + pos := bytes.Index(msg, queryMarker) + if pos == -1 { + return 0 + } + for i, c := range msg[pos+len(queryMarker):] { + if i == 0 { + if c == '?' { + // Indicates support for version 1, but we don't + // implement that. + continue + } + + if c != 'v' { + // Invalid message + return 0 + } + + continue + } + + if c == '?' { + // End of message + return + } + + if c == ' ' || c == '\t' { + // Probably an invalid message + return 0 + } + + if c == '2' { + greatestCommonVersion = 2 + } + } + + return 0 +} + +const ( + statePlaintext = iota + stateEncrypted + stateFinished +) + +const ( + authStateNone = iota + authStateAwaitingDHKey + authStateAwaitingRevealSig + authStateAwaitingSig +) + +const ( + msgTypeDHCommit = 2 + msgTypeData = 3 + msgTypeDHKey = 10 + msgTypeRevealSig = 17 + msgTypeSig = 18 +) + +const ( + // If the requested fragment size is less than this, it will be ignored. + minFragmentSize = 18 + // Messages are padded to a multiple of this number of bytes. + paddingGranularity = 256 + // The number of bytes in a Diffie-Hellman private value (320-bits). + dhPrivateBytes = 40 + // The number of bytes needed to represent an element of the DSA + // subgroup (160-bits). + dsaSubgroupBytes = 20 + // The number of bytes of the MAC that are sent on the wire (160-bits). + macPrefixBytes = 20 +) + +// These are the global, common group parameters for OTR. +var ( + p *big.Int // group prime + g *big.Int // group generator + q *big.Int // group order + pMinus2 *big.Int +) + +func init() { + p, _ = new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB9ED529077096966D670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF", 16) + q, _ = new(big.Int).SetString("7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68948127044533E63A0105DF531D89CD9128A5043CC71A026EF7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6F71C35FDAD44CFD2D74F9208BE258FF324943328F6722D9EE1003E5C50B1DF82CC6D241B0E2AE9CD348B1FD47E9267AFC1B2AE91EE51D6CB0E3179AB1042A95DCF6A9483B84B4B36B3861AA7255E4C0278BA36046511B993FFFFFFFFFFFFFFFF", 16) + g = new(big.Int).SetInt64(2) + pMinus2 = new(big.Int).Sub(p, g) +} + +// Conversation represents a relation with a peer. The zero value is a valid +// Conversation, although PrivateKey must be set. +// +// When communicating with a peer, all inbound messages should be passed to +// Conversation.Receive and all outbound messages to Conversation.Send. The +// Conversation will take care of maintaining the encryption state and +// negotiating encryption as needed. +type Conversation struct { + // PrivateKey contains the private key to use to sign key exchanges. + PrivateKey *PrivateKey + + // Rand can be set to override the entropy source. Otherwise, + // crypto/rand will be used. + Rand io.Reader + // If FragmentSize is set, all messages produced by Receive and Send + // will be fragmented into messages of, at most, this number of bytes. + FragmentSize int + + // Once Receive has returned NewKeys once, the following fields are + // valid. + SSID [8]byte + TheirPublicKey PublicKey + + state, authState int + + r [16]byte + x, y *big.Int + gx, gy *big.Int + gxBytes []byte + digest [sha256.Size]byte + + revealKeys, sigKeys akeKeys + + myKeyId uint32 + myCurrentDHPub *big.Int + myCurrentDHPriv *big.Int + myLastDHPub *big.Int + myLastDHPriv *big.Int + + theirKeyId uint32 + theirCurrentDHPub *big.Int + theirLastDHPub *big.Int + + keySlots [4]keySlot + + myCounter [8]byte + theirLastCtr [8]byte + oldMACs []byte + + k, n int // fragment state + frag []byte + + smp smpState +} + +// A keySlot contains key material for a specific (their keyid, my keyid) pair. +type keySlot struct { + // used is true if this slot is valid. If false, it's free for reuse. + used bool + theirKeyId uint32 + myKeyId uint32 + sendAESKey, recvAESKey []byte + sendMACKey, recvMACKey []byte + theirLastCtr [8]byte +} + +// akeKeys are generated during key exchange. There's one set for the reveal +// signature message and another for the signature message. In the protocol +// spec the latter are indicated with a prime mark. +type akeKeys struct { + c [16]byte + m1, m2 [32]byte +} + +func (c *Conversation) rand() io.Reader { + if c.Rand != nil { + return c.Rand + } + return rand.Reader +} + +func (c *Conversation) randMPI(buf []byte) *big.Int { + _, err := io.ReadFull(c.rand(), buf) + if err != nil { + panic("otr: short read from random source") + } + + return new(big.Int).SetBytes(buf) +} + +// tlv represents the type-length value from the protocol. +type tlv struct { + typ, length uint16 + data []byte +} + +const ( + tlvTypePadding = 0 + tlvTypeDisconnected = 1 + tlvTypeSMP1 = 2 + tlvTypeSMP2 = 3 + tlvTypeSMP3 = 4 + tlvTypeSMP4 = 5 + tlvTypeSMPAbort = 6 + tlvTypeSMP1WithQuestion = 7 +) + +// Receive handles a message from a peer. It returns a human readable message, +// an indicator of whether that message was encrypted, a hint about the +// encryption state and zero or more messages to send back to the peer. +// These messages do not need to be passed to Send before transmission. +func (c *Conversation) Receive(in []byte) (out []byte, encrypted bool, change SecurityChange, toSend [][]byte, err error) { + if bytes.HasPrefix(in, fragmentPrefix) { + in, err = c.processFragment(in) + if in == nil || err != nil { + return + } + } + + if bytes.HasPrefix(in, msgPrefix) && in[len(in)-1] == '.' { + in = in[len(msgPrefix) : len(in)-1] + } else if version := isQuery(in); version > 0 { + c.authState = authStateAwaitingDHKey + c.reset() + toSend = c.encode(c.generateDHCommit()) + return + } else { + // plaintext message + out = in + return + } + + msg := make([]byte, base64.StdEncoding.DecodedLen(len(in))) + msgLen, err := base64.StdEncoding.Decode(msg, in) + if err != nil { + err = errors.New("otr: invalid base64 encoding in message") + return + } + msg = msg[:msgLen] + + // The first two bytes are the protocol version (2) + if len(msg) < 3 || msg[0] != 0 || msg[1] != 2 { + err = errors.New("otr: invalid OTR message") + return + } + + msgType := int(msg[2]) + msg = msg[3:] + + switch msgType { + case msgTypeDHCommit: + switch c.authState { + case authStateNone: + c.authState = authStateAwaitingRevealSig + if err = c.processDHCommit(msg); err != nil { + return + } + c.reset() + toSend = c.encode(c.generateDHKey()) + return + case authStateAwaitingDHKey: + // This is a 'SYN-crossing'. The greater digest wins. + var cmp int + if cmp, err = c.compareToDHCommit(msg); err != nil { + return + } + if cmp > 0 { + // We win. Retransmit DH commit. + toSend = c.encode(c.serializeDHCommit()) + return + } else { + // They win. We forget about our DH commit. + c.authState = authStateAwaitingRevealSig + if err = c.processDHCommit(msg); err != nil { + return + } + c.reset() + toSend = c.encode(c.generateDHKey()) + return + } + case authStateAwaitingRevealSig: + if err = c.processDHCommit(msg); err != nil { + return + } + toSend = c.encode(c.serializeDHKey()) + case authStateAwaitingSig: + if err = c.processDHCommit(msg); err != nil { + return + } + c.reset() + toSend = c.encode(c.generateDHKey()) + c.authState = authStateAwaitingRevealSig + default: + panic("bad state") + } + case msgTypeDHKey: + switch c.authState { + case authStateAwaitingDHKey: + var isSame bool + if isSame, err = c.processDHKey(msg); err != nil { + return + } + if isSame { + err = errors.New("otr: unexpected duplicate DH key") + return + } + toSend = c.encode(c.generateRevealSig()) + c.authState = authStateAwaitingSig + case authStateAwaitingSig: + var isSame bool + if isSame, err = c.processDHKey(msg); err != nil { + return + } + if isSame { + toSend = c.encode(c.serializeDHKey()) + } + } + case msgTypeRevealSig: + if c.authState != authStateAwaitingRevealSig { + return + } + if err = c.processRevealSig(msg); err != nil { + return + } + toSend = c.encode(c.generateSig()) + c.authState = authStateNone + c.state = stateEncrypted + change = NewKeys + case msgTypeSig: + if c.authState != authStateAwaitingSig { + return + } + if err = c.processSig(msg); err != nil { + return + } + c.authState = authStateNone + c.state = stateEncrypted + change = NewKeys + case msgTypeData: + if c.state != stateEncrypted { + err = errors.New("otr: encrypted message received without encrypted session established") + return + } + var tlvs []tlv + out, tlvs, err = c.processData(msg) + encrypted = true + + EachTLV: + for _, inTLV := range tlvs { + switch inTLV.typ { + case tlvTypeDisconnected: + change = ConversationEnded + c.state = stateFinished + break EachTLV + case tlvTypeSMP1, tlvTypeSMP2, tlvTypeSMP3, tlvTypeSMP4, tlvTypeSMPAbort, tlvTypeSMP1WithQuestion: + var reply tlv + var complete bool + reply, complete, err = c.processSMP(inTLV) + if err == smpSecretMissingError { + err = nil + change = SMPSecretNeeded + c.smp.saved = &inTLV + return + } + if err == smpFailureError { + err = nil + change = SMPFailed + } else if complete { + change = SMPComplete + } + if reply.typ != 0 { + toSend = c.encode(c.generateData(nil, &reply)) + } + break EachTLV + default: + // skip unknown TLVs + } + } + default: + err = errors.New("otr: unknown message type " + strconv.Itoa(msgType)) + } + + return +} + +// Send takes a human readable message from the local user, possibly encrypts +// it and returns zero one or more messages to send to the peer. +func (c *Conversation) Send(msg []byte) ([][]byte, error) { + switch c.state { + case statePlaintext: + return [][]byte{msg}, nil + case stateEncrypted: + return c.encode(c.generateData(msg, nil)), nil + case stateFinished: + return nil, errors.New("otr: cannot send message because secure conversation has finished") + } + + return nil, errors.New("otr: cannot send message in current state") +} + +// SMPQuestion returns the human readable challenge question from the peer. +// It's only valid after Receive has returned SMPSecretNeeded. +func (c *Conversation) SMPQuestion() string { + return c.smp.question +} + +// Authenticate begins an authentication with the peer. Authentication involves +// an optional challenge message and a shared secret. The authentication +// proceeds until either Receive returns SMPComplete, SMPSecretNeeded (which +// indicates that a new authentication is happening and thus this one was +// aborted) or SMPFailed. +func (c *Conversation) Authenticate(question string, mutualSecret []byte) (toSend [][]byte, err error) { + if c.state != stateEncrypted { + err = errors.New("otr: can't authenticate a peer without a secure conversation established") + return + } + + if c.smp.saved != nil { + c.calcSMPSecret(mutualSecret, false /* they started it */) + + var out tlv + var complete bool + out, complete, err = c.processSMP(*c.smp.saved) + if complete { + panic("SMP completed on the first message") + } + c.smp.saved = nil + if out.typ != 0 { + toSend = c.encode(c.generateData(nil, &out)) + } + return + } + + c.calcSMPSecret(mutualSecret, true /* we started it */) + outs := c.startSMP(question) + for _, out := range outs { + toSend = append(toSend, c.encode(c.generateData(nil, &out))...) + } + return +} + +// End ends a secure conversation by generating a termination message for +// the peer and switches to unencrypted communication. +func (c *Conversation) End() (toSend [][]byte) { + switch c.state { + case statePlaintext: + return nil + case stateEncrypted: + c.state = statePlaintext + return c.encode(c.generateData(nil, &tlv{typ: tlvTypeDisconnected})) + case stateFinished: + c.state = statePlaintext + return nil + } + panic("unreachable") +} + +// IsEncrypted returns true if a message passed to Send would be encrypted +// before transmission. This result remains valid until the next call to +// Receive or End, which may change the state of the Conversation. +func (c *Conversation) IsEncrypted() bool { + return c.state == stateEncrypted +} + +var fragmentError = errors.New("otr: invalid OTR fragment") + +// processFragment processes a fragmented OTR message and possibly returns a +// complete message. Fragmented messages look like "?OTR,k,n,msg," where k is +// the fragment number (starting from 1), n is the number of fragments in this +// message and msg is a substring of the base64 encoded message. +func (c *Conversation) processFragment(in []byte) (out []byte, err error) { + in = in[len(fragmentPrefix):] // remove "?OTR," + parts := bytes.Split(in, fragmentPartSeparator) + if len(parts) != 4 || len(parts[3]) != 0 { + return nil, fragmentError + } + + k, err := strconv.Atoi(string(parts[0])) + if err != nil { + return nil, fragmentError + } + + n, err := strconv.Atoi(string(parts[1])) + if err != nil { + return nil, fragmentError + } + + if k < 1 || n < 1 || k > n { + return nil, fragmentError + } + + if k == 1 { + c.frag = append(c.frag[:0], parts[2]...) + c.k, c.n = k, n + } else if n == c.n && k == c.k+1 { + c.frag = append(c.frag, parts[2]...) + c.k++ + } else { + c.frag = c.frag[:0] + c.n, c.k = 0, 0 + } + + if c.n > 0 && c.k == c.n { + c.n, c.k = 0, 0 + return c.frag, nil + } + + return nil, nil +} + +func (c *Conversation) generateDHCommit() []byte { + _, err := io.ReadFull(c.rand(), c.r[:]) + if err != nil { + panic("otr: short read from random source") + } + + var xBytes [dhPrivateBytes]byte + c.x = c.randMPI(xBytes[:]) + c.gx = new(big.Int).Exp(g, c.x, p) + c.gy = nil + c.gxBytes = appendMPI(nil, c.gx) + + h := sha256.New() + h.Write(c.gxBytes) + h.Sum(c.digest[:0]) + + aesCipher, err := aes.NewCipher(c.r[:]) + if err != nil { + panic(err.Error()) + } + + var iv [aes.BlockSize]byte + ctr := cipher.NewCTR(aesCipher, iv[:]) + ctr.XORKeyStream(c.gxBytes, c.gxBytes) + + return c.serializeDHCommit() +} + +func (c *Conversation) serializeDHCommit() []byte { + var ret []byte + ret = appendU16(ret, 2) // protocol version + ret = append(ret, msgTypeDHCommit) + ret = appendData(ret, c.gxBytes) + ret = appendData(ret, c.digest[:]) + return ret +} + +func (c *Conversation) processDHCommit(in []byte) error { + var ok1, ok2 bool + c.gxBytes, in, ok1 = getData(in) + digest, in, ok2 := getData(in) + if !ok1 || !ok2 || len(in) > 0 { + return errors.New("otr: corrupt DH commit message") + } + copy(c.digest[:], digest) + return nil +} + +func (c *Conversation) compareToDHCommit(in []byte) (int, error) { + _, in, ok1 := getData(in) + digest, in, ok2 := getData(in) + if !ok1 || !ok2 || len(in) > 0 { + return 0, errors.New("otr: corrupt DH commit message") + } + return bytes.Compare(c.digest[:], digest), nil +} + +func (c *Conversation) generateDHKey() []byte { + var yBytes [dhPrivateBytes]byte + c.y = c.randMPI(yBytes[:]) + c.gy = new(big.Int).Exp(g, c.y, p) + return c.serializeDHKey() +} + +func (c *Conversation) serializeDHKey() []byte { + var ret []byte + ret = appendU16(ret, 2) // protocol version + ret = append(ret, msgTypeDHKey) + ret = appendMPI(ret, c.gy) + return ret +} + +func (c *Conversation) processDHKey(in []byte) (isSame bool, err error) { + gy, in, ok := getMPI(in) + if !ok { + err = errors.New("otr: corrupt DH key message") + return + } + if gy.Cmp(g) < 0 || gy.Cmp(pMinus2) > 0 { + err = errors.New("otr: DH value out of range") + return + } + if c.gy != nil { + isSame = c.gy.Cmp(gy) == 0 + return + } + c.gy = gy + return +} + +func (c *Conversation) generateEncryptedSignature(keys *akeKeys, xFirst bool) ([]byte, []byte) { + var xb []byte + xb = c.PrivateKey.PublicKey.Serialize(xb) + + var verifyData []byte + if xFirst { + verifyData = appendMPI(verifyData, c.gx) + verifyData = appendMPI(verifyData, c.gy) + } else { + verifyData = appendMPI(verifyData, c.gy) + verifyData = appendMPI(verifyData, c.gx) + } + verifyData = append(verifyData, xb...) + verifyData = appendU32(verifyData, c.myKeyId) + + mac := hmac.New(sha256.New, keys.m1[:]) + mac.Write(verifyData) + mb := mac.Sum(nil) + + xb = appendU32(xb, c.myKeyId) + xb = append(xb, c.PrivateKey.Sign(c.rand(), mb)...) + + aesCipher, err := aes.NewCipher(keys.c[:]) + if err != nil { + panic(err.Error()) + } + var iv [aes.BlockSize]byte + ctr := cipher.NewCTR(aesCipher, iv[:]) + ctr.XORKeyStream(xb, xb) + + mac = hmac.New(sha256.New, keys.m2[:]) + encryptedSig := appendData(nil, xb) + mac.Write(encryptedSig) + + return encryptedSig, mac.Sum(nil) +} + +func (c *Conversation) generateRevealSig() []byte { + s := new(big.Int).Exp(c.gy, c.x, p) + c.calcAKEKeys(s) + c.myKeyId++ + + encryptedSig, mac := c.generateEncryptedSignature(&c.revealKeys, true /* gx comes first */) + + c.myCurrentDHPub = c.gx + c.myCurrentDHPriv = c.x + c.rotateDHKeys() + incCounter(&c.myCounter) + + var ret []byte + ret = appendU16(ret, 2) + ret = append(ret, msgTypeRevealSig) + ret = appendData(ret, c.r[:]) + ret = append(ret, encryptedSig...) + ret = append(ret, mac[:20]...) + return ret +} + +func (c *Conversation) processEncryptedSig(encryptedSig, theirMAC []byte, keys *akeKeys, xFirst bool) error { + mac := hmac.New(sha256.New, keys.m2[:]) + mac.Write(appendData(nil, encryptedSig)) + myMAC := mac.Sum(nil)[:20] + + if len(myMAC) != len(theirMAC) || subtle.ConstantTimeCompare(myMAC, theirMAC) == 0 { + return errors.New("bad signature MAC in encrypted signature") + } + + aesCipher, err := aes.NewCipher(keys.c[:]) + if err != nil { + panic(err.Error()) + } + var iv [aes.BlockSize]byte + ctr := cipher.NewCTR(aesCipher, iv[:]) + ctr.XORKeyStream(encryptedSig, encryptedSig) + + sig := encryptedSig + sig, ok1 := c.TheirPublicKey.Parse(sig) + keyId, sig, ok2 := getU32(sig) + if !ok1 || !ok2 { + return errors.New("otr: corrupt encrypted signature") + } + + var verifyData []byte + if xFirst { + verifyData = appendMPI(verifyData, c.gx) + verifyData = appendMPI(verifyData, c.gy) + } else { + verifyData = appendMPI(verifyData, c.gy) + verifyData = appendMPI(verifyData, c.gx) + } + verifyData = c.TheirPublicKey.Serialize(verifyData) + verifyData = appendU32(verifyData, keyId) + + mac = hmac.New(sha256.New, keys.m1[:]) + mac.Write(verifyData) + mb := mac.Sum(nil) + + sig, ok1 = c.TheirPublicKey.Verify(mb, sig) + if !ok1 { + return errors.New("bad signature in encrypted signature") + } + if len(sig) > 0 { + return errors.New("corrupt encrypted signature") + } + + c.theirKeyId = keyId + zero(c.theirLastCtr[:]) + return nil +} + +func (c *Conversation) processRevealSig(in []byte) error { + r, in, ok1 := getData(in) + encryptedSig, in, ok2 := getData(in) + theirMAC := in + if !ok1 || !ok2 || len(theirMAC) != 20 { + return errors.New("otr: corrupt reveal signature message") + } + + aesCipher, err := aes.NewCipher(r) + if err != nil { + return errors.New("otr: cannot create AES cipher from reveal signature message: " + err.Error()) + } + var iv [aes.BlockSize]byte + ctr := cipher.NewCTR(aesCipher, iv[:]) + ctr.XORKeyStream(c.gxBytes, c.gxBytes) + h := sha256.New() + h.Write(c.gxBytes) + digest := h.Sum(nil) + if len(digest) != len(c.digest) || subtle.ConstantTimeCompare(digest, c.digest[:]) == 0 { + return errors.New("otr: bad commit MAC in reveal signature message") + } + var rest []byte + c.gx, rest, ok1 = getMPI(c.gxBytes) + if !ok1 || len(rest) > 0 { + return errors.New("otr: gx corrupt after decryption") + } + if c.gx.Cmp(g) < 0 || c.gx.Cmp(pMinus2) > 0 { + return errors.New("otr: DH value out of range") + } + s := new(big.Int).Exp(c.gx, c.y, p) + c.calcAKEKeys(s) + + if err := c.processEncryptedSig(encryptedSig, theirMAC, &c.revealKeys, true /* gx comes first */); err != nil { + return errors.New("otr: in reveal signature message: " + err.Error()) + } + + c.theirCurrentDHPub = c.gx + c.theirLastDHPub = nil + + return nil +} + +func (c *Conversation) generateSig() []byte { + c.myKeyId++ + + encryptedSig, mac := c.generateEncryptedSignature(&c.sigKeys, false /* gy comes first */) + + c.myCurrentDHPub = c.gy + c.myCurrentDHPriv = c.y + c.rotateDHKeys() + incCounter(&c.myCounter) + + var ret []byte + ret = appendU16(ret, 2) + ret = append(ret, msgTypeSig) + ret = append(ret, encryptedSig...) + ret = append(ret, mac[:macPrefixBytes]...) + return ret +} + +func (c *Conversation) processSig(in []byte) error { + encryptedSig, in, ok1 := getData(in) + theirMAC := in + if !ok1 || len(theirMAC) != macPrefixBytes { + return errors.New("otr: corrupt signature message") + } + + if err := c.processEncryptedSig(encryptedSig, theirMAC, &c.sigKeys, false /* gy comes first */); err != nil { + return errors.New("otr: in signature message: " + err.Error()) + } + + c.theirCurrentDHPub = c.gy + c.theirLastDHPub = nil + + return nil +} + +func (c *Conversation) rotateDHKeys() { + // evict slots using our retired key id + for i := range c.keySlots { + slot := &c.keySlots[i] + if slot.used && slot.myKeyId == c.myKeyId-1 { + slot.used = false + c.oldMACs = append(c.oldMACs, slot.recvMACKey...) + } + } + + c.myLastDHPriv = c.myCurrentDHPriv + c.myLastDHPub = c.myCurrentDHPub + + var xBytes [dhPrivateBytes]byte + c.myCurrentDHPriv = c.randMPI(xBytes[:]) + c.myCurrentDHPub = new(big.Int).Exp(g, c.myCurrentDHPriv, p) + c.myKeyId++ +} + +func (c *Conversation) processData(in []byte) (out []byte, tlvs []tlv, err error) { + origIn := in + flags, in, ok1 := getU8(in) + theirKeyId, in, ok2 := getU32(in) + myKeyId, in, ok3 := getU32(in) + y, in, ok4 := getMPI(in) + counter, in, ok5 := getNBytes(in, 8) + encrypted, in, ok6 := getData(in) + macedData := origIn[:len(origIn)-len(in)] + theirMAC, in, ok7 := getNBytes(in, macPrefixBytes) + _, in, ok8 := getData(in) + if !ok1 || !ok2 || !ok3 || !ok4 || !ok5 || !ok6 || !ok7 || !ok8 || len(in) > 0 { + err = errors.New("otr: corrupt data message") + return + } + + ignoreErrors := flags&1 != 0 + + slot, err := c.calcDataKeys(myKeyId, theirKeyId) + if err != nil { + if ignoreErrors { + err = nil + } + return + } + + mac := hmac.New(sha1.New, slot.recvMACKey) + mac.Write([]byte{0, 2, 3}) + mac.Write(macedData) + myMAC := mac.Sum(nil) + if len(myMAC) != len(theirMAC) || subtle.ConstantTimeCompare(myMAC, theirMAC) == 0 { + if !ignoreErrors { + err = errors.New("otr: bad MAC on data message") + } + return + } + + if bytes.Compare(counter, slot.theirLastCtr[:]) <= 0 { + err = errors.New("otr: counter regressed") + return + } + copy(slot.theirLastCtr[:], counter) + + var iv [aes.BlockSize]byte + copy(iv[:], counter) + aesCipher, err := aes.NewCipher(slot.recvAESKey) + if err != nil { + panic(err.Error()) + } + ctr := cipher.NewCTR(aesCipher, iv[:]) + ctr.XORKeyStream(encrypted, encrypted) + decrypted := encrypted + + if myKeyId == c.myKeyId { + c.rotateDHKeys() + } + if theirKeyId == c.theirKeyId { + // evict slots using their retired key id + for i := range c.keySlots { + slot := &c.keySlots[i] + if slot.used && slot.theirKeyId == theirKeyId-1 { + slot.used = false + c.oldMACs = append(c.oldMACs, slot.recvMACKey...) + } + } + + c.theirLastDHPub = c.theirCurrentDHPub + c.theirKeyId++ + c.theirCurrentDHPub = y + } + + if nulPos := bytes.IndexByte(decrypted, 0); nulPos >= 0 { + out = decrypted[:nulPos] + tlvData := decrypted[nulPos+1:] + for len(tlvData) > 0 { + var t tlv + var ok1, ok2, ok3 bool + + t.typ, tlvData, ok1 = getU16(tlvData) + t.length, tlvData, ok2 = getU16(tlvData) + t.data, tlvData, ok3 = getNBytes(tlvData, int(t.length)) + if !ok1 || !ok2 || !ok3 { + err = errors.New("otr: corrupt tlv data") + return + } + tlvs = append(tlvs, t) + } + } else { + out = decrypted + } + + return +} + +func (c *Conversation) generateData(msg []byte, extra *tlv) []byte { + slot, err := c.calcDataKeys(c.myKeyId-1, c.theirKeyId) + if err != nil { + panic("otr: failed to generate sending keys: " + err.Error()) + } + + var plaintext []byte + plaintext = append(plaintext, msg...) + plaintext = append(plaintext, 0) + + padding := paddingGranularity - ((len(plaintext) + 4) % paddingGranularity) + plaintext = appendU16(plaintext, tlvTypePadding) + plaintext = appendU16(plaintext, uint16(padding)) + for i := 0; i < padding; i++ { + plaintext = append(plaintext, 0) + } + + if extra != nil { + plaintext = appendU16(plaintext, extra.typ) + plaintext = appendU16(plaintext, uint16(len(extra.data))) + plaintext = append(plaintext, extra.data...) + } + + encrypted := make([]byte, len(plaintext)) + + var iv [aes.BlockSize]byte + copy(iv[:], c.myCounter[:]) + aesCipher, err := aes.NewCipher(slot.sendAESKey) + if err != nil { + panic(err.Error()) + } + ctr := cipher.NewCTR(aesCipher, iv[:]) + ctr.XORKeyStream(encrypted, plaintext) + + var ret []byte + ret = appendU16(ret, 2) + ret = append(ret, msgTypeData) + ret = append(ret, 0 /* flags */) + ret = appendU32(ret, c.myKeyId-1) + ret = appendU32(ret, c.theirKeyId) + ret = appendMPI(ret, c.myCurrentDHPub) + ret = append(ret, c.myCounter[:]...) + ret = appendData(ret, encrypted) + + mac := hmac.New(sha1.New, slot.sendMACKey) + mac.Write(ret) + ret = append(ret, mac.Sum(nil)[:macPrefixBytes]...) + ret = appendData(ret, c.oldMACs) + c.oldMACs = nil + incCounter(&c.myCounter) + + return ret +} + +func incCounter(counter *[8]byte) { + for i := 7; i >= 0; i-- { + counter[i]++ + if counter[i] > 0 { + break + } + } +} + +// calcDataKeys computes the keys used to encrypt a data message given the key +// IDs. +func (c *Conversation) calcDataKeys(myKeyId, theirKeyId uint32) (slot *keySlot, err error) { + // Check for a cache hit. + for i := range c.keySlots { + slot = &c.keySlots[i] + if slot.used && slot.theirKeyId == theirKeyId && slot.myKeyId == myKeyId { + return + } + } + + // Find an empty slot to write into. + slot = nil + for i := range c.keySlots { + if !c.keySlots[i].used { + slot = &c.keySlots[i] + break + } + } + if slot == nil { + return nil, errors.New("otr: internal error: no more key slots") + } + + var myPriv, myPub, theirPub *big.Int + + if myKeyId == c.myKeyId { + myPriv = c.myCurrentDHPriv + myPub = c.myCurrentDHPub + } else if myKeyId == c.myKeyId-1 { + myPriv = c.myLastDHPriv + myPub = c.myLastDHPub + } else { + err = errors.New("otr: peer requested keyid " + strconv.FormatUint(uint64(myKeyId), 10) + " when I'm on " + strconv.FormatUint(uint64(c.myKeyId), 10)) + return + } + + if theirKeyId == c.theirKeyId { + theirPub = c.theirCurrentDHPub + } else if theirKeyId == c.theirKeyId-1 && c.theirLastDHPub != nil { + theirPub = c.theirLastDHPub + } else { + err = errors.New("otr: peer requested keyid " + strconv.FormatUint(uint64(myKeyId), 10) + " when they're on " + strconv.FormatUint(uint64(c.myKeyId), 10)) + return + } + + var sendPrefixByte, recvPrefixByte [1]byte + + if myPub.Cmp(theirPub) > 0 { + // we're the high end + sendPrefixByte[0], recvPrefixByte[0] = 1, 2 + } else { + // we're the low end + sendPrefixByte[0], recvPrefixByte[0] = 2, 1 + } + + s := new(big.Int).Exp(theirPub, myPriv, p) + sBytes := appendMPI(nil, s) + + h := sha1.New() + h.Write(sendPrefixByte[:]) + h.Write(sBytes) + slot.sendAESKey = h.Sum(slot.sendAESKey[:0])[:16] + + h.Reset() + h.Write(slot.sendAESKey) + slot.sendMACKey = h.Sum(slot.sendMACKey[:0]) + + h.Reset() + h.Write(recvPrefixByte[:]) + h.Write(sBytes) + slot.recvAESKey = h.Sum(slot.recvAESKey[:0])[:16] + + h.Reset() + h.Write(slot.recvAESKey) + slot.recvMACKey = h.Sum(slot.recvMACKey[:0]) + + slot.theirKeyId = theirKeyId + slot.myKeyId = myKeyId + slot.used = true + + zero(slot.theirLastCtr[:]) + return +} + +func (c *Conversation) calcAKEKeys(s *big.Int) { + mpi := appendMPI(nil, s) + h := sha256.New() + + var cBytes [32]byte + hashWithPrefix(c.SSID[:], 0, mpi, h) + + hashWithPrefix(cBytes[:], 1, mpi, h) + copy(c.revealKeys.c[:], cBytes[:16]) + copy(c.sigKeys.c[:], cBytes[16:]) + + hashWithPrefix(c.revealKeys.m1[:], 2, mpi, h) + hashWithPrefix(c.revealKeys.m2[:], 3, mpi, h) + hashWithPrefix(c.sigKeys.m1[:], 4, mpi, h) + hashWithPrefix(c.sigKeys.m2[:], 5, mpi, h) +} + +func hashWithPrefix(out []byte, prefix byte, in []byte, h hash.Hash) { + h.Reset() + var p [1]byte + p[0] = prefix + h.Write(p[:]) + h.Write(in) + if len(out) == h.Size() { + h.Sum(out[:0]) + } else { + digest := h.Sum(nil) + copy(out, digest) + } +} + +func (c *Conversation) encode(msg []byte) [][]byte { + b64 := make([]byte, base64.StdEncoding.EncodedLen(len(msg))+len(msgPrefix)+1) + base64.StdEncoding.Encode(b64[len(msgPrefix):], msg) + copy(b64, msgPrefix) + b64[len(b64)-1] = '.' + + if c.FragmentSize < minFragmentSize || len(b64) <= c.FragmentSize { + // We can encode this in a single fragment. + return [][]byte{b64} + } + + // We have to fragment this message. + var ret [][]byte + bytesPerFragment := c.FragmentSize - minFragmentSize + numFragments := (len(b64) + bytesPerFragment) / bytesPerFragment + + for i := 0; i < numFragments; i++ { + frag := []byte("?OTR," + strconv.Itoa(i+1) + "," + strconv.Itoa(numFragments) + ",") + todo := bytesPerFragment + if todo > len(b64) { + todo = len(b64) + } + frag = append(frag, b64[:todo]...) + b64 = b64[todo:] + frag = append(frag, ',') + ret = append(ret, frag) + } + + return ret +} + +func (c *Conversation) reset() { + c.myKeyId = 0 + + for i := range c.keySlots { + c.keySlots[i].used = false + } +} + +type PublicKey struct { + dsa.PublicKey +} + +func (pk *PublicKey) Parse(in []byte) ([]byte, bool) { + var ok bool + var pubKeyType uint16 + + if pubKeyType, in, ok = getU16(in); !ok || pubKeyType != 0 { + return nil, false + } + if pk.P, in, ok = getMPI(in); !ok { + return nil, false + } + if pk.Q, in, ok = getMPI(in); !ok { + return nil, false + } + if pk.G, in, ok = getMPI(in); !ok { + return nil, false + } + if pk.Y, in, ok = getMPI(in); !ok { + return nil, false + } + + return in, true +} + +func (pk *PublicKey) Serialize(in []byte) []byte { + in = appendU16(in, 0) + in = appendMPI(in, pk.P) + in = appendMPI(in, pk.Q) + in = appendMPI(in, pk.G) + in = appendMPI(in, pk.Y) + return in +} + +// Fingerprint returns the 20-byte, binary fingerprint of the PublicKey. +func (pk *PublicKey) Fingerprint() []byte { + b := pk.Serialize(nil) + h := sha1.New() + h.Write(b[2:]) + return h.Sum(nil) +} + +func (pk *PublicKey) Verify(hashed, sig []byte) ([]byte, bool) { + if len(sig) != 2*dsaSubgroupBytes { + return nil, false + } + r := new(big.Int).SetBytes(sig[:dsaSubgroupBytes]) + s := new(big.Int).SetBytes(sig[dsaSubgroupBytes:]) + ok := dsa.Verify(&pk.PublicKey, hashed, r, s) + return sig[dsaSubgroupBytes*2:], ok +} + +type PrivateKey struct { + PublicKey + dsa.PrivateKey +} + +func (priv *PrivateKey) Sign(rand io.Reader, hashed []byte) []byte { + r, s, err := dsa.Sign(rand, &priv.PrivateKey, hashed) + if err != nil { + panic(err.Error()) + } + rBytes := r.Bytes() + sBytes := s.Bytes() + if len(rBytes) > dsaSubgroupBytes || len(sBytes) > dsaSubgroupBytes { + panic("DSA signature too large") + } + + out := make([]byte, 2*dsaSubgroupBytes) + copy(out[dsaSubgroupBytes-len(rBytes):], rBytes) + copy(out[len(out)-len(sBytes):], sBytes) + return out +} + +func (priv *PrivateKey) Serialize(in []byte) []byte { + in = priv.PublicKey.Serialize(in) + in = appendMPI(in, priv.PrivateKey.X) + return in +} + +func (priv *PrivateKey) Parse(in []byte) ([]byte, bool) { + in, ok := priv.PublicKey.Parse(in) + if !ok { + return in, ok + } + priv.PrivateKey.PublicKey = priv.PublicKey.PublicKey + priv.PrivateKey.X, in, ok = getMPI(in) + return in, ok +} + +func (priv *PrivateKey) Generate(rand io.Reader) { + if err := dsa.GenerateParameters(&priv.PrivateKey.PublicKey.Parameters, rand, dsa.L1024N160); err != nil { + panic(err.Error()) + } + if err := dsa.GenerateKey(&priv.PrivateKey, rand); err != nil { + panic(err.Error()) + } + priv.PublicKey.PublicKey = priv.PrivateKey.PublicKey +} + +func notHex(r rune) bool { + if r >= '0' && r <= '9' || + r >= 'a' && r <= 'f' || + r >= 'A' && r <= 'F' { + return false + } + + return true +} + +// Import parses the contents of a libotr private key file. +func (priv *PrivateKey) Import(in []byte) bool { + mpiStart := []byte(" #") + + mpis := make([]*big.Int, 5) + + for i := 0; i < len(mpis); i++ { + start := bytes.Index(in, mpiStart) + if start == -1 { + return false + } + in = in[start+len(mpiStart):] + end := bytes.IndexFunc(in, notHex) + if end == -1 { + return false + } + hexBytes := in[:end] + in = in[end:] + + if len(hexBytes)&1 != 0 { + return false + } + + mpiBytes := make([]byte, len(hexBytes)/2) + if _, err := hex.Decode(mpiBytes, hexBytes); err != nil { + return false + } + + mpis[i] = new(big.Int).SetBytes(mpiBytes) + } + + for _, mpi := range mpis { + if mpi.Sign() <= 0 { + return false + } + } + + priv.PrivateKey.P = mpis[0] + priv.PrivateKey.Q = mpis[1] + priv.PrivateKey.G = mpis[2] + priv.PrivateKey.Y = mpis[3] + priv.PrivateKey.X = mpis[4] + priv.PublicKey.PublicKey = priv.PrivateKey.PublicKey + + a := new(big.Int).Exp(priv.PrivateKey.G, priv.PrivateKey.X, priv.PrivateKey.P) + return a.Cmp(priv.PrivateKey.Y) == 0 +} + +func getU8(in []byte) (uint8, []byte, bool) { + if len(in) < 1 { + return 0, in, false + } + return in[0], in[1:], true +} + +func getU16(in []byte) (uint16, []byte, bool) { + if len(in) < 2 { + return 0, in, false + } + r := uint16(in[0])<<8 | uint16(in[1]) + return r, in[2:], true +} + +func getU32(in []byte) (uint32, []byte, bool) { + if len(in) < 4 { + return 0, in, false + } + r := uint32(in[0])<<24 | uint32(in[1])<<16 | uint32(in[2])<<8 | uint32(in[3]) + return r, in[4:], true +} + +func getMPI(in []byte) (*big.Int, []byte, bool) { + l, in, ok := getU32(in) + if !ok || uint32(len(in)) < l { + return nil, in, false + } + r := new(big.Int).SetBytes(in[:l]) + return r, in[l:], true +} + +func getData(in []byte) ([]byte, []byte, bool) { + l, in, ok := getU32(in) + if !ok || uint32(len(in)) < l { + return nil, in, false + } + return in[:l], in[l:], true +} + +func getNBytes(in []byte, n int) ([]byte, []byte, bool) { + if len(in) < n { + return nil, in, false + } + return in[:n], in[n:], true +} + +func appendU16(out []byte, v uint16) []byte { + out = append(out, byte(v>>8), byte(v)) + return out +} + +func appendU32(out []byte, v uint32) []byte { + out = append(out, byte(v>>24), byte(v>>16), byte(v>>8), byte(v)) + return out +} + +func appendData(out, v []byte) []byte { + out = appendU32(out, uint32(len(v))) + out = append(out, v...) + return out +} + +func appendMPI(out []byte, v *big.Int) []byte { + vBytes := v.Bytes() + out = appendU32(out, uint32(len(vBytes))) + out = append(out, vBytes...) + return out +} + +func appendMPIs(out []byte, mpis ...*big.Int) []byte { + for _, mpi := range mpis { + out = appendMPI(out, mpi) + } + return out +} + +func zero(b []byte) { + for i := range b { + b[i] = 0 + } +} |