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// 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
//
// The version of OTR implemented by this package has been deprecated
// (https://bugs.otr.im/lib/libotr/issues/140). An implementation of OTRv3 is
// available at https://github.com/coyim/otr3.
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, _, 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
}
}