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decrypt.go
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decrypt.go
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// Copyright (c) 2015 Mute Communications Ltd.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package msg
import (
"bytes"
"crypto/aes"
"crypto/hmac"
"crypto/sha512"
"io"
"github.com/agl/ed25519"
"github.com/mutecomm/mute/cipher"
"github.com/mutecomm/mute/encode/base64"
"github.com/mutecomm/mute/log"
"github.com/mutecomm/mute/msg/mime"
"github.com/mutecomm/mute/msg/session"
"github.com/mutecomm/mute/uid"
)
func rootKeyAgreementRecipient(
senderHeaderPub *[32]byte,
senderIdentity, recipientIdentity string,
senderSession, senderID, recipientKI, recipientID *uid.KeyEntry,
previousRootKeyHash *[64]byte,
numOfKeys uint64,
keyStore session.Store,
) error {
recipientIdentityPub := recipientID.PublicKey32()
recipientIdentityPriv := recipientID.PrivateKey32()
recipientKeyInitPub := recipientKI.PublicKey32()
recipientKeyInitPriv := recipientKI.PrivateKey32()
// sender cannot cause panic here, because keys have been validated in header
senderSessionPub := senderSession.PublicKey32()
senderIdentityPub := senderID.PublicKey32()
log.Debugf("senderIdentityPub: %s", base64.Encode(senderIdentityPub[:]))
log.Debugf("senderSessionPub: %s", base64.Encode(senderSessionPub[:]))
log.Debugf("recipientIdentityPub: %s", base64.Encode(recipientIdentityPub[:]))
log.Debugf("recipientKeyInitPub: %s", base64.Encode(recipientKeyInitPub[:]))
// check keys to prevent reflection attacks and replays
err := checkKeys(senderHeaderPub, senderIdentityPub, senderSessionPub,
recipientIdentityPub, recipientKeyInitPub)
if err != nil {
return err
}
// compute t1
t1, err := cipher.ECDH(recipientKeyInitPriv, senderIdentityPub, recipientKeyInitPub)
if err != nil {
return err
}
// compute t2
t2, err := cipher.ECDH(recipientKeyInitPriv, senderSessionPub, recipientKeyInitPub)
if err != nil {
return err
}
// compute t3
t3, err := cipher.ECDH(recipientIdentityPriv, senderSessionPub, recipientIdentityPub)
if err != nil {
return err
}
// derive root key
rootKey, err := deriveRootKey(t1, t2, t3, previousRootKeyHash)
if err != nil {
return err
}
// generate message keys
err = generateMessageKeys(senderIdentity, recipientIdentity,
senderID.HASH, recipientID.HASH, rootKey, true, senderSessionPub,
recipientKeyInitPub, numOfKeys, keyStore)
if err != nil {
return err
}
return nil
}
// DecryptArgs contains all arguments for a message decryption.
type DecryptArgs struct {
Writer io.Writer // decrypted message is written here
Identities []*uid.Message // list of recipient UID messages
PreHeader []byte // preHeader read with ReadFirstOuterHeader()
Reader io.Reader // data to decrypt is read here (not base64 encoded)
NumOfKeys uint64 // number of generated sessions keys (default: NumOfFutureKeys)
Rand io.Reader // random source
KeyStore session.Store // for managing session keys
}
// Decrypt decrypts a message with the argument given in args.
// The senderID is returned.
// If the message was signed and the signature could be verified successfully
// the base64 encoded signature is returned. If the message was signed and the
// signature could not be verfied an error is returned.
func Decrypt(args *DecryptArgs) (senderID, sig string, err error) {
log.Debug("msg.Decrypt()")
// set default
if args.NumOfKeys == 0 {
args.NumOfKeys = NumOfFutureKeys
}
// read pre-header
ph, err := readPreHeader(bytes.NewBuffer(args.PreHeader))
if err != nil {
return "", "", err
}
if ph.LengthSenderHeaderPub != 32 {
return "", "", log.Errorf("msg: ph.LengthSenderHeaderPub != 32")
}
var senderHeaderPub [32]byte
copy(senderHeaderPub[:], ph.SenderHeaderPub)
// read header packet
oh, err := readOuterHeader(args.Reader)
if err != nil {
return "", "", err
}
if oh.Type != encryptedHeader {
return "", "", log.Error(ErrNotEncryptedHeader)
}
count := uint32(1)
if oh.PacketCount != count {
return "", "", log.Error(ErrWrongCount)
}
count++
identity, h, err := readHeader(&senderHeaderPub, args.Identities,
bytes.NewBuffer(oh.inner))
if err != nil {
return "", "", err
}
senderID = h.SenderIdentity
recipientID := identity.PubKey()
log.Debugf("senderID: %s", h.SenderIdentityPub.HASH)
log.Debugf("recipientID: %s", recipientID.HASH)
log.Debugf("h.SenderSessionCount: %d", h.SenderSessionCount)
log.Debugf("h.SenderMessageCount: %d", h.SenderMessageCount)
log.Debugf("h.SenderSessionPub: %s", h.SenderSessionPub.HASH)
if h.NextSenderSessionPub != nil {
log.Debugf("h.NextSenderSessionPub: %s", h.NextSenderSessionPub.HASH)
}
if h.NextRecipientSessionPubSeen != nil {
log.Debugf("h.NextRecipientSessionPubSeen: %s",
h.NextRecipientSessionPubSeen.HASH)
}
// proc sender UID in parallel
res := make(chan *procUIDResult, 1)
go procUID(h.SenderUID, res)
// get session state
sender := h.SenderIdentity
recipient := identity.Identity()
log.Debugf("%s -> %s", sender, recipient)
sessionStateKey := session.CalcStateKey(recipientID.PublicKey32(),
h.SenderIdentityPub.PublicKey32())
ss, err := args.KeyStore.GetSessionState(sessionStateKey)
if err != nil {
return "", "", err
}
sessionKey := session.CalcKey(recipientID.HASH, h.SenderIdentityPub.HASH,
h.RecipientTempHash, h.SenderSessionPub.HASH)
if !args.KeyStore.HasSession(sessionKey) { // session unknown
// try to start session from KeyInit message
recipientKI, err := args.KeyStore.GetPrivateKeyEntry(h.RecipientTempHash)
if err != nil && err != session.ErrNoKeyEntry {
return "", "", err
}
if err != session.ErrNoKeyEntry { // KeyInit message found
// root key agreement
err = rootKeyAgreementRecipient(&senderHeaderPub, sender, recipient,
&h.SenderSessionPub, &h.SenderIdentityPub, recipientKI, recipientID,
nil, args.NumOfKeys, args.KeyStore)
if err != nil {
return "", "", err
}
// TODO: delete single-use KeyInit message
// use the 'smaller' session as the definite one
// TODO: h.SenderSessionPub.HASH < ss.SenderSessionPub.HASH
if ss == nil || (ss.KeyInitSession && sender < recipient) {
// create next session key
var nextSenderSession uid.KeyEntry
if err := nextSenderSession.InitDHKey(args.Rand); err != nil {
return "", "", err
}
// store next session key
err := addSessionKey(args.KeyStore, &nextSenderSession)
if err != nil {
return "", "", err
}
// if we already got h.NextSenderSessionPub prepare next session
if h.NextSenderSessionPub != nil {
previousRootKeyHash, err := args.KeyStore.GetRootKeyHash(sessionKey)
if err != nil {
return "", "", err
}
// root key agreement
err = rootKeyAgreementSender(&senderHeaderPub, recipient,
sender, &nextSenderSession, recipientID,
h.NextSenderSessionPub, &h.SenderIdentityPub,
previousRootKeyHash, args.NumOfKeys, args.KeyStore)
if err != nil {
return "", "", err
}
}
// set session state
ss = &session.State{
SenderSessionCount: 0,
SenderMessageCount: 0,
MaxRecipientCount: 0,
RecipientTemp: h.SenderSessionPub,
SenderSessionPub: *recipientKI,
NextSenderSessionPub: &nextSenderSession,
NextRecipientSessionPubSeen: h.NextSenderSessionPub,
NymAddress: h.NymAddress,
KeyInitSession: false,
}
err = args.KeyStore.SetSessionState(sessionStateKey, ss)
if err != nil {
return "", "", err
}
}
} else { // no KeyInit message found
// TODO: ???
}
} else { // session known
log.Debug("session known")
// check if session state reflects that session
if h.RecipientTempHash == ss.SenderSessionPub.HASH &&
h.SenderSessionPub.HASH == ss.RecipientTemp.HASH {
log.Debug("session state reflects that session")
if h.NextSenderSessionPub != nil {
log.Debug("h.NextSenderSessionPub is defined")
}
if h.NextRecipientSessionPubSeen != nil {
log.Debug("h.NextRecipientSessionPubSeen is defined")
}
if h.NextSenderSessionPub != nil {
// if other side has set its NextSenderSessionPubKey we set
// ours immediately
if ss.NextSenderSessionPub == nil {
// prepare upcoming session, but do not switch to it yet
nextSenderSession, err := setNextSenderSessionPub(args.KeyStore, ss,
sessionStateKey, args.Rand)
if err != nil {
return "", "", err
}
previousRootKeyHash, err := args.KeyStore.GetRootKeyHash(sessionKey)
if err != nil {
return "", "", err
}
// root key agreement
err = rootKeyAgreementSender(&senderHeaderPub, recipient,
sender, nextSenderSession, recipientID,
h.NextSenderSessionPub, &h.SenderIdentityPub,
previousRootKeyHash, args.NumOfKeys, args.KeyStore)
if err != nil {
return "", "", err
}
if ss.NextRecipientSessionPubSeen == nil {
// save h.NextSenderSessionPub, if necessary
ss.NextRecipientSessionPubSeen = h.NextSenderSessionPub
err := args.KeyStore.SetSessionState(sessionStateKey, ss)
if err != nil {
return "", "", err
}
}
} else if h.NextRecipientSessionPubSeen != nil &&
h.NextRecipientSessionPubSeen.HASH == ss.NextSenderSessionPub.HASH {
// switch to next session
nextSenderSession, err := getSessionKey(args.KeyStore,
ss.NextSenderSessionPub.HASH)
if err != nil {
return "", "", err
}
previousRootKeyHash, err := args.KeyStore.GetRootKeyHash(sessionKey)
if err != nil {
return "", "", err
}
// root key agreement
err = rootKeyAgreementRecipient(&senderHeaderPub, sender,
recipient, h.NextSenderSessionPub, &h.SenderIdentityPub,
nextSenderSession, recipientID, previousRootKeyHash,
args.NumOfKeys, args.KeyStore)
if err != nil {
return "", "", err
}
// store new session state
ss = &session.State{
SenderSessionCount: ss.SenderSessionCount + ss.SenderMessageCount,
SenderMessageCount: 0,
MaxRecipientCount: 0,
RecipientTemp: *h.NextSenderSessionPub,
SenderSessionPub: *nextSenderSession,
NextSenderSessionPub: nil,
NextRecipientSessionPubSeen: nil,
NymAddress: h.NymAddress,
KeyInitSession: false,
}
err = args.KeyStore.SetSessionState(sessionStateKey, ss)
if err != nil {
return "", "", err
}
}
}
} else {
// check if session matches next session
if ss.NextSenderSessionPub != nil &&
ss.NextRecipientSessionPubSeen != nil &&
ss.NextSenderSessionPub.HASH == h.RecipientTempHash &&
ss.NextRecipientSessionPubSeen.HASH == h.SenderSessionPub.HASH {
// switch session
ss = &session.State{
SenderSessionCount: ss.SenderSessionCount + ss.SenderMessageCount,
SenderMessageCount: 0,
MaxRecipientCount: 0,
RecipientTemp: h.SenderSessionPub,
SenderSessionPub: *ss.NextSenderSessionPub,
NextSenderSessionPub: nil,
NextRecipientSessionPubSeen: nil,
NymAddress: h.NymAddress,
KeyInitSession: false,
}
err = args.KeyStore.SetSessionState(sessionStateKey, ss)
if err != nil {
return "", "", err
}
}
}
// a message with this session key has been decrypted -> delete key
if err := args.KeyStore.DelPrivSessionKey(h.RecipientTempHash); err != nil {
return "", "", err
}
}
// make sure we got enough message keys
n, err := args.KeyStore.NumMessageKeys(sessionKey)
if err != nil {
return "", "", err
}
if h.SenderMessageCount >= n {
// generate more message keys
log.Debugf("generate more message keys (h.SenderMessageCount=%d, n=%d)",
h.SenderMessageCount, n)
chainKey, err := args.KeyStore.GetChainKey(sessionKey)
if err != nil {
return "", "", err
}
// prevent denial of service attack by very large h.SenderMessageCount
numOfKeys := h.SenderMessageCount / args.NumOfKeys
if h.SenderMessageCount%args.NumOfKeys > 0 {
numOfKeys++
}
numOfKeys *= args.NumOfKeys
if numOfKeys > mime.MaxMsgSize/MaxContentLength+NumOfFutureKeys {
return "", "",
log.Errorf("msg: requested number of message keys too large")
}
log.Debugf("numOfKeys=%d", numOfKeys)
var recipientPub *[32]byte
if h.RecipientTempHash == ss.SenderSessionPub.HASH {
recipientPub = ss.SenderSessionPub.PublicKey32()
} else {
log.Debug("different session")
recipientKI, err := args.KeyStore.GetPrivateKeyEntry(h.RecipientTempHash)
if err != nil && err != session.ErrNoKeyEntry {
return "", "", err
}
if err != session.ErrNoKeyEntry {
recipientPub = recipientKI.PublicKey32()
} else {
recipientKE, err := getSessionKey(args.KeyStore,
h.RecipientTempHash)
if err != nil {
return "", "", err
}
recipientPub = recipientKE.PublicKey32()
}
}
err = generateMessageKeys(sender, recipient, h.SenderIdentityPub.HASH,
recipientID.HASH, chainKey, true,
h.SenderSessionPub.PublicKey32(), recipientPub, numOfKeys,
args.KeyStore)
if err != nil {
return "", "", err
}
}
// get message key
messageKey, err := args.KeyStore.GetMessageKey(sessionKey, false,
h.SenderMessageCount)
if err != nil {
return "", "", err
}
// derive symmetric keys
cryptoKey, hmacKey, err := deriveSymmetricKeys(messageKey)
if err != nil {
return "", "", err
}
// read crypto setup packet
oh, err = readOuterHeader(args.Reader)
if err != nil {
return "", "", err
}
if oh.Type != cryptoSetup {
return "", "", log.Error(ErrNotCryptoSetup)
}
if oh.PacketCount != count {
return "", "", log.Error(ErrWrongCount)
}
count++
if oh.PLen != aes.BlockSize {
return "", "", log.Error(ErrWrongCryptoSetup)
}
iv := oh.inner
// start HMAC calculation
mac := hmac.New(sha512.New, hmacKey)
if err := oh.write(mac, true); err != nil {
return "", "", err
}
// actual decryption
oh, err = readOuterHeader(args.Reader)
if err != nil {
return "", "", err
}
if oh.Type != encryptedPacket {
return "", "", log.Error(ErrNotEncryptedPacket)
}
if oh.PacketCount != count {
return "", "", log.Error(ErrWrongCount)
}
count++
ciphertext := oh.inner
plaintext := make([]byte, len(ciphertext))
stream := cipher.AES256CTRStream(cryptoKey, iv)
stream.XORKeyStream(plaintext, ciphertext)
ih, err := readInnerHeader(bytes.NewBuffer(plaintext))
if err != nil {
return "", "", err
}
if ih.Type&dataType == 0 {
return "", "", log.Error(ErrNotData)
}
var contentHash []byte
if ih.Type&signType != 0 {
// create signature hash
contentHash = cipher.SHA512(ih.content)
}
if _, err := args.Writer.Write(ih.content); err != nil {
return "", "", log.Error(err)
}
// continue HMAC calculation
if err := oh.write(mac, true); err != nil {
return "", "", err
}
// verify signature
var sigBuf [ed25519.SignatureSize]byte
if contentHash != nil {
oh, err = readOuterHeader(args.Reader)
if err != nil {
return "", "", err
}
if oh.Type != encryptedPacket {
return "", "", log.Error(ErrNotEncryptedPacket)
}
if oh.PacketCount != count {
return "", "", log.Error(ErrWrongCount)
}
count++
// continue HMAC calculation
if err := oh.write(mac, true); err != nil {
return "", "", err
}
ciphertext = oh.inner
plaintext = make([]byte, len(ciphertext))
stream.XORKeyStream(plaintext, ciphertext)
ih, err = readInnerHeader(bytes.NewBuffer(plaintext))
if err != nil {
return "", "", err
}
if ih.Type&signatureType == 0 {
return "", "", log.Error(ErrNotSignaturePacket)
}
if len(ih.content) != ed25519.SignatureSize {
return "", "", log.Error(ErrWrongSignatureLength)
}
copy(sigBuf[:], ih.content)
} else {
oh, err = readOuterHeader(args.Reader)
if err != nil {
return "", "", err
}
if oh.Type != encryptedPacket {
return "", "", log.Error(ErrNotEncryptedPacket)
}
if oh.PacketCount != count {
return "", "", log.Error(ErrWrongCount)
}
count++
// continue HMAC calculation
if err := oh.write(mac, true); err != nil {
return "", "", err
}
ciphertext = oh.inner
plaintext = make([]byte, len(ciphertext))
stream.XORKeyStream(plaintext, ciphertext)
ih, err = readInnerHeader(bytes.NewBuffer(plaintext))
if err != nil {
return "", "", err
}
if ih.Type&paddingType == 0 {
return "", "", log.Error(ErrNotPaddingPacket)
}
}
// get processed sender UID
uidRes := <-res
if uidRes.err != nil {
return "", "", uidRes.err
}
// verify signature, if necessary
if contentHash != nil {
if !ed25519.Verify(uidRes.msg.PublicSigKey32(), contentHash, &sigBuf) {
return "", "", log.Error(ErrInvalidSignature)
}
// encode signature to base64 as return value
sig = base64.Encode(sigBuf[:])
}
// read HMAC packet
oh, err = readOuterHeader(args.Reader)
if err != nil {
return "", "", err
}
if oh.Type != hmacPacket {
return "", "", log.Error(ErrNotHMACPacket)
}
if oh.PacketCount != count {
return "", "", log.Error(ErrWrongCount)
}
count++
if err := oh.write(mac, false); err != nil {
return "", "", err
}
sum := mac.Sum(nil)
log.Debugf("HMAC: %s", base64.Encode(sum))
if !hmac.Equal(sum, oh.inner) {
return "", "", log.Error(ErrHMACsDiffer)
}
// delete message key
err = args.KeyStore.DelMessageKey(sessionKey, false, h.SenderMessageCount)
if err != nil {
return "", "", err
}
return
}