func (c *cipher) DecryptMessage(localKey, remoteKey cipherset.Key, p []byte) ([]byte, error) {
if len(p) < lenKey+lenNonce+lenAuth {
return nil, cipherset.ErrInvalidMessage
}
var (
ctLen = len(p) - (lenKey + lenNonce + lenAuth)
out = make([]byte, ctLen)
cs3aLocalKey, _ = localKey.(*key)
cs3aRemoteKey, _ = remoteKey.(*key)
mac [lenAuth]byte
nonce [lenNonce]byte
macKey [lenKey]byte
agreedKey [lenKey]byte
remoteLineKey [lenKey]byte
ciphertext []byte
ok bool
)
if cs3aLocalKey == nil || cs3aRemoteKey == nil {
return nil, cipherset.ErrInvalidState
}
copy(remoteLineKey[:], p[:lenKey])
copy(nonce[:], p[lenKey:lenKey+lenNonce])
copy(mac[:], p[lenKey+lenNonce+ctLen:])
ciphertext = p[lenKey+lenNonce : lenKey+lenNonce+ctLen]
{ // make macKey
box.Precompute(&macKey, cs3aRemoteKey.pub, cs3aLocalKey.prv)
var (
sha = sha256.New()
)
sha.Write(p[lenKey : lenKey+lenNonce])
sha.Write(macKey[:])
sha.Sum(macKey[:0])
}
if !poly1305.Verify(&mac, p[:lenKey+lenNonce+ctLen], &macKey) {
return nil, cipherset.ErrInvalidMessage
}
// make agreedKey
box.Precompute(&agreedKey, &remoteLineKey, cs3aLocalKey.prv)
// decode BODY
out, ok = box.OpenAfterPrecomputation(out[:0], ciphertext, &nonce, &agreedKey)
if !ok {
return nil, cipherset.ErrInvalidMessage
}
return out, nil
}
func (s *state) DecryptPacket(pkt *lob.Packet) (*lob.Packet, error) {
s.mtx.RLock()
defer s.mtx.RUnlock()
if !s.CanDecryptPacket() {
return nil, cipherset.ErrInvalidState
}
if pkt == nil {
return nil, nil
}
if !pkt.Header().IsZero() || pkt.BodyLen() < lenToken+lenNonce {
return nil, cipherset.ErrInvalidPacket
}
var (
nonce [lenNonce]byte
bodyRaw []byte
innerRaw []byte
innerPkt *lob.Packet
body = bufpool.New()
inner = bufpool.New()
ok bool
)
pkt.Body(body.SetLen(pkt.BodyLen()).RawBytes()[:0])
bodyRaw = body.RawBytes()
innerRaw = inner.RawBytes()
// compare token
if !bytes.Equal(bodyRaw[:lenToken], (*s.localToken)[:]) {
inner.Free()
body.Free()
return nil, cipherset.ErrInvalidPacket
}
// copy nonce
copy(nonce[:], bodyRaw[lenToken:lenToken+lenNonce])
// decrypt inner packet
innerRaw, ok = box.OpenAfterPrecomputation(
innerRaw[:0], bodyRaw[lenToken+lenNonce:], &nonce, s.lineDecryptionKey)
if !ok {
inner.Free()
body.Free()
return nil, cipherset.ErrInvalidPacket
}
inner.SetLen(len(innerRaw))
innerPkt, err := lob.Decode(inner)
if err != nil {
inner.Free()
body.Free()
return nil, err
}
inner.Free()
body.Free()
return innerPkt, nil
}
func (c *cipher) DecryptHandshake(localKey cipherset.Key, p []byte) (cipherset.Handshake, error) {
if len(p) < lenKey+lenNonce+lenAuth {
return nil, cipherset.ErrInvalidMessage
}
var (
ctLen = len(p) - (lenKey + lenNonce + lenAuth)
out = bufpool.New()
handshake = &handshake{}
cs3aLocalKey, _ = localKey.(*key)
at uint32
hasAt bool
mac [lenAuth]byte
nonce [lenNonce]byte
macKey [lenKey]byte
agreedKey [lenKey]byte
remoteKey [lenKey]byte
remoteLineKey [lenKey]byte
ciphertext []byte
ok bool
)
if cs3aLocalKey == nil {
return nil, cipherset.ErrInvalidState
}
copy(remoteLineKey[:], p[:lenKey])
copy(nonce[:], p[lenKey:lenKey+lenNonce])
copy(mac[:], p[lenKey+lenNonce+ctLen:])
ciphertext = p[lenKey+lenNonce : lenKey+lenNonce+ctLen]
// make agreedKey
box.Precompute(&agreedKey, &remoteLineKey, cs3aLocalKey.prv)
// decode BODY
outBuf, ok := box.OpenAfterPrecomputation(out.RawBytes(), ciphertext, &nonce, &agreedKey)
if !ok {
return nil, cipherset.ErrInvalidMessage
}
out.SetLen(len(outBuf))
{ // decode inner
inner, err := lob.Decode(out)
if err != nil {
return nil, cipherset.ErrInvalidMessage
}
at, hasAt = inner.Header().GetUint32("at")
if !hasAt {
return nil, cipherset.ErrInvalidMessage
}
delete(inner.Header().Extra, "at")
parts, err := cipherset.PartsFromHeader(inner.Header())
if err != nil {
return nil, cipherset.ErrInvalidMessage
}
if inner.BodyLen() != lenKey {
return nil, cipherset.ErrInvalidMessage
}
inner.Body(remoteKey[:0])
handshake.at = at
handshake.key = makeKey(nil, &remoteKey)
handshake.lineKey = makeKey(nil, &remoteLineKey)
handshake.parts = parts
}
{ // make macKey
box.Precompute(&macKey, &remoteKey, cs3aLocalKey.prv)
var (
sha = sha256.New()
)
sha.Write(p[lenKey : lenKey+lenNonce])
sha.Write(macKey[:])
sha.Sum(macKey[:0])
}
if !poly1305.Verify(&mac, p[:lenKey+lenNonce+ctLen], &macKey) {
return nil, cipherset.ErrInvalidMessage
}
return handshake, nil
}
