Exemplo n.º 1
0
func (c *cipher) DecryptHandshake(localKey cipherset.Key, p []byte) (cipherset.Handshake, error) {
	if len(p) < 21+4+4 {
		return nil, cipherset.ErrInvalidMessage
	}

	var (
		ctLen             = len(p) - (21 + 4 + 4)
		out               = bufpool.New()
		cs1aLocalKey, _   = localKey.(*key)
		remoteKey         *key
		remoteLineKey     *key
		hshake            *handshake
		remoteLineKeyData = p[:21]
		iv                = p[21 : 21+4]
		ciphertext        = p[21+4 : 21+4+ctLen]
		mac               = p[21+4+ctLen:]
	)

	if cs1aLocalKey == nil {
		return nil, cipherset.ErrInvalidState
	}

	{ // decrypt inner
		ephemX, ephemY := eccp.Unmarshal(secp160r1.P160(), remoteLineKeyData)
		if ephemX == nil || ephemY == nil {
			return nil, cipherset.ErrInvalidMessage
		}

		shared := ecdh.ComputeShared(secp160r1.P160(), ephemX, ephemY, cs1aLocalKey.prv.d)
		if shared == nil {
			return nil, cipherset.ErrInvalidMessage
		}

		aharedSum := sha256.Sum256(shared)
		aesKey := fold(aharedSum[:], 16)
		if aesKey == nil {
			return nil, cipherset.ErrInvalidMessage
		}

		aesBlock, err := aes.NewCipher(aesKey)
		if err != nil {
			return nil, cipherset.ErrInvalidMessage
		}

		var aesIv [16]byte
		copy(aesIv[:], iv)

		aes := Cipher.NewCTR(aesBlock, aesIv[:])
		if aes == nil {
			return nil, cipherset.ErrInvalidMessage
		}

		out.SetLen(ctLen)
		aes.XORKeyStream(out.RawBytes(), ciphertext)
		remoteLineKey = &key{}
		remoteLineKey.pub.x, remoteLineKey.pub.y = ephemX, ephemY
	}

	{ // 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() != 21 {
			return nil, cipherset.ErrInvalidMessage
		}

		remoteKey = &key{}
		remoteKey.pub.x, remoteKey.pub.y = eccp.Unmarshal(secp160r1.P160(), inner.Body(nil))
		if !remoteKey.CanEncrypt() {
			return nil, cipherset.ErrInvalidMessage
		}

		hshake = &handshake{}
		hshake.at = at
		hshake.key = remoteKey
		hshake.lineKey = remoteLineKey
		hshake.parts = parts
	}

	{ // verify mac
		var nonce [16]byte
		copy(nonce[:], iv)

		macKey := ecdh.ComputeShared(secp160r1.P160(),
			remoteKey.pub.x, remoteKey.pub.y, cs1aLocalKey.prv.d)
		macKey = append(macKey, nonce[:]...)

		h := hmac.New(sha256.New, macKey)
		h.Write(p[:21+4+ctLen])
		if subtle.ConstantTimeCompare(mac, fold(h.Sum(nil), 4)) != 1 {
			return nil, cipherset.ErrInvalidMessage
		}
	}

	return hshake, nil
}
Exemplo n.º 2
0
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
}