def _get_key(self, alg, key, p2s, p2c):
if isinstance(key, bytes):
plain = key
else:
plain = key.encode('utf8')
salt = bytes(self.name.encode('utf8')) + b'\x00' + p2s
if self.hashsize == 256:
hashalg = hashes.SHA256()
elif self.hashsize == 384:
hashalg = hashes.SHA384()
elif self.hashsize == 512:
hashalg = hashes.SHA512()
else:
raise ValueError('Unknown Hash Size')
kdf = PBKDF2HMAC(algorithm=hashalg,
length=_inbytes(self.keysize),
salt=salt,
iterations=p2c,
backend=self.backend)
rk = kdf.derive(plain)
if _bitsize(rk) != self.keysize:
raise InvalidJWEKeyLength(self.keysize, len(rk))
return JWK(kty="oct", use="enc", k=base64url_encode(rk))
def unwrap(self, key, bitsize, ek, headers):
rk = self._get_key(key, 'decrypt')
# Implement RFC 3394 Key Unwrap - 2.2.3
# TODO: Use cryptography once issue #1733 is resolved
iv = 'a6a6a6a6a6a6a6a6'
aiv = unhexlify(iv)
r = [ek[i:i + 8] for i in range(0, len(ek), 8)]
a = r.pop(0)
n = len(r)
for j in range(5, -1, -1):
for i in range(n - 1, -1, -1):
da = _decode_int(a)
atr = _encode_int((da ^ ((n * j) + i + 1)), 64) + r[i]
d = Cipher(algorithms.AES(rk),
modes.ECB(),
backend=self.backend).decryptor()
b = d.update(atr) + d.finalize()
a = b[:8]
r[i] = b[-8:]
if a != aiv:
raise RuntimeError('Decryption Failed')
cek = b''.join(r)
if _bitsize(cek) != bitsize:
raise InvalidJWEKeyLength(bitsize, _bitsize(cek))
return cek
def unwrap(self, key, bitsize, ek, headers):
self._check_key(key)
rk = key.get_op_key('decrypt')
cek = rk.decrypt(ek, self.padfn)
if _bitsize(cek) != bitsize:
raise InvalidJWEKeyLength(bitsize, _bitsize(cek))
return cek
def unwrap(self, key, bitsize, ek, headers):
self._check_key(key)
if ek != b'':
raise ValueError('Invalid Encryption Key.')
cek = base64url_decode(key.get_op_key('decrypt'))
if _bitsize(cek) != bitsize:
raise InvalidJWEKeyLength(bitsize, _bitsize(cek))
return cek
def _get_key(self, key, op):
if not isinstance(key, JWK):
raise ValueError('key is not a JWK object')
if key.key_type != 'oct':
raise InvalidJWEKeyType('oct', key.key_type)
rk = base64url_decode(key.get_op_key(op))
if _bitsize(rk) != self.keysize:
raise InvalidJWEKeyLength(self.keysize, _bitsize(rk))
return rk
def unwrap(self, key, bitsize, ek, headers):
rk = self._get_key(key, 'decrypt')
if 'iv' not in headers:
raise ValueError('Invalid Header, missing "iv" parameter')
iv = base64url_decode(headers['iv'])
if 'tag' not in headers:
raise ValueError('Invalid Header, missing "tag" parameter')
tag = base64url_decode(headers['tag'])
cipher = Cipher(algorithms.AES(rk), modes.GCM(iv, tag),
backend=self.backend)
decryptor = cipher.decryptor()
cek = decryptor.update(ek) + decryptor.finalize()
if _bitsize(cek) != bitsize:
raise InvalidJWEKeyLength(bitsize, _bitsize(cek))
return cek
