110 lines
3.8 KiB
Python
110 lines
3.8 KiB
Python
import base64, enum, hashlib, hmac, os, typing
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# IANA Hash Function Textual Names
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# https://tools.ietf.org/html/rfc5802#section-4
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# https://www.iana.org/assignments/hash-function-text-names/
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# MD2 has been removed as it's unacceptably weak
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ALGORITHMS = [
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"MD5", "SHA-1", "SHA-224", "SHA-256", "SHA-384", "SHA-512"]
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def _scram_nonce() -> bytes:
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return base64.b64encode(os.urandom(32))
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def _scram_escape(s: bytes) -> bytes:
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return s.replace(b"=", b"=3D").replace(b",", b"=2C")
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def _scram_unescape(s: bytes) -> bytes:
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return s.replace(b"=3D", b"=").replace(b"=2C", b",")
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def _scram_xor(s1: bytes, s2: bytes) -> bytes:
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return bytes(a ^ b for a, b in zip(s1, s2))
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class SCRAMState(enum.Enum):
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Uninitialised = 0
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ClientFirst = 1
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ClientFinal = 2
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Success = 3
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Failed = 4
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VerifyFailed = 5
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class SCRAMError(Exception):
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pass
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class SCRAM(object):
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def __init__(self, algo: str, username: str, password: str):
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if not algo in ALGORITHMS:
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raise ValueError("Unknown SCRAM algorithm '%s'" % algo)
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self._algo = algo.replace("-", "") # SHA-1 -> SHA1
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self._username = username.encode("utf8")
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self._password = password.encode("utf8")
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self.state = SCRAMState.Uninitialised
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self.error = ""
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self._client_first = b""
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self._salted_password = b""
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self._auth_message = b""
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def _get_pieces(self, data: bytes) -> typing.Dict[bytes, bytes]:
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pieces = (piece.split(b"=", 1) for piece in data.split(b","))
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return dict((piece[0], piece[1]) for piece in pieces)
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def _hmac(self, key: bytes, msg: bytes) -> bytes:
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return hmac.digest(key, msg, self._algo)
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def _hash(self, msg: bytes) -> bytes:
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return hashlib.new(self._algo, msg).digest()
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def _constant_time_compare(self, b1: bytes, b2: bytes):
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return hmac.compare_digest(b1, b2)
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def client_first(self) -> bytes:
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self.state = SCRAMState.ClientFirst
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self._client_first = b"n=%s,r=%s" % (
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_scram_escape(self._username), _scram_nonce())
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# n,,n=<username>,r=<nonce>
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return b"n,,%s" % self._client_first
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def server_first(self, data: bytes) -> bytes:
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self.state = SCRAMState.ClientFinal
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pieces = self._get_pieces(data)
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nonce = pieces[b"r"] # server combines your nonce with it's own
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salt = base64.b64decode(pieces[b"s"]) # salt is b64encoded
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iterations = int(pieces[b"i"])
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salted_password = hashlib.pbkdf2_hmac(self._algo, self._password,
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salt, iterations, dklen=None)
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self._salted_password = salted_password
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client_key = self._hmac(salted_password, b"Client Key")
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stored_key = self._hash(client_key)
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channel = base64.b64encode(b"n,,")
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auth_noproof = b"c=%s,r=%s" % (channel, nonce)
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auth_message = b"%s,%s,%s" % (self._client_first, data, auth_noproof)
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self._auth_message = auth_message
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client_signature = self._hmac(stored_key, auth_message)
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client_proof_xor = _scram_xor(client_key, client_signature)
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client_proof = base64.b64encode(client_proof_xor)
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# c=<b64encode("n,,")>,r=<nonce>,p=<proof>
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return b"%s,p=%s" % (auth_noproof, client_proof)
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def server_final(self, data: bytes) -> bool:
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pieces = self._get_pieces(data)
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if b"e" in pieces:
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self.error = pieces[b"e"].decode("utf8")
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self.state = SCRAMState.Failed
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return False
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verifier = base64.b64decode(pieces[b"v"])
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server_key = self._hmac(self._salted_password, b"Server Key")
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server_signature = self._hmac(server_key, self._auth_message)
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if server_signature == verifier:
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self.state = SCRAMState.Success
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return True
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else:
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self.state = SCRAMState.VerifyFailed
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return False
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