CasperSecurity
"""JSON Web Algorithms.
https://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-40
"""
import abc
import logging
from typing import Dict, Any, Callable
import cryptography.exceptions
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import hmac
from cryptography.hazmat.primitives.asymmetric import padding, ec, rsa
from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature
from cryptography.hazmat.primitives.asymmetric.utils import encode_dss_signature
from cryptography.hazmat.primitives.hashes import HashAlgorithm
from josepy import errors, interfaces, jwk
from collections.abc import Hashable
logger = logging.getLogger(__name__)
class JWA(interfaces.JSONDeSerializable): # pylint: disable=abstract-method
# pylint: disable=too-few-public-methods
# for some reason disable=abstract-method has to be on the line
# above...
"""JSON Web Algorithm."""
class JWASignature(JWA, Hashable):
"""Base class for JSON Web Signature Algorithms."""
SIGNATURES: Dict[str, 'JWASignature'] = {}
kty: Any
def __init__(self, name: str) -> None:
self.name = name
def __eq__(self, other: Any) -> bool:
if not isinstance(other, JWASignature):
return NotImplemented
return self.name == other.name
def __hash__(self) -> int:
return hash((self.__class__, self.name))
@classmethod
def register(cls, signature_cls: 'JWASignature') -> 'JWASignature':
"""Register class for JSON deserialization."""
cls.SIGNATURES[signature_cls.name] = signature_cls
return signature_cls
def to_partial_json(self) -> Any:
return self.name
@classmethod
def from_json(cls, jobj: Any) -> 'JWASignature':
return cls.SIGNATURES[jobj]
@abc.abstractmethod
def sign(self, key: Any, msg: bytes) -> bytes: # pragma: no cover
"""Sign the ``msg`` using ``key``."""
raise NotImplementedError()
@abc.abstractmethod
def verify(self, key: Any, msg: bytes, sig: bytes) -> bool: # pragma: no cover
"""Verify the ``msg`` and ``sig`` using ``key``."""
raise NotImplementedError()
def __repr__(self) -> str:
return self.name
class _JWAHS(JWASignature):
kty = jwk.JWKOct
def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]):
super().__init__(name)
self.hash = hash_()
def sign(self, key: bytes, msg: bytes) -> bytes:
signer = hmac.HMAC(key, self.hash, backend=default_backend())
signer.update(msg)
return signer.finalize()
def verify(self, key: bytes, msg: bytes, sig: bytes) -> bool:
verifier = hmac.HMAC(key, self.hash, backend=default_backend())
verifier.update(msg)
try:
verifier.verify(sig)
except cryptography.exceptions.InvalidSignature as error:
logger.debug(error, exc_info=True)
return False
else:
return True
class _JWARSA:
kty = jwk.JWKRSA
padding: Any = NotImplemented
hash: HashAlgorithm = NotImplemented
def sign(self, key: rsa.RSAPrivateKey, msg: bytes) -> bytes:
"""Sign the ``msg`` using ``key``."""
# If cryptography library supports new style api (v1.4 and later)
new_api = hasattr(key, "sign")
try:
if new_api:
return key.sign(msg, self.padding, self.hash)
signer = key.signer(self.padding, self.hash)
except AttributeError as error:
logger.debug(error, exc_info=True)
raise errors.Error("Public key cannot be used for signing")
except ValueError as error: # digest too large
logger.debug(error, exc_info=True)
raise errors.Error(str(error))
signer.update(msg)
try:
return signer.finalize()
except ValueError as error:
logger.debug(error, exc_info=True)
raise errors.Error(str(error))
def verify(self, key: rsa.RSAPublicKey, msg: bytes, sig: bytes) -> bool:
"""Verify the ``msg` and ``sig`` using ``key``."""
# If cryptography library supports new style api (v1.4 and later)
new_api = hasattr(key, "verify")
if not new_api:
verifier = key.verifier(sig, self.padding, self.hash)
verifier.update(msg)
try:
if new_api:
key.verify(sig, msg, self.padding, self.hash)
else:
verifier.verify()
except cryptography.exceptions.InvalidSignature as error:
logger.debug(error, exc_info=True)
return False
else:
return True
class _JWARS(_JWARSA, JWASignature):
def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]) -> None:
super().__init__(name)
self.padding = padding.PKCS1v15()
self.hash = hash_()
class _JWAPS(_JWARSA, JWASignature):
def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]) -> None:
super().__init__(name)
self.padding = padding.PSS(
mgf=padding.MGF1(hash_()),
salt_length=padding.PSS.MAX_LENGTH)
self.hash = hash_()
class _JWAEC(JWASignature):
kty = jwk.JWKEC
def __init__(self, name: str, hash_: Callable[[], HashAlgorithm]):
super().__init__(name)
self.hash = hash_()
def sign(self, key: ec.EllipticCurvePrivateKey, msg: bytes) -> bytes:
"""Sign the ``msg`` using ``key``."""
sig = self._sign(key, msg)
dr, ds = decode_dss_signature(sig)
length = jwk.JWKEC.expected_length_for_curve(key.curve)
return (dr.to_bytes(length=length, byteorder='big') +
ds.to_bytes(length=length, byteorder='big'))
def _sign(self, key: ec.EllipticCurvePrivateKey, msg: bytes) -> bytes:
# If cryptography library supports new style api (v1.4 and later)
new_api = hasattr(key, 'sign')
try:
if new_api:
return key.sign(msg, ec.ECDSA(self.hash))
signer = key.signer(ec.ECDSA(self.hash))
except AttributeError as error:
logger.debug(error, exc_info=True)
raise errors.Error('Public key cannot be used for signing')
except ValueError as error: # digest too large
logger.debug(error, exc_info=True)
raise errors.Error(str(error))
signer.update(msg)
try:
return signer.finalize()
except ValueError as error:
logger.debug(error, exc_info=True)
raise errors.Error(str(error))
def verify(self, key: ec.EllipticCurvePublicKey, msg: bytes, sig: bytes) -> bool:
"""Verify the ``msg` and ``sig`` using ``key``."""
rlen = jwk.JWKEC.expected_length_for_curve(key.curve)
if len(sig) != 2 * rlen:
# Format error - rfc7518 - 3.4 … MUST NOT be shortened to omit any leading zero octets
return False
asn1sig = encode_dss_signature(
int.from_bytes(sig[0:rlen], byteorder='big'),
int.from_bytes(sig[rlen:], byteorder='big')
)
return self._verify(key, msg, asn1sig)
def _verify(self, key: ec.EllipticCurvePublicKey, msg: bytes, asn1sig: bytes) -> bool:
# If cryptography library supports new style api (v1.4 and later)
new_api = hasattr(key, 'verify')
if not new_api:
verifier = key.verifier(asn1sig, ec.ECDSA(self.hash))
verifier.update(msg)
try:
if new_api:
key.verify(asn1sig, msg, ec.ECDSA(self.hash))
else:
verifier.verify()
except cryptography.exceptions.InvalidSignature as error:
logger.debug(error, exc_info=True)
return False
else:
return True
#: HMAC using SHA-256
HS256 = JWASignature.register(_JWAHS('HS256', hashes.SHA256))
#: HMAC using SHA-384
HS384 = JWASignature.register(_JWAHS('HS384', hashes.SHA384))
#: HMAC using SHA-512
HS512 = JWASignature.register(_JWAHS('HS512', hashes.SHA512))
#: RSASSA-PKCS-v1_5 using SHA-256
RS256 = JWASignature.register(_JWARS('RS256', hashes.SHA256))
#: RSASSA-PKCS-v1_5 using SHA-384
RS384 = JWASignature.register(_JWARS('RS384', hashes.SHA384))
#: RSASSA-PKCS-v1_5 using SHA-512
RS512 = JWASignature.register(_JWARS('RS512', hashes.SHA512))
#: RSASSA-PSS using SHA-256 and MGF1 with SHA-256
PS256 = JWASignature.register(_JWAPS('PS256', hashes.SHA256))
#: RSASSA-PSS using SHA-384 and MGF1 with SHA-384
PS384 = JWASignature.register(_JWAPS('PS384', hashes.SHA384))
#: RSASSA-PSS using SHA-512 and MGF1 with SHA-512
PS512 = JWASignature.register(_JWAPS('PS512', hashes.SHA512))
#: ECDSA using P-256 and SHA-256
ES256 = JWASignature.register(_JWAEC('ES256', hashes.SHA256))
#: ECDSA using P-384 and SHA-384
ES384 = JWASignature.register(_JWAEC('ES384', hashes.SHA384))
#: ECDSA using P-521 and SHA-512
ES512 = JWASignature.register(_JWAEC('ES512', hashes.SHA512))