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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
from cryptography import utils
from cryptography.exceptions import (
InvalidSignature, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.backends.openssl.utils import _truncate_digest
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import (
AsymmetricSignatureContext, AsymmetricVerificationContext, ec
)
def _truncate_digest_for_ecdsa(ec_key_cdata, digest, backend):
"""
This function truncates digests that are longer than a given elliptic
curve key's length so they can be signed. Since elliptic curve keys are
much shorter than RSA keys many digests (e.g. SHA-512) may require
truncation.
"""
_lib = backend._lib
_ffi = backend._ffi
group = _lib.EC_KEY_get0_group(ec_key_cdata)
with backend._tmp_bn_ctx() as bn_ctx:
order = _lib.BN_CTX_get(bn_ctx)
backend.openssl_assert(order != _ffi.NULL)
res = _lib.EC_GROUP_get_order(group, order, bn_ctx)
backend.openssl_assert(res == 1)
order_bits = _lib.BN_num_bits(order)
return _truncate_digest(digest, order_bits)
def _ec_key_curve_sn(backend, ec_key):
group = backend._lib.EC_KEY_get0_group(ec_key)
backend.openssl_assert(group != backend._ffi.NULL)
nid = backend._lib.EC_GROUP_get_curve_name(group)
# The following check is to find EC keys with unnamed curves and raise
# an error for now.
if nid == backend._lib.NID_undef:
raise NotImplementedError(
"ECDSA certificates with unnamed curves are unsupported "
"at this time"
)
curve_name = backend._lib.OBJ_nid2sn(nid)
backend.openssl_assert(curve_name != backend._ffi.NULL)
sn = backend._ffi.string(curve_name).decode('ascii')
return sn
def _mark_asn1_named_ec_curve(backend, ec_cdata):
"""
Set the named curve flag on the EC_KEY. This causes OpenSSL to
serialize EC keys along with their curve OID which makes
deserialization easier.
"""
backend._lib.EC_KEY_set_asn1_flag(
ec_cdata, backend._lib.OPENSSL_EC_NAMED_CURVE
)
def _sn_to_elliptic_curve(backend, sn):
try:
return ec._CURVE_TYPES[sn]()
except KeyError:
raise UnsupportedAlgorithm(
"{0} is not a supported elliptic curve".format(sn),
_Reasons.UNSUPPORTED_ELLIPTIC_CURVE
)
@utils.register_interface(AsymmetricSignatureContext)
class _ECDSASignatureContext(object):
def __init__(self, backend, private_key, algorithm):
self._backend = backend
self._private_key = private_key
self._digest = hashes.Hash(algorithm, backend)
def update(self, data):
self._digest.update(data)
def finalize(self):
ec_key = self._private_key._ec_key
digest = self._digest.finalize()
digest = _truncate_digest_for_ecdsa(ec_key, digest, self._backend)
max_size = self._backend._lib.ECDSA_size(ec_key)
self._backend.openssl_assert(max_size > 0)
sigbuf = self._backend._ffi.new("char[]", max_size)
siglen_ptr = self._backend._ffi.new("unsigned int[]", 1)
res = self._backend._lib.ECDSA_sign(
0,
digest,
len(digest),
sigbuf,
siglen_ptr,
ec_key
)
self._backend.openssl_assert(res == 1)
return self._backend._ffi.buffer(sigbuf)[:siglen_ptr[0]]
@utils.register_interface(AsymmetricVerificationContext)
class _ECDSAVerificationContext(object):
def __init__(self, backend, public_key, signature, algorithm):
self._backend = backend
self._public_key = public_key
self._signature = signature
self._digest = hashes.Hash(algorithm, backend)
def update(self, data):
self._digest.update(data)
def verify(self):
ec_key = self._public_key._ec_key
digest = self._digest.finalize()
digest = _truncate_digest_for_ecdsa(ec_key, digest, self._backend)
res = self._backend._lib.ECDSA_verify(
0,
digest,
len(digest),
self._signature,
len(self._signature),
ec_key
)
if res != 1:
self._backend._consume_errors()
raise InvalidSignature
return True
@utils.register_interface(ec.EllipticCurvePrivateKeyWithSerialization)
class _EllipticCurvePrivateKey(object):
def __init__(self, backend, ec_key_cdata, evp_pkey):
self._backend = backend
_mark_asn1_named_ec_curve(backend, ec_key_cdata)
self._ec_key = ec_key_cdata
self._evp_pkey = evp_pkey
sn = _ec_key_curve_sn(backend, ec_key_cdata)
self._curve = _sn_to_elliptic_curve(backend, sn)
curve = utils.read_only_property("_curve")
def signer(self, signature_algorithm):
if isinstance(signature_algorithm, ec.ECDSA):
return _ECDSASignatureContext(
self._backend, self, signature_algorithm.algorithm
)
else:
raise UnsupportedAlgorithm(
"Unsupported elliptic curve signature algorithm.",
_Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
def exchange(self, algorithm, peer_public_key):
if not (
self._backend.elliptic_curve_exchange_algorithm_supported(
algorithm, self.curve
)
):
raise UnsupportedAlgorithm(
"This backend does not support the ECDH algorithm.",
_Reasons.UNSUPPORTED_EXCHANGE_ALGORITHM
)
if peer_public_key.curve.name != self.curve.name:
raise ValueError(
"peer_public_key and self are not on the same curve"
)
group = self._backend._lib.EC_KEY_get0_group(self._ec_key)
z_len = (self._backend._lib.EC_GROUP_get_degree(group) + 7) // 8
self._backend.openssl_assert(z_len > 0)
z_buf = self._backend._ffi.new("uint8_t[]", z_len)
peer_key = self._backend._lib.EC_KEY_get0_public_key(
peer_public_key._ec_key
)
r = self._backend._lib.ECDH_compute_key(
z_buf, z_len, peer_key, self._ec_key, self._backend._ffi.NULL
)
self._backend.openssl_assert(r > 0)
return self._backend._ffi.buffer(z_buf)[:z_len]
def public_key(self):
group = self._backend._lib.EC_KEY_get0_group(self._ec_key)
self._backend.openssl_assert(group != self._backend._ffi.NULL)
curve_nid = self._backend._lib.EC_GROUP_get_curve_name(group)
public_ec_key = self._backend._lib.EC_KEY_new_by_curve_name(curve_nid)
self._backend.openssl_assert(public_ec_key != self._backend._ffi.NULL)
public_ec_key = self._backend._ffi.gc(
public_ec_key, self._backend._lib.EC_KEY_free
)
point = self._backend._lib.EC_KEY_get0_public_key(self._ec_key)
self._backend.openssl_assert(point != self._backend._ffi.NULL)
res = self._backend._lib.EC_KEY_set_public_key(public_ec_key, point)
self._backend.openssl_assert(res == 1)
evp_pkey = self._backend._ec_cdata_to_evp_pkey(public_ec_key)
return _EllipticCurvePublicKey(self._backend, public_ec_key, evp_pkey)
def private_numbers(self):
bn = self._backend._lib.EC_KEY_get0_private_key(self._ec_key)
private_value = self._backend._bn_to_int(bn)
return ec.EllipticCurvePrivateNumbers(
private_value=private_value,
public_numbers=self.public_key().public_numbers()
)
def private_bytes(self, encoding, format, encryption_algorithm):
return self._backend._private_key_bytes(
encoding,
format,
encryption_algorithm,
self._evp_pkey,
self._ec_key
)
@utils.register_interface(ec.EllipticCurvePublicKeyWithSerialization)
class _EllipticCurvePublicKey(object):
def __init__(self, backend, ec_key_cdata, evp_pkey):
self._backend = backend
_mark_asn1_named_ec_curve(backend, ec_key_cdata)
self._ec_key = ec_key_cdata
self._evp_pkey = evp_pkey
sn = _ec_key_curve_sn(backend, ec_key_cdata)
self._curve = _sn_to_elliptic_curve(backend, sn)
curve = utils.read_only_property("_curve")
def verifier(self, signature, signature_algorithm):
if not isinstance(signature, bytes):
raise TypeError("signature must be bytes.")
if isinstance(signature_algorithm, ec.ECDSA):
return _ECDSAVerificationContext(
self._backend, self, signature, signature_algorithm.algorithm
)
else:
raise UnsupportedAlgorithm(
"Unsupported elliptic curve signature algorithm.",
_Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
def public_numbers(self):
set_func, get_func, group = (
self._backend._ec_key_determine_group_get_set_funcs(self._ec_key)
)
point = self._backend._lib.EC_KEY_get0_public_key(self._ec_key)
self._backend.openssl_assert(point != self._backend._ffi.NULL)
with self._backend._tmp_bn_ctx() as bn_ctx:
bn_x = self._backend._lib.BN_CTX_get(bn_ctx)
bn_y = self._backend._lib.BN_CTX_get(bn_ctx)
res = get_func(group, point, bn_x, bn_y, bn_ctx)
self._backend.openssl_assert(res == 1)
x = self._backend._bn_to_int(bn_x)
y = self._backend._bn_to_int(bn_y)
return ec.EllipticCurvePublicNumbers(
x=x,
y=y,
curve=self._curve
)
def public_bytes(self, encoding, format):
if format is serialization.PublicFormat.PKCS1:
raise ValueError(
"EC public keys do not support PKCS1 serialization"
)
return self._backend._public_key_bytes(
encoding,
format,
self._evp_pkey,
None
)
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