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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
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, interfaces
from cryptography.hazmat.primitives.asymmetric import 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)
assert order != _ffi.NULL
res = _lib.EC_GROUP_get_order(group, order, bn_ctx)
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)
assert group != backend._ffi.NULL
nid = backend._lib.EC_GROUP_get_curve_name(group)
assert nid != backend._lib.NID_undef
curve_name = backend._lib.OBJ_nid2sn(nid)
assert curve_name != backend._ffi.NULL
sn = backend._ffi.string(curve_name).decode('ascii')
return sn
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(interfaces.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)
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
)
assert res == 1
return self._backend._ffi.buffer(sigbuf)[:siglen_ptr[0]]
@utils.register_interface(interfaces.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(interfaces.EllipticCurvePrivateKeyWithNumbers)
class _EllipticCurvePrivateKey(object):
def __init__(self, backend, ec_key_cdata):
self._backend = backend
self._ec_key = ec_key_cdata
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 public_key(self):
group = self._backend._lib.EC_KEY_get0_group(self._ec_key)
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)
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)
assert point != self._backend._ffi.NULL
res = self._backend._lib.EC_KEY_set_public_key(public_ec_key, point)
assert res == 1
return _EllipticCurvePublicKey(
self._backend, public_ec_key
)
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()
)
@utils.register_interface(interfaces.EllipticCurvePublicKeyWithNumbers)
class _EllipticCurvePublicKey(object):
def __init__(self, backend, ec_key_cdata):
self._backend = backend
self._ec_key = ec_key_cdata
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 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)
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)
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
)
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