# 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.
import typing
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric.utils import Prehashed
if typing.TYPE_CHECKING:
from cryptography.hazmat.backends.openssl.backend import Backend
def _evp_pkey_derive(backend: "Backend", evp_pkey, peer_public_key) -> bytes:
ctx = backend._lib.EVP_PKEY_CTX_new(evp_pkey, backend._ffi.NULL)
backend.openssl_assert(ctx != backend._ffi.NULL)
ctx = backend._ffi.gc(ctx, backend._lib.EVP_PKEY_CTX_free)
res = backend._lib.EVP_PKEY_derive_init(ctx)
backend.openssl_assert(res == 1)
res = backend._lib.EVP_PKEY_derive_set_peer(ctx, peer_public_key._evp_pkey)
backend.openssl_assert(res == 1)
keylen = backend._ffi.new("size_t *")
res = backend._lib.EVP_PKEY_derive(ctx, backend._ffi.NULL, keylen)
backend.openssl_assert(res == 1)
backend.openssl_assert(keylen[0] > 0)
buf = backend._ffi.new("unsigned char[]", keylen[0])
res = backend._lib.EVP_PKEY_derive(ctx, buf, keylen)
if res != 1:
errors_with_text = backend._consume_errors_with_text()
raise ValueError("Error computing shared key.", errors_with_text)
return backend._ffi.buffer(buf, keylen[0])[:]
def _calculate_digest_and_algorithm(
data: bytes,
algorithm: typing.Union[Prehashed, hashes.HashAlgorithm],
) -> typing.Tuple[bytes, hashes.HashAlgorithm]:
if not isinstance(algorithm, Prehashed):
hash_ctx = hashes.Hash(algorithm)
hash_ctx.update(data)
data = hash_ctx.finalize()
else:
algorithm = algorithm._algorithm
if len(data) != algorithm.digest_size:
raise ValueError(
"The provided data must be the same length as the hash "
"algorithm's digest size."
)
return (data, algorithm)
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