hashes.py 文件源码

def __init__(self, backend, algorithm, ctx=None):
        self._algorithm = algorithm

        self._backend = backend

        if ctx is None:
            ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new()
            ctx = self._backend._ffi.gc(
                ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free
            )
            evp_md = self._backend._lib.EVP_get_digestbyname(
                algorithm.name.encode("ascii"))
            if evp_md == self._backend._ffi.NULL:
                raise UnsupportedAlgorithm(
                    "{0} is not a supported hash on this backend.".format(
                        algorithm.name),
                    _Reasons.UNSUPPORTED_HASH
                )
            res = self._backend._lib.EVP_DigestInit_ex(ctx, evp_md,
                                                       self._backend._ffi.NULL)
            self._backend.openssl_assert(res != 0)

        self._ctx = ctx