ciphers.py 文件源码

def update(self, data):
        # OpenSSL 0.9.8e has an assertion in its EVP code that causes it
        # to SIGABRT if you call update with an empty byte string. This can be
        # removed when we drop support for 0.9.8e (CentOS/RHEL 5). This branch
        # should be taken only when length is zero and mode is not GCM because
        # AES GCM can return improper tag values if you don't call update
        # with empty plaintext when authenticating AAD for ...reasons.
        if len(data) == 0 and not isinstance(self._mode, modes.GCM):
            return b""

        buf = self._backend._ffi.new("unsigned char[]",
                                     len(data) + self._block_size - 1)
        outlen = self._backend._ffi.new("int *")
        res = self._backend._lib.EVP_CipherUpdate(self._ctx, buf, outlen, data,
                                                  len(data))
        assert res != 0
        return self._backend._ffi.buffer(buf)[:outlen[0]]