ciphers.py 文件源码

def finalize(self):
        # OpenSSL 1.0.1 on Ubuntu 12.04 (and possibly other distributions)
        # appears to have a bug where you must make at least one call to update
        # even if you are only using authenticate_additional_data or the
        # GCM tag will be wrong. An (empty) call to update resolves this
        # and is harmless for all other versions of OpenSSL.
        if isinstance(self._mode, modes.GCM):
            self.update(b"")

        buf = self._backend._ffi.new("unsigned char[]", self._block_size)
        outlen = self._backend._ffi.new("int *")
        res = self._backend._lib.EVP_CipherFinal_ex(self._ctx, buf, outlen)
        if res == 0:
            errors = self._backend._consume_errors()

            if not errors and isinstance(self._mode, modes.GCM):
                raise InvalidTag

            self._backend.openssl_assert(
                errors[0][1:] == (
                    self._backend._lib.ERR_LIB_EVP,
                    self._backend._lib.EVP_F_EVP_ENCRYPTFINAL_EX,
                    self._backend._lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH
                ) or errors[0][1:] == (
                    self._backend._lib.ERR_LIB_EVP,
                    self._backend._lib.EVP_F_EVP_DECRYPTFINAL_EX,
                    self._backend._lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH
                )
            )
            raise ValueError(
                "The length of the provided data is not a multiple of "
                "the block length."
            )

        if (isinstance(self._mode, modes.GCM) and
           self._operation == self._ENCRYPT):
            block_byte_size = self._block_size // 8
            tag_buf = self._backend._ffi.new(
                "unsigned char[]", block_byte_size
            )
            res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
                self._ctx, self._backend._lib.EVP_CTRL_GCM_GET_TAG,
                block_byte_size, tag_buf
            )
            self._backend.openssl_assert(res != 0)
            self._tag = self._backend._ffi.buffer(tag_buf)[:]

        res = self._backend._lib.EVP_CIPHER_CTX_cleanup(self._ctx)
        self._backend.openssl_assert(res == 1)
        return self._backend._ffi.buffer(buf)[:outlen[0]]