aes_gcm.py 文件源码

def __ghash(self, aad, txt):
        len_aad = len(aad)
        len_txt = len(txt)

        # padding
        if 0 == len_aad % 16:
            data = aad
        else:
            data = aad + b'\x00' * (16 - len_aad % 16)
        if 0 == len_txt % 16:
            data += txt
        else:
            data += txt + b'\x00' * (16 - len_txt % 16)

        tag = 0
        assert len(data) % 16 == 0
        for i in range(len(data) // 16):
            tag ^= bytes_to_long(data[i * 16: (i + 1) * 16])
            tag = self.__times_auth_key(tag)
            # print 'X\t', hex(tag)
        tag ^= ((8 * len_aad) << 64) | (8 * len_txt)
        tag = self.__times_auth_key(tag)

        return tag