$J$ and $K$. The message is seen as a sequence of blocks. If the number of bytes of the message is not a multiple of four, extra null bytes are added at the end of the message to complete the last block. The size of the message should be less than 1,000,000 blocks; otherwise, the MAA result is said to be undefined; we believe that this restriction, which is not inherent to the algorithm itself, was added in the ISO 8731-2 standard to provide MAA implementations with an upper bound (four megabytes) on the size of memory buffers used to store messages.

The MAA produces as output a block, which is the MAC value computed from the key and the message. The fact that this result has only 32 bits proved to be a major weakness enabling cryptographic attacks; MAC values computed by modern algorithms now have a much larger number of bits. Apart from the aforementioned restriction on the size of messages, the MAA behaves as a totally-defined function; its result is deterministic in the sense that, given a key and a message, there is only a single MAC result, which neither depends on implementation choices nor on hidden 