This problem introduces a hash function similar in spirit to SHA that operates on letters instead of binary data. It is called the toy tetragraph hash (tth).2 Given a message consisting of a sequence of letters, tth produces a hash value consisting of four letters. First, tth divides the message into blocks of 16 letters, ignoring spaces, punctuation, and capitalization. If the message length is not divisible by 16, it is padded out with nulls. A four-number running total is maintained that starts out with the value (0, 0, 0, 0); this is input to the compression function for processing the first block.

The compression function consists of two rounds.

Round 1 Get the next block of text and arrange it as a row-wise 4 X 4 block of text and covert it to numbers (A = 0, B = 1, etc.). For example, for the block ABCDEFGHIJKLMNOP, we have