From AES to Red Pike

The Mighty Prof Ross Anderson

The AES method is a block cipher which uses a block size of 128-bits and key sizes of 128 bits, 192 bits and 256 bits. It operates by uses a key scheduling method which takes part of the key for a number of rounds. For a 128-bit key, we have 10 rounds, and for a 256-bit key, we have 14 rounds. In each round, we take a 4ⅹ4 matrix of byte values (16 bytes = 128 bits), and then swap rows and columns. We also use an S-box to scramble the bytes:

But what happens if we want to make our block cipher simpler, and just implement it in just a few lines of code? This might be the case for a limited-memory IoT device. One such cipher is Red Pike, which was proposed as a standard for the NHS in 1996 [here]:

the NHS’s needs should be addressed by a family of related encryption products built on the Red Pike encryption algorithm. This algorithm has recently been made available to the NHS by CESG, the National Technical Security Authority within HMG

Red Pike — a name which is likely to derive from an area of the English Lake District —…