Square (cipher)

Square, sometimes written SQUARE, is a block cipher invented by Joan Daemen and Vincent Rijmen. Its design was published in 1997 and is a forerunner to Rijndael, the cipher that was later adopted as the Advanced Encryption Standard. The structure of Square is a substitution-permutation network with eight rounds, operating on 128-bit blocks and using a 128-bit key. Square was introduced together with a new form of cryptanalysis discovered by Lars Knudsen, which became known as the Square attack, so the cipher is remembered both as a design in its own right and as the place where that attack technique first appeared. The cipher is not patented. The design paper, titled The Block Cipher Square, appeared in the proceedings of Fast Software Encryption in 1997 and is the main reference for the cipher.