JH (hash function)

JH is a cryptographic hash function designed by Hongjun Wu and submitted to the NIST hash function competition. It was chosen as one of the five finalists, along with BLAKE, Grostl, Keccak and Skein, but in 2012 it lost to Keccak, which became SHA-3. JH keeps a 1024-bit internal state and consumes the message in 512-bit blocks. Each block is combined with the state in three steps: the block is XORed into the left half of the state, a 42-round unkeyed permutation is applied, and the block is XORed into the right half. Every round maps 4-bit pieces of the state through S-boxes chosen by a round-dependent key schedule, mixes adjacent pieces with a maximum distance separable code over a finite field, and permutes the pieces so they meet different neighbours in the next round. The digest is the last 224, 256, 384 or 512 bits of the final 1024-bit value. The design suits bit-sliced implementations using the SSE2 instruction set, which reach about 16.8 cycles per byte. NIST's final report found that JH received relatively little cryptanalysis, had the smallest security margin of the finalists, and was among the slowest in most software implementations.