The FSB (Fast Syndrome Based) hash family is a set of cryptographic hash functions introduced in 2003 by Daniel Augot, Matthieu Finiasz, and Nicolas Sendrier. It can be proven that breaking FSB is at least as difficult as solving the NP-complete regular syndrome decoding problem, granting provable security. However this provability comes at the cost of efficiency in both computation, and the complexity of the algorithm itself
The original paper by Daniel Augot, Matthieu Finiasz, and Nicolas Sendrier can be found at https://link.springer.com/chapter/10.1007/11554868_6.