Practical Key-Recovery for All Possible Parameters of SFLASH
In this paper, the authors present a new practical key-recovery attack on the SFLASH signature scheme. SFLASH is a derivative of the older C encryption and signature scheme that was broken in 1995 by Patarin. In SFLASH, the public key is truncated, and this simple countermeasure prevents Patarin's attack. The scheme is well-known for have been considered secure and selected in 2004 by the NESSIE project of the European Union to be standardized. However, SFLASH was practically broken in 2007 by Dubois, Fouque, Stern and Shamir. Their attack breaks the original (and most relevant) parameters, but does not apply when more than half of the public key is truncated.