## Cryptology ePrint Archive: Report 2007/366

Breaking the Symmetry: a Way to Resist the New Differential Attack

Jintai Ding and Bo-Yin Yang and Chen-Mou Cheng and Owen Chen and Vivien Dubois

Abstract: Sflash had recently been broken by Dubois, Stern, Shamir, etc., using a differential attack on the public key. The $C^{\ast-}$ signature schemes are hence no longer practical. In this paper, we will study the new attack from the point view of symmetry, then (1) present a simple concept (projection) to modify several multivariate schemes to resist the new attacks; (2) demonstrate with practical examples that this simple method could work well; and (3) show that the same discussion of attack-and-defence applies to other big-field multivariates. The speed of encryption schemes is not affected, and we can still have a big-field multivariate signatures resisting the new differential attacks with speeds comparable to Sflash.

Category / Keywords: public-key cryptography /

Publication Info: multivariate public key cryptography,differential, symmetry, projection