## CryptoDB

### Vivien Dubois

#### Publications

Year
Venue
Title
2014
EPRINT
2011
PKC
2010
EPRINT
We describe an attack on the family of Diffie-Hellman and El-Gamal like cryptosystems recently presented at PQ Crypto 2010. We show that the reference hard problem is not hard.
2010
ASIACRYPT
2007
CRYPTO
2007
EUROCRYPT
2007
PKC
2007
EPRINT
In this paper, we present a practical attack on the signature scheme SFLASH proposed by Patarin, Goubin and Courtois in 2001 following a design they had introduced in 1998. The attack only needs the public key and requires about one second to forge a signature for any message, after a one-time computation of several minutes. It can be applied to both SFLASHv2 which was accepted by NESSIE, as well as to SFLASHv3 which is a higher security version.
2007
EPRINT
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.