ElGamal Signature Scheme Immune to Fault Analysis

Fault attacks have been introduced in late 90´s and since then they attracted a lot of attention. Last years many authors have presented that almost all contemporary cryptographic algorithms are susceptible to the fault analysis. Unfortunately, only a few propositions to overcome this threat have been proposed. Moreover most works focus on secret key cryptosystems (e.g. AES, RC6, Blowfish) and the RSA encryption and signing algorithm. On the other hand much less attention have been paid to other signature and identification schemes.In this paper we will investigate the fault attack on the ElGamal signature scheme. We briefly present two attacks on this scheme and propose a modification that ensures immunity to transient and permanent faults. This is achieved without using comparisons, at cost of increased computational overhead similar to signature verification.