A differential fault attack against early rounds of (Triple

Abstract. Previously proposed differential fault analysis (DFA) tech-niques against iterated block ciphers mostly exploit computational er-rors in the last few rounds of the cipher to extract the secret key. In this paper we describe a DFA attack that exploits computational errors in early rounds of a Feistel cipher. The principle of the attack is to force collisions by inducing faults in intermediate results of the cipher. We put this attack into practice against DES implemented on a smart card and extracted the full round key of the first round within a few hours by inducing one bit errors in the second and third round, respectively.