Reducing the Collision Probability of Alleged Comp128
Wagner, Goldberg and Briceno have recently published an attack  on what they believe to be Comp128, the GSM A3A8 authentication function . Provided that the attacker has physical access to the card and to its secret PIN code (the card has to be activated), this chosen plaintext attack recovers the secret key of the personalized SIM (Secure Identification Module) card by inducing collisions on the second (out of 40) round of the compression function. In this paper we suggest two different approaches to strengthen the alleged Comp128 algorithm with respect to this attack. An evaluation of the number of chosen plaintexts and the new complexity of the attack are given.
KeywordsAlleged Comp128 chosen plaintext attack authentication compression function cryptanalysis smart cards GSM
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