Golbal System for Mobile Communications

Marc Briceno

Smartcard Developer Association

Ian Goldberg

UC Berkeley

The Global System for Mobile communications (GSM) is the world's most widely used digital mobile telephony system. With over 120 million subscribers worldwide, the GSM network is the world's largest digital network of any kind. The GSM network contains more nodes than even the Internet. Cryptographic protections are employed throughout the GSM network, both for authentication and voice-privacy purposes. Since the cryptographic algorithms used within GSM had not been published outside the membership of the GSM MoU, our group first reverse engineered the algorithms. We then subjected the reverse-engineered algorithms to cryptanalysis. We will present the three core algorithms used in GSM followed by a presentation of cryptanalytical attacks on all three ciphers. Having demonstrated that GSM mobile phones are subject to both cloning and eavesdropping, we will trace the severe design flaws present in the GSM algorithms to the fundamentally flawed design procedure employed by the GSM MoU. We will conclude our presentation with recommendations for a better design procedure that would prevent such flawed cryptographic systems from entering production mode in the future. For additional information about our work regarding GSM, visit the Smartcard Developer Association and the ISAAC Group.

Gates 498, 10/12/99, 4:15 PM