International Association for Cryptologic Research (IACR)
Abstract
In this paper we analyze the E0 cipher, which is the cipher used
in the Bluetooth specifications. We adapted and optimized the Binary
Decision Diagram attack of Krause, for the specific details of
E0. Our method requires 128 known bits of the keystream in order
to recover the initial value of the four LFSR\u27s in the E0 system.
We describe several variants which we built to lower the complexity
of the attack. We evaluated our attack against the real
(non-reduced) E0 cipher. Our best attack can recover the initial
value of the four LFSR\u27s, for the first time, with a realistic space
complexity of 2^23 (84MB RAM), and with a time complexity of
2^87. This attack can be massively parallelized to
lower the overall time complexity. Beyond the
specifics of E0, our work describes practical experience with
BDD-based cryptanalysis, which so far has mostly been a theoretical
concept
