Elements of information theory
Elements of information theory
Fast computation of large distributions and its cryptographic applications
ASIACRYPT'05 Proceedings of the 11th international conference on Theory and Application of Cryptology and Information Security
Cascade Jump Controlled Sequence Generator and Pomaranch Stream Cipher
New Stream Cipher Designs
Two general attacks on pomaranch-like keystream generators
FSE'07 Proceedings of the 14th international conference on Fast Software Encryption
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We give a simple algorithm that can find biased linear approximations of nonlinear building blocks. The algorithm is useful if the building block is relatively small and exhaustive search is possible. Instead of searching all possible linear relations individually, we show how the most biased relation can be found in just a few steps. As an example we show how we can find a biased relation in the output bits of the stream cipher Pomaranch Version 2, a tweaked variant of Pomaranch, resulting in both distinguishing and key recovery attacks. These attacks will break both the 128-bit variant and the 80-bit variant of the cipher with complexity faster than exhaustive key search.