Cryptology ePrint Archive: Report 2008/405

Slid Pairs in Salsa20 and Trivium

Deike Priemuth-Schmid and Alex Biryukov

Abstract: The stream ciphers Salsa20 and Trivium are two of the finalists of the eSTREAM project which are in the final portfolio of new promising stream ciphers. In this paper we show that initialization and key-stream generation of these ciphers is {\em slidable}, i.e. one can find distinct (Key, IV) pairs that produce identical (or closely related) key-streams. There are $2^{256}$ and more then $2^{39}$ such pairs in Salsa20 and Trivium respectively. We write out and solve the non-linear equations which describe such related (Key, IV) pairs. This allows us to sample the space of such related pairs efficiently as well as detect such pairs in large portions of key-stream very efficiently. We show that Salsa20 does not have 256-bit security if one considers general birthday and related key distinguishing and key-recovery attacks.

Category / Keywords: secret-key cryptography / Salsa20, Trivium, eSTREAM, stream ciphers, cryptanalysis

Publication Info: Full version of the paper published on Indocrypt 2008

Date: received 23 Sep 2008

Contact author: deike priemuth-schmid at uni lu

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Version: 20080924:041104 (All versions of this report)

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