Rabbit (cipher)

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Rabbit is a high-speed stream cipher first presented[1] in February 2003 at the 10th FSE workshop. In May 2005, it was submitted to the eSTREAM project of the ECRYPT network.

Rabbit was designed by Martin Boesgaard, Mette Vesterager, Thomas Pedersen, Jesper Christiansen and Ove Scavenius.

Rabbit uses a 128-bit key and a 64-bit initialization vector. The cipher was designed with high performance in software in mind, where fully optimized implementations achieve an encryption speed of up to 3.7 CPB on a Pentium 3, and of 9.7 CPB on an ARM7. However, the cipher also turns out to be very fast and compact in hardware.

The core component of the cipher is a bitstream generator which encrypts 128 message bits per iteration. The cipher's strength rests on a strong mixing of its inner state between two consecutive iterations. The mixing function is entirely based on arithmetical operations that are available on a modern processor, i.e., no S-boxes or lookup tables are required to implement the cipher.

The authors of the cipher have provided a full set of cryptanalytic white papers on the Cryptico home page.[2] It is also described in RFC 4503. Cryptico had patents pending for the algorithm and for many years required a license fee for commercial use of the cipher which was waived for non-commercial uses. However, the algorithm was made free for any use on October 6, 2008.[3]

Security[edit]

Rabbit claims 128-bit security against attackers whose target is one specific key. If, however, the attacker targets a large number of keys at once and does not really care which one he breaks, then the small IV size results in a reduced security level of 96 bit. This is due to generic TMD trade-off attacks.[4]

A small bias in the output of Rabbit exists,[5] resulting in a distinguisher with 2247 complexity discovered by Jean-Philippe Aumasson in December 2006. Even though this distinguisher was improved to 2158 in 2008,[6] it's not a threat to Rabbit's security because its complexity is significantly higher than the brute-force of the key space (2128).

References[edit]

  1. ^ M. Boesgaard, M. Vesterager, T. Pedersen, J. Christiansen, O. Scavenius. Rabbit: A High-Performance Stream Cipher. Proc. FSE 2003. Springer LNCS 2887, pp. 307-329 (PDF)
  2. ^ M. Boesgaard, T. Pedersen, M. Vesterager, E. Zenner. The Rabbit Stream Cipher - Design and Security Analysis. Proc. SASC 2004. (PDF)
  3. ^ http://www.ecrypt.eu.org/stream/phorum/read.php?1,1244
  4. ^ Christophe De Cannière, Joseph Lano, and Bart Preneel, "Comments on the Rediscovery of Time Memory Data Tradeoffs", 2005. (PDF)
  5. ^ Jean-Philippe Aumasson, "On a bias of Rabbit", Proc. SASC 2007. (PDF)
  6. ^ Yi Lu, Huaxiong Wang, San Ling, "Cryptanalysis of Rabbit", Proc. ISC 2008 ([1])

External links[edit]