Rabbit is a high-speed stream cipher from 2003. The algorithm and

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was released in 2008 as

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History

''Rabbit'' was first presented in February 2003 at the 10th FSE workshop. In May 2005, it was submitted to the

eSTREAM eSTREAM is a project to "identify new stream ciphers suitable for widespread adoption", organised by the EU ECRYPT network. It was set up as a result of the failure of all six stream ciphers submitted to the NESSIE project. The call for primi ...

project of the

ECRYPT ECRYPT (European Network of Excellence in Cryptology) was a 4-year European research initiative launched on 1 February 2004 with the stated objective of promoting the collaboration of European researchers in information security, and especially in ...

network. Rabbit was designed by Martin Boesgaard, Mette Vesterager, Thomas Pedersen, Jesper Christiansen and Ove Scavenius. The authors of the cipher have provided a full set of cryptanalytic white papers on the Cryptico home page. It is also described in RFC 4503. Cryptico had

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s 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. Also the website states that the algorithm and implementation is

and offers the

free for download.

Functionality

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 cost of up to 3.7

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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 In cryptography, an S-box (substitution-box) is a basic component of symmetric key algorithms which performs substitution. In block ciphers, they are typically used to obscure the relationship between the key and the ciphertext, thus ensuring Shan ...

or lookup tables are required to implement the cipher. The mixing function uses a g-function based on arithmetical squaring, and the ARX operations – logical XOR, bit-wise rotation with fixed rotation amounts, and addition modulo 2³². The g-function used in Rabbit – squaring a 32-bit number to produce a 64-bit number, and then combining the left half and the right half of that square number with xor, to produce a 32-bit result – provides much better results than using the 32 middle bits of that squared number (the middle-square method).

Security

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. A small bias in the output of Rabbit exists, 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,Yi Lu, Huaxiong Wang, San Ling, "Cryptanalysis of Rabbit", Proc. ISC 2008

it is not a threat to Rabbit's security because its complexity is significantly higher than the brute-force of the key space (2¹²⁸).

References

External links

Rabbit RFC

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