Anubis (cipher)

Anubis (cipher). Anubis is a block cipher designed as a candidate for the NESSIE project, a European initiative to identify secure cryptographic primitives. It was created by cryptographers Paulo S. L. M. Barreto and Vincent Rijmen, the latter also a co-designer of the Advanced Encryption Standard. The cipher employs a substitution–permutation network structure and operates on 128-bit blocks with a variable key length.

Overview

The cipher was submitted to the NESSIE consortium for evaluation alongside other prominent algorithms like Twofish and Camellia (cipher). Its design shares conceptual similarities with the earlier KHAZAD cipher, also developed by Barreto and Rijmen. Anubis was not selected for the final NESSIE portfolio, but its design contributed to the broader field of cryptography research. The algorithm's structure is considered elegant by many in the cryptographic community, particularly for its use of efficient mathematical components.

Design and Operation

Anubis uses a classic substitution–permutation network framework, iterating through multiple rounds of transformation. Each round applies a non-linear substitution layer using an S-box derived from the inverse function in a finite field, followed by a linear diffusion layer. The linear transformation is implemented via a maximum distance separable matrix multiplication, a technique also seen in designs like the Advanced Encryption Standard. The cipher supports a key schedule that expands a user key of 128 to 320 bits into round keys, with the number of rounds varying from 12 to 18 depending on the key size.

Security Analysis

During the NESSIE evaluation process, Anubis was found to be resistant to several known cryptanalytic attacks. It demonstrated strong security against differential cryptanalysis and linear cryptanalysis, the primary techniques used against algorithms like the Data Encryption Standard. No practical attacks faster than brute-force attack have been published against the full-round cipher. However, some theoretical reduced-round analyses have been presented in academic forums like the Fast Software Encryption workshop. Its security margins are considered conservative, comparable to other well-regarded ciphers from the same era such as Serpent (cipher).

Applications and Use

Despite its technical strengths, Anubis saw limited adoption in major commercial or governmental systems, which largely standardized on the Advanced Encryption Standard after its selection by the National Institute of Standards and Technology. It has been implemented in some cryptographic libraries, such as the Crypto++ library, for academic and research purposes. The cipher is occasionally referenced in comparative studies of block cipher designs and within the International Association for Cryptologic Research community. Its primary legacy lies in its influence on subsequent cipher designs and as a subject of study in cryptography courses.

Development and History

Anubis was developed in 2000 specifically for submission to the NESSIE project, a European counterpart to the Advanced Encryption Standard process. The designers, Paulo S. L. M. Barreto and Vincent Rijmen, were already established figures due to their work on KHAZAD and the Advanced Encryption Standard respectively. After the conclusion of the NESSIE project, the cipher was published in the open academic literature, with specifications appearing in proceedings from conferences like Selected Areas in Cryptography. While not standardized, its design continues to be cited in cryptographic literature analyzing substitution–permutation network constructions.

Category:Block ciphers