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The SHA-3 competition: lessons learned

Cryptographic hash functions play a central role in cryptography: they map arbitrarily large input strings to fixed length output strings. The main applications are to create a short unique identifier to a string, to transform a string with a one-way mapping, and to commit to a string or to confirm its knowledge without revealing it. Additional applications are the mapping of group or field elements to strings, key derivation and the extraction of entropy. The main security requirements are preimage and second preimage resistance, collision resistance and indifferentiability from a random oracle. During the last three decades, more than 200 hash functions designs have been published; many of those have been cryptanalyzed, including widely used schemes such as MD5 and SHA-1. Moreover, there was a lack of theoretical understanding of their constructions; as a consequence, structural flaws were identified in widely used designs. These concerns also undermined to some extent the confidence in the SHA-2 hash functions, that have been designed for long term security. As a consequence, the US National Institute for Standards and Technology has organized an open competition. The competition started in November 2007; after five years of intense design, analysis and debate the Keccak function was announced as the winner in October 2012. The new FIPS standard is expected to be published in 2014. This extended abstract will identify some lessons learned during this competition.