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SHA Family Functions
Keywords
Keccak, SHA-3, hash function, collision resistance, preimage attack, sponge construction
Abstract
This paper presents a general overview regarding SHA family functions. A lot of hash functions were proposed in the last three decades and most of them are based upon the MD construction, especially the MD4 family. The most popular hash functions that belong to the MD4 family are: MD5, the SHA family (SHA-0, SHA-1, SHA-224, SHA-256, SHA-384, SHA-512) and the RIPEMD family (RIPEMD, RIPEMD-128, RIPEMD-160, RIPEMD-256, RIPEMD-320). In 2004, collision attacks against MD5 and SHA-0 were demonstrated by Xiaoyun Wang and one year later she extended a theoretical attack against SHA-1. NIST took the Wang attack into serious consideration and decided to open a competition to develop the next secure hash algorithm, named SHA-3. After five years of competition NIST selected Keccak as winner. Keccak is a family of sponge functions. Also, this paper describes the sponge construction and its security. Various comparisons between SHA-3, SHA-2 and SHA-1 regarding the security strengths, performances and construction details are summarized. The conclusions are presented at the end of the paper.