SHA-256

SHA-256 ( Secure Hash Algorithm ) is a cryptographic Fonction of chopping conceived by the National Security Agency of the United States (NSA), and published in 2000. It produces a result (called “ hash ” or condensate ) of 256 bits and derives from SHA-1.

Operation

Very near to the SHA-1 from which it is resulting, remote SHA-256 by the length of the result obtained but also by certain operations, functions and constants specific which bring this result. Those are structured on the same model as SHA-1 (pretreatment and calculation) but work is carried out in 64 rounds with 8 variables initialized with specific constants. The Boolean functions used are different from SHA-1.

At the end of the 64 turns the eight concaténées variables form the result.

See also: Amorce=Pour more details, to see, Specifications SHA-256

Cryptanalyse

SHA-256 became the new standard recommended as regards cryptographic chopping after the attacks on MD5 and SHA-1. Other family members SHA were cryptanalysés relatively little compared to SHA-0 and SHA-1. In 2003, Helena Handschuh and Henri Gilbert published an analysis of SHA-256, 384 and 512. Their study shows that the other members of SHA are not reached by the attacks which had proven reliable on the other functions of chopping (MD4, MD5 and SHA-1 inter alia). The linear Cryptanalyse and differential do not apply.

On the other hand, the two cryptologists highlighted significant weaknesses on modified versions. By changing the constants or the parameters of initialization so as to make them symmetrical while replacing the modular addition by a XOR, one obtains a chopping which produces a symmetrical print if the message in entry is also.

References

Henri Gilbert, Helena Handschuh: Security Analysis off SHA-256 and Sisters . Selected Areas in Cryptography 2003:175 - 193

See too

External bonds

On-line computer Encoding of character strings by the most used functions of chopping.

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