GOST (hash function)

The GOST hash function, defined in the standards GOST R 34.11-94 and GOST 34.311-95, is a 256-bit cryptographic hash function. It was initially defined in the Russian national standard GOST R 34.11-94 Information Technology - Cryptographic Information Security - Hash Function. The equivalent standard used by other member-states of the CIS is GOST 34.311-95.

The hash function is based on the GOST block cipher.

Algorithm

GOST processes a variable-length message into a fixed-length output of 256 bits. The input message is broken up into chunks of 256-bit blocks (eight 32-bit little endian integers); the message is padded by appending as many zeros to it as are required to bring the length of the message up to 256 bits. The remaining bits are filled up with a 256-bit integer arithmetic sum of all previously hashed blocks and then a 256-bit integer representing the length of the original message, in bits.

Basic notations

The algorithm descriptions uses the following notations:

• <math>mathcal0mathcal^j</math> — j-bit block filled with zeroes.
• <math>mathcalMmathcal</math> — length of the M block in bits modulo 2²⁵⁶.
• <math>mathcal</math> — concatenation of two blocks.
• <math>+</math> — arithmetic sum of two blocks modulo 2²⁵⁶
• <math>oplus</math> — logical xor of two blocks

Further we consider that the little-order bit is located at the left of a block,...
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