GOST cipher: Difference between revisions
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resembles [[Data Encryption Standard| DES]] in some ways; it is an iterated [[block cipher]] with a [[Feistel cipher|Feistel structure]] using eight S-boxes in the F function; each S-box produces four bits of output and these are combined to produce the 32-bit output. However, it differs from DES in other ways. There is no expansion from 32 bits to 48, so s-box inputs are only four bits rather than six, and there is no permutation of the output bits, only an 11-bit circular shift; these differences make GOST easier to implement in software than DES. However, they may also weaken the cipher; GOST compensates by increasing the number of rounds to 32 rather than DES's 16. | resembles [[Data Encryption Standard| DES]] in some ways; it is an iterated [[block cipher]] with a [[Feistel cipher|Feistel structure]] using eight S-boxes in the F function; each S-box produces four bits of output and these are combined to produce the 32-bit output. However, it differs from DES in other ways. There is no expansion from 32 bits to 48, so s-box inputs are only four bits rather than six, and there is no permutation of the output bits, only an 11-bit circular shift; these differences make GOST easier to implement in software than DES. However, they may also weaken the cipher; GOST compensates by increasing the number of rounds to 32 rather than DES's 16. | ||
GOST also uses a 256-bit key which makes it, unlike DES, thoroughly resistant to [[brute force]] | GOST also uses a 256-bit key which makes it, unlike DES, thoroughly resistant to [[brute force attack]]s. | ||
Moreover, each implementation of GOST can use different S-boxes; an organisation can have its own implementation with its own S-boxes. If those S-boxes are kept secret, the total secret information is about 610 bits <ref name="schneier" />, | Moreover, each implementation of GOST can use different S-boxes; an organisation can have its own implementation with its own S-boxes. If those S-boxes are kept secret, the total secret information is about 610 bits <ref name="schneier" />, | ||
Revision as of 06:21, 30 November 2009
The GOST cipher, and the related GOST hash algorithm, were standards in the Soviet Union. GOST was a Soviet national standards body.
The GOST cipher [1] resembles DES in some ways; it is an iterated block cipher with a Feistel structure using eight S-boxes in the F function; each S-box produces four bits of output and these are combined to produce the 32-bit output. However, it differs from DES in other ways. There is no expansion from 32 bits to 48, so s-box inputs are only four bits rather than six, and there is no permutation of the output bits, only an 11-bit circular shift; these differences make GOST easier to implement in software than DES. However, they may also weaken the cipher; GOST compensates by increasing the number of rounds to 32 rather than DES's 16.
GOST also uses a 256-bit key which makes it, unlike DES, thoroughly resistant to brute force attacks.
Moreover, each implementation of GOST can use different S-boxes; an organisation can have its own implementation with its own S-boxes. If those S-boxes are kept secret, the total secret information is about 610 bits [1],
- ↑ 1.0 1.1 Schneier, Bruce (2nd edition, 1996,), Applied Cryptography, John Wiley & Sons, ISBN 0-471-11709-9