GDES

GDES

General
Designers	Ingrid Schaumuller-Bichl
First published	1981
Derived from	DES
Cipher detail
Block sizes	variable, multiple of 32
Structure	generalized Feistel network
Rounds	variable, even
Best public cryptanalysis
differential cryptanalysis breaks most variants more easily than DES

In cryptography, the Generalized DES Scheme (GDES or G-DES) is a variant of the DES symmetric-key block cipher designed with the intention of speeding up the encryption process while improving its security. The scheme was proposed by Ingrid Schaumuller-Bichl in 1981.

In 1990, Eli Biham and Adi Shamir showed that GDES was vulnerable to differential cryptanalysis, and that any GDES variant faster than DES is also less secure than DES.

GDES generalizes the Feistel network structure of DES to larger block sizes. In each round, the DES round function is applied to the rightmost 32-bit subblock, and the result is XORed with all the other parts. Then the block is rotated 32 bits to the right.

References

• Eli Biham, Adi Shamir: Differential Cryptanalysis of DES-like Cryptosystems. CRYPTO 1990: 2-21
• Ingrid Schaumuller-Bichl, Zur Analyse des Data Encryption Standard und Synthese Verwandter Chiffriersysteme, Ph.D. Thesis, Linz university, May 1981. (In German).
• I. Schaumuller-Bichl, "On the Design and Analysis of New Cipher Systems Related to DES," Technical Report, Linz University, 1983.