In cryptography

Cryptography

Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

, the Generalized DES Scheme (GDES or G-DES) is a variant of the DES

Data Encryption Standard

The Data Encryption Standard is a block cipher that uses shared secret encryption. It was selected by the National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally. It is...

 block cipher

Block cipher

In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...

 designed with the intention of speeding up the encryption

Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...

 process while improving its security. The scheme was proposed by Ingrid Schaumuller-Bichl in 1981.

In 1990, Eli Biham

Eli Biham

Eli Biham is an Israeli cryptographer and cryptanalyst, currently a professor at the Technion Israeli Institute of Technology Computer Science department. Starting from October 2008, Biham is the dean of the Technion Computer Science department, after serving for two years as chief of CS graduate...

 and Adi Shamir

Adi Shamir

Adi Shamir is an Israeli cryptographer. He is a co-inventor of the RSA algorithm , a co-inventor of the Feige–Fiat–Shamir identification scheme , one of the inventors of differential cryptanalysis and has made numerous contributions to the fields of cryptography and computer...

 showed that GDES was vulnerable to differential cryptanalysis

Differential cryptanalysis

Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in an input can affect the resultant difference at the output...

, and that any GDES variant faster than DES is also less secure than DES.

GDES generalizes the Feistel network

Feistel cipher

In cryptography, a Feistel cipher is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel who did pioneering research while working for IBM ; it is also commonly known as a Feistel network. A large proportion of block...

 structure of DES to larger block sizes

Block size (cryptography)

In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. Block ciphers operate on a fixed length string of bits. The length of this bit string is the block size...

. 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.