MARS
Encyclopedia
MARS is a block cipher
that was IBM
's submission to the Advanced Encryption Standard process
. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm.
The MARS design team included Don Coppersmith
, who had been involved in the creation of the previous Data Encryption Standard
(DES) twenty years earlier. The project was specifically designed to resist future advances in cryptography by adopting a layered, compartmentalized approach.
IBM
's official report stated that MARS and Serpent
were the only two finalists to implement any form of safety net with regard to would-be advances in cryptographic mathematics. The Twofish
team made a similar statement about its cipher.
MARS has a 128-bit block size
and a variable key size
of between 128 and 448 bits (in 32-bit increments). Unlike most block ciphers, MARS has a heterogeneous structure: several rounds of a cryptographic core are "jacketed" by unkeyed mixing rounds, together with key whitening
.
always set to the value 1. Thus, there are always two inputs that are unchanged through the multiplication process regardless of the subkey, and two others which have fixed output regardless of the subkey.
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...
that was IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
's submission to the Advanced Encryption Standard process
Advanced Encryption Standard process
The Advanced Encryption Standard , the block cipher ratified as a standard by National Institute of Standards and Technology of the United States , was chosen using a process markedly more open and transparent than its predecessor, the aging Data Encryption Standard...
. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm.
The MARS design team included Don Coppersmith
Don Coppersmith
Don Coppersmith is a cryptographer and mathematician. He was involved in the design of the Data Encryption Standard block cipher at IBM, particularly the design of the S-boxes, strengthening them against differential cryptanalysis...
, who had been involved in the creation of the previous Data Encryption Standard
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...
(DES) twenty years earlier. The project was specifically designed to resist future advances in cryptography by adopting a layered, compartmentalized approach.
IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
's official report stated that MARS and Serpent
Serpent (cipher)
Serpent is a symmetric key block cipher which was a finalist in the Advanced Encryption Standard contest, where it came second to Rijndael. Serpent was designed by Ross Anderson, Eli Biham, and Lars Knudsen....
were the only two finalists to implement any form of safety net with regard to would-be advances in cryptographic mathematics. The Twofish
Twofish
In cryptography, Twofish is a symmetric key block cipher with a block size of 128 bits and key sizes up to 256 bits. It was one of the five finalists of the Advanced Encryption Standard contest, but was not selected for standardisation...
team made a similar statement about its cipher.
MARS has a 128-bit block size
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...
and a variable key size
Key size
In cryptography, key size or key length is the size measured in bits of the key used in a cryptographic algorithm . An algorithm's key length is distinct from its cryptographic security, which is a logarithmic measure of the fastest known computational attack on the algorithm, also measured in bits...
of between 128 and 448 bits (in 32-bit increments). Unlike most block ciphers, MARS has a heterogeneous structure: several rounds of a cryptographic core are "jacketed" by unkeyed mixing rounds, together with key whitening
Key whitening
In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that combine the data with portions of the key before the first round and after the last round of encryption.The first block cipher to use a form of key whitening is...
.
Security analysis
Subkeys with long runs of ones or zeroes may lead to efficient attacks on MARS. The two least significant bits of round keys used in multiplication arealways set to the value 1. Thus, there are always two inputs that are unchanged through the multiplication process regardless of the subkey, and two others which have fixed output regardless of the subkey.