General  

Designers  IBM 
First published  1998 
Certification  AES finalist 
Cipher detail  
Key sizes  128, 192, or 256 bits 
Block sizes  128 bits 
Structure  Type3 Feistel network 
Rounds  32 
In cryptography, 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 wouldbe advances in cryptographic mathematics. Interestingly, the Twofish team made a similar statement about its cipher.^{[1 ]}.
MARS has a 128bit block size and a variable key size of between 128 and 448 bits (in 32bit 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.
Subkeys with long runs of ones or zeroes may lead to efficient attacks on MARS ^{ [2]}. The two least significant bits of round keys used in multiplication are 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 ^{ [2]}.
