Editing MARS (cipher)

{{Short description|Block cipher}}
{{Infobox block cipher
| name          = MARS
| image         =
| caption       =
| designers     = [[IBM]]
| publish date  = 1998
| derived from  =
| derived to    =
| related to    = 
| certification = [[AES finalist]]
| key size      = 128 to 448 bits
| block size    = 128 bits
| structure     = Type-3 [[Feistel cipher|Feistel network]]<ref>{{cite conference |title=On Generalized Feistel Networks |last1=Hoang |first1=Viet Tung |last2=Rogaway |first2=Phillip |date=2010 |publisher=Springer |book-title=LNCS 6223 |pages=613–630 |location=USA |conference=CRYPTO 2010|doi=10.1007/978-3-642-14623-7_33 |doi-access=free }}</ref>
| rounds        = 32
| cryptanalysis =
}}

'''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 (cipher)|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.<ref name="NIST-report-on-development-of-AES">{{citation
| author = NIST
| title = Report on the Development of the Advanced Encryption Standard (AES)
| url = http://csrc.nist.gov/archive/aes/round2/r2report.pdf
| publisher = NIST
| year = 2000
}}</ref>

MARS has a 128-bit [[block size (cryptography)|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]].

==Security analysis==
Subkeys with long runs of ones or zeroes may lead to efficient attacks on MARS.<ref name="Preneel-Comments-by-NESSIE-Project-on-AES-Finalists">{{citation
| author = B. Preneel
| title = Comments by the NESSIE Project on the AES Finalists
| url = http://csrc.nist.gov/archive/aes/round2/comments/20000524-bpreneel.pdf
| publisher = NIST
| year = 2000
|display-authors=etal}}</ref> 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.<ref name="Preneel-Comments-by-NESSIE-Project-on-AES-Finalists"/>

A [[meet-in-the-middle attack]] published in 2004 by [[John Kelsey (cryptanalyst)|John Kelsey]] and [[Bruce Schneier]] can break 21 out of 32 rounds of MARS.<ref>[https://www.schneier.com/wp-content/uploads/2016/02/paper-mars-attacks.pdf ''MARS Attacks! Preliminary Cryptanalysis of Reduced-Round MARS Variants''] John Kelsey, Bruce Schneier, 2004</ref>

==Notes and references==
{{reflist}}

==External links==
* [http://embeddedsw.net/Cipher_Reference_Home.html 256bit Ciphers - MARS Reference implementation and derived code]
* [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.35.5887&rep=rep1&type=pdf Specification of MARS] {{Webarchive|url=https://web.archive.org/web/20180911225347/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.35.5887&rep=rep1&type=pdf |date=2018-09-11 }}
* [https://archive.today/20060326012245/http://domino.research.ibm.com/comm/research_projects.nsf/pages/security.mars.html IBM's page on MARS]
* [http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html#MARS SCAN's entry on MARS]
* [http://www.quadibloc.com/crypto/co040406.htm John Savard's description of MARS]

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