View source for International Data Encryption Algorithm

[[File:International Data Encryption Algorithm InfoBox Diagram.svg|thumb|250px|An encryption round of IDEA using six sub-keys]]

In [[cryptography]], the '''International Data Encryption Algorithm''' ('''IDEA''') is a [[block cipher]] [[design]]ed by Xuejia Lai and James Massey of [[ETH Zurich]] in 1991. It was meant to be a replacement for the [[Data Encryption Standard]]. IDEA is much like an earlier [[cipher]] called '''Proposed Encryption Standard''' ('''PES'''), but with some improvements. Because of this, IDEA was first called '''IPES''' ('''Improved PES''').

The cipher was [[patent]]ed in a number of countries for a long period of time. The name "IDEA" is also a [[trademark]]. The [[patent]]s expired in 2010–2011, so it is now free for everyone to use. IDEA was [[license]]d worldwide by a company called '''MediaCrypt'''.

IDEA was used in [[Pretty Good Privacy]] (PGP) v2.0 after the cipher used in v1.0, [[BassOmatic]], was found to be breakable.<ref>{{cite book | last = Garfinkel | first = Simson | authorlink = Simson Garfinkel | title = PGP: Pretty Good Privacy | publisher = [[O'Reilly Media]] | date = December 1, 1994 | location = | pages = 101–102 | isbn = 978-1565920989}}</ref> IDEA can be used with the [[Pretty Good Privacy#OpenPGP implementations|OpenPGP]] standard.
== How it works ==
IDEA operates on 64-bit [[Block size (cryptography)|blocks]], using a 128-bit [[key (cryptography)|key]]. It contains a series of eight identical transformations (''rounds'') and one output transformation (the ''half-round''). It does this for a total of 8.5 rounds. The processes for [[encryption]] and [[decryption]] are similar.

IDEA derives much of its security by [[Interleave sequence|interleaving]] operations from different [[group (mathematics)|groups]] — [[modular arithmetic|modular]] addition and [[multiplication]], and [[Bitwise operation|bitwise]] [[Exclusive or|eXclusive OR (XOR)]] — which are chosen to be "algebraically incompatible".

Each of the eight round uses six sub-keys, while the half-round uses four; for a total of 52 sub-keys. Each sub-key is a [[Key size|16-bit in length]]. The first eight sub-keys are extracted directly from the 128-bit [[key (cryptography)|key]], with K1 being the lowest sixteen bits and K8 is the highest sixteen bits; further groups of eight keys are created by [[Rotation|rotating]] the main key left 25 bits after the creation of the previous group; six rotations generate all sub-keys.
== Security ==
The makers looked at IDEA to measure (look at the size of) its strength against [[differential cryptanalysis]] and found out that it is [[unsusceptible]] only under specific [[Assumption|assumptions]]. No successful [[Linear cryptanalysis|linear]] or [[Differential cryptanalysis|differential attacks]] have been seen. Some types of [[weak key]]s have been found — like (Daemen ''et al.'', 1994) — but these are not very important, being so rare that they can be specifically avoided. [[As of 2007]], the best attack which applies to all keys can break IDEA if reduced to 6 rounds (the full IDEA cipher uses 8.5 rounds).<ref name="A-New Attack-on-6-Round-IDEA">
{{cite book
| author = Biham, E. and Dunkelman, O. and Keller, N
| chapter = A New Attack on 6-Round IDEA
| url = http://www.cosic.esat.kuleuven.be/publications/article-920.ps
| title = Proceedings of Fast Software Encryption, 2007, Lecture Notes in Computer Science
| publisher = COmputer Security and Industrial Cryptography (COSIC)
| format = [[Postscript]]
}}</ref>

In 1996, [[Bruce Schneier]] wrote about IDEA, "In my opinion, it is the best and most secure [[block algorithm]] available to the public at this time." (''Applied Cryptography'', 2nd ed.) However, by 1999 he was no longer recommending IDEA due to the presence of faster [[Cryptography|cryptographic]] [[algorithm]]s, some progress in its [[cryptanalysis]], and the problem of [[patent]]s. [http://slashdot.org/interviews/99/10/29/0832246.shtml]
== Availability ==
A [[patent]] application for IDEA was first used in [[Switzerland]] (CH A 1690/90) on May 18, 1990, then an international patent application was used under the [[Patent Cooperation Treaty]] on May 16, 1991. Patents were eventually given in Austria, France, [[Germany]], [[Italy]], the Netherlands, [[Spain]], [[Sweden]], Switzerland, the [[United Kingdom]], (European Patent Register entry for European patent no. 0482154, asked May 16, 1991, given June 22, 1994 and stopped working on May 16, 2011), the United States (U.S. patent 5,214,703, given May 25, 1993 and stopped working January 7, 2012) and Japan (JP 3225440, stopped working on May 16, 2011).

MediaCrypt AG has made a successor to IDEA and focuses on its new cipher (official release in May 2005) IDEA NXT, which was before this named FOX.

== International Data Encryption Algorithm Media ==
<gallery widths='160px' heights='100%' mode='traditional' caption=''>
File:International Data Encryption Algorithm InfoBox Diagram Output Trans.png|International Data Encryption Algorithm InfoBox Diagram Output Trans
</gallery>
== References ==
<references/>
* [[Joan Daemen|J. Daemen]], R. Govaerts, and [[Joos Vandewalle|J. Vandewalle]], [http://www.cosic.esat.kuleuven.ac.be/publications/article-140.pdf Weak keys for IDEA] {{Webarchive|url=https://web.archive.org/web/20060621204124/http://www.cosic.esat.kuleuven.ac.be/publications/article-140.pdf |date=2006-06-21 }}, [[CRYPTO]] '93. pp224–231.
* Hüseyin Demirci, Erkan Türe, Ali Aydin Selçuk, A New Meet in the Middle Attack on The IDEA Block Cipher, 10th Annual Workshop on [[Selected Areas in Cryptography]], 2004.
* Xuejia Lai and James L. Massey, A Proposal for a New Block Encryption Standard, [[EUROCRYPT]] 1990, pp389–404
* Xuejia Lai and James L. Massey and S. Murphy, Markov ciphers and differential cryptanalysis, ''Advances in Cryptology — Eurocrypt <nowiki>'</nowiki>91'', Springer-Verlag (1992), pp17–38.
* [[Eli Biham]], Orr Dunkelman, Nathan Keller, A New Attack on 6-round IDEA, Fast [[Software]] Encryption Workshop, 2007.
== Other websites ==
* [http://www.rsasecurity.com/rsalabs/node.asp?id=2254 RSA FAQ on Block Ciphers] {{Webarchive|url=https://web.archive.org/web/20041019102316/http://www.rsasecurity.com/rsalabs/node.asp?id=2254 |date=2004-10-19 }}
* [http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html#IDEA SCAN entry for IDEA]
* [http://cypherspace.org/adam/rsa/idea.html IDEA in 448 bytes of 80x86]
* [http://www.informationsuebertragung.ch/indexAlgorithmen.html IDEA Applet]

[[Category:Cryptography]]