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Encyclopedia > International Data Encryption Algorithm
An encryption round of IDEA
Designer(s): James Massey, Xuejia Lai
First published: 1991
Derived from: PES
Successor(s): MESH, Akelarre,
Key size(s): 128 bits
Block size(s): 64 bits
Structure: Substitution-permutation network
Rounds: 8.5
Best public cryptanalysis:
A collision attack requiring 224 chosen plaintexts breaks 5 rounds with a complexity of 2126 (Demirci et al, 2003).

In cryptography, the International Data Encryption Algorithm (IDEA) is a block cipher designed by Xuejia Lai (來學嘉) and James L. Massey of ETH Zurich and was first described in 1991. The algorithm was intended as a replacement for the Data Encryption Standard. IDEA is a minor revision of an earlier cipher, PES (Proposed Encryption Standard); IDEA was originally called IPES (Improved PES). Image File history File links Download high resolution version (640x658, 56 KB)Original diagram for Wikipedia File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... In cryptography, MESH is a block cipher designed in 2002 by Jorge Nakahara, Jr. ... Akelarre can mean: a place in Navarre, Spain that gave its name to the meeting places of witches: see Akelarre, Navarre a block cipher: see Akelarre (cipher) This is a disambiguation page: a list of articles associated with the same title. ... In cryptography, the IDEA NXT algorithm (previously known as FOX) is a block cipher designed by Pascal Junod and Serge Vaudenay of EPFL (Lausanne, Switzerland). ... In cryptography, the key size (alternatively key length) is a measure of the number of possible keys which can be used in a cipher. ... In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. ... In cryptography, an SP-network, or substitution-permutation network (SPN), is a series of linked mathematical operations used in block cipher algorithms such as AES. These networks consist of S-boxes and P-boxes that transform blocks of input bits into output bits. ... Cryptanalysis (from the Greek kryptós, hidden, and analýein, to loosen or to untie) is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. ... A chosen plaintext attack is any form of cryptanalysis which presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the corresponding ciphertexts. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and γράφειν gráfein to write) is the study of message secrecy. ... Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... The ETH Zurich, often called Swiss Federal Institute of Technology, is a science and technology university in the city of Zurich, Switzerland. ... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... This article is about algorithms for encryption and decryption. ...

The cipher was designed under a research contract with the Hasler Foundation, which became part of Ascom-Tech AG. The cipher is patented in a number of countries but is freely available for non-commercial use. The name "IDEA" is also a trademark. The patents will expire in 2010–2011. Today, IDEA is licensed worldwide by MediaCrypt. A trademark, trade mark, â„¢ or ®[1] is a distinctive sign of some kind which is used by an organization to uniquely identify itself and its products and services to consumers, and to distinguish the organization and its products or services from those of other organizations. ... A patent is a set of exclusive rights granted by a state to a patentee (the inventor or assignee) for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which...

IDEA was used in Pretty Good Privacy (PGP) V2.0, and was incorporated after the original cipher used in v1.0 ("Bass-O-Matic") was found to be insecure. It is an optional algorithm in OpenPGP. PGP Encryption (Pretty Good Privacy) is a computer program which provides cryptographic privacy and authentication. ... An Open Specification for Pretty Good Privacy (openpgp) OpenPGP is defined by the OpenPGP Working Group of the Internet Engineering Task Force (IETF) Proposed Standard RFC 2440. ...



IDEA operates on 64-bit blocks using a 128-bit key, and consists of a series of eight identical transformations (a round, see the illustration) and an output transformation (the half-round). The processes for encryption and decryption are similar. IDEA derives much of its security by interleaving operations from different groupsmodular addition and multiplication, and bitwise eXclusive OR (XOR) — which are algebraically "incompatible" in some sense. In more detail, these operators, which all deal with 16-bit quantities, are: In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. ... A key is a piece of information that controls the operation of a cryptography algorithm. ... In mathematics, a group is a set, together with a binary operation, such as multiplication or addition, satisfying certain axioms, detailed below. ... Modular arithmetic (sometimes called modulo arithmetic) is a system of arithmetic for integers, where numbers wrap around after they reach a certain value — the modulus. ... Exclusive disjunction (usual symbol xor) is a logical operator that results in true if one of the operands (not both) is true. ...

  • Bitwise eXclusive OR (denoted with a blue ⊕).
  • Addition modulo 216 (denoted with a green boxplus).
  • Multiplication modulo 216+1, where the all-zero word (0x0000) is interpreted as 216 (denoted by a red odot).

After the eight rounds have been completed the logic of the output transformation shown below: Exclusive disjunction (usual symbol xor) is a logical operator that results in true if one of the operands (not both) is true. ... a LaTeX boxplus File links The following pages link to this file: International Data Encryption Algorithm MD5 Categories: User-created public domain images ... Image File history File links a LaTeX odot File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

Image:International_Data_Encryption_Algorithm_InfoBox_Diagram_Output_Trans.png Image File history File links International_Data_Encryption_Algorithm_InfoBox_Diagram_Output_Trans. ...


The designers analysed IDEA to measure its strength against differential cryptanalysis and concluded that it is immune under certain assumptions. No successful linear or algebraic weaknesses have been reported. Some classes of weak keys have been found — E.g. (Daemen et al, 1994) — but these are of little concern in practice, being so rare as to be unnecessary to avoid explicitly. As of 2004, the best attack which applies to all keys can break IDEA reduced to 5 rounds (the full IDEA cipher uses 8.5 rounds) (Demirci et al, 2003). Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. ... In cryptography, linear cryptanalysis is a general form of cryptanalysis based on finding affine approximations to the action of a cipher. ... In cryptography, a weak key is a key which when used with a specific cipher, makes the cipher behave in some undesirable way. ... 2004 is a leap year starting on Thursday of the Gregorian calendar. ...

IDEA is patented in Austria, France, Germany, Italy, Netherlands, Spain, Sweden, Switzerland, United Kingdom, (European patent EP-B-0482154), the United States (US patent #5,214,703) and Japan (JP 3225440).

MediaCrypt is now also offering a successor to IDEA and focuses on its new cipher (official release on May 2005) IDEA NXT, which was previously called FOX. In cryptography, the IDEA NXT algorithm (previously known as FOX) is a block cipher designed by Pascal Junod and Serge Vaudenay of EPFL (Lausanne, Switzerland). ...


  • J. Daemen, R. Govaerts, and J. Vandewalle, Weak keys for IDEA, 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, 2003.
  • 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 '91, Springer-Verlag (1992), pp17–38.

Joan Daemen (born 1965) is a Belgian cryptographer and one of the designers of Rijndael, the Advanced Encryption Standard (AES), together with Vincent Rijmen. ...

External links

  • RSA FAQ on Block Ciphers
  • Mediacrypt homepage — IDEA licensor
  • SCAN entry for IDEA
  • Helger Lipmaa's links for IDEA
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  Results from FactBites:
IDEA (International Data Encryption Algorithm) (843 words)
IDEA, unlike the other block cipher algorithms discussed in this section, is patented by the Swiss firm of Ascom.
In IDEA, for purposes of multiplication, a 16 bit word containing all zeroes is considered to represent the number 65,536; other numbers are represented in conventional unsigned notation, and multiplication is modulo the prime number 65,537.
Those that are multiplied in are replaced by their multiplicative inverse, modulo 65,537, in IDEA notation when used to change blocks directly, but those used to calculate the cross-footed F-functions are not changed.
data encryption. The Columbia Encyclopedia, Sixth Edition. 2001-05 (520 words)
Until 1976 the algorithms were symmetric, that is, the key used to encrypt the plaintext was the same as the key used to decrypt the ciphertext.
This algorithm requires two keys, an unguarded public key used to encrypt the plaintext and a guarded private key used for decryption of the ciphertext; the two keys are mathematically related but cannot be deduced from one another.
Data encryption is regarded by the U.S. government as a national-security issue because it can interfere with intelligence gathering—therefore, it is subject to export controls, which in turn make it difficult for U.S. companies to function competitively in the international marketplace.
  More results at FactBites »



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