What is the International Data Encryption Algorithm (IDEA)?
Q: What is the International Data Encryption Algorithm (IDEA)?
A: IDEA is a block cipher designed by Xuejia Lai and James Massey of ETH Zurich in 1991. It was meant to be a replacement for the Data Encryption Standard and contains a series of eight identical transformations (rounds) and one output transformation (the half-round).
Q: How does IDEA work?
A: IDEA operates on 64-bit blocks, using a 128-bit key. 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 interleaving operations from different groups — modular addition and multiplication, and bitwise 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 16-bit in length.
Q: Is IDEA patented?
A: Yes, it is patented in several countries but can be used by anyone for non-commercial use. The name "IDEA" is also trademarked, with patents expiring in 2010–2011. Today, it is licensed worldwide by MediaCrypt.
Q: Was IDEA used in Pretty Good Privacy (PGP)?
A: Yes, it was used in PGP v2 after BassOmatic - the cipher used in v1 - was found to be breakable. It can also be used with the OpenPGP standard today.
Q: Has any successful attack been reported against IDEA?
A: No successful linear or differential attacks have been reported against it yet; however some classes of weak keys have been found but these are so rare that they can easily be avoided when using the algorithm securely. As of 2007, the best attack which applies to all keys can break IDEA if reduced to 6 rounds (the full version uses 8).
Q: What did Bruce Schneier say about IDEA?
A: In 1996 he wrote that it was “the best and most secure block algorithm available” at that time; however by 1999 he no longer recommended it due to faster algorithms being available as well as some progress made into its cryptanalysis plus patent issues surrounding its use
