International Data Encryption Algorithm

IDEA

An encryption round of IDEA
General
Designers	Xuejia Lai and James Massey
Derived from	PES
Successors	MMB, MESH, Akelarre, IDEA NXT (FOX)
Cipher detail
Key sizes	128 bits
Block sizes	64 bits
Structure	Lai–Massey scheme
Rounds	8.5
Best public cryptanalysis
The key can be recovered with a computational complexity of 2 using narrow bicliques. This attack is computationally faster than a full brute-force attack, though not, as of 2013, computationally feasible.

In cryptography, the International Data Encryption Algorithm (IDEA), originally called Improved Proposed Encryption Standard (IPES), is a symmetric-key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and was first described in 1991. The algorithm was intended as a replacement for the Data Encryption Standard (DES). IDEA is a minor revision of an earlier cipher, the Proposed Encryption Standard (PES).

The cipher was designed under a research contract with the Hasler Foundation, which became part of Ascom-Tech AG. The cipher was patented in a number of countries but was freely available for non-commercial use. The name "IDEA" is also a trademark. The last patents expired in 2012, and IDEA is now patent-free and thus completely free for all uses.

IDEA was used in Pretty Good Privacy (PGP) v2.0 and was incorporated after the original cipher used in v1.0, BassOmatic, was found to be insecure. IDEA is an optional algorithm in the OpenPGP standard.