International Data Encryption Algorithm (IDEA) is a symmetric cypher algorithm used to encrypt and decrypt data. A key (which must be randomly chosen) is used to encrypt the data, and that same secret key is needed for decrypting the data again.
IDEA is the second version of a block cipher designed by Xuejia Lai and James L. Massey of ETH-Zürich. RSA Security [1] describes it this way:
- [IDEA] is a 64-bit iterative block cipher with a 128-bit key. The encryption process requires eight complex rounds. Decryption is carried out in the same manner as encryption once the decryption subkeys have been calculated from the encryption subkeys. The cipher structure was designed to be easily implemented in both software and hardware, and the security of IDEA relies on the use of three incompatible types of arithmetic operations on 16-bit words. However some of the arithmetic operations used in IDEA are not that fast in software. As a result the speed of IDEA in software is similar to that of DES. [1]
IDEA encryption is somewhat faster and generally considered to be more secure than DES encryption. But IDEA is newer and therefore has not been as extensively tested, and it is patented which restricts its commercial use. The patent will expire in 2011.
Further Reading
[LM92] X. Lai, J.L. Massey and S. Murphy, Markov ciphers and differential cryptanalysis, Advances in Cryptology - Eurocrypt '91, Springer-Verlag (1992), 17-38.
[DGV94] J. Daemen, R. Govaerts, and J. Vandewalle, Weak keys for IDEA, Advances in Cryptology - Crypto '93, Springer-Verlag (1994), 224-231.