1. IDEA is a symmetric block cipher algorithm. It is popular because it is used in PGP, but due to commercial licensing issues, it is not popular elsewhere. Controversy: IDEA is one of the few (widely-used) ciphers protected by patents; it requires a license for commercial use. PGP is no longer using IDEA as its default cipher because of this. Notes: It was developed by Xuejia Lai and James L. Massey. It uses 128-bit keys. There is no known way to break it other than brute-force. It was published in 1990. Its patents are held by the Swiss company "Ascom-Tech AG". Misconception: The name implies that IDEA is some sort of official standard -- it isn't. However, it is is widely used, and is an option on many standards. Applications: PGP From Hacking-Lexicon