International data encryption algorithm(IDEA) was used in Pretty Good Privacy (PGP) v2.0 and was incorporated after the original cipher used inv1.0, Bassomatic, was found to be insecure.
IDEA is an optional algorithm in the Open PGP standard. PGP encrypts data by using a block cipher called international data encryption algorithm
IDEA operates on 64-bit blocks using a 128-bit key and consists of a series of 8 identical transformations (a round, see the illustration) and an output transformation (the half-round).The processes for encryption and decryption are similar.