The Free On-line Dictionary of Computing (30 December 2018):

International Data Encryption Algorithm

    (IDEA) A conventional encryption
   algorithm, written by Xuejia Lai and James Massey, in 1992.

   It is a block cipher, considered to be the best and most
   secure available, and operates on 64-bit blocks with a 128 bit
   key.

   It is used by Pretty Good Privacy.

   (1996-03-07)