The International Data Encryption Algorithm (IDEA) is a data encryption algorithm, which is internationally available. It operates on 64-bit plaintext block with a 128 bit key. The same algorithm is used for encryption and decryption (like DES), and it is considered by many to be superior to DES, and to have a much cooler-sounding name.

The 64 bit input block is divided into four 16 bit blocks: X1, X2, X3, and X4 which become the input blocks to the first round of the algorithm. In each of the eight total rounds, the four sub-blocks are XORed, added, and multiplied with one another and with six 16 bit sub-blocks of key material. Between each round the second and third sub-blocks are swapped.

Software implementation speeds are comparable with those for DES; Hardware implementations are fractionally faster.

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