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IDEA (previous name IPES) is a 64-bit, 8.5-round non-Feistel block cipher with 128-bit keys, proposed by Lai and Massey in 1991 [12]. It is a modified version of a previous design called PES (Proposed Encryption Standard) by the same authors [11], with added strength against differential cryptanalysis. The key-schedule of the cipher is completely linear. The main idea behind the design is the mix of non-commuting group operations: addition mod 216 (denoted by ⊞), XOR (denoted by ⊕), multiplication \(\bmod (2^{16}-1)\) (denoted by ⊙, with \(0\equiv 2^{16}\)). These operations work with 16-bit words. One round of IDEA is split into two different half-round operations: key mixing (denoted by T) and M-mixing denoted by \(M = s\circ MA\), where MA denotes a multiplication–addition structure and s denotes a swap of two middle words.Footnote 1 T divides the 64-bit block into four 16-bit words X 1,X 2,X 3,X 4 and mixes the key words Z 1,Z 2,Z 3,Z 4 with the data using ⊙ and ⊞:

The transform MA...

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Notes

  1. 1.

    As usual the composition of transformations is applied from right to left, i.e., MA is applied first, and the swap s is applied to the result.

References

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© 2005 International Federation for Information Processing

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Biryukov, A. (2005). IDEA. In: van Tilborg, H.C.A. (eds) Encyclopedia of Cryptography and Security. Springer, Boston, MA . https://doi.org/10.1007/0-387-23483-7_190

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