E2

In cryptography, E2 is a block cipher which was created in 1998 by NTT and submitted to the AES competition.

Like other AES candidates, E2 operates on blocks of 128 bits, using a key of 128, 192, or 256 bits. It uses a 12-round Feistel network. E2 has an input transformation and output transformation that both use modular multiplication, but the round function itself consists only of XORs and S-box lookups. The single 8×8-bit S-box is constructed from the composition of an affine transformation with the discrete exponentiation x¹²⁷ over the finite field GF(2⁸). NTT adopted many of E2's special characteristics in Camellia, which has essentially replaced E2.

There has been no published cryptanalysis of the full E2, but removing the input and output transformations and reducing to 8 rounds leaves a variant that is vulnerable to truncated differential cryptanalysis.

References

• M. Matsui, T. Tokita (March 1999). "Cryptanalysis of a Reduced Version of the Block Cipher E2" (PDF). 6th International Workshop on Fast Software Encryption (FSE 1999). Rome: Springer-Verlag. pp. pp.71–80. 

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