1 research outputs found
Minimizing the Two-Round Tweakable Even-Mansour Cipher
In CRYPTO 2015, Cogliati et al. have proposed one-round tweakable Even-Mansour (\textsf{1-TEM}) cipher constructed out of a single -bit public permutation and a uniform and almost XOR-universal hash function \textsf{H} as , where is the tweak, and is the -bit message. Authors have shown that its two-round extension, which we refer to as \textsf{2-TEM}, obtained by cascading -independent instances of the construction gives -bit security and -round cascading gives -bit security. In ASIACRYPT 2015, Cogliati and Seurin have shown that four-round tweakable Even-Mansour cipher, which we refer to as \textsf{4-TEM}, constructed out of four independent -bit permutations and two independent -bit keys , defined as is secure upto adversarial queries. In this paper, we have shown that if we replace two independent permutations of \textsf{2-TEM} (Cogliati et al., CRYPTO 2015) with a single -bit public permutation, then the resultant construction still guarrantees security upto adversarial queries. Using the results derived therein, we also show that replacing the permutation with in the above equation preserves security upto adversarial queries