International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Qi Da

Publications

Year
Venue
Title
2023
TOSC
Chosen-Key Secure Even-Mansour Cipher from a Single Permutation
At EUROCRYPT 2015, Cogliati and Seurin proved that the 4-round Iterated Even-Mansour (IEM) cipher with Independent random Permutations and no key schedule EMIP4(k, u) = k⊕p4 ( k⊕p3 ( k⊕p2 (k⊕p1 (k⊕u)))) is sequentially indifferentiable from an ideal cipher, which implies chosen-key security in the sense of correlation intractability. In practice, however, blockciphers such as the AES typically employ the same permutation at each round. To bridge the gap, we prove that the 4-round IEM cipher EMSP[φ]p4 (k, u) = k4⊕p (k3⊕p (k2⊕p(k1⊕p(k0⊕u)))), whose round keys ki = φi(k) are derived using an affine permutation φ : {0, 1}n → {0, 1}n with certain properties, is sequentially indifferentiable from an ideal cipher. The function φ can be a linear orthomorphism, or φ(k) := k≫a for some fixed integer a using cyclic shift. To our knowledge, this is the first indifferentiability-type result for blockciphers using identical round functions.

Coauthors

Qi Da (1)
Chun Guo (1)
Shanjie Xu (1)