International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

ByeongHak Lee

Publications

Year
Venue
Title
2018
ASIACRYPT
Tweakable Block Ciphers Secure Beyond the Birthday Bound in the Ideal Cipher Model
ByeongHak Lee Jooyoung Lee
We propose a new construction of tweakable block ciphers from standard block ciphers. Our construction, dubbed $$\mathsf {XHX2}$$, is the cascade of two independent $$\mathsf {XHX}$$ block ciphers, so it makes two calls to the underlying block cipher using tweak-dependent keys. We prove the security of $$\mathsf {XHX2}$$ up to $$\min \{2^{2(n+m)/3},2^{n+m/2}\}$$ queries (ignoring logarithmic factors) in the ideal cipher model, when the block cipher operates on n-bit blocks using m-bit keys. The $$\mathsf {XHX2}$$ tweakable block cipher is the first construction that achieves beyond-birthday-bound security with respect to the input size of the underlying block cipher in the ideal cipher model.

Coauthors

Jooyoung Lee (1)