International Association
for Cryptologic Research

Alomair proposed a new authenticated encryption scheme OKH at ACNS 2012, and proved the security, i.e. authenticity and privacy, of OKH. Our research shows that it is not the case. We only need one query to break the authenticity of OKH with success probability of $1$, and two queries to break the privacy of OKH with success probability of $1-1/2^n$, where $n$ is the block-length of underlying blockcipher.