Linear Analysis of Reduced-Round CubeHash

Abstract. Recent developments in the field of cryptanalysis of hash functions has inspired NIST to announce a competition for selecting a new cryptographic hash function to join the SHA family of standards. One of the 14 second-round candidates is CubeHash designed by Daniel J. Bernstein. CubeHash is a unique hash function in the sense that it does not iterate a common compression function, and offers a structure which resembles a sponge function, even though it is not exactly a sponge function. In this paper we analyze reduced-round variants of CubeHash where the adversary controls the full 1024-bit input to reduced-round CubeHash and can observe its full output. We show that linear approximations with high biases exist in reduced-round variants. For example, we present an 11-round linear approximation with bias of 2−235 , which allows distinguishing 11round CubeHash using about 2470 queries. We also discuss the extension of this distinguisher to 12 rounds using message modificat...

• Type: Journal
• Year: 2011
• Where: ACNS
• Authors: Tomer Ashur, Orr Dunkelman
• Keywords: ACNS 2011, Cryptographic Hash Function, Cryptology, Linear Approximations, Linear Cryptanalysis