XCRUSH: A Family of ARX Block Ciphers

TL;DR

XCRUSH is a family of ARX block ciphers optimized for fast software implementation on modern 64-bit processors, achieving high diffusion with few rounds through data-dependent rotations, but without security claims.

Contribution

Introduces XCRUSH, a new ARX cipher family with a simple, efficient design leveraging data-dependent rotations for rapid diffusion in software.

Findings

Achieves near-total diffusion after two rounds.

Runs at approximately 7.3 cycles per byte on Intel Haswell.

Uses a pseudorandom generator for key scheduling.

Abstract

The XCRUSH family of non-Feistel, ARX block ciphers is designed to make efficient use of modern 64-bit general-purpose processors using a small number of encryption rounds which are simple to implement in software. The avalanche function, which applies one data-dependent, key-dependent rotation per 64-bit word of plaintext per round, allows XCRUSH to achieve an almost totally diffuse 256-bit block after just the first two rounds. Designed for speed in software, 3-round XCRUSH is measured at ~7.3 cycles/byte single-threaded on an Intel Haswell processor. A pseudorandom number generator, constructed using the avalanche function, serves as a key scheduling algorithm. No security claims are made in this paper.