MV3: A new word based stream cipher using rapid mixing and revolving buffers

TL;DR

MV3 is a novel word-based stream cipher that employs rapid mixing of random walks and revolving buffers to achieve fast encryption with strong security features suitable for long data streams.

Contribution

It introduces a new word-based cipher design using nonlinear random walks and revolving buffers, addressing scaling issues and enhancing security over previous byte-based ciphers.

Findings

Runs at less than 5 cycles per byte on Pentium IV

Provides negligible long-term statistical correlations

Security estimated close to exhaustive search for keys under 256 bits

Abstract

MV3 is a new word based stream cipher for encrypting long streams of data. A direct adaptation of a byte based cipher such as RC4 into a 32- or 64-bit word version will obviously need vast amounts of memory. This scaling issue necessitates a look for new components and principles, as well as mathematical analysis to justify their use. Our approach, like RC4's, is based on rapidly mixing random walks on directed graphs (that is, walks which reach a random state quickly, from any starting point). We begin with some well understood walks, and then introduce nonlinearity in their steps in order to improve security and show long term statistical correlations are negligible. To minimize the short term correlations, as well as to deter attacks using equations involving successive outputs, we provide a method for sequencing the outputs derived from the walk using three revolving buffers. The cipher is fast -- it runs at a speed of less than 5 cycles per byte on a Pentium IV processor. A word based cipher needs to output more bits per step, which exposes more correlations for attacks. Moreover we seek simplicity of construction and transparent analysis. To meet these requirements, we use a larger state and claim security corresponding to only a fraction of it. Our design is for an adequately secure word-based cipher; our very preliminary estimate puts the security close to exhaustive search for keys of size < 256 bits.