Failure of A Mix Network

TL;DR

This paper critically analyzes Wikstrom's mix network, revealing fundamental flaws in correctness, privacy, and soundness, and demonstrates that fixing these issues is either impractical or impossible, raising concerns about its security claims.

Contribution

It provides a formal proof that Wikstrom's shuffling scheme cannot be sound in practice, highlighting critical security vulnerabilities.

Findings

Wikstrom's mix network fails in correctness, privacy, and soundness.

Proposes modifications to fix correctness and privacy issues.

Shows that soundness cannot be practically fixed, exposing security risks.

Abstract

A mix network by Wikstrom fails in correctness, provable privacy and soundness. Its claimed advantages in security and efficiency are compromised. The analysis in this paper illustrates that although the first two failures may be fixed by modifying the shuffling protocol, the last one is too serious to fix at a tolerable cost. Especially, an attack is proposed to show how easily soundness of the shuffling scheme can be compromised. Moreover, the most surprising discovery in this paper is that it is formally illustrated that in practice it is impossible to fix soundness of the shuffling scheme by Wikstrom.