OmniSphinx: Active Mix Networks (Extended Version)

2026-08-13

AI Summary

Existing mix networks suffer from protocol-specific packet formats that are mutually incompatible, necessitating separate infrastructure deployments for each protocol and thereby hindering the unification and scalability of anonymous communication systems. This work proposes OmniSphinx, a universal mix packet format supporting active processing, which for the first time enables a single deployment to dynamically emulate arbitrary mix protocols by embedding executable logic directly within packets. The design integrates a programmable packet header with an interpretation mechanism, leveraging semantic models derived from protocols such as Sphinx to achieve runtime multi-protocol compatibility. Experimental evaluation demonstrates that OmniSphinx incurs only modest overhead: compared to native Sphinx, it introduces approximately 90 microseconds of additional computational latency and a 33% increase in header size.

Abstract

Mix networks are an important tool to implement anonymous communication, which protects not just the content but also the metadata of messages. Over time, various packet formats for mix networks have been proposed, usually with single, specific goals in mind. These formats are incompatible with each other, requiring separate software and infrastructure to be set up. In this paper, we propose a new format, OmniSphinx, which solves this issue. In OmniSphinx, senders embed code in their packets that determines how they must be processed. The resulting active mix network can emulate any other mix format within a single deployment. Our empirical evaluation shows that emulation in OmniSphinx incurs reasonable overhead compared to native execution for typical mix network use cases: For Sphinx, the most compact format, computation time increases by around 90μs, while headers increase by 33% in size.

Problem

• mix networks
• packet formats
• incompatibility
• anonymous communication
• metadata protection

Innovation

• OmniSphinx
• Active Mix Networks
• Anonymous Communication
• Packet Format Interoperability
• Metadata Protection