Paper 2016/008

cMix: Mixing with Minimal Real-Time Asymmetric Cryptographic Operations

David Chaum, Debajyoti Das, Farid Javani, Aniket Kate, Anna Krasnova, Joeri de Ruiter, and Alan T. Sherman


We introduce cMix, a new approach to anonymous communications. Through a precomputation, the core cMix protocol eliminates all expensive realtime public-key operations --- at the senders, recipients and mixnodes --- thereby decreasing real-time cryptographic latency and lowering computational costs for clients. The core real-time phase performs only a few fast modular multiplications. In these times of surveillance and extensive profiling there is a great need for an anonymous communication system that resists global attackers. One widely recognized solution to the challenge of traffic analysis is a mixnet, which anonymizes a batch of messages by sending the batch through a fixed cascade of mixnodes. Mixnets can offer excellent privacy guarantees, including unlinkability of sender and receiver, and resistance to many traffic-analysis attacks that undermine many other approaches including onion routing. Existing mixnet designs, however, suffer from high latency in part because of the need for real-time public-key operations. Precomputation greatly improves the real-time performance of cMix, while its fixed cascade of mixnodes yields the strong anonymity guarantees of mixnets. cMix is unique in not requiring any real-time public-key operations by users. Consequently, cMix is the first mixing suitable for low latency chat for lightweight devices. Our presentation includes a specification of cMix, security arguments, anonymity analysis, and a performance comparison with selected other approaches. We also give benchmarks from our prototype.

Note: Revised version of previous manuscript.

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Preprint. MINOR revision.
Anonymous communicationsmix networkscMixgroup-homomorphic encryptionPrivaTegrity
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das48 @ purdue edu
2018-03-21: last of 4 revisions
2016-01-06: received
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      author = {David Chaum and Debajyoti Das and Farid Javani and Aniket Kate and Anna Krasnova and Joeri de Ruiter and Alan T.  Sherman},
      title = {cMix: Mixing with Minimal Real-Time Asymmetric Cryptographic Operations},
      howpublished = {Cryptology ePrint Archive, Paper 2016/008},
      year = {2016},
      note = {\url{}},
      url = {}
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