What is cMix?

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All messaging between users in the xx network is sent through cMix, a [mixed network (mixnet)] anonymous communications protocol. The cMix protocol offers protection for each xx Messenger user's metadata—the who, what, when, where, and how details of any message or activity—giving them unparalleled privacy guarantees. These guarantees include unlinkability of sender and receiver, and resistance to many traffic-analysis attacks that undermine many other approaches found in onion routing, proxies, and other mixnets.

On the web and other online platforms users are surveilled everywhere they go, but the services built on cMix respect user privacy by default because the users cannot be tracked. With xx cMix, all transactions are mixed together in batches or “anonymity sets” and processed together, thereby shredding all metadata and preventing third parties from analyzing activity patterns and connecting senders to receivers. The cMix protocol provides unprecedented consumer protections by eliminating the risk posed by perverse economic incentives to correlate all of the online and offline behaviors of their users.  Using xx cMix allows users to interact and transact free from such abuse, avoiding the harms caused by privacy violations from centralized entities.

Unlike many other anonymous communications systems and mixnets, cMix aims to be secure against a global adversary that controls and monitors the internet. This design goal protects users from abuse and manipulation by foreign governments and their internet service providers. It also prevents discrimination of users based on their geographic locations.

Whereas other mixnet designs suffer from high latency in part because of the need for real-time public-key operations, cMix—through a precomputation—eliminates all expensive realtime public-key operations at the senders, recipients, and nodes. Precomputation decreases real-time cryptographic latency and lowers computational costs for clients, greatly improving the real-time performance of cMix that performs only a few fast modular multiplications. Consequently, cMix is the first mixing suitable for low latency chat for lightweight devices.

The xx cMix protocol provides the base for anonymous communication, but there are many other protocols built on top of it to provide a seamless user experience inside the xx Messenger:

  • End-to-End Encryption (E2EE)
  • User Discovery
  • Anonymous Message Return
  • Insert others here

Other Resources

  • cMix Whitepaper
  • cMix Technical paper