The goal of mixnets is to solve the problem of metadata privacy. In other words, they ensure that anonymity is preserved during user communication within the transport layer (TCP/IP). Transport-layer data can re-identify perfectly anonymous users in the application layer. These metadata include IP addresses, timestamps, etc.
Mixnets are an intermediary network that user A uses to communicate with user B to protect their anonymity. The role of mixnets is to hide user A and user B's metadata.
The most widely used and mature mixnet is Tor.
Advantages
- Mixnets are fundamental to providing metadata privacy. Without metadata privacy, no credible anonymity is possible on the application layer.
Limitations
- By communicating through a third-party network instead of directly with each other, the performance of this communication is affected (especially the latency).
- Mixnet exit nodes are publicly known, may have to bear legal responsibility for the content they distribute, and can be blocked by internet or service providers.
- Tor faces multiple challenges:
- With enough effort, an attacker can re-identify Tor packets by measuring their size and timing patterns.
- Running a Tor node is purely voluntary. However, the more people run Tor nodes, the higher the anonymity guarantees, and the more performant the network becomes.
- The above limitations of the Tor Network are being addressed by innovative upcoming mixnets, such as HOPR and NYM. They both create an incentive layer on top of the communication network that compensates the node runners while improving the anonymity guarantees.
Could it be useful for our requirements?
- Yes, it is crucial to preserve user anonymity. ZKP provides application-level anonymity, while mixnets provide transport-level anonymity.