As their name implies, “mixnodes” are the central nodes of the Nym “mixnet,” and as such, they are essential to the efficient operation of the overall Nym system. Before sending identically structured encrypted data packets, known as Sphinx packets, on to the final recipient of the original message, mixnodes “mix and relay these packets multiple times.”
In addition to describing how mixnodes specifically shield network traffic from prying eyes, this article will delve deeper into the work that mixnodes do and highlight some intriguing parameters that node operators can adjust to personalise their mixnode and provide more robust anonymity protections for various applications.
The Mixing
Mixnodes receive Sphinx packets from gateways, which provide as the interface between Nym clients and the mixnet, as depicted in the diagram above, travelling from left to right. Prior to sending the packets to the subsequent mixnodes and finally to a gateway, who will send the packets to the intended recipients, they mix these and reorder them by adding randomised per-packet delays.
The mixing makes it practically hard to identify who is speaking to whom because it defends against time-based correlation attacks and traffic analysis. In order to maintain a constant volume of network traffic, Mixnodes may additionally contribute “cover traffic,” which makes it even more difficult for observers to track data packets and offers “lost in the crowd” privacy.
Three unique layers of mixnodes make up the mixnet’s organisation. Before being sent to the proper gateway (the one connected to the recipient’s client) and forwarded to the recipient, where it will be encrypted, each packet will first be mixed by a mixnode on each layer. The sender’s Nym client chooses the route that packets go. Using the public keys of the three mixnodes that the message will be forwarded to during its route across the mixnet, the client encrypts the packet multiple times.
Reducing and increasing the mixnet
A number of the architecture’s more structural features, which guarantee a sufficient scale of the mixnet and good mixing quality, also contribute to unlinkability.
First off, the mixnet has discrete time intervals known as epochs, during which a specific network size and configuration are defined (at the moment, they are configured to last an hour). As a result, the network’s configuration and size can change.
The ‘active set’, or predetermined number of mixnodes, will mix and route data packets via the mixnet layers. Other mixnodes will be sitting idle in the interim, waiting to maybe be chosen as active in the upcoming epoch. As a result, the network can expand and contract to meet demand and keep capacity in reserve while ensuring resource efficiency.
Additionally, epochs enable the network to periodically reconfigure, varying the total number of mixnodes per layer and the mixnodes that are assigned to each layer. This enables the network to maintain the general health of the network by removing underperforming or “dead” nodes that have (for example) gone offline in the previous epoch.
Mixnode incentives
Which takes us to the financial incentive used by mixnode operators to participate in the mixnet: network incentives. To be a part of the network, Mixnodes must stake their NYM tokens. Their likelihood of being chosen to be a part of the active set for that period will depend on the quantity of stake.
Anyone else who has NYM tokens can also assign stake to the mixnode, boosting its likelihood of selection by raising their aggregate stake, and receive a portion of the profits in exchange. People will be more willing to bet on well-performing nodes since they will then be more likely to earn a bigger share of rewards. This functions as a form of reputation assuring strong Quality of Service.
Mixnodes can set themselves apart from other nodes by creating profiles on the Nym mixnet explorer in order to draw in more stake and gain more rewards. They can do this both implicitly by raising their quality of service and openly by setting specific pricing parameters and adding any extras they see fit.
The aforementioned details demonstrate just how intricate mixnodes are, yet they are only one element of the Nym system!
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