Mix Transport Implementation: Progress and Challenges

[AkshayaMani]

This PR introduces some updates to the Mix transport implementation. However, there are some unique challenges posed by the Mix transport.

Implemented Changes

• Updated switch creation with full multiaddress, including /mix/.
• Modified MixnetTransportAdapter to listen and dial on full addresses.

Key Challenges

• Unlike other transports, the Mix transport establishes only a logical connection (no real physical connection) when dialing a destination.
• Mix nodes are randomly selected per message at send time. This differs from establishing fixed routes at connection time.
• Modifying the write function of the logical connection to dial a mix node would require using the MixnetTransportAdapter's dial function. This approach risks creating undesirable tight coupling between transport and connection layers.
• Need to implement embedding the destination address in the Sphinx packet.

Next Steps

• Given these challenges, we may need to reconsider our approach to integrating Mix Transport.
• Need some inputs on how to best address these issues while maintaining the integrity and flexibility of the libp2p framework.

[AkshayaMani]

Significant progress has been made in the Mix transport implementation, addressing many of the initial challenges outlined in the previous discussion. Here’s a detailed update since last week:

Implemented Changes

Logical Connection Establishment

• Introduced MixnetLogicalConnection to represent the logical connection created at dial time

Message Routing and Sphinx Integration

• Developed mixDialer within MixnetTransportAdapter for per-message routing, ensuring that we maintain a clear separation between the connection and transport layers
• Integrated Sphinx packet creation
• Enhanced acceptWithMixnet to process incoming Sphinx packets

Generic Upgrades and Error Handling

• Removed unnecessary files (anon_muxer.nim, muxer.nim, upgrade.nim)
• Updated poc_ping to utilize generic upgrade
• Improved error handling in functions like multiAddrToBytes
• Added utility function unpadMessage with corresponding tests

Key Challenges Addressed

• Implemented logical connection for the Mix transport while maintaining libp2p framework compatibility
• Achieved per-message routing with mixDialer, effectively avoiding tight coupling between transport and connection layers

Next Steps

• Develop custom connection type for physical connections at exit nodes
• Conduct end-to-end testing of one-way ping functionality
• Incorporate Single-Use Reply Blocks (SURBs) into Sphinx packet creation for Ping response

[AkshayaMani]

Since last week, the following changes have been implemented:

• Fixed mixDialer Call: Resolved issues with the mixDialer invocation in MixLogicalConnection.

• Removed mixDialer Field: Eliminated the mixDialer callback field from MixnetTransportAdapter and passed it as a parameter to MixLogicalConnection.

• Implemented MixPhysicalConnection: For the message handling at the exit.

• Enhanced Error Handling in sendThroughMixnet:

  • Added checks for insufficient nodes (less than L).
  • Implemented handling for potential divide-by-zero error in cryptoRandomInt.

• Adapted ping_poc for Generic Node Count:

  • Corrected the switch creation process to ensure all necessary files are written before switches are instantiated.
  • Included logic to properly stop switches and clean up node info folders.

Next Steps

• Review PR #10: Ensure that the proposed changes align with the proposed changes on custom upgrade bellow.

• Implement Custom Upgrade: To handle and pass the end protocol codec to sendThroughMixnet, as well as from the previous hop to the exit. This will ensure proper end protocol handling.

• Complete Accept with Mixnet: Wrap connection and return MixPhysicalConnection.

• Test End-to-End Functionality of Ping without Response

These next steps will help complete the transport and test it end-to-end.