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mpc-module.md

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MPC module

Multi Party Computation (MPC) module is a part of Sequencer node and is responsible for the management of the entire life-cycle of the multisignature keys. Conducts external operations such as:

  1. Multisig generation
  2. Key resharing
  3. Applying the signature
  4. Deletion of signature
  5. Provides support for the asynchronous usage of many multisignatures

Core method processing flow

keyGen process flow

Phase 1: Notifying MPC Nodes to Prepare

  • Generate a random sessionID locally;
  • Broadcast the keyGenPrepare message to all MPC nodes using the p2p network;
  • Upon receiving the keyGenPrepare message, each MPC node starts its processing goroutine;
  • Check the local data (the data means whether the TSS module has stored the mpc information corresponding to the id) based on the keyId;
  • If there is existing data in the READY state, return the data from storage directly. No need to proceed with the keyGen operation;
  • If there is existing data with a PENDING state, return an error to avoid inconsistencies in key generation due to concurrent execution of different key generation calls;
  • Establish a p2p communication channel;
  • Return the keyGenReady message to the initiating node;

Phase 2: Initiating the keyGen process

  • The initiating node waits to receive keyGenReady messages from all nodes;
  • Once the initiating node receives keyGenReady messages from all nodes, it broadcasts the keyGenStart message to all MPC nodes using the p2p network;
  • Upon receiving the keyGenStart message, each MPC node:
    • Constructs a LocalParty instance locally;
    • Begins receiving information from other nodes;

Additional processes flow

  • In essence, the processing flow of keySign is similar to keyGen, with the difference lying in some data transmission and verification..
  • On the other hand, keyDelete does not involve any TSS-lib operations. It only requires broadcasting the KeyDeleteMessage message to all nodes to request the deletion of the key.

TSS Library:

Threshold Signature Scheme Library - open-source multisig tool library and the main source of MPC logic:

  • Responsible for the multisig key algorithm layer

Key Local Storage:

  • Conducts the saving and encrypting the key’s info in the local kv storage (levelDB) provided by the corresponding node
  • The specific fields are described as follows:
    • keyId: The unique identifier of the multi-signature key pair. Passed in by the consensus layer caller, it is guaranteed that only one key pair can be generated for the same keyID;
    • keySsessionId: The session id when the key is generated (keyGen), randomly generated. The module will ensure that the value is different every time it is called;
    • data: Key storage data, generated by tss-lib. It mainly includes: public key (address), private key fragmentation, and all partyIds participating in multi-signature. The specific data is in tss-libkeygen.LocalPartySaveData;
    • status: The status of the current key data, mainly consists of three types:
      • PENDING (processing)
      • READY (already available)
      • ERROR (An error occurred during generation, the current key cannot be used to sign)

Tendermint channel:

Open-source p2p communication and consensus library provided by cosmos-sdk:

  • POS Node creates a separate Tendermint channel for communication messages between multiple p2p nodes during MPC operations

libp2p

ibp2p Is an open-source p2p network communication library

  • MPC uses libp2p inCommunication messages between multiple different p2p nodes, supporting information transmission during MPC operation