Sign Bidirectional Flow

The Sign Bidirectional flow enables cross-chain transaction execution with verified response callbacks. It allows a source chain contract to execute a transaction on a destination chain and receive the execution result back on-chain with cryptographic proof.

For example, a Solana program can execute a transaction on Ethereum and receive the contract return value or success/failure status back on Solana—all verified by the MPC network.

Comprehensive Documentation: For detailed documentation including request ID generation, serialization schemas, response verification, error handling, and security considerations, see the Signet Solana Program Rust Docs.

Supported Chains

Overview

The bidirectional flow enables a source chain contract to:

1. Request a signature for a destination chain transaction
2. Broadcast the signed transaction to the destination chain
3. Receive the execution result (contract return value or success/failure) back on the source chain

User                   Source Chain              MPC               Destination Chain
  │                         │                        │                        │
  │ sign_bidirectional()    │                        │                        │
  ├────────────────────────►│                        │                        │
  │                         │ SignBidirectionalEvent │                        │
  │                         ├───────────────────────►│ Sign & store           │
  │                         │◄───── respond() ───────┤                        │
  │ Poll signature          │                        │                        │
  │◄─ SignatureRespondedEvent                        │                        │
  │                         │                        │                        │
  │ Broadcast ──────────────┼────────────────────────┼───────────────────────►│
  │                         │                        │◄──── Observe tx ───────┤
  │                         │◄─ respond_bidirectional()                       │
  │ Poll response           │                        │                        │
  │◄─ RespondBidirectionalEvent                      │                        │
  │                         │                        │                        │

Flow Steps

1. Sign Request: User calls sign_bidirectional with a serialized unsigned transaction for the destination chain
2. Signature Delivery: MPC signs the transaction and returns the signature via respond()
3. User Broadcast: User assembles and broadcasts the signed transaction to the destination chain
4. Observation: MPC Indexer (using a light client) observes the destination chain and detects confirmation
5. Output Extraction: MPC extracts execution result (contract return value or transfer success)
6. Response Callback: MPC calls respond_bidirectional with the result and a cryptographic proof. The RespondBidirectional event is indexed and sent to processing on the source chain contract

Related Documentation

• Signet Solana Program Rust Docs - Complete reference (instructions, events, types, security)
• Chain Signatures Contract - Contract interface