Cross-Chain Bridge

Specifications: LP-6000 B-Chain Bridge | LP-6015 MPC Bridge Protocol | LP-6016 Teleport Protocol | LP-333 Dynamic Signer Rotation

Implementation: github.com/luxfi/node/vms/bridgevm | github.com/luxfi/node/vms/thresholdvm | github.com/luxfi/threshold

The LX bridge enables secure, quantum-safe cross-chain asset transfers through a dedicated B-Chain (Bridge Chain) using MPC threshold signatures.

Implementation Status

Component	Source	Specification	Status
BridgeVM (B-Chain)	`vms/bridgevm/`	LP-6000	Complete
ThresholdVM (T-Chain)	`vms/thresholdvm/`	LP-6015	Complete
LP-333 Signer Management	`vms/bridgevm/rpc.go`	LP-333	Complete
Threshold Crypto	`github.com/luxfi/threshold`	LP-6015	Complete
Ringtail Signatures	`vms/platformvm/warp/signature.go`	Warp 1.5	Complete
Teleport Protocol	`vms/platformvm/warp/teleport.go`	LP-6016	Complete
Bridge Contracts	`github.com/luxfi/standard`	LP-6000	Complete

Architecture Overview

The bridge operates through a dedicated B-Chain VM that coordinates with the T-Chain (ThresholdVM) for MPC operations:

                    Lux Network
+------------------------------------------------------------------+
|                                                                  |
|  +-------------+     +-------------+     +-------------+         |
|  |  B-Chain    |<--->|  T-Chain    |<--->|  Warp 1.5   |         |
|  |  BridgeVM   |     |  ThresholdVM|     |  Messaging  |         |
|  |             |     |             |     |             |         |
|  | - Signer    |     | - DKG       |     | - Ringtail  |         |
|  |   Set Mgmt  |     | - Reshare   |     | - ML-KEM    |         |
|  | - Bridge    |     | - Sign      |     | - Teleport  |         |
|  |   Requests  |     | - Refresh   |     |             |         |
|  +------+------+     +------+------+     +------+------+         |
|         |                   |                   |                |
|         +-------------------+-------------------+                |
|                             |                                    |
|                    CrossChainAppRequest                          |
+------------------------------------------------------------------+
                              |
        +---------------------+---------------------+
        |                     |                     |
   +----+----+           +----+----+           +----+----+
   | Ethereum|           | Bitcoin |           |  Cosmos |
   | Bridge  |           | Bridge  |           |   IBC   |
   | Contract|           | (MPC)   |           | Channel |
   +----+----+           +----+----+           +----+----+

Core Concepts

B-Chain (Bridge Chain)

The B-Chain is a purpose-built VM for cross-chain operations:

Signer Set Management: LP-333 opt-in model with 100 validator limit
Bridge Orchestration: Coordinates lock/mint/burn operations
Slashing: 100M LUX bond requirement with partial/full slashing

T-Chain (Threshold Chain)

The T-Chain provides MPC-as-a-service:

Distributed Key Generation (DKG): CGGMP21/LSS protocols
Threshold Signing: t-of-n signatures without key reconstruction
Key Resharing: Add/remove signers without changing public key

Warp 1.5 (Quantum-Safe Messaging)

Cross-chain messages use Warp 1.5 with quantum-safe primitives:

Ringtail Signatures: LWE-based threshold signatures (post-quantum)
ML-KEM Encryption: FIPS 203 key encapsulation for private transfers
Teleport Protocol: High-level abstraction for bridge operations

Bridge Flow

Source Chain                B-Chain                  T-Chain              Destination
+----------+              +---------+              +---------+            +----------+
|          |  1. Lock     |         |  2. Sign    |         |            |          |
| Lock TX  | -----------> | Bridge  | ----------> | MPC     |            |          |
|          |              | Request |  Request    | Keygen/ |            |          |
+----------+              |         |             | Sign    |            |          |
                          |         | <---------- |         |            |          |
                          |         |  3. Sig     +---------+            |          |
                          |         |                                    |          |
                          |         |  4. Warp Message (Ringtail)        |          |
                          |         | ---------------------------------> | Mint TX  |
                          +---------+                                    +----------+

Step-by-Step Process

Lock: User locks assets on source chain via bridge contract
Verify: B-Chain validators verify lock transaction
Sign: T-Chain signers produce threshold signature
Relay: Warp message with Ringtail signature sent to destination
Mint: Destination chain verifies signature and mints wrapped assets

Supported Chains

Chain	Protocol	Status	Assets
Lux Network	Native	Live	LUX, all DEX assets
Ethereum	Lock/Mint	Live	ETH, ERC-20
Arbitrum	Lock/Mint	Live	ARB, ERC-20
Optimism	Lock/Mint	Live	OP, ERC-20
Polygon	Lock/Mint	Live	MATIC, ERC-20
BNB Chain	Lock/Mint	Live	BNB, BEP-20
Bitcoin	MPC Custody	Live	BTC
Cosmos	IBC/Teleport	Beta	ATOM, IBC tokens
Solana	MPC Custody	Beta	SOL, SPL tokens

Quick Start

Bridge to Lux

import "github.com/luxfi/bridge/client"

// Create bridge client
bridge, err := client.NewBridgeClient(client.Config{
    Network:  "mainnet",
    Endpoint: "https://bridge.lux.network",
})
if err != nil {
    log.Fatal(err)
}

// Bridge ETH from Ethereum to Lux
transfer, err := bridge.TransferToLux(ctx, &client.TransferParams{
    SourceChain: "ethereum",
    Asset:       "ETH",
    Amount:      "1.5",
    Recipient:   "lux1qp2xqwh8j3...",
})
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Transfer ID: %s\n", transfer.ID)
fmt.Printf("Estimated time: %s\n", transfer.EstimatedTime)

Bridge from Lux

// Bridge wrapped ETH from Lux back to Ethereum
transfer, err := bridge.TransferFromLux(ctx, &client.TransferParams{
    DestChain:  "ethereum",
    Asset:      "wETH",
    Amount:     "1.5",
    Recipient:  "0x742d35Cc...",
})
if err != nil {
    log.Fatal(err)
}

// Wait for completion
result, err := transfer.Wait(ctx)
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Destination TX: %s\n", result.DestTxHash)

Security Model

Validator Requirements (LP-333)

100M LUX Bond: Slashable deposit (NOT staked rewards)
Opt-in Registration: First 100 validators accepted, then waitlist
Reshare on Removal Only: Epoch increments only when signer replaced

Threshold Security

2/3 Threshold: 67% of signers required for valid signature
No Single Point of Failure: Key never exists in one place
Quantum-Safe: Ringtail signatures resist quantum attacks

Slashing Conditions

Violation	Slash Amount
Signing invalid message	50-100%
Double signing	100%
Offline during signing	10-20%
Censoring valid requests	25-50%

Documentation Sections

Section	Description
B-Chain	BridgeVM architecture, state machine, block structure
MPC Custody	CGGMP21 protocol, threshold signatures, key management
ThresholdVM	T-Chain VM, DKG, resharing, cross-chain requests
Ringtail	Quantum-safe signatures, Warp 1.5, ML-KEM encryption
Teleport	Teleport protocol, IBC integration, message types
Contracts	Bridge smart contracts, lock/mint/burn mechanics
Security	Security model, bonds, slashing, threat analysis
Fees	Fee structure, gas sponsorship, fee estimation
Integration	DEX integration, API reference, SDK usage

RPC Endpoints

The B-Chain exposes LP-333 compliant JSON-RPC endpoints:

Method	Description
`bridge_registerValidator`	Register as bridge signer (opt-in)
`bridge_getSignerSetInfo`	Get current signer set state
`bridge_replaceSigner`	Remove failed signer (triggers reshare)
`bridge_hasSigner`	Check if node is active signer
`bridge_getWaitlist`	Get validators waiting for slots
`bridge_getCurrentEpoch`	Get epoch (increments on reshare)
`bridge_slashSigner`	Slash misbehaving signer's bond

LP-6000: B-Chain Bridge Specification
LP-6015: MPC Bridge Protocol (CGGMP21 + LSS)
LP-6016: Teleport Cross-Chain Protocol
LP-333: Dynamic Signer Rotation with LSS Protocol
Warp 1.5: Quantum-Safe Cross-Chain Messaging

Cross-Chain Bridge

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