Architecture Overview

AstralBeam is a decentralized cross-chain bridge connecting EVM-compatible blockchains (Ethereum, Base, etc.) with Casper Network. This section provides a comprehensive overview of the system architecture.

High-Level Architecture

The bridge consists of four main layers:

flowchart TB
    subgraph Users[User Layer]
        WebApp[Web Application astralbeam.io]
        CLI[Bridge CLI]
        DirectAPI[Direct API/Contract Calls]
    end

    subgraph Relayers[Relayer Network M-of-N]
        R1[Relayer 1]
        R2[Relayer 2]
        R3[Relayer N]
        P2P[P2P Network HTTPS/TLS]
        R1 <--> P2P
        R2 <--> P2P
        R3 <--> P2P
    end

    subgraph EVMContracts[EVM Contracts]
        Locker[MultiSigLocker Lock/Unlock ERC-20]
        Wrapped[Wrapped Tokens Casper-native on EVM]
    end

    subgraph CasperContracts[Casper Contracts]
        EthClient[EthClient Store EVM Block Headers]
        TokenFactory[TokenFactory Mint/Burn CEP-18]
        CEP18[CEP-18 Tokens Wrapped Tokens]
    end

    WebApp --> Locker
    WebApp --> TokenFactory
    CLI --> Locker
    CLI --> TokenFactory
    DirectAPI --> Locker
    DirectAPI --> TokenFactory

    R1 --> Locker
    R1 --> EthClient
    R1 --> TokenFactory
    R2 --> Locker
    R2 --> EthClient
    R2 --> TokenFactory
    R3 --> Locker
    R3 --> EthClient
    R3 --> TokenFactory

    TokenFactory --> EthClient
    TokenFactory --> CEP18

Core Components

1. Smart Contracts

2. Relayer Network

A decentralized network of relayers that:

• Monitor blockchain events on all chains
• Verify MPT proofs independently (EVM → Casper direction)
• Exchange signatures via P2P network
• Submit cross-chain transactions with M-of-N attestation

3. Verification Systems

The bridge uses a consensus-aware verification model:

Key Security Property: For EVM → Casper, the EthClient stores block headers with receipts roots. The TokenFactory verifies that the receipts root in attestations matches the stored block header - this is the consensus-aware aspect of the security model.

Bridge Flow Summary

EVM → Casper (Lock and Mint)

sequenceDiagram
    participant User
    participant EVM as EVM Chain
    participant Relayers as Relayer Network
    participant Casper as Casper Network

    User->>EVM: 1. Lock ERC-20 tokens
    EVM-->>EVM: 2. Wait for finality
    Relayers->>EVM: 3. Detect finalized lock event
    Relayers->>Relayers: 4. Verify MPT proof independently
    Relayers->>Relayers: 5. Exchange signatures (P2P)
    Relayers->>Casper: 6. Submit block header + signatures
    Relayers->>Casper: 7. Submit mint attestation
    Note over Casper: TokenFactory verifies receipts root matches stored block header
    Casper->>User: 8. Receive CEP-18 tokens

Casper → EVM (Burn and Unlock)

sequenceDiagram
    participant User
    participant Casper as Casper Network
    participant Relayers as Relayer Network
    participant EVM as EVM Chain

    User->>Casper: 1. Burn CEP-18 tokens
    Casper-->>Casper: 2. Instant Finality
    Relayers->>Casper: 3. Detect burn event
    Relayers->>Relayers: 4. Sign attestation
    Relayers->>Relayers: 5. Exchange signatures (P2P)
    Relayers->>EVM: 6. Submit unlock + M-of-N signatures
    Note over EVM: Locker verifies 3-of-5 valid signatures
    EVM->>User: 7. Receive ERC-20 tokens

Design Principles

1. Security First

• M-of-N Multi-signature: Requires threshold signatures (3-of-5) to prevent single points of failure
• MPT Proof Verification: Each relayer independently verifies transaction receipts against block headers
• Consensus-Aware: Block headers stored on Casper; TokenFactory validates receipts roots
• Finality Protection: Waits for finality-threshold EVM blocks before processing
• Replay Prevention: Nonces and chain IDs included in attestation hashes

2. Decentralization

• Independent Relayers: Each relayer operates independently and verifies proofs
• P2P Communication: No central coordinator for signature exchange
• Permissionless Verification: Anyone can verify bridge operations

3. Transparency

• On-chain State: All bridge state stored on-chain
• Event Emission: All operations emit verifiable events
• Open Source: All code publicly available

4. Multi-Chain Ready

• Chain ID Awareness: All operations include source chain identification
• Per-Chain Contracts: Separate lockers for each EVM chain
• Unified Casper Entry: Single TokenFactory handles all chains

Technology Stack

Smart Contracts

Relayer Infrastructure

Monitoring & Operations

Network Architecture

flowchart LR
    subgraph Internet
        Users[Users]
        API[Bridge API]
    end

    subgraph AWS[AWS Infrastructure]
        subgraph RelayerNodes[Relayer Nodes]
            R1[Relayer 1]
            R2[Relayer 2]
            R3[Relayer 3]
            R4[Relayer 4]
            R5[Relayer 5]
        end
        DB[MySQL/Aurora]
        Grafana[Grafana]
        Prometheus[Prometheus]
    end

    subgraph Blockchains
        Sepolia[Ethereum Sepolia]
        Base[Base Sepolia]
        Polygon[Polygon Amoy]
        Casper[Casper Testnet]
    end

    Users --> API
    Users --> Blockchains
    API --> DB

    Sepolia --> R1
    Base --> R1
    Polygon --> R1
    Casper --> R1

    RelayerNodes --> Prometheus
    Prometheus --> Grafana

Further Reading

• System Components - Detailed component descriptions
• Bridge Flows - Complete flow documentation
• Multi-Chain Support - Multi-chain architecture
• Security Model - Security architecture