Cross-Chain Privacy Layer

Cross-Chain Privacy Layer - Technical Specification

This document describes how the Roru Protocol maintains privacy across multiple blockchains through a unified shielded state.

Architecture

Unified Shielded State

Concept: Single shielded state across all chains

Benefits:

• Privacy maintained across chains

• Unified user experience

• Efficient cross-chain operations

• Consistent privacy guarantees

Layer Structure

┌─────────────────────────────────────┐
│     Unified Shielded State          │
│     (Privacy Layer)                 │
└──────────────┬──────────────────────┘
               │
    ┌──────────┼──────────┐
    │          │          │
┌───▼───┐ ┌───▼───┐ ┌───▼───┐
│Chain 1│ │Chain 2│ │Chain 3│
│Adapter│ │Adapter│ │Adapter│
└───┬───┘ └───┬───┘ └───┬───┘
    │          │          │
┌───▼───┐ ┌───▼───┐ ┌───▼───┐
│Chain 1│ │Chain 2│ │Chain 3│
│Block- │ │Block- │ │Block- │
│chain  │ │chain  │ │chain  │
└───────┘ └───────┘ └───────┘

Cross-Chain Operations

Shielded Transfers

Process:

1. User initiates cross-chain transfer

2. Source chain adapter locks assets

3. Shielded state updated

4. Destination chain adapter unlocks

5. Privacy maintained throughout

Implementation:

fn cross_chain_transfer(
    source_chain: ChainId,
    dest_chain: ChainId,
    amount: u64,
    recipient: ShieldedAddress,
) -> Result<Transaction> {
    // Lock on source chain
    let lock_tx = source_adapter.lock(amount)?;
    
    // Update shielded state
    let note = create_note(amount, recipient);
    shielded_state.add_note(note)?;
    
    // Unlock on destination chain
    let unlock_tx = dest_adapter.unlock(amount)?;
    
    Ok(Transaction::CrossChain {
        lock_tx,
        unlock_tx,
    })
}

Privacy Preservation

Privacy Properties:

• Source chain hidden

• Destination chain hidden

• Amount hidden

• Recipient hidden

• Complete privacy

Adapter Layer

Adapter Interface

Interface Definition:

pub trait ChainAdapter {
    async fn lock_assets(&self, amount: u64) -> Result<LockTx>;
    async fn unlock_assets(&self, amount: u64, proof: &Proof) -> Result<UnlockTx>;
    async fn get_balance(&self, address: &Address) -> Result<u64>;
    async fn submit_settlement(&self, tx: &SettlementTx) -> Result<TxHash>;
}

Adapter Implementation

Ethereum Adapter:

• Smart contract integration

• ERC-20 token support

• Gas optimization

• Event listening

Solana Adapter:

• Program integration

• SPL token support

• Transaction building

• Account management

Settlement Mechanism

Unified Settlement

Settlement Process:

1. Transaction validated in shielded state

2. Settlement transactions created per chain

3. Transactions broadcast to chains

4. Confirmations received

5. State finalized

Settlement Code:

fn settle_cross_chain(
    transaction: &Transaction,
    adapters: &[ChainAdapter],
) -> Result<Vec<SettlementResult>> {
    let mut results = Vec::new();
    
    for adapter in adapters {
        let settlement_tx = adapter.create_settlement(transaction)?;
        let hash = adapter.submit_settlement(&settlement_tx).await?;
        results.push(SettlementResult {
            chain: adapter.chain_id(),
            tx_hash: hash,
        });
    }
    
    Ok(results)
}

State Synchronization

Cross-Chain Sync

Sync Process:

1. Monitor all chains

2. Detect lock/unlock events

3. Update shielded state

4. Maintain consistency

5. Handle conflicts

Sync Implementation:

async fn sync_cross_chain_state(
    shielded_state: &mut ShieldedState,
    adapters: &[ChainAdapter],
) -> Result<()> {
    for adapter in adapters {
        let events = adapter.get_lock_events().await?;
        for event in events {
            shielded_state.process_lock(event)?;
        }
        
        let events = adapter.get_unlock_events().await?;
        for event in events {
            shielded_state.process_unlock(event)?;
        }
    }
    
    Ok(())
}

Privacy Guarantees

Cross-Chain Privacy

Privacy Properties:

• No chain linkability

• Unified anonymity set

• No cross-chain correlation

• Complete privacy

Privacy Mechanisms

Mechanisms:

• Shielded state hides chains

• Zero-knowledge proofs

• Encrypted communications

• No metadata leakage

Bridge Integration

Bridge Architecture

Bridge Components:

• Lock mechanism

• Proof verification

• Unlock mechanism

• State tracking

Bridge Flow:

Source Chain          Shielded State          Dest Chain
    │                      │                      │
    ├─ Lock Assets ────────┼──────────────────────┤
    │                      │                      │
    │              Update State                    │
    │                      │                      │
    │                      ├─ Unlock Assets ──────┤
    │                      │                      │

Multi-Asset Support

Asset Abstraction

Asset Handling:

• Unified asset representation

• Chain-specific assets

• Cross-asset operations

• Asset conversion

Asset Format:

pub struct CrossChainAsset {
    pub chain_id: ChainId,
    pub asset_id: AssetId,
    pub amount: u64,
}

Performance

Efficiency

Optimizations:

• Batch settlements

• Parallel processing

• Efficient state updates

• Optimized proofs

Latency

Typical Latencies:

• Shielded state update: <1s

• Chain settlement: Chain-dependent

• Cross-chain transfer: 1-5 minutes

• Final confirmation: Chain-dependent

Security

Security Properties

Security Guarantees:

• Atomic operations

• No double-spending

• State consistency

• Cryptographic security

Threat Model

Protected Against:

• Cross-chain attacks

• State inconsistencies

• Double-spending

• Privacy breaches

Conclusion

The cross-chain privacy layer provides:

• Privacy: Maintained across chains

• Unification: Single shielded state

• Flexibility: Multiple chains

• Security: Cryptographic guarantees

• Efficiency: Optimized operations

Understanding this layer is essential for cross-chain development.