# Architecture and Design Steering Document

**Version**: 1.0  
**Last Updated**: 2025-01-16  
**Status**: Active  

## Executive Summary

This document establishes the architectural principles, design patterns, and technical direction for Saorsa Core, a next-generation peer-to-peer networking foundation. The architecture prioritizes security, performance, and decentralization while maintaining developer ergonomics and production reliability.

## Core Architectural Principles

### 1. Security by Design

**Principle**: Security is integrated into every layer, not added as an afterthought.

**Implementation**:
- Zero-trust network model with cryptographic verification
- Post-quantum cryptography readiness (ML-KEM, ML-DSA)
- EigenTrust reputation system for Byzantine fault tolerance
- Comprehensive audit trails and tamper detection

**Rationale**: P2P networks face unique security challenges including Sybil attacks, eclipse attacks, and Byzantine behavior. Security must be foundational.

### 2. Performance and Scalability

**Principle**: The system must scale to millions of nodes while maintaining low latency.

**Implementation**:
- QUIC transport for reduced connection overhead
- Adaptive routing with machine learning optimization
- Geographic-aware placement and routing
- Efficient caching strategies with Q-learning

**Rationale**: Network effects require the system to handle exponential growth gracefully while maintaining user experience quality.

### 3. Decentralization and Autonomy

**Principle**: No single point of failure or control.

**Implementation**:
- Distributed Hash Table (DHT) for peer discovery
- Consensus-free operation where possible
- Self-organizing network topology
- Autonomous repair and maintenance systems

**Rationale**: Centralized systems are vulnerable to censorship, single points of failure, and regulatory capture.

### 4. Developer Experience

**Principle**: The system should be approachable for developers while maintaining power and flexibility.

**Implementation**:
- Comprehensive documentation and examples
- Type-safe APIs with clear error handling
- Four-word human-readable addresses

**Rationale**: Adoption depends on developer productivity and ease of integration.

## System Architecture

### Layer 1: Transport Layer

**Purpose**: Reliable, secure, and efficient network communication.

**Components**:
- **QUIC Transport**: Primary transport with NAT traversal via `ant-quic`
- **Connection Management**: Pool management with LRU eviction
- **Encryption**: TLS 1.3 for transport security
- **Compression**: Adaptive compression based on content type

**Key Decisions**:
- QUIC chosen over TCP for reduced handshake overhead and better congestion control
- Connection pooling to amortize connection establishment costs
- Automatic compression to reduce bandwidth usage

### Layer 2: Network Layer

**Purpose**: Peer discovery, routing, and network topology management.

**Components**:
- **DHT**: Kademlia-based with geographic awareness
- **Routing**: Adaptive selection between DHT, hyperbolic, and trust-based routing
- **Peer Discovery**: Bootstrap nodes with peer exchange protocol
- **NAT Traversal**: Integrated with QUIC for firewall penetration

**Key Decisions**:
- Kademlia DHT provides O(log n) routing complexity
- Multiple routing strategies allow optimization for different use cases
- Geographic awareness improves locality and reduces latency

### Layer 3: Storage and Placement Layer

**Purpose**: Intelligent data placement with fault tolerance and optimal performance.

**Components**:
- **Placement Engine**: Weighted selection using Efraimidis-Spirakis algorithm
- **EigenTrust Integration**: Reputation-based node selection
- **Geographic Diversity**: Multi-region placement constraints
- **Audit and Repair**: Continuous monitoring with hysteresis control

**Key Decisions**:
- Weighted placement formula: `w_i = (τ_i^α) * (p_i^β) * (c_i^γ) * d_i`
- Byzantine fault tolerance with f-out-of-3f+1 model
- Hysteresis prevents repair storms while maintaining availability

### Layer 4: Application Layer

**Purpose**: High-level services and user-facing functionality.

**Components**:
- **Identity Management**: ML-DSA-based with four-word addresses
- **Messaging**: End-to-end encrypted communication
- **File Storage**: Distributed storage with versioning
- **WebRTC Integration**: Real-time audio/video communication

**Key Decisions**:
- ML-DSA provides quantum-resistant security with strong performance
- Four-word addresses improve usability over raw cryptographic identifiers
- WebRTC enables real-time applications on top of P2P infrastructure

## Design Patterns and Standards

### 1. Error Handling

**Standard**: All operations return `Result<T, E>` with structured error types.

```rust
// ✅ CORRECT
fn operation() -> Result<Value, P2PError> {
    let result = fallible_operation()
        .context("Operation failed")?;
    Ok(result)
}

// ❌ FORBIDDEN
fn operation() -> Value {
    fallible_operation().unwrap() // Panics in production
}
```

**Rationale**: P2P networks are unreliable by nature. Explicit error handling prevents cascading failures.

### 2. Async/Await

**Standard**: All I/O operations use async/await with structured concurrency.

```rust
// ✅ CORRECT
async fn process_messages(receiver: Receiver<Message>) -> Result<(), Error> {
    while let Some(message) = receiver.recv().await {
        tokio::spawn(async move {
            process_message(message).await
        });
    }
    Ok(())
}
```

**Rationale**: P2P networks require high concurrency. Async/await provides efficient cooperative multitasking.

### 3. Configuration

**Standard**: All components accept configuration structs with sensible defaults.

```rust
#[derive(Debug, Clone)]
pub struct PlacementConfig {
    pub replication_factor: ReplicationFactor,
    pub byzantine_tolerance: ByzantineTolerance,
    pub placement_timeout: Duration,
    pub weights: OptimizationWeights,
}

impl Default for PlacementConfig {
    fn default() -> Self {
        Self {
            replication_factor: (3, 8).into(),
            byzantine_tolerance: 2.into(),
            placement_timeout: Duration::from_secs(30),
            weights: OptimizationWeights::balanced(),
        }
    }
}
```

**Rationale**: Configuration flexibility enables adaptation to different environments while defaults ensure usability.

### 4. Testing Strategy

**Standard**: Test-driven development with property-based testing for critical algorithms.

```rust
#[cfg(test)]
mod tests {
    use proptest::prelude::*;
    
    proptest! {
        #[test]
        fn placement_preserves_replication(
            nodes in prop::collection::hash_set(node_strategy(), 10..100),
            replication_factor in 3u8..20u8,
        ) {
            let decision = placement_engine.select_nodes(&nodes, replication_factor)?;
            prop_assert_eq!(decision.selected_nodes.len(), replication_factor as usize);
        }
    }
}
```

**Rationale**: P2P systems have complex emergent behaviors. Property-based testing finds edge cases that unit tests miss.

## Technology Choices

### Core Language: Rust

**Rationale**:
- Memory safety prevents entire classes of security vulnerabilities
- Zero-cost abstractions enable high performance
- Strong type system catches errors at compile time
- Excellent async ecosystem with Tokio

### Transport: QUIC via ant-quic

**Rationale**:
- Reduced connection establishment latency (1-RTT)
- Built-in encryption and authentication
- Multiplexing without head-of-line blocking
- Mature NAT traversal support

### Cryptography: Post-Quantum Ready

**Current**: ML-DSA, ML-KEM, ChaCha20-Poly1305, BLAKE3
**Future**: ML-KEM, ML-DSA for quantum resistance

**Rationale**:
- ML-DSA provides quantum-resistant security with strong performance
- BLAKE3 is faster than SHA-2 with parallel processing
- Post-quantum algorithms prepare for cryptographically relevant quantum computers

### Database: SQLite via SQLx

**Rationale**:
- Embedded database reduces operational complexity
- ACID transactions ensure data consistency
- Excellent Rust integration with compile-time query checking
- Cross-platform compatibility

## Performance Targets

### Latency Requirements

- **Peer Discovery**: <100ms for initial connection
- **Message Routing**: <50ms average hop latency
- **Placement Decisions**: <1s for 8-node selection
- **Shard Retrieval**: <500ms for cached content

### Throughput Requirements

- **DHT Operations**: >10,000 ops/sec per node
- **Storage Bandwidth**: >100 MB/sec per node
- **Concurrent Connections**: >1,000 peers per node
- **Message Processing**: >50,000 messages/sec per node

### Scalability Targets

- **Network Size**: Support up to 10 million nodes
- **Geographic Distribution**: Sub-100ms cross-region latency
- **Storage Capacity**: Petabyte-scale distributed storage
- **Fault Tolerance**: 99.9% availability with <30% node churn

## Security Model

### Threat Model

**Adversaries**:
- State-level actors with significant resources
- Criminal organizations seeking to exploit the network
- Malicious users attempting to disrupt service
- Honest-but-curious nodes collecting private information

**Attack Vectors**:
- Sybil attacks creating multiple fake identities
- Eclipse attacks isolating nodes from the network
- Traffic analysis to deanonymize users
- Byzantine behavior in consensus protocols

### Defense Mechanisms

**Cryptographic**:
- All communications encrypted with forward secrecy
- Digital signatures on all network messages
- Merkle trees for data integrity verification
- Zero-knowledge proofs for privacy-preserving operations

**Network-Level**:
- EigenTrust reputation system detects Byzantine behavior
- Geographic diversity prevents localized attacks
- Rate limiting and proof-of-work prevent spam
- Connection limits prevent resource exhaustion

**Application-Level**:
- End-to-end encryption for user content
- Perfect forward secrecy for messaging
- Secure key derivation with hardware entropy
- Audit logs for forensic analysis

## Evolution Strategy

### Version 1.0 (Current)

**Focus**: Core P2P infrastructure with basic security
- DHT-based peer discovery and routing
- QUIC transport with basic encryption
- Simple placement algorithms
- Basic reputation system

### Version 2.0 (Q2 2025)

**Focus**: Advanced placement and security
- Full EigenTrust implementation with placement integration
- Post-quantum cryptography deployment
- Advanced ML-driven routing optimization
- Cross-shard atomic operations

### Version 3.0 (Q4 2025)

**Focus**: Scalability and performance
- Hierarchical DHT for billion-node networks
- Hardware acceleration for cryptographic operations
- Advanced consensus mechanisms for coordination
- Full WebRTC integration with mesh networking

### Version 4.0 (2026)

**Focus**: Ecosystem and applications
- Plugin architecture for third-party applications
- Decentralized governance mechanisms
- Economic incentives and tokenomics
- Mobile-first optimizations

## Governance and Decision Making

### Architecture Review Board

**Composition**: Lead architects, security experts, performance engineers
**Responsibilities**: Major architectural decisions, technology choices, security reviews
**Process**: RFC-based proposals with public comment period

### Technical RFCs

**Scope**: Changes affecting public APIs, security model, or performance characteristics
**Process**: 
1. Draft RFC with motivation and detailed design
2. Public comment period (minimum 2 weeks)
3. Architecture Review Board decision
4. Implementation with continuous review

### Emergency Changes

**Scope**: Critical security vulnerabilities or performance regressions
**Process**: Expedited review with post-implementation documentation
**Requirements**: Security audit and performance validation

## Monitoring and Metrics

### System Health Metrics

- **Network Connectivity**: Peer count, connection success rate, latency distribution
- **Storage Performance**: Read/write latency, replication success rate, repair frequency
- **Security Events**: Failed authentication attempts, Byzantine node detection
- **Resource Usage**: CPU, memory, bandwidth, storage utilization

### Business Metrics

- **User Engagement**: Active users, message volume, storage usage
- **Network Growth**: New node registration rate, geographic distribution
- **Feature Adoption**: API usage patterns, advanced feature utilization
- **Reliability**: Uptime, error rates, user-reported issues

### Alerting Thresholds

- **Critical**: >5% error rate, >10s latency, security breach detection
- **Warning**: >2% error rate, >5s latency, unusual traffic patterns
- **Info**: New feature deployments, scheduled maintenance

## Conclusion

This architecture provides a solid foundation for a scalable, secure, and decentralized P2P network while maintaining the flexibility to evolve with changing requirements and technology advances. The emphasis on security, performance, and developer experience positions Saorsa Core for long-term success in the decentralized ecosystem.

## References

- [Kademlia: A Peer-to-peer Information System Based on the XOR Metric](https://pdos.csail.mit.edu/~petar/papers/maymounkov-kademlia-lncs.pdf)
- [EigenTrust: Reputation Management in P2P Networks](https://nlp.stanford.edu/pubs/eigentrust.pdf)
- [QUIC: A UDP-Based Multiplexed and Secure Transport](https://tools.ietf.org/html/rfc9000)
- [Post-Quantum Cryptography Standardization](https://csrc.nist.gov/projects/post-quantum-cryptography)
- [Byzantine Fault Tolerance in Distributed Systems](https://people.eecs.berkeley.edu/~luca/cs174/byzantine.pdf)
