# Security Model

## Overview

Self implements a comprehensive security model based on self-sovereign identity principles, cryptographic authentication, and zero-knowledge architecture. The security model prioritizes user control, data minimization, and defense in depth.

## Security Principles

### 1. Self-Sovereign Identity
- **User Control**: Users generate and control their own cryptographic keys
- **No Central Authority**: No single point of failure or control
- **Decentralized Trust**: Trust distributed across cryptographic proofs
- **Data Ownership**: Users own and control their identity data

### 2. Zero-Knowledge Architecture
- **Client-Side Encryption**: All sensitive operations performed locally
- **No Server Secrets**: Server never sees private keys or passwords
- **Minimal Data Collection**: Only necessary public information stored
- **Cryptographic Proofs**: Authentication without revealing secrets

### 3. Defense in Depth
- **Multiple Security Layers**: Transport, application, and storage security
- **Fail-Safe Defaults**: Secure by default configuration
- **Principle of Least Privilege**: Minimal necessary permissions
- **Security Monitoring**: Comprehensive logging and monitoring

## Threat Model

### Assets to Protect

1. **Private Keys**: User's cryptographic private keys
2. **Passwords**: User-chosen encryption passwords
3. **Identity Data**: Personal information and metadata
4. **Session Tokens**: Authentication tokens and sessions
5. **Communication**: Data in transit between client and server

### Threat Actors

#### 1. External Attackers
- **Capabilities**: Network access, public endpoints
- **Motivations**: Identity theft, financial gain, disruption
- **Attack Vectors**: Network attacks, social engineering, malware

#### 2. Malicious Insiders
- **Capabilities**: Server access, code modification
- **Motivations**: Data theft, sabotage, espionage
- **Attack Vectors**: Privilege abuse, backdoors, data exfiltration

#### 3. Nation-State Actors
- **Capabilities**: Advanced persistent threats, zero-days
- **Motivations**: Surveillance, intelligence gathering
- **Attack Vectors**: Supply chain attacks, infrastructure compromise

#### 4. Compromised Infrastructure
- **Capabilities**: Server compromise, DNS hijacking
- **Motivations**: Data theft, service disruption
- **Attack Vectors**: Infrastructure attacks, certificate compromise

### Attack Scenarios

#### Scenario 1: Private Key Theft
**Attack**: Malware extracts encrypted private keys from localStorage
```
Threat: Malware on user device
Impact: Identity compromise if password is weak
Mitigation: Strong encryption, password requirements
Residual Risk: Weak user passwords
```

#### Scenario 2: Server Compromise
**Attack**: Attacker gains full server access
```
Threat: Server infrastructure compromise
Impact: User data exposure, service disruption
Mitigation: No private keys on server, encrypted storage
Residual Risk: Public key and email exposure
```

#### Scenario 3: Man-in-the-Middle
**Attack**: Network traffic interception and modification
```
Threat: Network-level attacker
Impact: Authentication bypass, data theft
Mitigation: HTTPS, certificate pinning, signature verification
Residual Risk: Certificate authority compromise
```

#### Scenario 4: Social Engineering
**Attack**: Trick user into revealing password or private key
```
Threat: Social engineering attack
Impact: Full identity compromise
Mitigation: User education, secure key handling
Residual Risk: User susceptibility to social engineering
```

## Security Controls

### Cryptographic Controls

#### 1. Key Generation
```rust
// Secure random number generation
use getrandom::getrandom;

fn generate_secure_key() -> Result<[u8; 32], CryptoError> {
    let mut key = [0u8; 32];
    getrandom(&mut key)?;
    
    // Validate key is not weak
    if key.iter().all(|&b| b == 0) {
        return Err(CryptoError::WeakKey);
    }
    
    Ok(key)
}
```

**Controls:**
- Cryptographically secure random number generation
- Key validation to prevent weak keys
- Proper entropy collection from OS

#### 2. Encryption
```rust
// AES-256-GCM with proper nonce handling
use aes_gcm::{Aes256Gcm, Key, Nonce, aead::{Aead, KeyInit}};

fn encrypt_data(data: &[u8], key: &[u8; 32]) -> Result<EncryptedData, CryptoError> {
    let cipher = Aes256Gcm::new(Key::from_slice(key));
    
    // Generate random nonce
    let mut nonce_bytes = [0u8; 12];
    getrandom(&mut nonce_bytes)?;
    let nonce = Nonce::from_slice(&nonce_bytes);
    
    let ciphertext = cipher.encrypt(nonce, data)?;
    
    Ok(EncryptedData {
        ciphertext,
        nonce: nonce_bytes,
    })
}
```

**Controls:**
- AES-256-GCM authenticated encryption
- Random nonce generation for each encryption
- Authenticated encryption prevents tampering

#### 3. Key Derivation
```rust
// PBKDF2 with configurable iterations
use pbkdf2::{pbkdf2_hmac};
use sha2::Sha256;

fn derive_key(password: &str, salt: &[u8], iterations: u32) -> [u8; 32] {
    let mut key = [0u8; 32];
    pbkdf2_hmac::<Sha256>(password.as_bytes(), salt, iterations, &mut key);
    key
}
```

**Controls:**
- PBKDF2 with SHA-256 for key derivation
- Configurable iteration count (minimum 10,000)
- Random salt for each key derivation

### Access Controls

#### 1. Authentication
```rust
pub enum AuthenticationLevel {
    None,           // No authentication required
    PublicKey,      // Public key verification only
    Signature,      // Cryptographic signature required
    Password,       // Password-based access
}

impl AccessControl {
    pub fn check_authentication(&self, level: AuthenticationLevel) -> Result<(), AuthError> {
        match level {
            AuthenticationLevel::None => Ok(()),
            AuthenticationLevel::PublicKey => self.verify_public_key(),
            AuthenticationLevel::Signature => self.verify_signature(),
            AuthenticationLevel::Password => self.verify_password(),
        }
    }
}
```

#### 2. Authorization
```rust
pub struct Permission {
    pub resource: String,
    pub action: String,
    pub conditions: Vec<String>,
}

impl Authorization {
    pub fn check_permission(&self, user: &User, permission: &Permission) -> bool {
        // Check if user has required permission
        self.user_permissions.get(&user.id)
            .map(|perms| perms.contains(permission))
            .unwrap_or(false)
    }
}
```

### Network Security

#### 1. Transport Layer Security
```rust
// HTTPS configuration
use axum_server::tls_rustls::RustlsConfig;

async fn create_tls_server() -> Result<(), ServerError> {
    let config = RustlsConfig::from_pem_file(
        PathBuf::from("cert.pem"),
        PathBuf::from("key.pem"),
    ).await?;
    
    let app = create_app();
    
    axum_server::bind_rustls("0.0.0.0:443".parse()?, config)
        .serve(app.into_make_service())
        .await?;
    
    Ok(())
}
```

**Controls:**
- TLS 1.3 for all communications
- Certificate validation and pinning
- HSTS headers for HTTPS enforcement

#### 2. CORS Configuration
```rust
use tower_http::cors::{CorsLayer, Any};

fn configure_cors() -> CorsLayer {
    CorsLayer::new()
        .allow_origin(Any) // Configure for production
        .allow_methods([Method::GET, Method::POST])
        .allow_headers([header::CONTENT_TYPE, header::AUTHORIZATION])
        .allow_credentials(false)
}
```

### Application Security

#### 1. Input Validation
```rust
use validator::{Validate, ValidationError};

#[derive(Validate)]
pub struct RegistrationRequest {
    #[validate(email)]
    pub email: String,
    
    #[validate(length(min = 1, max = 100))]
    pub name: String,
    
    #[validate(custom = "validate_public_key")]
    pub public_key: String,
}

fn validate_public_key(public_key: &str) -> Result<(), ValidationError> {
    if !is_valid_hex(public_key) || public_key.len() != 130 {
        return Err(ValidationError::new("invalid_public_key"));
    }
    Ok(())
}
```

#### 2. Error Handling
```rust
pub enum SecurityError {
    InvalidInput(String),
    AuthenticationFailed,
    AuthorizationDenied,
    CryptographicError(String),
    RateLimitExceeded,
}

impl SecurityError {
    pub fn safe_message(&self) -> &'static str {
        match self {
            SecurityError::InvalidInput(_) => "Invalid input provided",
            SecurityError::AuthenticationFailed => "Authentication failed",
            SecurityError::AuthorizationDenied => "Access denied",
            SecurityError::CryptographicError(_) => "Cryptographic operation failed",
            SecurityError::RateLimitExceeded => "Rate limit exceeded",
        }
    }
}
```

### Storage Security

#### 1. Client-Side Storage
```rust
// Secure localStorage usage
pub struct SecureStorage {
    prefix: String,
}

impl SecureStorage {
    pub fn store_encrypted(&self, key: &str, data: &EncryptedData) -> Result<(), StorageError> {
        let storage_key = format!("{}_{}", self.prefix, key);
        let serialized = serde_json::to_string(data)?;
        
        web_sys::window()
            .and_then(|w| w.local_storage().ok().flatten())
            .ok_or(StorageError::NotAvailable)?
            .set_item(&storage_key, &serialized)
            .map_err(|_| StorageError::WriteFailed)?;
        
        Ok(())
    }
}
```

#### 2. Server-Side Storage
```rust
// Minimal server storage
pub struct UserRecord {
    pub id: String,
    pub email: String,          // Not sensitive
    pub public_key: String,     // Public by definition
    pub name: String,           // User-provided, not sensitive
    pub created_at: String,     // Timestamp, not sensitive
    // Note: No private keys or passwords stored
}
```

## Security Monitoring

### Logging Strategy

#### 1. Security Events
```rust
use tracing::{info, warn, error};

pub fn log_authentication_attempt(public_key: &str, success: bool) {
    if success {
        info!(
            event = "authentication_success",
            public_key = %public_key[..8], // Log only prefix
            timestamp = %Utc::now()
        );
    } else {
        warn!(
            event = "authentication_failure",
            public_key = %public_key[..8],
            timestamp = %Utc::now()
        );
    }
}
```

#### 2. Anomaly Detection
```rust
pub struct SecurityMonitor {
    failed_attempts: HashMap<String, Vec<DateTime<Utc>>>,
    rate_limits: HashMap<String, RateLimit>,
}

impl SecurityMonitor {
    pub fn check_suspicious_activity(&mut self, public_key: &str) -> bool {
        let now = Utc::now();
        let attempts = self.failed_attempts.entry(public_key.to_string()).or_default();
        
        // Remove old attempts (older than 1 hour)
        attempts.retain(|&time| now.signed_duration_since(time).num_hours() < 1);
        
        // Check if too many recent failures
        attempts.len() > 5
    }
}
```

### Metrics Collection

#### 1. Security Metrics
```rust
use prometheus::{Counter, Histogram, Gauge};

lazy_static! {
    static ref AUTH_ATTEMPTS: Counter = Counter::new(
        "auth_attempts_total", "Total authentication attempts"
    ).unwrap();
    
    static ref AUTH_FAILURES: Counter = Counter::new(
        "auth_failures_total", "Total authentication failures"
    ).unwrap();
    
    static ref CRYPTO_OPERATIONS: Histogram = Histogram::new(
        "crypto_operation_duration_seconds", "Cryptographic operation duration"
    ).unwrap();
}
```

## Incident Response

### Security Incident Types

#### 1. Key Compromise
**Response Procedure:**
1. Immediately revoke affected tokens
2. Notify user through secure channel
3. Guide user through key rotation process
4. Monitor for unauthorized usage
5. Update security controls if needed

#### 2. Server Compromise
**Response Procedure:**
1. Isolate affected systems
2. Assess scope of compromise
3. Rotate server secrets and certificates
4. Notify users of potential impact
5. Implement additional monitoring

#### 3. Vulnerability Discovery
**Response Procedure:**
1. Assess vulnerability severity
2. Develop and test fix
3. Deploy fix to production
4. Notify users if necessary
5. Conduct post-incident review

### Recovery Procedures

#### 1. Key Recovery
```rust
pub struct KeyRecovery {
    pub backup_methods: Vec<BackupMethod>,
    pub recovery_contacts: Vec<String>,
}

pub enum BackupMethod {
    ExportedVault,
    PaperBackup,
    HardwareToken,
    SocialRecovery,
}
```

#### 2. Service Recovery
```rust
pub struct ServiceRecovery {
    pub backup_servers: Vec<String>,
    pub database_backups: Vec<BackupInfo>,
    pub recovery_time_objective: Duration,
    pub recovery_point_objective: Duration,
}
```

## Compliance and Auditing

### Regulatory Compliance

#### 1. GDPR Compliance
- **Right to Access**: Users can export their data
- **Right to Rectification**: Users can update their information
- **Right to Erasure**: Users can delete their accounts
- **Data Portability**: Vault export functionality
- **Privacy by Design**: Minimal data collection

#### 2. SOX Compliance
- **Access Controls**: Role-based access control
- **Audit Trails**: Comprehensive logging
- **Data Integrity**: Cryptographic verification
- **Change Management**: Controlled deployment process

### Security Auditing

#### 1. Code Auditing
```rust
// Security-focused code review checklist
pub struct SecurityAudit {
    pub crypto_review: bool,        // Cryptographic implementation review
    pub input_validation: bool,     // Input validation coverage
    pub error_handling: bool,       // Secure error handling
    pub access_control: bool,       // Authorization checks
    pub logging_review: bool,       // Security logging adequacy
}
```

#### 2. Penetration Testing
- **Network Security**: External network testing
- **Application Security**: Web application testing
- **Client Security**: Browser-based testing
- **Social Engineering**: User awareness testing

## Security Best Practices

### Development Security

1. **Secure Coding Standards**
   - Input validation on all user inputs
   - Output encoding for all outputs
   - Proper error handling without information leakage
   - Secure random number generation

2. **Code Review Process**
   - Security-focused peer reviews
   - Automated security scanning
   - Cryptographic implementation review
   - Third-party security audits

3. **Testing Strategy**
   - Unit tests for security functions
   - Integration tests for auth flows
   - Penetration testing
   - Fuzzing for input validation

### Deployment Security

1. **Infrastructure Security**
   - Hardened server configurations
   - Network segmentation
   - Intrusion detection systems
   - Regular security updates

2. **Configuration Management**
   - Secure default configurations
   - Environment-specific settings
   - Secret management systems
   - Configuration validation

### Operational Security

1. **Monitoring and Alerting**
   - Real-time security monitoring
   - Automated threat detection
   - Incident response procedures
   - Regular security assessments

2. **User Education**
   - Security awareness training
   - Best practice documentation
   - Phishing awareness
   - Incident reporting procedures