Security Fundamentals

Core Principles

Defense in Depth

Multiple layers of security controls:

• Network security (firewalls, VPCs)
• Application security (input validation, output encoding)
• Data security (encryption at rest and in transit)
• Identity security (authentication, authorization)

Least Privilege

Grant minimum permissions necessary:

• Service accounts with scoped permissions
• Role-based access control (RBAC)
• Time-limited credentials
• Regular permission audits

Secure by Default

Systems should be secure without additional configuration:

• Deny by default, allow by exception
• Secure defaults in configuration
• Fail securely (deny access on error)

Input Validation

Always Validate

// CORRECT - Validate all input
public void processOrder(OrderRequest request) {
    Objects.requireNonNull(request, "Request cannot be null");
    validateOrderId(request.getOrderId());
    validateAmount(request.getAmount());
    // Process...
}

// WRONG - Trusting input
public void processOrder(OrderRequest request) {
    repository.findById(request.getOrderId()); // SQL injection risk
}

Validation Patterns

• Whitelist over blacklist
• Validate type, length, format, range
• Sanitize before storage
• Encode before output

Authentication

Token Handling

// Headers for authentication only
@RequestHeader("X-Violet-Token") String token      // Auth verification
@RequestHeader("X-Violet-App-Id") Integer appId    // Auth context

// Path parameters for resource identification
@PathVariable("app_id") Integer targetAppId         // Database queries

Credential Storage

• Never store plaintext passwords
• Use encryption for API keys and tokens
• Rotate credentials regularly
• Audit credential access

Authorization

Check at Every Layer

// Controller level
@PreAuthorize("hasRole('ADMIN')")
public ResponseEntity<?> adminEndpoint() { }

// Service level
if (!userService.canAccessResource(userId, resourceId)) {
    throw new AccessDeniedException();
}

// Data level (row-level security)
repository.findByIdAndAppId(id, authenticatedAppId);

Data Protection

Encryption

• At rest: AWS KMS, AES-256
• In transit: TLS 1.3
• Sensitive fields: Encrypted in database

PII Handling

• Minimize collection
• Mask in logs (email → e***@example.com)
• Encrypt in storage
• Define retention policies

Logging & Monitoring

Security Logging

// Log security events
logger.info("Authentication successful",
    Map.of("userId", userId, "ip", clientIp));

logger.warn("Failed login attempt",
    Map.of("username", username, "ip", clientIp, "attempts", attemptCount));

// Never log sensitive data
// WRONG: logger.info("Token: " + token);

Monitoring

• Failed authentication attempts
• Unusual access patterns
• Privilege escalation attempts
• Data exfiltration indicators

OWASP Top 10 Awareness