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Security Whitepaper

Last updated: November 3, 2025

Executive Summary

SecureMail implements a privacy-first architecture with end-to-end encryption, zero-access encryption, and comprehensive security measures to ensure user communications remain private and secure. This whitepaper details our security architecture, encryption protocols, and privacy protection mechanisms.

1. Cryptographic Architecture

1.1 End-to-End Encryption

All email content is encrypted on the sender's device and can only be decrypted by the intended recipient:

  • Algorithm: AES-256-GCM for symmetric encryption
  • Key Exchange: Elliptic Curve Diffie-Hellman (ECDH) P-256
  • Digital Signatures: Ed25519 for message authentication
  • Perfect Forward Secrecy: Session keys are rotated for each message
Message Format:
{ciphertext: AES-256-GCM(content + metadata),
iv: random_96_bit,
auth_tag: 128_bit,
signature: Ed25519(ciphertext || iv || timestamp)}

2. Zero-Access Encryption

2.1 Server-Side Security Model

Our servers operate in a zero-knowledge environment:

  • No access to plaintext content or metadata
  • User private keys are never sent to servers
  • Encryption keys are derived client-side
  • All processing of sensitive data occurs on user devices
Security Note: Even if our servers were compromised, attackers would only have access to encrypted data that cannot be decrypted without the user's private keys.

3. Authentication & Account Recovery

3.1 Seed Phrase Recovery

Account recovery uses a cryptographically secure seed phrase system:

  • Algorithm: BIP39 mnemonic generation from entropy
  • Word Count: 24 words (256-bit entropy)
  • Backup Strategy: Users can write down and store offline
  • Security: No phone or email recovery options compromise privacy
Recovery Process:
1. User enters 24-word seed phrase
2. Generate master key using PBKDF2 (2048 iterations)
3. Derive account private keys
4. Decrypt locally stored data

4. Infrastructure Security

4.1 Server Hardening

  • Operating System: Hardened Linux distributions
  • Network: Isolated private networks with firewall rules
  • Access: SSH key-based authentication only
  • Monitoring: Real-time security event monitoring

4.2 Data Protection

  • Encryption at Rest: AES-256 encryption for all stored data
  • Key Management: Hardware Security Modules (HSM)
  • Backup Security: Encrypted backups with separate key management

5. Privacy Protection

5.1 Metadata Protection

  • Minimal Collection: Only essential metadata stored
  • Short Retention: Technical logs rotated within 24-48 hours
  • No Tracking: No analytics or user behavior tracking
  • Anonymous Operations: No IP-based user profiling

5.2 Self-Destructing Messages

Time-based message deletion with cryptographic security:

Self-Destruct Process:
1. Timer expires on encrypted message
2. Server marks message for deletion
3. Secure deletion using cryptographic erasure
4. Permanent removal from all backup systems

6. Security Audits & Compliance

6.1 Regular Audits

  • Annual third-party security audits
  • Continuous vulnerability scanning
  • Penetration testing by external security firms
  • Open-source code review and verification

6.2 Compliance Standards

  • GDPR compliance for European users
  • CCPA compliance for California users
  • SOC 2 Type II certification in progress
  • ISO 27001 information security management

7. Threat Model Analysis

7.1 Threat Vectors Addressed

  • Server Compromise: Zero-access encryption prevents data access
  • Network Interception: TLS 1.3 encryption for all communications
  • Device Compromise: Client-side encryption with local key storage
  • Insider Threats: No access to user plaintext data
  • Legal Requests: Cannot provide decrypted data due to encryption

8. Future Security Enhancements

8.1 Planned Improvements

  • Post-quantum cryptography implementation
  • Enhanced metadata privacy with mix networks
  • Advanced threat detection using machine learning
  • Homomorphic encryption for server-side processing

9. Contact & Security Reporting

For security-related questions, vulnerability reports, or technical inquiries, please contact our security team through our secure channels. We take all security concerns seriously and will respond promptly to legitimate security research.