Encryption

When to Use

• Encrypting files, database fields, or app storage
• Password hashing (bcrypt, argon2)
• Key management, rotation, derivation
• TLS/certificate configuration
• Auditing code for crypto mistakes
• Mobile secure storage (Keychain, Keystore)

Algorithm Selection

| Purpose | Use | Avoid | |---------|-----|-------| | Passwords | argon2id, bcrypt (cost≥12) | MD5, SHA1, plain SHA256 | | Symmetric | AES-256-GCM, ChaCha20-Poly1305 | AES-ECB, DES, RC4 | | Asymmetric | RSA-4096+OAEP, Ed25519, P-256 | RSA-1024, PKCS#1 v1.5 | | Key derivation | PBKDF2 (≥600k), scrypt, argon2 | Single-pass hash | | JWT signing | RS256, ES256 | HS256 with weak secret | | TLS | 1.2+ only | TLS 1.0/1.1, SSLv3 |

Critical Rules

1. Never reuse IVs/nonces — AES-GCM + repeated nonce = catastrophic
2. Use authenticated encryption (AEAD) — Plain CBC enables padding oracles
3. Hash passwords, don't encrypt — Hashing is one-way
4. No hardcoded keys — Use env vars, KMS, or Vault
5. No Math.random() for crypto — Use CSPRNG only
6. Constant-time comparisons — Prevent timing attacks on secrets
7. Separate keys by purpose — Encryption ≠ signing ≠ backup

File Encryption (CLI)

# age (modern, simple)
age -p -o file.age file.txt
age -d -o file.txt file.age

# GPG
gpg -c --cipher-algo AES256 file.txt

Platform-Specific

See patterns.md for code snippets:

• Password hashing (Node, Python, Go)
• Envelope encryption with KMS
• JWT with RS256 key rotation
• Secure token generation

See mobile.md for:

• iOS Keychain wrapper
• Android EncryptedSharedPreferences
• SQLCipher setup
• Biometric auth integration
• Certificate pinning

See infra.md for:

• TLS certificate auto-renewal
• HashiCorp Vault policies
• mTLS between services
• Backup encryption verification

Audit Checklist

• [ ] No plaintext passwords in DB/logs/env
• [ ] No secrets in git history
• [ ] No hardcoded keys in source
• [ ] No Math.random() for security
• [ ] No deprecated algorithms (MD5, SHA1, DES)
• [ ] No disabled cert validation
• [ ] IVs/nonces never reused
• [ ] PBKDF2 iterations ≥600k / bcrypt cost ≥12
• [ ] TLS 1.2+ enforced, old protocols disabled
• [ ] Key rotation procedure documented