Cryptography

name: cryptography description: >- Applied cryptography security including TLS configuration and testing, certificate management (PKI/CA), key management best practices, cryptographic algorithm selection, common crypto failures (OWASP A02:2021), password hashing (Argon2/bcrypt/scrypt), HSM integration, quantum-readiness assessment, and crypto agility planning. domain: cybersecurity subdomain: cryptography tags: - cryptography - tls - pki - certificate-management - key-management - password-hashing - hsm - quantum-cryptography - encryption - crypto-agility version: "1.0" author: defconxt license: AGPL-3.0 compatibility: Designed for Claude Code, GitHub Copilot, OpenAI Codex, Cursor, Gemini CLI, and any agentskills.io-compatible agent. metadata: mitre-attack: ["T1557", "T1040", "T1552.004"] owasp: ["A02:2021"] nist-csf: ["PR.DS-1", "PR.DS-2", "PR.DS-5"] frameworks: ["NIST SP 800-57", "NIST SP 800-175B", "NIST PQC"]

Cryptography

When to Use

Activate when the operator asks about TLS hardening, certificate management, key rotation, password hashing, encryption implementation, PKI design, HSM, quantum cryptography readiness, or crypto failures.

Mode: [MODE: ARCHITECT] for crypto design; [MODE: BLUE] for crypto auditing; [MODE: RED] for crypto attacks.

Quick Reference

Workflow

1. Algorithm Selection Guide

Encryption (symmetric):
├── AES-256-GCM — Recommended for all new implementations
├── ChaCha20-Poly1305 — Alternative for mobile/embedded (no AES-NI)
├── AES-256-CBC — Acceptable with HMAC (encrypt-then-MAC)
└── ❌ DES, 3DES, RC4, Blowfish — Deprecated, do not use

Encryption (asymmetric):
├── X25519/Ed25519 — Recommended for key exchange/signatures
├── RSA-4096 — Acceptable (RSA-2048 minimum)
├── ECDSA P-256 — Acceptable for signatures
└── ❌ RSA-1024, DSA — Deprecated

Hashing:
├── SHA-256/SHA-384/SHA-512 — General purpose
├── SHA-3 — Alternative to SHA-2
├── BLAKE3 — High performance
└── ❌ MD5, SHA-1 — Deprecated (collision attacks)

Password hashing:
├── Argon2id — Recommended (memory-hard, GPU-resistant)
├── bcrypt (cost ≥ 12) — Acceptable
├── scrypt — Acceptable
└── ❌ PBKDF2-SHA1, MD5, SHA-256 without salt — Do not use

Key derivation:
├── HKDF — Recommended for key derivation from shared secrets
├── Argon2 — When deriving from passwords
└── PBKDF2-SHA256 (600,000+ iterations) — Acceptable per OWASP 2023

2. TLS Hardening

# Test TLS configuration
testssl.sh --severity HIGH target.com:443
sslyze --regular --certinfo target.com

# Nginx TLS configuration (modern)
ssl_protocols TLSv1.3;
ssl_prefer_server_ciphers off;
# TLS 1.3 ciphersuites are automatically configured

# Nginx TLS configuration (intermediate — supports TLS 1.2)
ssl_protocols TLSv1.2 TLSv1.3;
ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;
ssl_prefer_server_ciphers off;

# HSTS header
add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload";

# OCSP stapling
ssl_stapling on;
ssl_stapling_verify on;
ssl_trusted_certificate /etc/ssl/certs/chain.pem;

# Certificate Transparency
# Certificates must be logged to CT logs (Chrome requires it)

3. Certificate Management

# Let's Encrypt with certbot (automated)
certbot certonly --nginx -d example.com -d www.example.com
# Auto-renewal: certbot renew (runs via cron/systemd timer)

# Internal PKI with step-ca
step ca init --name "Internal CA" --provisioner admin --address ":443"
step ca certificate internal.example.com cert.pem key.pem

# Certificate monitoring
# Monitor expiry across all certificates
echo | openssl s_client -connect target.com:443 2>/dev/null | \
  openssl x509 -noout -enddate -subject

# Certificate transparency monitoring
# Monitor CT logs for unauthorized certs for your domain
# https://crt.sh/?q=%.example.com
curl -s "https://crt.sh/?q=%.example.com&output=json" | jq '.[0:10]'

4. Key Management

Key management lifecycle:
├── Generation: Use cryptographically secure RNG (CSPRNG)
├── Storage: HSM, cloud KMS, or Vault (never filesystem/env vars for long-term keys)
├── Distribution: TLS, out-of-band, or key wrapping
├── Rotation: Annual for data keys, on compromise immediately
├── Archival: Retain decryption keys for data retention period
├── Destruction: Crypto-shred when no longer needed

HSM integration:
├── AWS CloudHSM / Azure Dedicated HSM / GCP Cloud HSM
├── PKCS#11 interface for application integration
├── Key material never leaves HSM boundary
└── FIPS 140-2 Level 3 (tamper-evident)

Envelope encryption pattern:
├── Data Encryption Key (DEK): Random per-object, encrypts data
├── Key Encryption Key (KEK): Stored in KMS/HSM, wraps DEK
├── Encrypted DEK stored alongside ciphertext
└── Rotation: Rotate KEK, re-wrap DEKs (no re-encryption of data)

5. Post-Quantum Readiness

Quantum threat timeline:
├── Current: No cryptographically relevant quantum computers
├── 2030-2035: Estimated threat to RSA/ECC (harvest now, decrypt later)
├── Action now: Inventory all crypto, prepare for migration

NIST PQC Standards (August 2024):
├── ML-KEM (FIPS 203, formerly CRYSTALS-Kyber): Key encapsulation
├── ML-DSA (FIPS 204, formerly CRYSTALS-Dilithium): Digital signatures
├── SLH-DSA (FIPS 205, formerly SPHINCS+): Stateless hash signatures
└── FN-DSA (forthcoming, formerly FALCON): Compact signatures

Migration strategy:
├── Phase 1: Inventory all cryptographic assets (algorithms, key lengths, locations)
├── Phase 2: Implement crypto agility (abstraction layer for easy algorithm swap)
├── Phase 3: Hybrid mode (classical + PQC combined)
├── Phase 4: Full PQC migration for new deployments
└── Phase 5: Retire classical-only implementations

Verification

• TLS 1.2+ only (TLS 1.3 preferred), no weak cipher suites
• All certificates valid, monitored for expiry (>30 days warning)
• HSTS deployed with preload
• Password hashing uses Argon2id or bcrypt (cost ≥12)
• Encryption at rest uses AES-256-GCM or ChaCha20-Poly1305
• Key rotation schedule defined and automated
• No deprecated algorithms (MD5, SHA1, DES, RC4) in use
• Post-quantum migration plan documented