Cryptography Basics for Developers

Cryptography helps protect information by transforming it. It can keep secrets safe, prove who sent a message, and ensure it wasn’t tampered with. As a developer, you should rely on proven libraries rather than writing crypto code yourself. Small mistakes can undermine security and give attackers an easy path in.

What cryptography does

Cryptography has three main jobs: confidentiality (keeping data secret), integrity (detecting tampering), and authenticity (proving who sent something).

  • Confidentiality is achieved through encryption.
  • Integrity uses hashes or MACs to verify data hasn’t changed.
  • Authentication relies on digital signatures and certificates to prove identity.

Core ideas

Keys are the core asset. Protect them; treat them as secrets. Use randomness that is unpredictable. Use algorithms with standard security proofs and avoid custom schemes.

  • Keys must be kept secret and rotated regularly.
  • Randomness matters: use a good RNG from a trusted library.
  • Use authenticated encryption to combine confidentiality and integrity.
  • Be careful with padding, modes of operation, and side-channel risks.

Common algorithms

  • Symmetric encryption: AES-GCM, ChaCha20-Poly1305
  • Asymmetric: RSA, ECDSA, Ed25519
  • Hashes: SHA-256, SHA-3
  • Signatures and certificates: digital signatures, PKI
  • Key exchange: ECDH

How to use cryptography safely

  • Rely on well-maintained libraries; don’t write crypto code from scratch.
  • Let the library handle algorithms, modes, and keys.
  • Use TLS (preferably TLS 1.3) for data in transit.
  • For passwords, use strong hashing (Argon2id, bcrypt, or scrypt).
  • Store only derived keys or encrypted secrets, never plain data.
  • Prefer authenticated encryption and secure defaults; keep libraries up to date.

Practical steps for developers

  • Plan crypto early in design and document key lifecycles.
  • Use hardware security if possible (HSMs or secure enclaves).
  • Rotate keys and revoke them safely when needed.
  • Test with standard test vectors and real-world scenarios.
  • Monitor dependencies and follow security advisories.

Key Takeaways

  • Do not reinvent cryptography; use reputable libraries and standards.
  • Separate duties: protect keys, secure transmission, and verify integrity.
  • Plan, rotate, and audit your crypto choices to stay safer over time.