Cryptography fundamentals for developers

Data protection matters for apps, services, and users. Understanding a few fundamentals helps you choose safe patterns and avoid common mistakes. This guide uses plain language and practical tips you can apply today.

Symmetric vs. asymmetric encryption Symmetric encryption uses one secret key to both encrypt and decrypt data. It is fast and suitable for large data. In practice you use a strong algorithm like AES with a modern mode such as GCM to get both confidentiality and integrity. Asymmetric encryption uses a pair of keys: a public key for encryption and a private key for decryption. It helps with key distribution and digital signatures, but it is slower. A typical setup combines both: encrypt data with a symmetric key, then protect that key with an asymmetric public key.

Hash functions and data integrity Hashing turns data into a fixed-size digest. It is one-way: you should not try to reverse it. Use strong, modern hashes (SHA-256 or SHA-3) and apply a salt when needed. Hashes are essential for verifying integrity and for storing passwords with proper algorithms.

Digital signatures A digital signature proves who signed data is from and that it has not changed. It uses a private key to sign and a public key to verify. Rely on a trusted chain of certificates, and rotate keys when needed.

Randomness and entropy Cryptography relies on good randomness. Use a system cryptographic random number generator and avoid rolling your own RNG. Poor randomness can weaken keys and protocols.

Key management basics Protect keys as secrets. Store them in secure storage, limit access, and rotate them periodically. Backups, auditing, and disaster recovery are essential. If you lose a private key, you lose access.

Common mistakes to avoid

  • Re-inventing algorithms or protocols
  • Mixing encryption modes without understanding them
  • Storing secrets in logs or plain files
  • Using weak or outdated algorithms

Practical guidance

  • Rely on established libraries and standards. Do not implement crypto yourself.
  • Use TLS for network traffic and AEAD modes like AES-GCM for data at rest.
  • Derive keys from passwords with strong methods (Argon2, scrypt, PBKDF2).
  • Use key vaults or hardware security modules when possible.
  • Practice threat modeling and plan for key rotation and revocation.

Practical examples

  • Encrypt stored user files with AES-256-GCM and rotate keys.
  • Protect API tokens by encrypting them at rest and using short-lived tokens.
  • Hash and salt passwords with Argon2id; store only the salt and hash, not the password.

Putting it together With these basics, you can design safer features, review dependencies, and communicate risk clearly with your team. Start by mapping data flows, then apply proven cryptography choices rather than custom code.

Key Takeaways

  • Use established libraries and avoid rolling your own crypto.
  • Protect keys as sensitive data and rotate them regularly.
  • Apply secure defaults, audit dependencies, and keep algorithms up to date.