Symmetric vs Asymmetric Encryption¶

Cryptography is the mathematical foundation of confidentiality and integrity. You don't need to invent algorithms — you need to know which tool to use and how to use it correctly.

Symmetric Encryption — One Shared Key¶

The same key encrypts and decrypts.

• Fast — ideal for bulk data.
• Challenge: securely sharing the key with the other party.
• Algorithm to know: AES (Advanced Encryption Standard), typically AES-256.

Plaintext ──[ AES + key K ]──▶ Ciphertext Ciphertext ──[ AES + key K ]──▶ Plaintext

Avoid DES and 3DES (too weak/slow) and never use ECB mode — it leaks patterns. Prefer authenticated modes like AES-GCM.

Asymmetric Encryption — A Key Pair¶

Each party has a public key (shareable) and a private key (secret).

• Encrypt with the public key → only the matching private key can decrypt.
• Sign with the private key → anyone can verify with the public key.
• Slower — used for small data and key exchange, not bulk encryption.
• Algorithms to know: RSA, ECC (elliptic curve — smaller keys, same strength).

The Best of Both: Hybrid Encryption¶

This is how HTTPS actually works:

1. 1.Use asymmetric crypto to securely exchange a random session key.
2. 2.Use that symmetric session key (fast) to encrypt the actual data.

You get the key-distribution benefit of asymmetric crypto and the speed of symmetric crypto.

Key Length & Strength¶

The Cardinal Rule¶

Don't roll your own crypto. Use well-reviewed libraries (libsodium, the platform's crypto API) and vetted standards. Homegrown encryption is almost always broken — the failures are subtle and catastrophic.

Looking Ahead: Post-Quantum¶

Large quantum computers could one day break RSA and ECC. Post-quantum cryptography (e.g., NIST's ML-KEM / Kyber) is being standardized now. You don't need to deploy it today, but know the term — "crypto-agility" (the ability to swap algorithms) is becoming a design requirement.