1.4.1. Symmetric vs. Asymmetric Encryption

💡 First Principle: Symmetric encryption uses one shared key for both encryption and decryption — fast but requires secure key distribution. Asymmetric encryption uses a key pair (public + private) — slower but solves the key distribution problem. Most real-world systems use both: asymmetric to exchange keys, then symmetric for the actual data.

Symmetric encryption is like a shared combination lock. Both sender and receiver know the same combination (key). It's fast and efficient for large amounts of data, but the fundamental challenge is: how do you securely share the combination? If you send it over the network, an attacker could intercept it. Common symmetric algorithms include AES (the current standard) and DES (outdated, insecure).

Asymmetric encryption is like a mailbox with a slot. Anyone can drop a letter in (encrypt with the public key), but only the owner with the private key can open the box (decrypt). This elegantly solves key distribution — public keys can be shared openly — but it's much slower than symmetric encryption. Common asymmetric algorithms include RSA and Elliptic Curve Cryptography (ECC).

The real-world solution combines both: when your browser connects to a bank via HTTPS, it uses asymmetric encryption to securely exchange a symmetric session key, then switches to symmetric encryption for the actual data transfer. This gives you the security of asymmetric key exchange with the speed of symmetric data encryption.

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⚠️ Exam Trap: Asymmetric encryption is NOT "better" than symmetric — they solve different problems. Symmetric is faster and used for data encryption. Asymmetric is used for key exchange and digital signatures. The exam tests whether you know when to use each.