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Question
What are the three main types of cryptographic functions and how do they differ?
Answer
Symmetric uses one shared key (fast); asymmetric uses a public/private key pair (solves key exchange); hashing is one-way and keyless (irreversible).
| Type | Keys | Speed | Use case |
|---|---|---|---|
| Symmetric | Same key encrypts & decrypts | Fast | Bulk data encryption (AES) |
| Asymmetric | Public key encrypts, private key decrypts | Slow | Key exchange, digital signatures (RSA, ECDSA) |
| Hash | No key (one-way) | Fast | Password storage, integrity verification (SHA-256, bcrypt) |
Why all three exist: Symmetric is fast but requires secure key exchange. Asymmetric solves key exchange but is slow. In practice, TLS uses asymmetric to exchange a symmetric key, then symmetric for the actual data (hybrid approach). Hashing is fundamentally different — it's irreversible, which is exactly what you want for passwords.
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