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Symmetric vs asymmetric key encryption
Short answer
Symmetric encryption uses one shared key for both operations, is fast, and suits bulk data. Asymmetric uses a public/private key pair, is slower, and enables digital signatures, authentication, and secure key exchange without pre-shared secrets.
Compare symmetric key encryption method with asymmetric (public) key encryption.
Symmetric-key encryption uses one shared secret key for both encryption and decryption. Asymmetric (public-key) encryption uses a pair of keys: a public key to encrypt and a related private key to decrypt.
| Point | Symmetric | Asymmetric |
|---|---|---|
| Keys | One shared secret key | Public key + private key |
| Key distribution | Hard: the key must be shared secretly | Easy: public key can be published |
| Speed | Fast | Slow (heavy mathematics) |
| Key size | 128 to 256 bits | 2048 bits or more (RSA) |
| Keys for n users | n(n − 1)/2 (4,950 for 100 users) | 2n (200 for 100 users) |
| Services | Confidentiality | Confidentiality, authentication, digital signature, key exchange |
| Non-repudiation | Not provided | Provided by digital signatures |
| Examples | DES, 3DES, AES, RC4, Blowfish | RSA, Diffie-Hellman, ElGamal, ECC |
| Typical use | Bulk data encryption | Exchanging session keys, signatures |
Symmetric : Plain --[K]--> Cipher --[K]--> Plain
Asymmetric: Plain --[Pub B]--> Cipher --[Priv B]--> Plain
In practice both are combined: the public-key method securely sends a symmetric session key, and the symmetric cipher encrypts the data (SSL/TLS, PGP).
✓ Answer checked by Claude Opus 5.5 (high effort)
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