What is the difference between symmetric and asymmetric encryption?

Symmetric encryption uses one shared key to lock and unlock; asymmetric, or public-key, encryption uses a pair: a public key anyone may know and a private key only its owner holds. Symmetric algorithms such as AES are fast and encrypt almost all real data. Their weak point is sharing the key safely. Public-key methods such as RSA, elliptic-curve Diffie-Hellman and their post-quantum successors solve that: two parties who have never met can agree on a fresh symmetric key over an open network, and a private key can sign data so that anyone with the public key can check it. Real protocols combine both. A TLSTLS: Transport Layer Security. The encryption that protects most internet traffic, such as HTTPS. connection uses public-key cryptography in the handshake to agree a key and prove the server's identity, then switches to AES or ChaCha20 for the data. That split also explains the quantum story: Shor's algorithm threatens the public-key part, while symmetric encryption with 256-bit keys stays strong.

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