What’s the difference between public-key and symmetric cryptography?

Symmetric cryptography uses one shared key for both encryption and decryption, running roughly 100 to 1,000 times faster than public-key methods. Public-key cryptography uses a mathematically linked key pair, a public key for encrypting and a private key for decrypting, so two parties never have to exchange a secret over an insecure channel first. AES-256, a symmetric cipher, carries a 256-bit security strength, while RSA-2048, the most common public-key algorithm, reaches an estimated 112-bit equivalent strength under NIST SP 800-57.

How do the two actually compare?

When does symmetric cryptography make sense?

Symmetric cryptography fits anywhere you're encrypting large volumes of data and already have a secure way to share the key: disk encryption, database fields, or VPN traffic once a session is running. AES-256 is the standard choice here, built into TLS 1.3 cipher suites, because it processes large amounts of data at a fraction of the CPU cost of RSA.

When does public-key cryptography make sense?

Public-key cryptography fits the moment two parties need to establish trust or exchange a secret without a prior shared channel: logging into a website, verifying a software signature, or completing the initial handshake in TLS. RSA and elliptic-curve algorithms handle that first exchange, then hand off to a symmetric cipher for the actual session, which is exactly what happens when a browser connects to an HTTPS site.

Which one should you use?

A product that only needs to encrypt data sitting on one server or one device, a local database, a backup file, usually runs on AES-256 alone. A product that talks to clients it hasn't met before, an API, a login flow, a certificate-based service, needs public-key cryptography for that first trust step. Most production systems combine both rather than picking a single algorithm for everything.