Asymmetric encryption, also called public-key cryptography, uses two related keys: a public key that can be shared with anyone and a private key that must stay secret. Data encrypted with one key can only be decrypted with the other of the pair.
Why it matters
It solves the key distribution problem of symmetric encryption, because strangers can send you protected data using only your public key. It also enables digital signatures and the certificates behind HTTPS. It is slow, so it is normally used to exchange a symmetric key or to sign small values, not to encrypt large files directly.
Example
A server publishes a certificate containing its public key. Your browser uses it to help establish a shared session secret, and only the server, holding the matching private key, can complete the exchange. Common algorithms include RSA and elliptic curve schemes such as ECDSA and X25519.
Common mistakes
- Thinking the public key must be kept secret. Only the private key is secret.
- Encrypting bulk data with RSA directly instead of using hybrid encryption.
- Using key sizes that are too small, for example RSA below 2048 bits.
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