publickeyprivatekey

PublicKeyPrivateKey refers to a cryptographic key pair consisting of a public key and a corresponding private key. The public key is freely distributed to anyone who wishes to communicate securely with the key holder, while the private key is kept confidential. In asymmetric cryptography, the algorithm guarantees that data encrypted or signed with one key can only be decrypted or verified with the paired key. This one-to-many property allows secure communication over untrusted channels and authenticates the source of messages.

The most common algorithms that use public–private key pairs are RSA, elliptic‑curve cryptography (ECC), and Diffie‑Hellman variants. RSA generates large integer keys whose security relies on integer factorization, whereas ECC uses points on an elliptic curve, achieving comparable security with shorter keys. Diffie‑Hellman is primarily a key‑exchange protocol, but ECC can also support it. Key sizes vary: RSA keys traditionally use 2048‑bit or 4096‑bit lengths, while ECC keys of 256‑bit or 384‑bit provide similar strength.

Public and private keys appear in many protocols. In TLS/SSL, a server presents a certificate containing its public key; the client verifies it against trusted authorities, then uses the public key to establish a shared secret. For digital signatures, a sender signs a message with its private key; anyone can verify with the public key. In blockchain systems, a private key controls ownership of funds, and the public key derives the address displayed publicly.

Secure generation, storage, and management of private keys are critical. Hardware security modules (HSMs), smart cards, and secure enclaves protect private keys from extraction. Backup and key recovery strategies must be robust to prevent loss of access. Public keys can be stored openly, often embedded in certificates with a status such as revoked or expired. Proper key lifecycle policies, including rotation and revocation, enforce security across networked services.