Public key cryptography is a method of securing information using two keys: a public key and a private key. The public key can be shared with anyone, allowing them to encrypt messages intended for the key's owner. Only the owner, who possesses the corresponding private key, can decrypt these messages, ensuring confidentiality. This system also enables digital signatures, where a sender can sign a message with their private key. Recipients can verify the signature using the sender's public key, confirming the message's authenticity and integrity. This dual-key approach enhances security in online communications and transactions.