Public key encryption involves two corresponding keys, commonly known as a key-pair. One of these keys is private (private key) and the other key is widely known (public key). The owner needs to know the private key, and the public key is available and known to anyone. Since only one party needs to know the private key, it does not need to be transmitted between parties. Therefore, the private key is never at the risk of interception. Knowledge of the public key by a third party does not compromise the security of data transmission.
The owner of the private key can digitally sign a document by encrypting a unique digest of the message with the private key. The source of the document can be verified by decrypting the digital signature with the public key and comparing it to the digest of the message.