In a U. V., the sender encrypts his message with a publicly accessible key calculated by the recipient from his private key and sends this encrypted message through the transmission channel (e.g. via the Internet) to the recipient, who decrypts the message using his private key known only to him (e.g. password).
Different encryption methods on the sender and receiver side ensure that the receiver can pass on the public key it has calculated to a large number of senders without jeopardizing the security of the data transmission.

Source: logipedia / Fraunhofer IML