Hash functions are fixed values derived mathematically from a text message.
A single secret key is used to encrypt the message, because secret key encryption requires less processing power than using public and private keys. A digital certificate, signed by a certificate authority, validates senders' and recipients' public keys. A pre hash code is derived mathematically from the message to be sent. The pre hash code is encrypted using the sender's private key. The encrypted pre hash code and the message are encrypted using the secret key.