Digital Signatures using Public Key Cryptography

Let’s continue with the previous example. Where Bob receives a message, which when he decrypts says “Meet me at 11:00 tomorrow”. How can Bob know for sure that the message was sent by Alice and not Chris?

This can be achieved if the message is “signed” by its sender (Alice). The receiver of the message can then verify the signatures.

We need a way for Alice to “digitally sign” the message so the receiver of the message (Bob) can trust that the message was sent by Alice. Alice can add a digital signature to the message by using her private key to encrypt it. When the message is decrypted by her public key only, Bob can know for sure it came from Alice.