In this section, we will cover digital signatures and public and private keys. In the preceding description, we saw that messages are signed by the subject. Signing a message is termed the digital signature of the message. It is the digital signature that guarantees message integrity and authentication. Authentication ensures that parties involved in a transaction are sure about the identity of the message sender or creator, and integrity affirms that the message was not modified/tampered with during transit. Hence, it is the digital signature that guarantees integrity and authentication. The transaction (message) sender will sign the message using their private key and send it to the recipient. The recipient will use the sender's public key (widely known) to verify the integrity and authenticity of the message. This means that the recipient will use the sender's public key to ensure that it was sent by the sender who is claiming to be the sender, and who is the expected sender. A combination of keys, both public and private, ensures secure communication over the blockchain network.