What is the purpose of a digital signature?

A digital signature serves the dual purpose of verifying the authenticity and integrity of a message or document. It uses cryptographic algorithms to create a unique hash of the content, which is then encrypted with the sender's private key. This process ensures that any alterations to the document will change the hash value, signaling that the content has been tampered with. By validating the signature with the sender's public key, the recipient can confirm that the message was indeed sent by the stated sender and that it has not been modified during transit.

While the other options touch on important aspects of digital communications, they do not fully encapsulate the primary function of a digital signature. Encrypting a message focuses on confidentiality rather than integrity or authenticity. Preventing malware distribution is related to broader cybersecurity measures and is not specific to the purpose of a digital signature. Authenticating the sender's identity does form part of the digital signature's function but does not encompass the vital aspect of ensuring the message's integrity. Therefore, the correct choice highlights the comprehensive role that digital signatures play in safeguarding both authenticity and integrity in digital communications.