What is a digital signature?

A digital signature is a cryptographic mechanism that verifies the authenticity and integrity of data. It serves as a means to ensure that the message or document has not been altered in transit and that it indeed originates from the claimed sender. When a document is digitally signed, a hash of the data is created and then encrypted with the sender's private key. This signature can then be verified by anyone with access to the sender's public key, allowing them to confirm both the identity of the sender and the integrity of the data.

The process of using digital signatures is critical in many applications, such as secure communications, software distribution, and financial transactions, as it provides a level of assurance against forgery and tampering. In contrast, the other options do not accurately describe the function of a digital signature. For example, data compression focuses on reducing file size, encryption revolves around protecting data confidentiality, and user identification pertains to access control rather than document authenticity and integrity.