What is a digital signature used for?

A digital signature serves primarily to verify the authenticity and integrity of digital documents. By using cryptographic techniques, it provides assurance that the document was created by a known sender (authentication) and that the content has not been altered during transmission (integrity).

When a sender creates a digital signature, they apply a specific algorithm to the contents of the document, generating a unique hash value that is then encrypted with their private key. This process forms the digital signature. The recipient can use the sender's public key to decrypt this signature and compare the hash value with their own copy of the document. If the values match, it confirms that the document is authentic and has not been tampered with.

The other options do not accurately describe the purpose of a digital signature. Speeding up data encryption is not relevant as digital signatures focus on validation rather than encryption speed. Digital signatures do not encrypt files without keys since they rely on a keyed system for authentication. Lastly, generating copies of digital files is outside the scope of what a digital signature achieves, as it is intended for validation rather than duplication of content.