Skip to content

CS Professional · Artificial Intelligence, Data Analytics and Cyber Security - Laws and Practice · Network Basics and Security

A director receives a PDF of minutes bearing a valid digital signature from the Chairman. Later, one word in the PDF is altered by an unknown person and the file is re-verified. What will the verification show, and why?

Verification fails because the hash computed from the altered file no longer matches the hash recovered from the signature using the Chairman's public key. A valid certificate does not help, since the digital signature is bound to the exact original content, ensuring integrity.

  1. AVerification succeeds, because the Chairman's certificate is still valid
  2. BVerification fails, because the hash now computed differs from the hash recovered from the signatureCorrect
  3. CVerification succeeds, because digital signatures protect only the signer's identity and not the content
  4. DVerification fails only if the Chairman's private key has been revoked

Explanation

The signature encrypts the hash of the original content. After alteration, the newly computed hash differs from the decrypted original hash, so verification fails even though the certificate is valid. Signatures bind identity to content, hence integrity is protected; revocation is a separate check.

Did you get it right without looking?

One question tells you little. A timed set on Network Basics and Security shows your real accuracy, how long you take and where you lose marks.

Practise Network Basics and SecurityFree diagnostic mock

More Network Basics and Security questions