ITPEC IP April 2024 Question 39

Digital signature — verifying the signature shows whether the data changed after it was signed, and who signed it.

• •The sender computes a hash (message digest) of the data and encrypts it with the sender's private key: that is the signature, sent with the data
• •The receiver decrypts the signature with the sender's public key and computes the hash of the data received
• •If the two hashes match, the data is unchanged; if anyone altered even one bit, they differ and tampering is detected

Only the holder of the private key could have made the signature, so it also confirms the sender.

Answer (b)

Why not others:

• •(a) Compression — reduces the size of data; it neither proves nor checks that the content is unchanged
• •(c) Password authentication — confirms who a user is when logging in; it says nothing about whether data received was altered
• •(d) Filtering — passes or blocks traffic or content by rules; it does not check the integrity of data

Key rule: A digital signature, made with the sender's private key over a hash, gives integrity (detects tampering) and authenticity (confirms the sender); encryption is what gives confidentiality.

Security · AI-written, may contain errors