IPA IP 2022 Question 70
A question IPA Japan published in 令和4年度 ITパスポート試験 公開問題 問70, translated into English. ITPEC is based on the same exams.
Which of the following lists all and only the effects that are obtained by attaching a digital signature to an e-mail?
Explanation
Only B, integrity — a digital signature lets the recipient detect any change to the e-mail and confirm who sent it, but it neither hides the content nor keeps the service running.
The sender signs a hash of the message with the sender's private key. The recipient decrypts the signature with the sender's public key and compares it with a hash of the received message: if they match, the message was not altered on the way and came from the holder of that private key.
- •A Availability (being able to use the information when needed) is a matter of redundancy and backups; a signature does nothing for it
- •B Integrity (the information is accurate and unaltered) is what the signature proves: improved
- •C Confidentiality needs encryption with the recipient's public key; a signed e-mail is still readable by anyone who intercepts it
Answer (c)
Why not others:
- •(a) and (b) — include A, availability, which a signature does not affect
- •(d) — includes C; signing is not encrypting, so confidentiality is unchanged
Key rule: A digital signature gives integrity and authentication of the sender (and non-repudiation); confidentiality comes from encryption.
Security · AI-written, may contain errors
This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.