問70
頻出度★★★
電子メールにデジタル署名を付与することによって得られる効果だけを全て挙げたものはどれか。 a 可用性が向上する。 b 完全性が向上する。 c 機密性が向上する。
令和4年度 ITパスポート試験 問70
This question's explanation and your answers so far.
解説
問 70
Incorrectア
This includes a 'availability'. Availability (being able to use a system or data when needed) is not improved by a digital signature. Availability is ensured through measures such as redundancy and backups, and has nothing to do with signatures.
Incorrectイ
This includes a 'availability' and c 'confidentiality'. Neither is an effect obtained from a digital signature. Confidentiality protects the content with encryption so that third parties cannot read it, whereas a signature does not conceal the content.
- ウ
正解 A digital signature works by having the sender encrypt the hash value of the message with their own private key and attach it, while the receiver verifies it with the sender's public key. This lets the receiver confirm that the message has not been tampered with in transit (integrity) and that the sender is genuinely who they claim to be (authenticity / non-repudiation). Among a to c in the question, the only property that improves is b 'integrity', so 'ウ', which lists only b, is the correct answer.
Incorrectエ
This includes c 'confidentiality'. A digital signature only signs the hash value and does not encrypt the message body itself, so the confidentiality that prevents eavesdropping is not improved. If confidentiality is required, encryption must be used separately alongside it.
ここがポイント
- A digital signature guarantees integrity (tamper detection) and authenticity / non-repudiation; it does not guarantee confidentiality or availability.
- Among the three elements of information security (confidentiality, integrity, availability = CIA), a signature improves only integrity. Confidentiality is ensured by encryption, and availability by redundancy.
用語