問85
頻出度★★★
電子メールの内容が改ざんされていないことの確認に利用するものはどれか。
令和元年度 秋期 ITパスポート試験 問85
This question's explanation and your answers so far.
解説
問 85
Incorrectア
IMAP (Internet Message Access Protocol) is a protocol for viewing, managing, and receiving email stored on a mail server; it merely defines the communication procedure and has no mechanism to detect tampering of the body.
Incorrectイ
SMTP (Simple Mail Transfer Protocol) is a protocol for sending and forwarding email; it only handles delivery and has no function to confirm whether the content has been tampered with.
Incorrectウ
An information security policy is a document that sets out an organization's security policies and rules; it is not a technical means to detect tampering of an individual email body.
- エ
正解 Choice エ, the digital signature, is correct. With a digital signature, the sender computes a hash value (message digest) from the email body, encrypts it with their own private key, and attaches it to the email as a signature. The receiver compares the hash value obtained by decrypting the signature with the sender's public key against a hash value recomputed from the received body. If the content was tampered with along the way, the two hash values will not match, so tampering can be detected. In addition, because only the person holding the private key can sign, it also prevents impersonation of the sender (authentication). Therefore, what is used to confirm that the content has not been tampered with is the digital signature.
ここがポイント
- A digital signature combines a hash value with public-key cryptography to achieve integrity (tamper detection) and authentication (impersonation prevention).
- IMAP and SMTP are protocols for receiving and sending email; they are not themselves intended for encryption or tamper detection.
用語