問68
頻出度★★★
全ての通信区間で盗聴されるおそれがある通信環境において, 受信者以外に内容を知られたくないファイルを電子メールに添付して送る方法として, 最も適切なものはどれか。
令和3年度 ITパスポート試験 問68
This question's explanation and your answers so far.
解説
問 68
- ア
正解 The correct answer is “ア”. S/MIME encrypts the email body and attachments on the sender's side using the recipient's public key, and only the recipient (the holder of the corresponding private key) can decrypt it. In other words, the encryption is maintained across every segment of the whole path from sender to recipient (yourself ↔ provider, provider ↔ provider, provider ↔ recipient); this is so-called end-to-end encryption. The condition in the question is that there is a risk of eavesdropping in every communication segment, so this method, whose contents cannot be read no matter where along the route the eavesdropping occurs, is the most appropriate.
Incorrectイ
SSL/TLS only encrypts the segment between your own device and the provider's mail server. Beyond that (between the mail servers, and between the receiving provider and the recipient) it is not protected, so it cannot fully guard against eavesdropping across all segments, making it inappropriate.
Incorrectウ
WPA2 only encrypts the wireless LAN segment (between the device and the access point). The wired segments and the internet route beyond it are not protected, so it cannot cope with eavesdropping across all segments, making it inappropriate.
Incorrectエ
Even if the file is protected with a password, the password itself sent afterwards in a separate email travels the same route that is subject to eavesdropping. If both emails are eavesdropped, the file can be decrypted with the password, so under the premise that every segment is eavesdropped it cannot be regarded as secure, making it inappropriate (this is the well-known weakness of the so-called PPAP method).
ここがポイント
- S/MIME is end-to-end encryption that encrypts the email body and attachments using public-key cryptography, so it can protect the contents even in an environment where there is a risk of eavesdropping in every communication segment.
- SSL/TLS and WPA2 encrypt only one specific segment, so distinguish that they cannot meet the requirement of protecting the entire path (from end to end).
用語