問79
頻出度★★★
SSL の機能に関する記述のうち, 最も適切なものはどれか。
平成23年度 特別試験 ITパスポート試験 問79
This question's explanation and your answers so far.
解説
問 79
Incorrectア
Generating a one-time password (a password that is used only once and then discarded) is a function of a hardware token, a smartphone authentication app, or the authentication server that pairs with them; it is not a function of SSL. SSL is a mechanism that encrypts and protects data that has already been sent, not a mechanism that creates passwords for verifying who the user is. SSL/TLS does also have a server authentication function that uses a server certificate, but that confirms whether the server being connected to is genuine, which is a different thing from issuing a one-time password to the user.
- イ
正解 SSL (Secure Sockets Layer) is a protocol for protecting the communication between a web browser and a web server. What is actually used today is its successor TLS (Transport Layer Security), but the IT Passport exam covers them together as SSL/TLS. Its main role is to encrypt the data that is exchanged, so that even if someone eavesdrops partway along the communication path, the content cannot be read. In addition, it uses a server certificate to confirm whether the server being connected to is genuine (server authentication), and it also confirms that the data has not been rewritten along the way (tamper detection). Communication that combines HTTP with SSL/TLS is HTTPS; this is the state in which the browser address bar starts with https:// and a lock mark is displayed. Therefore, the most appropriate description of the function of SSL is イ, which says that it encrypts the communication between a web browser and a web server.
Incorrectウ
Blocking communication to websites that are not permitted is a function called URL filtering or content filtering, and it is handled by a proxy server, a firewall, or filtering software. SSL is not a mechanism that judges whether the other party is a safe site and screens which destinations may be connected to; it is a mechanism that encrypts the content of the communication with the party that has been connected to. On the contrary, because communication encrypted with SSL/TLS has content that can no longer be seen, from the filtering side it works in the direction of making the content harder to tell apart.
Incorrectエ
Detecting viruses that spread and infect over a network is a function of anti-virus software (anti-malware software) or an IDS (Intrusion Detection System); it is not a function of SSL. SSL does not judge what the content of the communication is; whether it is legitimate data or a virus, it encrypts and carries it as it is, without distinction. In other words, even communication protected by SSL cannot stop a virus contained inside it, so encryption and virus detection need to be combined as separate countermeasures.
ここがポイント
- Definition of SSL/TLS: a protocol that encrypts the communication between a web browser and a web server to prevent eavesdropping, and that also provides server authentication using a server certificate as well as tamper detection. The form combined with HTTP is HTTPS.
- Tell security functions apart by which component provides them: encryption of communication is handled by SSL/TLS, generation of one-time passwords by an OTP token or an authentication app, blocking of the sites that may be visited by URL filtering or a firewall, and detection of viruses by anti-virus software or an IDS.
用語