問66
頻出度★★★
PKI における CA (Certificate Authority) の役割に関する記述として, 適切なものはどれか。
令和6年度 ITパスポート試験 問66
This question's explanation and your answers so far.
解説
問 66
Incorrectア
“It sits between the Internet and the internal network and accesses the Internet on behalf of the computers on the internal network” describes a proxy server, not the role of a CA.
Incorrectイ
“It uses functions such as packet filtering to prevent unauthorized access from the Internet to the internal network” describes a firewall. This has nothing to do with issuing certificates and is not the role of a CA.
Incorrectウ
“Based on the domain name, it maps IP addresses to domain names so that the user accesses the intended server” describes DNS (Domain Name System). It is a name resolution mechanism, not the role of a CA.
- エ
正解 The correct answer is エ. In a PKI (public key infrastructure), a CA (Certificate Authority) is a trusted third party that guarantees that a user's public key really belongs to that user. Specifically, the CA issues a digital certificate (public key certificate) for the user's public key and attaches the CA's own digital signature to that certificate, thereby guaranteeing the legitimacy of the key. The CA also takes on the role of revoking a certificate — using a certificate revocation list (CRL) and similar mechanisms — when the certificate becomes invalid, for example because the key has been leaked or the holder's affiliation has changed. Option エ, “It issues and revokes public key certificates for a user's public key, thereby guaranteeing the legitimacy of the key”, describes exactly this role of the CA and is therefore appropriate.
ここがポイント
- In a PKI, a CA (Certificate Authority) issues and revokes digital certificates (public key certificates) for public keys, and is a trusted third party that guarantees that a public key really belongs to its owner.
- A proxy server, a firewall, and DNS are all network functions; distinguish them from a CA, which guarantees the legitimacy of keys — their roles are different.
用語