問83
頻出度★★★
PKIにおいて, 電子証明書が正当性を証明しているものはどれか。
平成27年度 秋期 ITパスポート試験 問83
This question's explanation and your answers so far.
解説
問 83
Incorrectア
An encryption algorithm such as RSA is a publicly available standard, not the object whose validity a certificate guarantees. A certificate does not certify the algorithm itself.
Incorrectイ
A symmetric (shared) key is a key that should be secretly shared only between sender and receiver, so by its nature it is not placed in a publicly distributed certificate. In PKI, what a certificate guarantees is the public key, not the symmetric key.
- ウ
正解 A digital certificate is issued by a certificate authority (CA) with a digital signature attached, and it guarantees that “this public key truly belongs to this owner.” In other words, the object whose validity is proven is the owner’s “public key.” Because the other party’s public key is guaranteed to be genuine, communication that encrypts with that public key or verifies signatures can be trusted. Therefore “ウ public key” is correct.
Incorrectエ
A private key is a key that only the owner keeps under strict protection and must never disclose to anyone. It is never listed in or distributed via a certificate, nor is it the object whose validity is proven.
ここがポイント
- A digital certificate is issued by a certificate authority (CA); it binds the owner to a “public key” and thereby guarantees the validity of that public key.
- In public-key cryptography, the public key may be distributed and made public, while the private key and symmetric key are kept secret. What a certificate guarantees is the distributed public key.
用語