Learn in the textbookThe Certificate Authority and the Operation and Revocation of Certificates
DefinitionThe Japanese term 認証局 (certificate authority) is what Japanese materials call a CA: a body that issues digital certificates as a third party with no stake in the communication or transaction.
ExplanationPKI (Public Key Infrastructure) is the whole system in which certificates show which public key belongs to whom, and a trusted body stands behind those certificates. The certificate authority sits at the center of this system, so by trusting it, users can trust the public key of someone they have never met. If the authority's signature checks out, it also shows the certificate was not swapped along the way.
AnalogyA passport works abroad because other countries trust the government that issued it. A certificate authority likewise gives a certificate its weight by being an issuer the other side trusts.
Memory hookIn the Japanese name, 認証 means confirming someone is who they say, and 局 is the character for a bureau or office: literally, "the bureau that confirms identity."