Learn in the textbookApplying Encryption and Digital Signatures
DefinitionTime authentication (時刻認証) is a trusted third party, the time-stamping authority (時刻認証局), attaching an accurate time to electronic data and certifying it.
ExplanationAs a disinterested third party, the time-stamping authority attaches the time based on an accurate time source. A time that the data's own creator attached counts for nothing as evidence if a dispute arises later.
Memory hookIf the name says “authority”, it is a third-party body. The certificate authority (認証局) vouches for who owns a public key and the time-stamping authority (時刻認証局) vouches for the time, so set them side by side to tell them apart.