Trusted Certificate Authorities

In PKI the attributes that are used to built the CA chain are:

Preferred method implemented most of the time: AKI/SKI attributes. Authority Key Identifier of the certificate points to the Subject Key Identifier of it's signer -- public key hash values.

Alternative method:: Subject/Issuer attributes. Issuer of the certificate points to the Subject of it's signer -- named values.

Furthermore, validity of a certificate is always checked based on the "valid to" (datetime attribute) and CRL/OCSP checks.