Digital certificate is an electronic attestation which links a signature verification data to a person, and confirms the identity of that person [Dir. 1999/93/EC].

Signature creation applications must perform validity checks of the signer certificate prior to the signing. These checks are not only limited to the signer certificate but also include validity checks of the TSP certificates, CRL, and OCSP that used for revocation checks. These checking controls are named as certificate validation process.

The certificate validation process that consist of many validation steps basically involves the followings:

• Certificate validity period should be checked.

• Signature on the certificate should be validated. If the signature is created by using an end-entity certificate, issuer certificates must be available. Also, validity period and signature validation controls must be performed for the issuer certificate.

• Certificate must not be revoked.