Certificate Problems and Solutions

Certificate-related issues represent the most common category of digital signature problems. Users often encounter messages like "certificate not trusted" or "certificate expired" without understanding what went wrong. These errors typically stem from certificate chain problems where the signing certificate cannot be traced back to a trusted root certificate authority. The solution involves ensuring the complete certificate chain is included with the signature and that the verifying system trusts the root certificate.

Expired certificates create particular frustration because they can invalidate previously valid signatures. When a certificate expires, new signatures cannot be created, but existing signatures should remain valid if they were timestamped while the certificate was valid. However, some systems incorrectly invalidate these historical signatures. The solution requires proper timestamp verification and long-term validation (LTV) information embedded in the signature. Organizations should monitor certificate expiration dates and renew well before expiry to avoid disruption.

Certificate revocation introduces another layer of complexity. When certificates are compromised or issued incorrectly, certificate authorities add them to Certificate Revocation Lists (CRLs) or update Online Certificate Status Protocol (OCSP) responders. Signature verification should check revocation status, but network problems or outdated CRL caches can cause false positives. Troubleshooting involves verifying network connectivity to revocation endpoints, clearing CRL caches, and ensuring signature creation includes current revocation information for offline verification.