Standard signatures often can no longer be validated correctly after the underlying certificate expires (usually after 2 to 3 years). sproof sign therefore consistently uses the LTV (Long-Term Validation) standard. In this process, revocation information (such as CRL or OCSP lists) is embedded directly into the document at the time of signing. This allows the validity of the signature to be verified in an audit-proof manner—even decades later—and independently of the issuer.