In order for the signed document to be considered durable for a longer period of time, ETSI has defined a standard (ESTI TS 103 172) with several levels of techniques to ensure that the PAdES document can be verified over time. TellusTalk uses the highest level, LTA (Long Term Archival), which includes, among other things, a time stamp that proves the certificate was valid at the time of signing. This means that the signature is considered valid even when the certificate has expired in the future.
