With the caveat that I'm no data archiving guru... As a source of inspiration a good place to start might be B-LTA in the ETSI standards. I believe this takes

With the caveat that I'm no data archiving guru... As a source of inspiration a good place to start might be B-LTA in the ETSI standards. I believe this takes into account the fact that the algorithm used for its creation might deprecated. IIRC the way it works is (basically) that signatures are given a finite validity period and you undertake periodic re-signing. Therefore you build up a audit trail history of signatures with current algos as you go along.