This comment in the scute code explains what this task is about:
/* We do not yet known about this object. If CKA_ISSUER and * CKA_SERIAL_NUMBER was requested, try to look it up via * gpgsm. The way we can implement this would be a new option to * gpgsm's LISTKEYS, named "--der" which takes the raw DER * encoding of both items. The advantage of doing this in gpgsm * is that we can use libksba there to build the actual * rfc-2253 search string from the DER. */