After some #Thunderbird update, I've started to get notices about incorrect S/MIME signatures in emails which was previously marked as correct. The error message was obscure - something about an unknown issue.
No quick solution was found. After some time, I've tried again to figure out what is the problem, and this Czech article solved it: https://www.postsignum.cz/files/navody/thunderbird_smime/index.html
Shortly - Thunderbird dropped support of #SHA1 #checksum in #SMIME signatures and failed to provide any human-readable error message in that regard.
I believe it is a suboptimal behavior for a number of reasons:
1. I can't avoid getting emails from this source and can't make them upgrade their certificate, really. I have only a choice either to drop the signature check completely or rely on the substandard check. Obviously, in this situation I prefer rather to see the results of the check and probably some info that it is, actually, substandard.
2. Solving the problem needs to realize it first. An obscure error message is not too helpful.
3. Such incidents actually undermine the opinion about #cryptographic #signature check. If you see some error, your first though is not "it is probably a #MITM attack" but "probably something is broken in the signature check".
The possibility to fix everything is, however, good.
