test storing S/MIME and OpenPGP with same cryptographic material

[tomholub]

Yes, I was thinking about creating an OpenPGP key having the same RSA public key as S/MIME. It's not quite straightforward to perform but in theory possible. Would you want me to spend time on this? Or we can simply add a test checking that OpenPGP keys' fingerprints are not suffixed in the storage?

Originally posted by @rrrooommmaaa in #3575 (comment)

[tomholub]

For actually creating such public key and a certificate, we may use Kotlin instead. Because this may be functionality that we'll add to our Email Key Manager to do for our customers. I'd introduce you to that codebase later whenever this becomes more current.