Transferring digital certificates from iPhone 4s to iPhone 6s

Hi,

In view of the "zoomed display" bug afflicting iPhone 6s's restored from backups of iPhone 5x (and, assuming the worst in my case, iPhone 4s's), I'm thinking about setting up my new iPhone 6s from scratch. As most of my content is either in iCloud or in IMAP e-mail accounts, this wouldn't be impossible. The only thing I would need to transfer from the old iPhone 4s (not yet decommissioned) that I may not be able to re-input are the expired digital secure e-mail certificates. I assume they are required when viewing encrypted a-mail sent to me when those certificates were still valid. Doss anybody know how to do this? There doesn't seem to be a way to export them from the old iPhone.

Regards,

Richard