How do I make the private key on a OpenPGP smartcard non exportable ?

[Heinz Diehl]

On 18.06.2013, NdK wrote: 

> If the key is generated on-card, you have no way to backup it. No need
> for "unexportable" flag: simply there's no command to export it.

And if the key is generated off-card and properly moved to the
smartcard afterwards, there's no way to export it either. It's only
the stub which points to the smartcard left on disk.