OpenPGP smartcard restore

[Tristan Williams]

I am experimenting with the OpenPGP smartcard. I have two OpenPGP smart
cards (smartA and smartB) and I want to verify that I can restore my
on-card generated private key should I loose the master card
(smartA). I only want to verify that I can do it - not discuss the
merits of on-card vs. off-card key generation.

I start with an empty ~/.gnupg

For smartA I have

(1) an on-card generated key
(2) the backup file created ~/.gnupg/sk_X.gpg at key generation
(3) a backup of ~/.gnupg/secring.gpg when the 
(4) a file with the exported associated public key 
(5) a test file encrypted with above public key which decrypts with smartA
(6) the pass phrase used at key generation
(7) second OpenPGP smartcard (smartB)

I then I imagine that I have lost my card (smartA), my computer hard disk has
died and I have to restore to a fresh new gpg environment (i.e. no
~/.gnupg) and smartB

I then issues these commands 

gpg --list-keys 
which creates ~/.gnupg and various files within it.

gpg --import public_key.asc 
using (4) from my backups

gpg --list-keys 
shows that the public key has been imported

I then copy my backup secring.gpg to ~/.gnugpg

gpg --edit-key KEYID 
shows that the secret key is present

gpg --list-secret-keys 
shows that the secret key is linked to card-no smartA

gpg --edit-key KEYID
toggle
bkuptocard sk_X.gpg

choose the (1) the signature 
replace existing key yes
enter pass phrase 
save changes yes

Now 

gpg --list-keys 
shows the key still linked to card-no smartA and not smartB

any action needing the private key using smartB results in gpg
requesting that you put in smartA (which is lost...)

Has anyone actually managed a functional OpenPGP card restore with on-card key
generation? And if so how please!

Tristan Williams