How to use the backup of the secret key?

[osresearch]

When using the gpg2 --card-edit generate command, one of the options is to create an off-device backup of the secret. How do you use this file? It seems that gpg2 hasn't changed since this mailing list post in 2017 with regards to importing a secret key to match it to the device.

Some things I've tried:

% gpg2 gnupg/sk_4FC1E4C20F8AC356.gpg  
gpg: WARNING: no command supplied.  Trying to guess what you mean ...
gpg: DBG: FIXME: merging secret key blocks is not anymore available
gpg: DBG: FIXME: No way to print secret key packets here

% gpg2 --allow-secret-key-import --import gnupg/sk_4FC1E4C20F8AC356.gpg  
gpg: key 4FC1E4C20F8AC356: no user ID
gpg: Total number processed: 1
gpg:       secret keys read: 1

% gpg2 --edit-key 4FC1E4C20F8AC356
gpg (GnuPG) 2.2.19; Copyright (C) 2019 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

pub  rsa2048/E7277F2F7193A538
     created: 2020-09-08  expires: 2021-09-08  usage: SC  
     trust: unknown       validity: unknown
sub  rsa2048/D03ED8B060CD46F0
     created: 2020-09-08  expires: 2021-09-08  usage: A   
sub  rsa2048/4FC1E4C20F8AC356
     created: 2020-09-08  expires: 2021-09-08  usage: E   
[ unknown] (1). TESTING

gpg> toggle
Need the secret key to do this.

gpg> bkuptocard
Need the secret key to do this.

[jans23]

Does this documentation help?

In general, please post usage-related questions in our support forum.

[szszszsz]

Hi!
With on-device generation only the encryption key's secret (usage: E) can be backed up - I guess you are more interested in the whole key backup, which is linked in #56 (comment) by @jans23 .