Nitrokey3 and GPG-Keys with unusual length + Multiple GPG-Keys

Nitrokeys Pro/Start/Storage (OpenPGP Card)
1

Hi,
I want to store a GnuPG-Key with an unusual bit size:
sec rsa3744/7C3192F14CF2D85A
the subkeys are rsa 2048.

when I try to import them into my nk3 (latest firmware version); i get a “bad secret” error. even when I try to use different keyysizes for the key-attrs in the admin-commands (I tried 2048, 4096, 3744), it didn’t work.
what do I need to do to import this key to the nk3?

And as far as I am aware, the nk3 should be able to hold three different GPG-Keys (including subkeys). how can I import a second and a third one?

best regards, Hanno

2

Quick answer to this one: yes, you can, see NK3C: Unable to generate RSA:4096 SSH key - #2 by saper for an example of multiple keys of different types on one card.

3

Functional Specification of the OpenPGP application on ISO Smart Card Operating Systems v3.4.1 does not seem to care (key lengths are specified in bits), but the card is free to reject unsupported key lengths.

Make RSA key size support a runtime configuration by sosthene-nitrokey · Pull Request #190 · Nitrokey/opcard-rs · GitHub indicates that only 2048, 3072 and 4096 are supported by the opcard-rs firmware.