For the put secret key operation, openpgp applet implementations differ
in their handling of attributes:
- there are four formats for sending key data: standard, standard with
modulus, with crt, and with crt and modulus.
- the key attributes (modulus length, public exponent length, key
format) can not be changed on all cards. changing them is only
necessary for cards that support different key lengths (that is,
RSA 4096)
- on the cards where they *can* be changed, not all parameters might be
changeable. in particular, modulus length may be changeable but not
key format.
Because of this constellation, the put key operation now only sets the
modulus of the key, while retaining the key format. At the time of
writing, the Gnuk and Nitrokey use the standard format, while the
Yubikey and other applets use crt+modulus.
This fixes loading keys into the Nitrokey Pro, and partially for the
Gnuk token.
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