Best practice to use several smartcards for a single key?

[Nicolas Boullis]

Hi,

Since the smartcard that held all my subkeys died, I have to replace my 
subkeys, and I’m willing to store them on several smartcards, just in 
case I am unlucky again…

I wonder whether I should the same subkey or different subkeys on 
different smartcards.

As far as I understand it, for encryption, if I have several encryption 
subkeys, people who send me encrypted messages will encrypt for single 
subkey. Hence, if I want to be able to decrypt the message with any 
smartcard, then I have to use a single subkey that is held by all 
smartcards.

As for signature subkeys, as I understand it, there is no problem with 
using several distinct subkeys, so I can sign with the one that is 
available, and people who verify the signature will accept any subkey. 
Moreover, if a smartcard is lost/stolen, I can revoke its signature 
subkey.

As for the authentication subkeys (that I use for SSH connection), it 
behaves like the signature subkeys, except that I have to explicitly 
allow each subkey on all machine that I want to connect to.

Any opinion on this?


As a bonus question: given that my “master” private key is also stored 
on a smartcard, is there a way to ask GnuPG to generate a signature 
subkey on a second smartcard, while signing it with the first smartcard?
Or do I have to first generate it in software and sign it with the first 
smartcard, and then export it to the second smartcard?


Best regards,

-- 
Nicolas