After having purchased a USB GnuPG smartcard, I visited the manufacturer's website. A tutorial by the FSFE was mentioned there as the preferred way of setting up the smartcard.
However, this tutorial seems to be a bit outdated as the output of
gpg --gen-key doesn't offer the option to create a "RSA + RSA"-keypair:
Please select what kind of key you want: (1) DSA and Elgamal (default) (2) DSA (sign only) (5) RSA (sign only)
The author chooses the first option and continues by generating two RSA subkeys of the DSA key. These two subkeys (one for signing, the second for encrypting) are then transferred to the smartcard. The Elgamal key is deleted, unused.
So my questions here – as an owner of a keypair consisting of two RSA keys, default in GnuPG for quite a long time – are: Do I really need to generate new subkeys for the smartcard? Or is this measure included in the tutorial for historical reasons (as smartcards seem to only support storing RSA keys)?
I don't know if, from the security point of view, there are reasons against putting your "master" key on a smartcard. But even if, wouldn't it be enough to generate one second subkey for signing instead of two new subkeys?