I store my PGP private key offline in a few different locations, in case of disk failure. However, in order to sign someone else's key, I must first import my private key back into my keyring. But this gives me a few questions, which I was unable to find answers to online.
1) Does signing their key modify my private key? Is it necessary to re-backup my private key after signing? (I would test this myself, but the output of
gpg --export-secret-keys -a seems to change every time regardless of modifications, so it's hard to be sure).
2) After signing a public key, you must send the owner back their key so they can share the new signature (possibly to a keyserver). But, the RFC specification on the private key packet format states that it contains all fields of the public key. Does this mean that when someone signs my public key, I need to update my private key backups to reflect this change?
3) What other situations require me to update my private key backups?