Does changing a key passphrase invalidate the old public key?
I have heard it recommended that the key passphrase should be changed periodically, not unlike your OS's login password. I know a key is really made up by two pieces, a public key (which everyone encrypts with) and a private key (which hopefully only YOU have). So, I really have several questions..
1) Does changing the passphrase invalidate the existing (published) public key?
2) If not, then does the passphrase really have anything to do with either of the keys, if you can change it without invalidating the keys themselves?
3) Or, is the passphrase just a local way for PGP Desktop to ensure that you really are the one who is allowed to USE the private key (like an additional security layer), in which case changing the passphrase just changes the "protective wrapper" around the private key?