Can somebody please tell me how to generate a PGP key with Mac GPG 2.0 that uses a DSA key for signing with a length of 1024 bits, and an El Gamal key for encryption with a length of 2048 bits ? I've tried using the tool both through the GUI and the command line, and it seems it only lets you generate keys that have symmetric lengths (ie 1024 or 2048 for both). I need the one specified above to communicate with somebody using a similar key.
I THINK you can do this by creating the signing key with the "sign only" option and then adding an encryption subkey with the settings you want afterwards.
However I would STRONGLY advise against generating 1024 bit RSA or DSA keys unless you have absolutely no other option. The spook can probablly crack them now and they are likely to get further weakened over time both by improvements in the mathematical algorithms used to crack them and by increases in computing power.
If your correspondent really is running a version of gnupg so ancient it can't handle a 4096/4096 RSA/RSA key then you should really tell them to upgrade.