It seems like it should be possible to make a much lighter weight encrypted email protocol than, say, GnuPG. Address books should have a public key field. Ema

It seems like it should be possible to make a much lighter weight encrypted email protocol than, say, GnuPG. Address books should have a public key field. Emails should have a X-Public-Key: and X-Signature: fields. You can add key exchange on the existing protocol. If you've got a public key in your address book, outgoing emails should be encrypted. It seems like it would be trivial for GMail or Thunderbird to support something like this. I realize this doesn't solve all the problems GnuPG does, but email exchange would be encrypted, it would be easy to adopt, and would let the end user choose manage keys and store emails encrypted (Thunderbird, say) or not (GMail).