> What about your friend's evil sysadmin who replaces the public key that you sent with another one, thereby enabling MITM? You could also send with it detache

> What about your friend's evil sysadmin who replaces the public key that you sent with another one, thereby enabling MITM? You could also send with it detached key signatures from mutually trusted friends. This would add weight to your claim that this key belongs to you. Then, your recipient can check that your message's contents (including your pubkey) are signed by a key that your receiver can adequately measure authenticity. Does that seem right? If a hostile MITM modifies your message and/or your key and signature, then these friend's signatures won't match. If they change these signatures as well, then those won't match the receiver's already trusted keys. [Aside: One other way I have played with was to rate another signed message by a friend (who sent me his pubkey as an email attachment) with a likelihood that he wrote it, and then I checked if that message's signature matched. As a qualitative heuristic test, it did increase my confidence in that key significantly, though I would have liked to have some trusted 3rd parties witness his possession of it.]