How, if at all, do SSH keys differ from asymmetric keys used for other purposes, e.g. email signing?
I'm prompted to ask this, in part, because on OS X, there are apps available to manage SSH keys (ssh-agent, SSHKeychain, etc) as well as apps designed to manage GPG keys (GPG Keychain Access, etc), and apparently ne'er the twain meet. However, I do not believe this is an OS X-specific issue.
Is this separation of concerns because the keys are of quite different kinds, or because they are stored in different places, or is it for some other reason or combination of reasons, e.g. historical reasons?