How do ZRTPs key continuity features compare with SSH?
The key continuity features of ZRTP are analogous to those provided by SSH, but they differ in one respect. SSH caches public signature keys that never change, and uses a permanent private signature key that must be guarded from disclosure. If someone steals your SSH private signature key, they can impersonate you in all future sessions and mount a successful man-in-the-middle (MiTM) attack any time they want. ZRTP caches symmetric key material that is mixed into the next session’s secret session key, which changes with each session. If someone steals your ZRTP shared secret cache, they only get one chance to mount a MiTM attack, in the very next session. If they miss that chance, the retained shared secret is refreshed with a new value, and the window of vulnerability heals itself, which means they are locked out of any future opportunities to mount a MiTM attack. This gives ZRTP a “self-healing” feature if any cached key material is compromised. A MiTM attacker must always be in the
