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Need a system for handing one's keys around that protects end users from the horrifying sight of actual keys or actual strong hashes of keys.
But at the same time the system has to not say, "I can't deliver your message to that person because an invisible gnotzaframmit that I won't describe to you seems to be unavailable to me in the flabogrommit."
It seems like the clever bit of CT is the insight that some actions, like a CA signing a cert, are intended to be public, and so should be forced (via clever crypto) to take place in public. This makes me wonder what other crypto actions should also take place in public, in a way that doesn't permit hiding them from the world.
Mapping of email address to public key
Delegation of DNSSEC keys
Of course, globally visible events need to take place at a globally visible time. The most widely available time is GPS time (which is 19 seconds off the commonly used time), and which is available from the seldom connected pps line.
At present, unfortunately, anyone who wants gps time has to do his own soldering and hack his own software. There is a pre soldered device available, but it is hard to get.
Imagine skype as originally designed, (central authority maps public and private keys to user names) plus a key continuity feature, plus the seldom used option of doing a zero knowledge shared passphrase to detect man in the middle.
The possibility that the zero knowledge check could be used would deter powerful adversaries, even if seldom used in practice. The more powerful, the greater the deterrent effect.
It is not totally end to end, central authority can listen in, but the check would limit the amount of listening.
It can be made completely end to end for strong passwords. Assume login is by zero knowledge password protocol, which means that the central authority does not know the end user's password, for strong passwords.
The secret key is generated from the strong secret supplied by central authority, plus the password.
When you change your password, you generate a certificate mapping your new public key to your old public key, which certificate makes other people's key continuity check happy.
If key continuity fails, people get a warning, but they don't have to click it away, for that just trains people to click it away. They can just continue right on and not pay attention to it.
Or they could use the zero knowledge shared passphrase procedure to detect man in the middle.
So, if non paranoid, and using easy passwords, works like skype used to work. No interception except by central authority, and central authority cannot intercept everyone, or even large numbers of people.
If paranoid and using strong passwords, provides OTR like end to end capability.
Key management is an unsolved problem. In my biased opinion the
solution was my Crypto Kong, which received limited takeup.
So, in conclusion, don't make people manage keys, though that should be an option for the seriously paranoid.
Instead, autogenerate the keys with zero knowledge passphrase logon.
If he uses a password weak enough to fall to an offline dictionary attack, this is equivalent to the old skype system, where central authority manages his keys and he has password logon. If he uses a stronger password, equivalent to a salted strong passphrase system.
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