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Date: Mon, 27 Nov 1995 11:06:13 -0800 (PST) From: Raph Levien <raph@c2.org>
Form this perspective, let's take a look at the recent thread on "establishing trust." Carl Ellison advocates the MOSS alias system. My understanding of this system is that individual users associate "aliases" with public keys. If done right, it can work well. However, from a usability perspective, it is just one more trouble spot.
Yes, it could easily be done wrong in such a way that the user gets confused rather than helped; burdened rather than relieved. I advocate aliases because that's how *I* think. I think in words so I assign my own names (aliases) for the people who populate my mental model of the world. By definition, these are all my correspondents. It's possible of course that some other people (of different Myers-Briggs type, perhaps) think differently -- not in words or aliases. If that's true, we should find out how they think and associate the right thing for them. For example, I had a friend (a painter/sculpter) who thought in images. She might prefer to use little pictures or icons (of her own drawing) as the aliases.
First, on what basis will users decide which keys are worthy of being assigned which aliases? Public keys are big hunks of base64 encoded gibberish. They are difficult to present in a user interface, difficult to communicate in alternate, known secure channels (such as telephone calls and face to face communication). There is no way that a person could memorize one.
That's true. What the user would have to see is some icon (or, for text-bound folks, a temporary unique string) until the user chooses and assigns the appropriate alias. That icon would have no meaning by itself. It would acquire a meaning by being associated with some message or set of messages: a) an attribute testimony (signed by someone with known authority to specify such an attribute -- the equivalent of a certificate) b) a set of messages signed by the key in question (tying the key to the source material from which the user formed his/her impression of the sender) I, the user, would want to be able to call up the set of defining messages for any key or alias at any time in the future -- just in case I get so many aliases that I forget who one belongs to.
The other issue is how much time and energy the user has to spend keeping the alias database up to date. There is no way to communicate securely with anyone who's not in the database. If the user is communicating with a large number of people, then it's very tempting to get sloppy.
I keep a fairly large database of aliases already, in my .mailrc on UNIX. Eudora permits a similar DB. So do a number of other mailers. Users must be demanding this feature and using it. All I say we have to add to that is protection from tampering.
There's no way around it. This kind of system will not make it in the big time.
I wouldn't be so quick to dismiss it.
As I see it, any system that does must have the following properties:
* Some variant on the Web of Trust.
Of course -- you have to have some means for communicating and recording attributions (that the person who owns a key is allowed to spend money on a given bank account; that the person who owns a key goes by the name Carl or receives mail at cme@acm.org; that the person who owns a key is a trusted developer of PGP; ...).
* Online key-servers for getting keys in real time. * A clean mechanism for validating keys through alternate channels.
These two have to go together -- but I'm curious what anyone means by "validating keys". I see this as the flaw killing certificate structures like X.509 or PGP's. [Even Steve Kent, a major X.509 advocate, seems to see this problem (with sadness, in his case).] I had a secretary once, long ago. I would drive her home from work occasionally -- or to parties -- when her husband wasn't around or wasn't interested in going someplace. One time, in passing, he noted that this arrangement was OK with him because he "trusted her". I trusted her, too. I knew her to be having affairs with various people (not me at the time) but he didn't. So we each trusted her but what we trusted her to be was different. Just saying that we trusted her wasn't saying anything. As soon as you qualify the "validated key" (e.g., to be allowed to spend money, etc.), you get to the signed attributes which I advocate over certificates. If all you do with the validated key is tie it to a text string which purports to specify a human being, as X.509 or PGP do, you haven't done anything for me. If all humans had unique names, then this might mean something to me (assuming I knew the human in question and knew his unique name). However, that's what killed X.509 -- the need for unique names. We don't have them and we're not about to adopt some new social structure which assigns them. Even if we did all adopt unique names, you postulated a *large* set of people to communicate with -- larger than my immediate circle of acquaintances, presumably -- so even a unique name would be meaningless to me because I would not have met the person in question. If the unique name certificate works at all it's because I have some mechanism (not mentioned in the certificate hierarchy design) for attaching attributes to the named person. However, if I haven't met the person in question, I don't have that mechanism already and it needs to be created alongside the certificate mechanism. I don't need testimony about the name (unique or otherwise) of the person who owns that key. I need testimony about the attributes of that person (PGP developer; fellow Cypherpunk; FBI agent; undercover NSA plant; permission to use a checking account; receives mail at xxx@yyy.com; ...). That testimony can be provided by referencing the key itself, rather than some (artificially unique) name which exists only to link the attribute to the key. The S/W which links these together and lets me find the various testimonies for a key has to be convenient -- but that was your original point and I concur. I object only to the implication that current certificate hierarchy thinking gets us closer to that goal than the direct signed attribute statements would.
There are three possible outcomes: we build it, the NSA builds it, or Microsoft/Netscape builds it. This last outcome might not be so bad, but only in the first one can we rely on our principles being advanced.
Amen! - Carl +--------------------------------------------------------------------------+ |Carl M. Ellison cme@tis.com http://www.clark.net/pub/cme | |Trusted Information Systems, Inc. http://www.tis.com/ | |3060 Washington Road PGP 2.6.2: 61E2DE7FCB9D7984E9C8048BA63221A2| |Glenwood MD 21738 Tel:(301)854-6889 FAX:(301)854-5363 | +--------------------------------------------------------------------------+ - -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMLtON1QXJENzYr45AQGiEwP+OpETJDPJ8rWbur4oH/PCZqKWtXmzTquV 4QIwoZlXoK6RnZ60szR/qqPxjnj+TtsO8FOQK5lWurv+FG67ma5PfyNbxU+WFapY uxwop8Ivb3bw0uFT2oh2VE5owAYFkmqz7kd7GleEG33dGOUz7jSELugzL4Ag8zRF 40qPwsU7B08= =aeKx - -----END PGP SIGNATURE----- -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMLtOvVQXJENzYr45AQH5RQP+JroFSz3bJapOGEqA2pfhZ1dn9d7VDEUd h/JLbhFkgYbzMGsVzpu20Ww0uOsOwxQR2ItLkaSlTG0O76rgATE2Cma9LEvdoque LMgN/xg0GmaSHoecHLuKJxRz/1xreKODuai2FvndyjspfgO/H6zrQOfhsWn3qa6a ZqnNaEY+kXw= =cuUk -----END PGP SIGNATURE-----