On 16 Jun 96 at 12:32, Vipul Ved Prakash wrote: [..]
That's the point, though. PGP *does not* try to model a reputation system. When you sign keys, you only attest that you are sure that that key belongs to the person whose name is on it. A signature says *nothing* about a person's reputation. [..] in that case if alice receives a key signed by bob, she would know the key is good.
Pretty-good, yes. (Assuming she trusts anything signed by Bob.)
... and there is no need for the two other fields. infact the reason why i felt pgp is trying to model a reputation system if because of these two fields that carry trust values.
Those are private/personal trust values only. Alice rates Bob on how well she'd trust a key signed by Bob. This is subjective for Alice, based on her relationship with Bob. She may not know him well and assign him a low rating. Or she may know him all too well, and give him a low rating. This has no meaning for Carol, or Don, or anyone else, since they have different (if any at all) relationships with Bob.
You can't set up a global web of trust. It's computationally infeasable, esp. with contradictions, to resolve. It's also meaningless. Say Alice trusts Bob. Bob trusts Carol. Carol trusts Don. Should Alice trust Don? No... subjective factors like "trust" don't commute.
this is precisely what i wanted to know. can there be a model wherein one can compute a trust-like parameter? if yes in what ways should this parameter
No, at least not one with meaning. There are many factors that would go into one's rating of another: how well one knows the other; part history; bias for or against another because of thing like race, religion, political viewpoint, favorite OS, skills/talent or lack thereof, etc. People's ratings of each other change as well... just imagine global ratings of a once overly well-liked famous person who after several years is now infamous (or an infamous person who is now forgiven). And again, social pressure to give someone a certain rating... [..]
lets say a reputation system involves alice, bob, carol and don. Computing trust parameter with respect to each other can lead to situtions where alice trusts bob x% and has y% proof that he is a liar, after considering all other relations. If this x% > y% she'll believe him, if not she won't.
Generally x+y=1 in this scheme. But lets say for a moment they are separate: x = trust level; y = mixtrust level, independent of x... that makes little sense, since if y>.5, then Bob isn't trustworthy, but why is x > y? x and y would always have to be adjusted for each other... (so it's better off to use something like x+y=1).
thats why i feel the liar paradox doesn't really pose much of a threat.
But even then, For Alice, x(Bob) > y(Bob), so Bob is trustworthy. For Bob though, x(Alice) < y(Alice). So what of Carol? She does not yet know Alice and Bob, and sees their ratings about each other [Note: some people would assign ratings based on others; others would assign ratings based on personal experience... another problem with a global rating scheme]. Carol asks Alice about Bob, who says he's trustworthy. She asks Bob about Alice, who says Alice is untrustworthy. If Alice is correct, then according to Bob she's not worth listening to, but then why listen to Bob. If Bob is correct, Alice isn't worth listening to, but then again, maybe Bob isn't since she says Bob is... so why should Carol bother with any of them. Ok, in real life it's possible to meet two people, one of him is a liar but not so much as to admit another is more truthful... and that truthful person agrees. It's actually quite common... but how does a third person who doesn't know any of them figure it out? How does a computer program using a formula? But given a system with several variables (ie, several people rating each other) you'll have something that's even harder to resolve. Given a global system with thousands or millions of variables... how does one make sense of all those ratings about a particular aspect of one person? [..]
There will be inconsistency only if trust/untrust values are absolute. that is you either trust someone or you don't. i am talking of a system wherein trust values lie between 0..1 which are derived from a set of
Oh no. There's also a lot of inconsistency there too. Doesn't matter if you use boolean or fuzzy values.
tags. in that case bob alice trusts bob x% bob trusts carol y% and carol trusts alice z%. if z < x, z < y simply implies alice trusts bob, bob trusts carol more than carol trusts alice. so the system will be relative rather than
You're ignoring how much Alice trusts Bob, how much Carol trusts Bob and how much Alice trusts Carol.
absolute. a person who is trusted by more people will carry greater weight
Why should that person carry more weight? (more weight than who else?) What if all the people who trust that person are idiots? Why should I, or you, or anyone else care about somebody more or less because "x number of people trust so-and-so"?
and people trusted by him will carry higher weight too. this way snoopy
There's another flaw. And what if those people trust him? Exponentially increasing trust?
who is not trusted by many people will automatically have a weak relationship with others.
Not many people know Snoopy, so he has no trust level. Nobody wants to get to know Snoopy just because he has no trust level. He's locked out. Bad idea.
There's the other point that someone else on the list (Perry?) brought up: if people publicly rate each other, there may be social/political pressure to give some people lower or higher ratings.
again these ratings will be decided in a web rather that on one-to-one basis. that way the social/political pressure can be reduced though not completely eliminated.
No. Individuals put their ratings in the web to skew or confuse things. Rob. --- No-frills sig. Befriend my mail filter by sending a message with the subject "send help" Key-ID: 5D3F2E99 1996/04/22 wlkngowl@unix.asb.com (root@magneto) AB1F4831 1993/05/10 Deranged Mutant <wlkngowl@unix.asb.com> Send a message with the subject "send pgp-key" for a copy of my key.