disjunct paths

[David Shaw]

On Wed, Nov 30, 2005 at 08:11:44PM +0100, Gregor Zattler wrote:
> Hi David,
> * David Shaw <dshaw at jabberwocky.com> [30. Nov. 2005]:
> > On Wed, Nov 30, 2005 at 04:29:21PM +0100, Gregor Zattler wrote:
> > > Hi David,
> > > * David Shaw <dshaw at jabberwocky.com> [28. Nov. 2005]:
> > > > On Sat, Nov 26, 2005 at 12:56:16AM +0100, Jaap Eldering wrote:
> > > > Yes, it is.  There are a few servers that do more or less what you
> > > > describe (for example http://www.lysator.liu.se/~jc/wotsap/).  It's
> > > > useful to see the various paths, but unless you trust each step in the
> > > > chain, it doesn't really help you get trust in the end point.
> > > 
> > > Doesn't it help if there are several disjunct paths?  Couldn't I
> > > say I trust a User-Id if more than n discunct paths of trust
> > > exist from my key to the other?
> > 
> > Yes, if you trust those disjunct paths :) A hundred disjunct paths
> > that you don't trust don't help much.
> 
> Why not?  The disjunct paths from my key to the target key
> all start with keys signed by me.  So all owners of this said
> keys must be part of an conspiracy.  If I met the different key
> owners in different contextes this isn't very likely to happen.

Unless you're talking about paths with only one hop, it doesn't work.
The paths *start* with keys signed by you.  After that, you have no
assurance.

Given these paths:

Gregor  ->  Alice  ->  Baker  ->  Charlie  ->  David
Gregor  ->  Lorina ->  Mark   ->  Nate     ->  David
Gregor  ->  Edith  ->  Frank  ->  George   ->  David

You know (because you signed them), that Alice, Lorina, and Edith are
valid.  Lets say that you also fully trust them to make good
signatures, so that makes Baker, Mark, and Frank fully valid as well.
However, not knowing how well Baker, Mark, or Frank issue signatures
stops you from making Charlie, Nate or George valid, which stops you
in turn from making my key valid.

> > There is a notion of partial trust, where if you gather enough
> > partially trusted signatures then it equals full trust.  You can tune
> > the trust calculations with the --marginals-needed and
> > --completes-needed options.  By default, you need 3 marginally trusted
> > signatures or 1 completely trusted signature.
> 
> !? Does gpg calculate trust several hops along the trust path? 

GPG will calculate trust for 5 hops along the path, by default.  You
can tune this with --max-cert-depth.

David