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Re: Trust and Transitivity


On Fri, 23 May 1997, E. Gerck wrote:

> Yes, it is relevant and it provides further logical consequences,
> which allow us to prove that "trust on matters of X" does NOT imply
> "trust on assigning trust on matters of X", which would be
> "transitive trust".

I'm afraid I phrased myself badly.  What I intended to say was that
from the point of view of SPKI, the default is that the trust is not
transitive.  I.e. you have to explicitly make a certificate that can
be delegated for trust to become transitive in the SPKI world.

> 3. Because Bob decided that he trusts Skywalker's in matters of X, this
> means that Bob can sign Skywalker's certificate on matters of X. (Easy)

Which is easily done using an SPKI auth tag.

> 4. Yet, Bob did NOT decide whether he trusts Skywalker's avaliation of
> other people on matters of X and so Bob does NOT sign Alice's certificate
> in matters of X. 

Which in SPKI would be expressed by not allowing Skywalker to delegate
the privileges of the certificate.   So we agree that trust is not
transitive, and I claim that SPKI makes the same basic assumption by
requiring express permission to delegate.  And if I'm wrong, I'm quite
sure someone will correct me.



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