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Re: single <auth> per cert (was Re: "auth" --> "tag" ?? )

At 4:50 PM -0800 4/1/97, Hal Finney wrote:
>Bryce, <bryce@digicash.com>, writes:
>> On to a more technical issue, I'm still trying to understand
>> the issues about having single or multiple <auth> (cum <tag>)
>> fields in a cert.  But even without understanding the issues,
>> can I suggest that having only one is simpler, and is easier to
>> use in simple applications?  Perhaps more complex applications
>> can (a) add a layer of abstraction on top of SPKI to handle
>> certs in bundles and/or (b) wait for SPKI 1.1.
>One point I don't fully understand relates to the certificate merging
>rules and to multiple authorization tags in a cert.  When we merge a
>cert chain, we are suppose to intersect the auth tags.  I never really
>knew what this intersection meant, but I had tentatively supposed that
>it referred to cases where there were multiple auth tags in a cert.
>The intersect would then be a matter of simply identifying those tags
>which match in all the certs being combined.  This could be an automated
>process which would not require understanding the actual meaning of the
>However, with one auth tag per cert this interpretation, shaky as it
>may have been, is certainly incorrect.  In that case, I suppose the
>intersection is a semantic operation which is tag specific.  For example,
>if the auth tag gave some authority to spend a certain amount of money,
>then the intersection might be a matter of choosing the minimum value
>specified in the tags.
>This would imply that there is no way for an automated process to
>perform the chain collapse unless it was armed with some understanding
>of the meaning of the auth tags, sufficient to identify what it meant
>to intersect them.

It seems to me that the only programs interested in the meaning of auth
tags will be the requesting program and the program validating that
request.  Both of them can be assumed to have an application level of what
intersection means for the tags in question.  Are there any other programs
who have such an interest?

Bill Frantz       | I have taken a real job at | Periwinkle -- Consulting
(408)356-8506     | Electric Communities as a  | 16345 Englewood Ave.
frantz@netcom.com | capability security guru.  | Los Gatos, CA 95032, USA

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