[x500standard] Lack of clarity in X.509
- From: David Chadwick <d.w.chadwick@xxxxxxxxxx>
- To: x500standard@xxxxxxxxxxxxx
- Date: Mon, 23 Jun 2008 09:34:09 +0100
Dear All
A colleague has been testing how various browsers behave when faced with
SSL certificates with various extensions marked critical or
not-critical. He has found that the browsers behave in different ways.
He says that one of the problems is that the standard is not specific
enough on how the browsers should behave in all circumstances.
Here is one scenario to consider. An extension is marked critical and
the RP software understands the extension but only implements part of it
(say it has an OID for describing elements of it, or it is a set of
choices). Does the text in X.509 say how the RP should handle this? I
think not. Should the unknown parts of the extension be ignored or
should the entire certificate be rejected? e.g. the extension is Subject
Alt Names and some of the names are understood and some are not.
As a side issue, an RP can decide to accept any certificate, regardless
of what the CA says in the certificate (and some browsers allow the user
to do this). In this case the CA wont accept any liability and the RP is
acting outside the standard. But is this stated clearly enough in the
standard?
regards
David
--
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David W. Chadwick, BSc PhD
Professor of Information Systems Security
The Computing Laboratory, University of Kent, Canterbury, CT2 7NF
Skype Name: davidwchadwick
Tel: +44 1227 82 3221
Fax +44 1227 762 811
Mobile: +44 77 96 44 7184
Email: D.W.Chadwick@xxxxxxxxxx
Home Page: http://www.cs.kent.ac.uk/people/staff/dwc8/index.html
Research Web site: http://www.cs.kent.ac.uk/research/groups/iss/index.html
Entrust key validation string: MLJ9-DU5T-HV8J
PGP Key ID is 0xBC238DE5
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