[caops-wg] Re: ca signing policy file
David Chadwick
d.w.chadwick at kent.ac.uk
Mon Oct 10 04:55:39 CDT 2005
Von
thats a nice summary of why you have put name constraints outside of the
certificates. I might add another reason for keeping it this way, and
that is that RFC 3280 allows the CA in the trusted domain, to blow the
trust bestowed in it and issue certificates with a different name form
and then the certificate will be trusted (e.g. give an email address to
someone using the subjectAltName extension, instead of a DN, because
their DN is outside the name constraints).
regards
David
Von Welch wrote:
>
> Here's a first attempt at explaining the relationship to Name
> Constraints - Von
>
> Comparison to RFC 3280 Name Constraints
>
> To understand our motivation for the creation of this specification
> instead of using Name Constraints as defined in RFC 3280 (section
> 4.2.1.11), one needs to understand the differences in models between
> what PKIX envisions and what is in use in the Grid.
>
> The PKI model envisioned in RFC 3820 is that each relying party will be
> part of a domain which has a CA associated with it. Any decision by
> that domain to trust another domain, and its associated CA, is
> instantiated by the CA of the trusting domain to cross sign the CA of
> the trusted domain, creating a new certificate for the trusted CA which
> will be used in the trusting domain. Trust can then be limited by using
> the Name Constraints extension in this new certificate, limiting trust
> by relying parties in the trusting domain and allowing the trusting
> domain to manage its view of the global namespace and ensure uniqueness
> of names.
>
> In the Grid model, relying parties make trust decisions directly by
> installing the self-issued certificates from CAs in their system
> configurations. There is often not a domain CA which can sign the
> trusted CA and there are issues with current open source path
> validation software which also make this approach problematic [1].
>
> The result of this is the need for mechanism for a relying party to
> specify their own policy on constraining what names they will allow a
> trusted CA to issue, which in turn allows them to manage their view of
> the global namespace in order to ensure names are unique. This
> specification is aimed at such a mechanism.
>
>
> [1] J. Jokl, J. Basney, and M. Humphrey. Experiences using Bridge CAs
> for Grids. Proceedings of the UK Workshop on Grid Security Experiences.
> Oxford 8th and 9th July 2004.
> http://www.cs.virginia.edu/~humphrey/papers/
> BridgeCAGridSecWorkshop2004.pdf
>
> On Oct 7, 2005, at 8:08 AM, David Groep wrote:
>
>> Hi Von, *,
>>
>> Von Welch wrote:
>>
>>> First a meta question - shall we move conversation to the caops
>>> email list?
>>>
>>
>> Yes, done, and set the reply-to address there as well.
>>
>>
>>> Onto the document:
>>> I find the language in the document is really odd in that it talks
>>> about "Authentication Identifiers" and "Issuers". Particularly if
>>> this document is going to end up in CAOPS, shall we not just bite
>>> the X509 bullet and say "X509 certificates" and "CAs", etc. I think
>>> it would make the document much more clear.
>>>
>>
>> I actually agree (it's just the habit that crept in here). I also
>> think that the "namespace constraints policy collection (file)" should
>> just be "namespace constraints file" or something similar.
>>
>>
>>> I think one question the document should address is why not use RFC
>>> 3280 Name Constraints? I think this mainly boils down to the fact
>>> that while they look suitable, they are intended for bridging
>>> situations and we'll never get commercial CAs to adopt them, hence
>>> always limiting ourselves to "Grid CAs". If everyone agrees with
>>> that statement, I'll plan on contributing some prose.
>>>
>>
>> I've a few other reasons to add to this as well:
>> For nameConstraints in the certificate itself is that it's the "wrong"
>> authority makiong the assertion. For these namespace policies, it's
>> not the
>> CA itself but rather the distributor or federation that makes the claim.
>>
>> The example again is SwissSign. In the federation, their
>> (top-level) CA is limited to signing only the "Bronze" CA. This
>> constraint is coded in the namespace constraints file. But of course,
>> they'll never but in a nameConstraints assertion in their top-level
>> limiting it to Bronze only :-)
>>
>> Also, only a subset of the certificates issued by a CA may be
>> part of the federation, and limiting the namespace is a relatively
>> straightforward way of doing that (instead of having to introduce
>> a subordinate CA for that).
>>
>> In all cases, the namespace constraints should be outside of the
>> certificate chain of the constraint CA.
>>
>>
>>
>>> With regards to the example policy, I think the question needs to
>>> be asked - why not use XACML or some other standard policy
>>> language? I suspect its an attempt to address requirement #5 -
>>> human readability. Seems like one could write a tool to display
>>> XACML in a context like this nicely, so I think we need to ask
>>> ourselves if we really want to define a new language.
>>>
>>
>> The other problem will be on the implementation side. As soon as
>> you start using XACML, you will use external parsing libraries and
>> thus introduce dependencies on yet more software. A structured
>> plain-text
>> format that translated almost one-to-one to a evaluation structure
>> is easy to process in any language, so I was hoping that more
>> software would actually implement it (and maybe even that it
>> ultimately could find it's way down in core OpenSSL, some time down
>> the road).
>> The example language translated 1-to-1 into a list of structures that
>> can be parsed top-down without need for any further libraries.
>>
>> And a tool would again mean coding and maintenance (and a distribution
>> problem for the tools), whereas human readable text is self-contained.
>>
>> But maybe I'm too pessimistic. Can you think of an XACML policy
>> whose text representation is still somewhat readable. Can we write
>> XACML "assuming we know the context", do away with all the
>> embedded schema namespaces, but still make sure that a standard
>> XACML parser can read it -- and a human as well?
>>
>>
>> Cheers,
>> DavidG.
>>
>>
>>> Von
>>> On Sep 15, 2005, at 7:57 AM, David Groep wrote:
>>>
>>>> Hi,
>>>>
>>>> As Olle pointed out to me over coffee, it might be good to write
>>>> down at least the requirements in a real document for GGF. I've
>>>> had a go at collecting the information from the email thread and
>>>> formatting it as
>>>> a GWD. It needs *definitely* work and more text before it could go
>>>> public,
>>>> but at least we can start hacking at it...
>>>>
>>>> DavidG.
>>>>
>>>> Olle Mulmo wrote:
>>>>
>>>>
>>>>> ... did the discussion stop at this point?
>>>>> There will be an opportunity to talk face-to-face at GGF15.
>>>>> Should we try to nail down and enumerate the requirements of
>>>>> what functionality we want until then?
>>>>> /Olle
>>>>> On Sep 2, 2005, at 08:28, David Groep wrote:
>>>>>
>>>>>
>>>>>> Hi Von,
>>>>>>
>>>>>> Von Welch wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Do I understand correctly that you are suggesting that a CA's
>>>>>>> namespace file can include rules for all of its subordinates?
>>>>>>> (These seems to be what your example implies.) I actually
>>>>>>> think I like this idea, see next comment.
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> That's indeed what I meant. It would enable new subordinates to
>>>>>> "glide in" without intervention from the admin, as long as they
>>>>>> stay within the namespace assigned for subordinates.
>>>>>>
>>>>>> I think that need not even be the same namespace as the root,
>>>>>> and for this the wildcards should likely work in the issuerName
>>>>>> as well.
>>>>>>
>>>>>> > If a subordinate file exists, it overrides any policy that
>>>>>> would be
>>>>>> > otherwise inherited.
>>>>>>
>>>>>> Since you will have to traverse up the tree anyway for validity
>>>>>> checks,
>>>>>> finding the specialised signing policies should not be much of a
>>>>>> problem,
>>>>>> but I can't find the use case for it either (at least not yet) :-)
>>>>>> Requiring it for root CAs seems like a good thing.
>>>>>>
>>>>>> DavidG.
>>>>>>
>>>>>>
>>>>>>
>>>>>>>>
>>>>>>>> * the action to take if no signing policy file is found
>>>>>>>> (should you
>>>>>>>> allow or deny by default) I think should in general be
>>>>>>>> configurable.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> Maybe require them for all root CAs and make them optional for
>>>>>>> subordinates? Given the root CA namespace config would cover
>>>>>>> the subordinates, I can't think of any situation we would want
>>>>>>> one for a subordinate.
>>>>>>> If a subordinate file exists, it overrides any policy that
>>>>>>> would be otherwise inherited.
>>>>>>> Von
>>>>>>> On Aug 31, 2005, at 11:08 AM, David Groep wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> What I got till now:
>>>>>>>> * subordinated should be supported without the need to install
>>>>>>>> any data in the trusted directory (this will work once we have
>>>>>>>> OCSP support or better, and the new policy format). I just
>>>>>>>> completely
>>>>>>>> agree here.
>>>>>>>>
>>>>>>>> The signing policy file should thus be applicable to "self"
>>>>>>>> and to any
>>>>>>>> subordinates that don't have their own singing policy file.
>>>>>>>> (I'd propose semantics that make a specialised signing_policy
>>>>>>>> take precedence over any higher-level policy file, so that once
>>>>>>>> you find one in the CA tree, you don't have to traverse
>>>>>>>> further up
>>>>>>>> to inspect the policies of the parent CAs. The admin supposedly
>>>>>>>> is in control of what goes in the trusted directory)
>>>>>>>>
>>>>>>>> * naming should comply with RFC2235
>>>>>>>>
>>>>>>>> * format should be easily parseable, and be "logical" for both
>>>>>>>> C/ OpenSSL
>>>>>>>> and Java implementations.
>>>>>>>> This likely precludes the use of c_hash-style CA indexes in the
>>>>>>>> singing policy file.
>>>>>>>>
>>>>>>>> * pattern matching:
>>>>>>>> Shell-style globs are fine with me as well (I could not think of
>>>>>>>> any real-life case where a regex could not be replaced by a
>>>>>>>> set of
>>>>>>>> PERMIT statements and shell globs), but the shell globs
>>>>>>>> should expand
>>>>>>>> in any position in the DN.
>>>>>>>>
>>>>>>>> * the action to take if no signing policy file is found
>>>>>>>> (should you
>>>>>>>> allow or deny by default) I think should in general be
>>>>>>>> configurable.
>>>>>>>>
>>>>>>>> Let's try the SWITCH CA example. They have a fairly complex
>>>>>>>> structure
>>>>>>>> with a hierarchy 5-levels deep:
>>>>>>>>
>>>>>>>> SwissSign Root (7b2d086c)
>>>>>>>> +- SwissSign Bronze (e36e7a72)
>>>>>>>> +- SwissSign Silver (e9d08b40)
>>>>>>>> +- SWITCH CA (c4435d12)
>>>>>>>> +- ... end-entities
>>>>>>>>
>>>>>>>> This would lead to a singing policy for the top-level
>>>>>>>> SwissSign Root CA, that contains all subordinate CAs down to
>>>>>>>> the SWITCH EE- issuing CA.
>>>>>>>> To get the signing policy, the algorithm would start at the
>>>>>>>> end- entity
>>>>>>>> cert, and traverse up the chain until it finds a CA with a signing
>>>>>>>> policy file. In this case, we could do with a singing policy
>>>>>>>> file for
>>>>>>>> the root only ("7b2d086c.namespace") that contains the limitations
>>>>>>>> for all subordinates, like:
>>>>>>>>
>>>>>>>> #
>>>>>>>> # @(#)7b2d086c.namespace
>>>>>>>> #
>>>>>>>> TO "CN=SwissSign CA (RSA IK May 6 1999
>>>>>>>> 18:00:58),O=SwissSign,C=CH" \
>>>>>>>> PERMIT \
>>>>>>>>
>>>>>>>> "C=CH,O=SwissSign,Email=bronze at swisssign.com,CN=SwissSign
>>>>>>>> Bronze CA"
>>>>>>>> TO "C=CH,O=SwissSign,Email=bronze at swisssign.com,CN=SwissSign
>>>>>>>> Bronze CA" \
>>>>>>>> PERMIT \
>>>>>>>>
>>>>>>>> "C=CH,O=SwissSign,Email=silver at swisssign.com,CN=SwissSign
>>>>>>>> Silver CA"
>>>>>>>> TO "C=CH,O=SwissSign,Email=silver at swisssign.com,CN=SwissSign
>>>>>>>> Silver CA" \
>>>>>>>> PERMIT \
>>>>>>>> "C=CH,O=Switch - Teleinformatikdienste,CN=SWITCH CA"
>>>>>>>> TO "C=CH,O=Switch - Teleinformatikdienste,CN=SWITCH CA" \
>>>>>>>> DENY \
>>>>>>>> "*,O=CERN,C=CH"
>>>>>>>> TO "C=CH,O=Switch - Teleinformatikdienste,CN=SWITCH CA" \
>>>>>>>> DENY \
>>>>>>>> "*,O=SwissSign,C=CH"
>>>>>>>> TO "C=CH,O=Switch - Teleinformatikdienste,CN=SWITCH CA" \
>>>>>>>> PERMIT \
>>>>>>>> "*,O=*,C=CH"
>>>>>>>>
>>>>>>>> (but now of course "*" and "?" should be escaped when the're
>>>>>>>> part of the actual RDN).
>>>>>>>>
>>>>>>>> In the Java world it seems slightly more complex. In the
>>>>>>>> CertPath API,
>>>>>>>> the TrustAnchor class takes a nameConstraints byte array, but
>>>>>>>> the byte
>>>>>>>> array must contain an ASN.1 DER encoding of a NameConstrains
>>>>>>>> extension
>>>>>>>> (as per RFC3280). There is AFAIK no way to express wildcards in a
>>>>>>>> GeneralName, so I think it will just not be possible to use
>>>>>>>> TrustAnchor.nameConstrains to encode this formation. Moreover, it
>>>>>>>> has no support for subordinated either. Like for C, in Java we
>>>>>>>> will
>>>>>>>> have to implement it ourselves...
>>>>>>>>
>>>>>>>> What concerns the matching algorithm: the only advantage that
>>>>>>>> formal
>>>>>>>> regex's would bring is to combine the two DENY statements into one
>>>>>>>> DENY "*,O=(CERN|SwissSign),C=CH", and that is no great loss.
>>>>>>>>
>>>>>>>> DavidG.
>>>>>>>>
>>>>>>>> Von Welch wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>> And one more point that just occurred to me, hierarchical
>>>>>>>>> CAs. A definite downside to our current signing policy
>>>>>>>>> scheme is that subordinate CAs are required to have a
>>>>>>>>> signing policy file, which means that they can't just show
>>>>>>>>> up unannounced (which is what people want to have happen,
>>>>>>>>> when a subordinate is replaced, just swap it out and go on
>>>>>>>>> with life).
>>>>>>>>> Von
>>>>>>>>> On Aug 31, 2005, at 5:46 AM, Olle Mulmo wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Hi David,
>>>>>>>>>>
>>>>>>>>>> Revamping this is definitely worth pursuing -- but we have
>>>>>>>>>> to think hard to get the design right. Von had some
>>>>>>>>>> excellent comments as well:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> This needs better specification, btw, how is whitespace
>>>>>>>>>>> handled? I'm not sure I like the use of the formal regex
>>>>>>>>>>> as opposed to the unix glob style ('.*' vs '*'). Do we
>>>>>>>>>>> want to continue using the forward slash style vs the
>>>>>>>>>>> more standard comma-separated?
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> If we are doing something like this, I would suggest that we
>>>>>>>>>> try to move towards RFC2253-style DN encoding: It's the
>>>>>>>>>> format that almost everything else but openssl spits out
>>>>>>>>>> by default nowadays, and it is UTF-8(!!!).
>>>>>>>>>>
>>>>>>>>>> /Olle
>>>>>>>>>>
>>>>>>>>>> On Aug 26, 2005, at 23:13, David Groep wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> Hi all,
>>>>>>>>>>>
>>>>>>>>>>> After a discussion on the CA mailing list, it is quite clear
>>>>>>>>>>> that the current way of expressing the namespace
>>>>>>>>>>> constraints for
>>>>>>>>>>> CAs is quite tedious: the EACLs have a far too complicated
>>>>>>>>>>> syntax
>>>>>>>>>>> for their simple use in the ca_signing_policy.conf file, their
>>>>>>>>>>> full syntax does not work, and they are used nowhere else.
>>>>>>>>>>>
>>>>>>>>>>> Also, at this time only a few parts of the system actually use
>>>>>>>>>>> the signing_policy file (only the C-based stuff that still
>>>>>>>>>>> calls the "oldgaa" callback), and a lot of implementation in
>>>>>>>>>>> other languages and systems is still to be done.
>>>>>>>>>>> This is true for the Java part of GT, for the EGEE Java stuff,
>>>>>>>>>>> and also I'm quite sure that Unicore does not do anything
>>>>>>>>>>> in this
>>>>>>>>>>> area (Jules, Ron?)
>>>>>>>>>>>
>>>>>>>>>>> What about changing to a new format for the signing_policy
>>>>>>>>>>> before
>>>>>>>>>>> we start all that work, a format like a simple set of
>>>>>>>>>>> ordered lines
>>>>>>>>>>> with an action and a regular expression. Like:
>>>>>>>>>>>
>>>>>>>>>>> # namespace constraint file
>>>>>>>>>>> #
>>>>>>>>>>> PERMIT /DC=org/DC=mydomain/.*
>>>>>>>>>>> PERMIT /DC=org/DC=alsomine/.*
>>>>>>>>>>> DENY /DC=org/DC=friend/OU=hisdept/.*
>>>>>>>>>>> PERMIT /DC=org/DC=friend/.* # my friend
>>>>>>>>>>> delegated rest to me
>>>>>>>>>>> #
>>>>>>>>>>>
>>>>>>>>>>> which would be almost trivial to parse in any language. I
>>>>>>>>>>> suggest
>>>>>>>>>>> adding the "DENY" because that would solve by problem with the
>>>>>>>>>>> SWITCH CA (they own all of "/C=CH/*", except for "/C=CH/
>>>>>>>>>>> O=CERN/*",
>>>>>>>>>>> so a ordered list with DENY prevents enumeration of all the
>>>>>>>>>>> possible "O="'s there).
>>>>>>>>>>> But if you don't like the deny we can even go to just a plain
>>>>>>>>>>> list of regex's.
>>>>>>>>>>>
>>>>>>>>>>> Of cource, we should distributed the "EACL" style policy files
>>>>>>>>>>> still for a long time, but eventually they would go away.
>>>>>>>>>>> For the standard CA distribution I can easily add the new
>>>>>>>>>>> format.
>>>>>>>>>>>
>>>>>>>>>>> Would this be useful and possible to do in a reasonable time?
>>>>>>>>>>> Is it possible to put this as a feature request on the
>>>>>>>>>>> current GT?
>>>>>>>>>>>
>>>>>>>>>>> Cheers,
>>>>>>>>>>> DavidG.
>>>>>>>>>>>
>>>>>>>>>>>
>>
>>
>> --
>> David Groep
>>
>> ** National Institute for Nuclear and High Energy Physics, PDP/Grid
>> group **
>> ** Room: H1.56 Phone: +31 20 5922179, PObox 41882, NL-1009DB
>> Amsterdam NL **
>>
>>
>
>
--
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David W. Chadwick, BSc PhD
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