Six.
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>From: "Hannes Tschofenig" <>
>To: "'Art Botterell'" <>,
> <>
>Date: Thu, 12 Mar 2009 18:40:36 +0200
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>Subject: Re: [CAP] CAP Security Using Digital Signatures
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>Hi Art,
>
>I believe a more urgent item for work on CAP is to come up with better
>semantic of the elements in the CAP XML spec itself.
>The lack of precise semantic will IMHO make end-to-end usage challenging.
>
>On the digital signature aspects I wonder whether there are (not just
>theoretical) threats that demand it's usage in the envisioned usage
>scenarios.
>
>Ciao
>Hannes
>
>>-----Original Message-----
>>From:
>>[mailto:] On Behalf Of Art Botterell
>>Sent: 12 March, 2009 17:32
>>To:
>>Subject: Re: [CAP] CAP Security Using Digital Signatures
>>
>>Interesting link, Matt. Sounds like an object lesson on why
>>we should resist the temptation to standardize what we don't
>>yet understand.
>>
>>I was thinking we might wind up proposing an erratum to OASIS
>>to fix the schema issue, but hadn't appreciated that
>>cannonicalization was still proving so intractable. Although
>>that article is from 2004, I take it the C14N situation hasn't
>>improved. So maybe it would make more sense to identify (and
>>demonstrate!) alternate approaches that could be fed back into
>>the standard.
>>
>>My concern is that if we don't address the end-to-end
>>signature problem as a community there might not be a business
>>incentive for any
>>particular implementer to design for that level of interoperability.
>>And while the OASIS process usually does a good job of
>>refining and ratifying contributed designs, it seems not to be
>>as effective as a framework for developing those designs in
>>the first place.
>>
>>- Art
>>
>>
>>
>>On Mar 12, 2009, at 3/12/09 5:59 AM, matt hoffman wrote:
>>
>>> I did a proof-of-concept implementation of this on a previous DHS
>>> system. Although, as you say, there was no way of verifying it with
>>> other providers or consumers at the time.
>>> However, a couple of points that I recall:
>>>
>>> a.) The document mentions that the signature element can be a child
>>> of "alert", but unless I'm mistaken it is not specified in the
>>> schema. So messages containing signatures fail schema
>>> validation ... I had to explicitly add it to the schema.
>>>
>>> b.) The signatures are delicate, and tricky:
>>http://www.cs.auckland.ac.nz/~pgut001/pubs/xmlsec.txt
>>>
>>> Unfortunately I no longer have access to that code, but I'd
>>be happy
>>> to help others if they're looking into it.
>>>
>>>
>>> - matt
>>>
>>> On Wed, Mar 11, 2009 at 11:20 PM, Art Botterell <>
>>> wrote:
>>> Friends -
>>>
>>> We're moving rapidly toward an important threshold in CAP
>>> implementations. So far, most CAP-based systems have been self-
>>> contained, single vendor/implementer arrangements. But soon we're
>>> going to need to "federate" CAP traffic among multiple
>>interoperable
>>> systems. And that has important implications for security.
>>>
>>> Most current systems use a trusted-link/trusted-host mode based on
> >> encrypted network links and password access control at a central
>>> server. That's a familiar Web 1.0 approach and it works fine for
>>> "single-hop" implementations. But it has a major drawback: As soon
>>> as messages are forwarded from one server to another, a security
>>> compromise anywhere can compromise the authentication and integrity
>>> of all CAP messages downstream.
>>>
>>> The alternative, of course, is to apply digital signatures to CAP
>>> messages at their origin, and to verify them at receiving points.
>>> That way, it doesn't matter if the links or intervening nodes are
>>> secure or not; any recipient can verify independently that the
>>> message is a) from who it says it's from, and b) hasn't been
>>> modified in transit.
>>>
>>> There's a standard way of doing this for XML, as cited in the CAP
>>> Specification:
>>>
>>> >3.3.2.1 Digital Signatures
>>> >The alert element of a CAP Alert Message MAY have an Enveloped
>>> Signature, as described by XML Signature and
>>> >Syntax Processing [XMLSIG]. Other XML signature mechanisms
>>MUST NOT
>>> be used in CAP Alert Messages. Processors
>>> >MUST NOT reject a CAP Alert Message containing such a signature
>>> simply because they are not capable of verifying
>>> >it; they MUST continue processing and MAY inform the user of their
>>> failure to validate the signature.
>>>
>>> But I'm not aware of anyone that's implemented it yet... partly
>>> because it hasn't been necessary in stand-alone systems, and partly
>>> because it involves a type of programming a lot of folks
>>haven't had
>>> occasion to explore yet.
>>>
>>> But ultimately, it's going to be essential for
>>interoperability. So
>>> I'd be interested in hearing, has anyone implemented XMLSIG on CAP
>>> yet? And would anyone be interested in doing some interoperability
>>> experiments? The standard is there, the technology is there (in
>>> Java and a number of other languages) and I see the requirement
>>> bearing down on us quickly.
>>>
>>> What say?
>>>
>>> - Art
>>>
>>>
>>> _______________________________________________
>>> This list is for public discussion of the Common Alerting
>>Protocol.
>>> This list is NOT part of the formal record of the OASIS Emergency
>>> Management TC. Comments for the OASIS record should be
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>>> the form at
>>http://www.oasis-open.org/committees/comments/form.php?wg_abbre
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>>
>>_______________________________________________
>>This list is for public discussion of the Common Alerting
>>Protocol. This list is NOT part of the formal record of the
>>OASIS Emergency Management TC. Comments for the OASIS record
>>should be posted using the form at
>>http://www.oasis-open.org/committees/comments/form.php?wg_abbre
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>>
>
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