Hi again,
This is the third message in the series.
Cheers,
Rex
>Date: Thu, 12 Mar 2009 08:59:23 -0400
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>From: matt hoffman <>
>To: Art Botterell <>
>Cc:
>Subject: Re: [CAP] CAP Security Using Digital Signatures
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>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
>>
>>
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--
Rex Brooks
President, CEO
Starbourne Communications Design
GeoAddress: 1361-A Addison
Berkeley, CA 94702
Tel: 510-898-0670
