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Re: Chartering work has started for a Linked Data Signature Working Group @W3C

From: Eric Prud'hommeaux <eric@w3.org>
Date: Fri, 21 May 2021 13:48:13 +0200
To: Peter Patel-Schneider <pfpschneider@gmail.com>
Cc: Dan Brickley <danbri@danbri.org>, Aidan Hogan <aidhog@gmail.com>, semantic-web@w3.org
Message-ID: <20210521114813.GA23721@w3.org>
On Fri, May 21, 2021 at 07:01:02AM -0400, Peter Patel-Schneider wrote:
> On Fri, 2021-05-21 at 09:20 +0100, Dan Brickley wrote:
> > 
> > 
> > On Fri, 21 May 2021 at 00:34, Peter Patel-Schneider <
> > pfpschneider@gmail.com> wrote:
> > > On Thu, 2021-05-20 at 18:58 -0400, Aidan Hogan wrote:
> > > > [...]
> > > > 
> > > > RDF Dataset canonicalisation has indeed undergone review by trained
> > > > mathematicians as mentioned before, but to the best of my
> > > knowledge,
> > > > the 
> > > > people involved (those findable from the explainer) are not
> > > security
> > > > or 
> > > > cryptography experts. Which security and cryptography engineers
> > > have 
> > > > reviewed which parts? It would be good to see input from such
> > > experts
> > > > regarding (2) and particularly (3).
> > > > 
> > > 
> > > Indeed.  As far as I know [3], i.e., the idea of augmenting graphs
> > > while signing and removing the augmentations while verifying isn't a
> > > standard part of security and cryptography.   Which experts have
> > > signed
> > > off on this?
> > > 
> > 
> > 
> > On this detail, does it recurse reliably? 
> > 
> > If Ale writes some RDF, Brin signs it to assure basic integrity of the
> > communication, publishes the result, and then a couple days later Cary
> > signs it to indicate institutional endorsement of the original claims,
> > etc. Are there any cases where manipulating an additional signing could
> > mess with embedded earlier signings, to malicious ends?
> > 
> > Dan
> 
> Indeed, my reading of https://w3c-ccg.github.io/ld-proofs/#algorithms
> leads me to believe that recursively signed graphs cannot be verified.
> I think the intent of recursive signing is slightly different than your
> gloss - the second signer is not signing the original graph but is
> signing the signed graph, perhaps to lend their approval of the first
> signing.
> 
> Ale writes G.
> Brin signs G and adds its own proof triples, resulting in G'.
> Cary takes G', removes the proof triples in it to get G, and uses
> Brin's proof triples to verify that Brin signed G.
> Cary takes G' and adds its own proof triples, resulting in G''.
> Dave takes G'', removes the proof triples in G'' to get G, and tries to
> use Cary's proof triples to verify that Cary signed G.  
> But Cary did not sign G so the verification fails!
> 
> I believe that the described process for manipulation of the graph
> permits an opponent to inject unsigned content into signed graphs and
> still have the verification succeed.

Of course, this is just a limitation of how you can sign graph. Nothing prevents you from creating a second graph which references the first, and signing that second graph, etc. I can sign your signature; I just can't sign it in the same document as your signature.


> peter
> 
> 
> 
> 
> 
Received on Friday, 21 May 2021 11:48:22 UTC

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