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

Hi Ivan:

As you should have suspected I have a very different take on this.

Sure any WG can take inputs and work on them.   But my, admittedly non-expert, 
view here is that the major input has significant flaws, and in computer 
security any flaw is fatal.  I've pointed out one but I think there are 
others.  (See below.)

I am in favour of W3C providing some way of securely transmitting RDF graphs 
and datasets.  Of course there already is a way of doing this by simply 
treating the serialization of the graph or dataset as a text document and 
transmitting that document bundled with its signature, much the same way that 
emails are signed.  The goal is to do something better.

My worry is that going through AC review with the proposed charter using 
Linked Data Proofs 1.0 as its major support will result in the working group 
being turned down because of flaws in Linked Data Proofs 1.0.

I would greatly appreciate a discussion of the possible flaws in that 
document.  This discussion does not appear to be happening, which I find 
worrisome.

peter


Technical Details:

I take the method to sign and verify RDF datasets to be as follows:

sign(document, private key, identity)
   let D be the RDF dataset serialized in document
   let C be the canonicalized version of D
   let S be triples representing a signature of C using private key
   let signed document be document plus a serialization of S,
     so signed document serializes D union (not merge) S
   return signed document

verify(signed document)
   let D' be the RDF dataset serialized in signed document
   let S be the signature in D'
   let D be D' - S
   let C be the canonicalized version of D
   return whether S is a valid signature for C

To my non-expert eye there are several significant problems here.
1/ The signature extracted from the signed document might be different from 
the signature used to sign the original document if the original document has 
signatures in it.
2/ The dataset extracted during verification might not be the dataset used 
during signing because
the original document if the original document has signatures in it.
3/ Adding extra information after signing might be possible without affecting 
verification if the extra information looks like a signature.
4/ The dataset extracted during verification might not be the dataset used 
during signing because the original document has relative IRIs.
5/ The dataset extracted during verification might not be the dataset used 
during signing because the original document is in a serialization that uses 
external resources to generate the dataset (like @context in JSON-LD) and this 
external resource may have changed.
6/ Only the serialized dataset is signed so changing comments in 
serializations that allow comments or other parts of the document that do not 
encode triples or quads results can be done without affecting the validity of 
the signature.  This is particularly problematic for RDFa.

I welcome discussion of these points and am open to being proven wrong on them..

On 5/22/21 6:43 AM, Ivan Herman wrote:
> Peter,
>
> I agree that these are issues to handle/settle in a final specification. And 
> I let Manu reply to the specifics.
>
> However, I would regard these to be done during the life time of the Working 
> Group, if it gets approved; after all, making sure of these required quality 
> checks are one of the strong points of the W3C Process. The Linked Data 
> Proof draft specification is not even the FPWD of the WG's deliverables, it 
> is just a referenced document.
>
> Thanks
>
> Ivan
>

Received on Saturday, 22 May 2021 12:31:25 UTC