Re: Signature in Wrong Position

On 17 January 2016 at 22:44, Henry Story <henry.story@bblfish.net> wrote:

>
> On 17 Jan 2016, at 20:38, Melvin Carvalho <melvincarvalho@gmail.com>
> wrote:
>
>
>
> On 17 January 2016 at 13:55, Henry Story <henry.story@bblfish.net> wrote:
>
>> I was looking at the Linked Data Signatures document
>>
>>   https://web-payments.org/specs/source/ld-signatures/
>>
>> I am not sure if this is the right list to discuss this.
>>
>> I am really keen to have something like this to work, and I like
>> most of it off the bat. But looking a bit closer I noticed what
>> I think is a serious error that has an easy fix though.
>>
>> The mistake is to put the signature *inside* the graph.
>> Take example 1:
>>
>> {
>>   "@context": "https://w3id.org/identity/v1",
>>   "title": "Hello World!",
>>   "signature": {
>>     "type": "LinkedDataSignature2015",
>>     "creator": "http://example.com/i/pat/keys/5",
>>     "created": "2011-09-23T20:21:34Z",
>>     "domain": "example.org",
>>     "nonce": "2bbgh3dgjg2302d-d2b3gi423d42",
>>     "signatureValue":
>> "OGQzNGVkMzVm4NTIyZTkZDYMmMzQzNmExMgoYzI43Q3ODIyOWM32NjI="
>>   }
>> }
>>
>> In short: Signatures should be external to the graph, since that is the
>> object
>> of the signature. By placing it inside the graph as above the problem is
>>
>> 1. the algorithm needs to remove elements from the signed graph
>> 2. The algorithm won't be able to cope with alignement of ontologies such
>> as
>>   a different relation being discovered to be owl:sameAs the :signature
>>   relation above. If another such widely used vocabulary is found, or
>> perhaps even
>>   if the current vocabulary is extended then the signature verification
>> systems won't
>>   necessarily be able to understand to remove those relations too.
>>
>> It is much better to put the signature outside of the graph. Then
>>
>> 1. The algorithm won't need to contain any condition about removing any
>> relation
>> which will be a lot better for large graphs, and speed up verification.
>> 2. New relations could be found or the vocabulary could be extended
>> without changing
>> the signature verification algorithm.
>>
>> Another way to think of this is that a named graph can always be mapped
>> to a literal.
>> ( This is why one can think of named graphs as already implicitly
>> contained in RDF/XML )
>> Signing documents is always external to the document in those
>> circumstances.
>>
>
> I think it depends on the use case.
>
> For LinkedDataSignature2015 the use case is so sign a canonical form of a
> graph pointed to by a subject.
>
> You could also imagine another algorithm that signed named graphs, I dont
> think the two are mutually exclusive.
>
>
> There should be no difference in the use cases.
>
> Each system has pros and cons, but if you canonicalize things well, the
> problem goes away, I think.  I think the way things are done currently
> reduces complexity, which in turn, increases adoption.
>
> For example, looking at your webid, you have a key in there, but it is
> unnamed ie a blank node.  This makes it impossible to do signing.  That is
> one of the reasons that work on WebID and work on web signatures diverged.
>
>
> You mean you can't refer to the key from outside the graph with a URI
> because it is a blank node? True, but that's not a problem for
> signatures. You can for example add the public key in the signature.
>
> {
>   "@context": "https://w3id.org/identity/v1",
>   "title": "Hello World!",
>   "signature": {
>     "type": "LinkedDataSignature2015",
>     "creator": { "cert:modulus": "DAB9D1E941F6F8...",
>                       "cert:exponent": 65537 }
>     "created": "2011-09-23T20:21:34Z",
>     "domain": "example.org",
>     "nonce": "2bbgh3dgjg2302d-d2b3gi423d42",
>     "signatureValue":
> "OGQzNGVkMzVm4NTIyZTkZDYMmMzQzNmExMgoYzI43Q3ODIyOWM32NjI="
>   }
> }
>

Well that wouldnt work, as you dont know what kind of key it is.  But I
guess going off topic.


>
> Anyway, that's neither here nor there. The question was one of where
> signatures should go: inside the graph or outside. One can
> put the signature outside the graph with keys too, just as one can if one
> uses URIs to identify the key.
>
> This is not something that affects any use cases. It's a question of
> simplicity of algorithms.
> It was pointed out in private conversation that the reason that this
> decision may have been made is because the other
> way around is less easy for beginner coders to get right for some reason.
>

Makes sense.  I do think the current formulation works, and is not in
error.  There's just different ways of doing things.


>
> My Json-LD is not so good. In N3 ( https://www.w3.org/2000/10/swap/Primer
>  )
> What would it look like with the signature outside of the graph?
>
>
> The convenience of using (which actually you argued for, and manu and
> others argued against) bnodes comes at a cost.  The cost in this case was
> to have two different communities working on liked data PKI solutions,
> neither with really a lot of resources.  So bear in mind there's always a
> trade off between convenience, utility and generalization.
>
>
> WebID does not disallow URIs for keys, as should be clear from reading the
> spec, and just from basic RDF principles. That point
> was made a few times on the webid mailing list.
>

Not really, using bnodes here is a serious anti pattern.  This is axiom 0
of the web.  Anything of significance should be given a URI.  This mistake
was one reason signatures have been developed independently.


>
>
> Not sure it would be correct to argue this is an error, simply a design
> decision.
>
> Work on signing other structures I think is also welcome, but maybe
> there's not (yet) enough use cases?
>
>
>>
>> Henry Story
>>
>>
>>
>>
>
>