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Subject: Re: [ubl-security] UBL-XAdES-Profile 1.0-RC1


At 2010-08-13 08:38 +0200, Andrea Caccia wrote:
>At 2010-08-11 23.14 GET, G. Ken Holman wrote:
> > (1) - Lines 430 and 435 - when using this 
> methodology, I gather that multiple signatures 
> are instantiated in the extension and that I 
> need only a single <cac:Signature> element in 
> the instance itself to indicate that *all* 
> XAdES signatures are in that extension ... so, 
> if I need two signatures, I still only have one 
> <cac:Signature> element and I put the two signatures in the extension
> > - if this is correct, then I can understand 
> <cbc:ID>UBLDSIG</cbc:ID> being a fixed value 
> and that value being a child of the document element
>Yes it is correct
>
> > - but in Certificate of Origin there are four <cac:Signature> elements:
> >
> >  <cac:CertificateOfOrigin>
> >    <cac:CertificateOfOriginApplication>
> >      <cac:Signature>  <!--for the document-->
> >    ...
> >    <cac:IssuerEndorsement>
> >      <cac:Signature>  <!--for the endorsement-->
> >    ...
> >    <cac:EmbassyEndorsement>
> >      <cac:Signature>  <!--for the endorsement-->
> >    ...
> >    <cac:InsuranceEndorsement>
> >      <cac:Signature>  <!--for the endorsement-->
> >
> > - and in the common library, an item can have 
> a signature, and there are 21 places where items are used:
> >
> >  <cac:Item>
> >    <cac:Certificate>
> >      <cac:Signature>
> >
> > ... so signatures can be used all over the UBL document.
>It seems I started from a wrong assumption.
>Is endorsements applied to the whole document or just a fragment?

As this is a business question, I cannot answer 
because I do not know.  The CertificateOfOrigin 
is not the responsibility of either the PSC nor 
the TSC.  I have copied Tim with your question 
and this issue in case he can answer for us.

The issue continues...

> > - does line 430 imply that this Security 
> methodology does *not* apply to the 
> endorsements but only to the signatures that apply to the entire document?
>If we can't find an arrangement to deal with 
>this situation we have to be explicit IMO
>
> > - shall we explicitly exclude the 
> endorsements (and future signatures) so that there isn't a conflict?
> > - if someone wants to use XAdES for an 
> endorsement and in the future writes a 
> methodology for that, is our current choice of 
> "UBLDSIG" too ambiguous?  Should it perhaps be 
> "UBLDOCDSIG" or some other value to imply this 
> is the signature ID for that block of signatures for the entire document?
>
>We can try to change current assumption that 
>there is only a single cac:Signature and I propose the following:
>- there is a 1:1 mapping between cac:Signature 
>elements and UBLextension elements containing signatures
>- we add a <cbc:ID> optional element inside 
><ublsig:document-signatures 
>xmlns:ublsig="urn:X-figure-this-out-later"> (as 
>you proposed in another mail in place of 
><odsig:document-signatures>). This new element 
>MAY be present if there is a cac:Signature and, 
>if present, MUST be set equal to the cbc:ID in 
>the corresponding cac:Signature. I see here a 
>good reason to have a new schema defined. I have 
>indeed a little preference for 
><ublsig:signatures> as it is the most used signature container wrapper.
>- if there is more than one cac:Signature in the 
>UBL document, each MUST have a <cbc:ID> that 
>maps to <cbc:ID> element inside 
><ublsig:document-signatures> that MUST be 
>present too. So, in case a single signature is 
>present as in most cases, the cac:Signature is 
>optional and everything is as it is now.
>- for detached signatures I propose to have them 
>applicable only to the whole document as it is now
>- for <cbc:ID> value it MUST be unique (this is 
>implicit I guess) and we can just suggest its 
>something starting with "UBLDSIG…" or "UBLDOCDSIG…" as you suggested
>...
> > - in fact I now believe (after working on 
> this document) that we should not use a simple 
> string that is too easily ambiguous with what 
> users might inadvertently use (yes, I know 
> "UBL" is not common, but why use an ad hoc 
> identification scheme when there is one we can 
> use) and select two URNs for the values on 
> lines 430 and 435, and the values along the lines of:
> >
> > <cac:Signature>
> > 
> <cbc:ID>http://docs.oasis-open.org/ubl/securitysc/cd-dsigp-1/signature</cbc:ID>
> >   [...]
> > 
> <cbc:SignatureMethod>http://docs.oasis-open.org/ubl/securitysc/cd-dsigp-1/xades-enveloped</cbc:SignatureMethod>
> >   <cac:SignatoryParty>
> >     <cac:PartyIdentification>
> > 
> <cbc:ID>http://docs.oasis-open.org/ubl/securitysc/cd-dsigp-1/signature-defined</cbc:ID>
> >     </cac:PartyIdentification>
> >   </cac:SignatoryParty>
> >   [...]
> > </cac:Signature>
> >
>it seems to me a good idea. So we can have also
>http://docs.oasis-open.org/ubl/securitysc/cd-dsigp-1/ubldsig/N 
>(where N=1, 2, … ) instead of UBLDSIG or 
>UBLDOCDSIG to identify the document signatures? 
>But are we following the UBL common practices here?

Yes, good point.  I missed the fact that we have 
to point to an ordinal signature.

With that in mind, I'm going to now propose a URN 
instead of a URI, and I will follow up this 
discussion in a reply to Roberto's recent post as 
it will address that issue as well.

> > (2) - do you believe the definition on UBL 
> 2.1 Common Library row 225 incorrect?  it 
> states it is a signature applied to the 
> document instance, but its placement implies it 
> is a signature applied only to the certificate
> > - if you agree it is wrong, then Jon this 
> goes onto the list of definitions to be repaired
> >
>I feel you're right. Can you point me to the right document?

It is the spreadsheet for the common library an you can see the latest at:

   http://www.oasis-open.org/committees/document.php?document_id=38804

... but there will be another one posted this 
morning by me, so look on that page under 
"Document Revisions" to find the latest.

> > (3) - I note that only 54 documents allow 
> <cac:Signature> as a child of the document 
> element, and Certificate Of Origin has the 
> document-wide signature in a grandchild of the 
> document element ... do we need to add for PRD2 
> a <cac:Signature> child of the document element 
> to the other 5 documents that do not have this today?
> > - my thought is "yes, every UBL document must 
> have a <cac:Signature> *somewhere* to apply to 
> the entire document scope, and from now on it 
> must be a child of the document element (so 
> that CoO is the one and only UBL document that doesn't have it as a child)"
> > - the five documents with a missing 
> cac:Signature as a child of the document element are:
> >  CallForTenders
> >  CatalogueRequest
> >  ContractAwardNotice
> >  ContractNotice
> >  PriorInformationNotice
> >
>At least to authenticate it I think that there 
>could be situations where the signature could be 
>a requirement. The approach of making it 
>optional for every document at document-wide levelis fine with me.

Good ... this has been added to the list of changes after PRD1.

I will continue now in reply to Roberto.....

. . . . . . . Ken

--
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