FW: Late comments on OASIS DSS-X Profile on visible signatures Committee

Hello Denis,

I’m very sorry for the late response.

Please see my comments below.

Thank you very much for the detailed review and the detailed remarks.

Ezer

-----Original Message-----
From: Denis Pinkas [mailto:denis.pinkas@bull.net]
Sent: Friday, July 24, 2009 10:38 AM
To: Juan Carlos Cruellas; stefan; Ezer Farhi
Subject: Late comments on OASIS DSS-X Profile on visible signatures Committee Draft
Importance: High

I sent the comments below to Juan-Carlos, but I got no reply from him.

So I send them directly to the people that have their e-mail address on the front page of the document.

BTW, the e-mail address from Juan-Carlos on teh front page is wrong: it should end with "edu" rather than "ede".

Regards,

Denis

=======================================================

Juan Carlos and all,

Please find below late comments.

Juan-Carlos would you be able to post them to the DSS-X committee
since the link indicated in the mail does not work ?

Denis

=======================================================

Late comments on version 1.0 of the "Visible Signature Profile".

Source: Denis Pinkas. Bull SAS.

After two readings of the document, I still have difficulties to understand
how the protocol may be usable in practice with signature formats like CAdES and XAdES.

EZER – The Visible Signature profile performs is aimed to embed visible information upon a given content such as PDF document, MS Office documents, etc in addition to the actual digital signature operation that is handled through the DSS core protocol.

In the case that the client wishes to use an advanced signature (CAdES, XAdES), the client will need to use two profiles in addition to the core:

The Advanced signature profile, which is specified at http://docs.oasis-open.org/dss/v1.0/oasis-dss-profiles-AdES-spec-v1.0-os.html and the visible signature profile.

As an example, you can incorporate a visible signature to a PDF document in addition to an advanced digital signature embedded in the PDF document (at the level of conformance that is applicable today by PDF).

The current ETSI standardization process that is aimed for enabling advanced signatures in PDF files will probably incorporated into a new version of the advanced signature profile (which also in combination with the visible signature profile, enable supporting visible advanced signature in PDF files).

Whatever the protocol may be, the end result should be incorporated either into the signed document itself
or in the electronic signature.

EZER – the protocol tries to be aligned with existing document implementations such as PDF or Office 2007. And indded it is incorporated into the signed document itself.

The abstract is only addressing the embedding of "visible signature characteristics into documents".
Should the abstract be left unchanged, then this would mean that support of visible signatures
would not be supported for detached signatures and embedding signatures.

EZER – The protocol mainly addresses documents types and not native XML, that inherently addresses visibility of information.

Secondly, the internationalization of such visible signatures is not addressed. Since electronic signatures
are intended to be made visible, an electronic signature generated in one country using a given language
should be made visible in another country using a different language. Each field should thus be made visible
using a local language. This document is silent about this aspect.

EZER – It is possible to include textual information in a variety of languages by indicating fonts for every textual element. Text can be either supplied by the client or incorporated by the server (for example, a common name can be extracted by the server from the user’s certificate).

Usually the visible content is signed by existing implementation that forbids any modifications to the visible content, therefore it will not be possible to translate visible content from one language to another.

So basically, I think that supporting different languages based on universal strings is possible.

Thirdly, all the characteristics of a signature should not necessarily be made visible at once. There should be
a concept of a first level of visibility, and for each first level, a second level of details. At the very end,
all the visible characteristics (as requested by the signer) should be made visible.

EZER – This “visibility level” is not embedded in the protocol since currently no existing implementation (PDF, MS Office) enables that. The protocol does enable you to control (in the time of the digital signature act) which information should be incorporated to the visible signature.

It is possible to incorporate such a parameter to the protocol, which may be used by future applications/implementations.

These observations let me to conclude that the signer should be able to incorporate a template for the visible signature
which will describe the first level, secondary level, etc ... of the visible signature in a language independent manner.
Applications able to handle these visible signatures fields should be able to interpret the template in a local language.

EZER – Please see previous remarks about languages. Since most existing and future implementations sign the visible content, I think that the protocol should handle actual textual content and not templates.
It is possible to bind a “display level” for every displayable field (as described above).

As already stated above, whatever the protocol may be, the end result should be incorporated either into
the signed document itself or in the electronic signature.

EZER – yes.

If incorporated into the electronic signature, the basic question is where to place that information ?

EZER – The protocol address that by either supplying a position or an existing signature field, which is a placeholder for the visible signature.

Should it be as signed attributes (or signed properties) or as unsigned attributes (or signed properties) ?

EZER – If you referring to whether the visible content is signed. It is very much depended on the document implementation. The protocol addresses both implementation types (that sign the visible content and do not sign the visible content). One of the implementations that do not sign the visible content actually incorporate to the visible content the actual digital signature in bar-code representation or other type of representation. In this case the visible signature content cannot be signed.

Whatever the response to the question is, this means that new signed attributes (or signed properties)
or new unsigned attributes (or signed properties) should be defined respectively for CAdES and XAdES.

EZER – This issue will be covered as well by the implementation and not the protocol. In most existing applications today (PDF, Office), the visible signature is incorporated into the document’s content and not to the digital signature content (for example, signed attributes).

If incorporated into the document, the incorporation depends upon the type of document. However, this approach
would be restricted to some types of documents and would not be as general as the other approach.
Even if the electronic signature is embedded into the document (as it is the case for PDF signatures), it appears better
to add the information related to the visible signature into the electronic signature itself (placed within the document),
rather than placing it somewhere else in the document.

EZER – This issue should be addressed by the documents standards. The specification (which is also true for other aspects of the DSS specification) addresses the protocol and not the actual implementation. As I know there is an ETSI committee that will address aspects of incorporating visible content into the PDF specification that may address the issue that you raise.

As stated above, this means that new signed attributes (or signed properties) or new unsigned attributes
(or signed properties) should be defined respectively for CAdES and XAdES.

EZER – As said above, this direction should be handled by the document standards themselves. The protocol is not aimed only for documents types that use advanced signatures, but if the documents types do support CAdES/XAdES, the DSS server implementation may use signed properties to include visible content.

In the draft document, there is intent to add information like a "scanned image of the user's hand-written signature".
While this is an interesting idea, this information, if added should be incorporated as a signed attribute and a signed property.

EZER – As said above, it is up to the document implementation. Today, both PDF and Office sign this content as well as any other content in the visible signature.

The visible signature fields should not contain any value. Values should always be computed by a verification service
using the signed attributes (or signed properties) or/and the unsigned attributes (or signed properties), so that
there is no conflict or ambiguity between values placed in the electronic signature and asserted values that would be placed
in the visible signature fields.

EZER – In most of the cases the claim is correct and most existing implementation assure that by signing the visible content and make sure it is aligned with values that are not part of the visible content. As I said, above, the protocol also addresses implementation that produces a digital signature image. In this case this image is not signed and content data.

To summarize the suggested approach:

when used by a signer in a signing protocol, the service should be able to incorporate a "visible signature template"
into the electronic signature, preferably as a signed attribute or a signed property. This template would support
different levels of visibility.

EZER – Please see the comments above. We can highly consider incorporation a visible display level attribute for every item in the visible content. The application can use this attribute to define the level of visibility.

when used by a verifier in a verifying protocol, the service should be able to interpret in a local language
the "visible signature template" placed into the electronic signature, to the desired level of visibility and say
whether the information that has been retrieved has been verified or has simply been copied and pasted
from the unverified signature. In the later case, if the signature is not verified as being valid, this would allow
to know more about the electronic signature. This interpretation would also be faster in practice.
Application displaying the visible signature fields should take care to make the difference between “verified values”
and “unverified values”.

EZER – The visible signature profile mainly addresses the digital signature operation and has limited functionality in the validation processing.

Currently, the only processing that is included is to mark the verification status of the digital signature, but this act by itself is mainly aimed for documents types that will not violate the digital signature.

The proposal you raise is interesting, but I need to consult with the DSS committee to whether this approach should be defined and described in the visible signature profile.

Are you familiar with such an implementation? What types of documents are used?

Denis

----------

De : esi : etsi tc esi (electronic signatures and infrastructures)

� : ESI

Date : 2009-06-10, 17:57:55

Sujet : [ESI] Deadline for commenting OASIS DSS-X Profile on visible signaturesCommittee Draft

Dear all,

Just these few lines to remark that the window for raising comments on
the the DSS-X Profile on Visible Signatures **ENDS THE 30TH OF JUNE 2009**.

The OASIS DSS-X Technical Committee strongly encourages feedback
from you for the sake of improving the interoperability and quality of
OASIS work. Please feel free to distribute this announcement within
your organization and to other appropriate mail lists.

This profile is aimed to incorporate visible information into documents
as part of the digital signature operation.

Incorporating a visible signature as part of a digital signature
operation is mandatory for the acceptance of digital signatures in many
business scenarios and applications.

Today, there is an existing support in several document types such as
PDF and MS Office 2007, as well as non standard support in other
documents types. Eventually, many document types will support the both
visible and non-visible digital signature embedded in the document.

The target of the Visible Signature profile is to provide a general
interface to a digital signature service for incorporating a visible
signature to any type of document.

To ease the collaboration of a visible signature into applications, the
profile defines several types of scenarios/policies. Two of the most
outstanding usages of implementing a digital signature into documents
are application workflow scenario and a document submission scenario.

The committee will appreciate any submitted component as part of
reviewing the profile specifications.

For more information of how to access the content of the profile use the
following details:

The specification document and related files are available here:
Editable Source:
http://docs.oasis-open.org/dss-x/profiles/visualsig/v1.0/cd01/oasis-dssx-1.0-profiles-visualsig-cd1.doc

PDF:
http://docs.oasis-open.org/dss-x/profiles/visualsig/v1.0/cd01/oasis-dssx-1.0-profiles-visualsig-cd1.pdf

HTML:
http://docs.oasis-open.org/dss-x/profiles/visualsig/v1.0/cd01/oasis-dssx-1.0-profiles-visualsig-cd1.html

Schema:
http://docs.oasis-open.org/dss-x/profiles/visualsig/v1.0/cd01/oasis-dss-vissig-schema-v1.0-cd1.xsd

Non-normative information about the specification and the technical
committee may be found at the public home page of the TC at:

http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=dss-x.

Comments may be submitted to the TC by any person through the use of the
OASIS TC Comment Facility which can be located via the button marked
"Send A Comment" at the top of that page, or directly at:
http://www.oasis-open.org/committees/comments/index.php?wg_abbrev=dss-x.

Submitted comments (for this work as well as other works of that TC) are
publicly archived and can be viewed at:
http://lists.oasis-open.org/archives/dss-x-comment/. All comments
submitted to OASIS are subject to the OASIS Feedback License, which
ensures that the feedback you provide carries the same obligations at
least as the obligations of the TC members.

OASIS and the DSS-X TC welcome your comments.

Best regards,

Juan Carlos

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