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Re: Reminder: January 31 comment deadline for LCWD of Widgets 1.0: Packaging & Configuration spec

From: Frederick Hirsch <frederick.hirsch@nokia.com>
Date: Tue, 24 Feb 2009 17:19:48 -0500
Cc: Frederick Hirsch <frederick.hirsch@nokia.com>, Marcos Caceres <marcosscaceres@gmail.com>, "Barstow Art (Nokia-CIC/Boston)" <Art.Barstow@nokia.com>, public-webapps <public-webapps@w3.org>
Message-Id: <9B4D9EE8-7CAE-430C-98C0-19AD6FD59041@nokia.com>
To: "ext Priestley, Mark, VF-Group" <Mark.Priestley@vodafone.com>
The Widget Signature spec is not an API definition so probably does  
not need to define how signature status information is returned. I  
also agree that it would be incorrect to define in the Widget  
Signature spec whether or not a widget is valid, that is out of scope.  
The spec limits itself to signature validation.  However I would not  
want to be prescriptive in the specification to the level of status  
return codes.

We may want to add a security considerations note along the lines of

"As distributor signatures are not included in an overall widget  
signature, it is possible for signatures to be added or removed and  
hence a secure channel for widget delivery  might be preferable."

regards, Frederick

Frederick Hirsch
Nokia



On Feb 6, 2009, at 10:51 AM, ext Priestley, Mark, VF-Group wrote:

>
>
> Hi Marcos,
>
> More responses to your comments below (marked [mp]). Still need to get
> back to you on the access element but I need to think about it a bit
> more first.
>
> Thanks,
>
> Mark
>
>
>> ----------------------
>> Step 5 Process the Digital Signatures
>>
>> We disagree with the stage 2, specifically "If the file entry is
>> deemed by the [Widgets-DigSig] to be an invalid widget, then a widget
>> user agent must treat this widget as an invalid widget.", on two
> grounds:
>>
>> (1) Because one signature is invalid it doesn't mean that all of the
>> signatures are invalid;
>> (2) Just because one signature or all signatures are invalid does not
>> mean that the widget should not be installed, only that it should
>> _not_ be treated as a signed widget. The security policy of the  
>> device
>
>> might be configured not to install an unsigned widget or a widget  
>> with
>
>> an invalid signature but this should be dependent on the security
>> policy implemented.
>
> Sorry, I think you might have misunderstood what I was trying to say
> here (probably I did not write it clearly enough). This assertion is
> here to deal with instances where the digital signature deemed by the
> Widgets Dig Sig spec to be somehow fully broken or completely
> non-conforming in such a way that all processing must stop. I don't  
> yet
> know if Widgets Dig Sig will spit out such a result for any digsig  
> it is
> processing, but it seemed like a good idea to put this in here at the
> time.
>
> [mp] No this was pretty much my understanding. Maybe my comment wasn't
> clear enough... IMO [Widgets-DigSig] should result in a list of
> signature status values. How the widget user agent responds to those
> values should be dependent on the security policy of the widget user
> agent.
>
> In other words, this is something that is controlled by the Widgets  
> Dig
> Sig spec. If it turns out that Widgets Dig Sig never results in an
> invalid widget situation, then I will take this out. I've created a  
> red
> note in the spec that says "Issue: [Widgets-DigSig] may never  
> identify a
> widget package as invalid" as a reminder that we need to sort this  
> out.
>
> [mp] Well I would argue that the [Widgets-DigSig] will never  
> identify a
> widget package as invalid although it may decide that one or more
> signature(s) are invalid. The security policy of the device may decide
> that the widget shouldn't be installed based on the result of  
> processing
> the signature file(s) but that is a different thing. I think that best
> we can do in the P&C spec is say whether or not the widget is signed
> (and even this could be tricky).
>
> FWIW, I think step 5  is buggy and needs a rewrite (I've added another
> issue to the spec stating as such). I'll need to work with you to  
> fix it
> as we progress the Dig Sig spec.
>
> [mp] I'll be available to work on this next week
>
>> -----------------------------------------------
>> Step 4 Locate Digital Signatures for the Widget
>>
>> I'm not sure whether the packaging and configuration specification is
>> the correct place to do this but IMHO there needs to be a statement
>> that a files with a file name corresponding to the naming convention
>> for digital signatures are not accessible from the widget once the
>> widget is installed / instantiated. Failure to impose this  
>> restriction
>
>> will make it possible to include a signature and then reference it
>> from the signed code, which presents a security hole.
>
> Good point. This seems like something that needs to be in the yet to  
> be
> written a widget runtime security spec.  I've added an issue note to  
> the
> spec so we don't forget about this.
>
> Just out of interest, can you present the nature of the security hole?
> i.e., once an attacker has the signature, say, via an XSS attack, what
> could they do with it?
>
> [mp] The hole is that signature files are excluded from the generation
> of the signature values in any other signature files. This means that
> if, for example, an attacker added to the widget resource a signature
> file containing some malicious content, the malicious content of that
> file wouldn't be covered by any of the other signatures but the widget
> user agent thinks the entire widget resource is signed. This could
> happen regardless of whether or not the signature file was actually
> valid, or was just named according to the convention for digital
> signature.
>
> To be abused by an attacker it would either be necessary to inject a
> reference to the file into the widget, which might be difficult, or to
> hijack an existing reference to a signature file by swapping the
> intended signature file for the attacker's signature file (with the  
> same
> name). While this later attack depends on the author providing such a
> reference in their widget, there are two reasons why the author may
> currently choose to do this - to get some information about the
> signature to display to the user, or possibly more likely, to get  
> around
> the need to sign everything in their widget resource (I thought of  
> this
> as a way around signing everything so developers will too!).
>
> It's not a big hole and the attacks require some "assistance" from
> developers, but unless there's a reason not to it should be pretty  
> easy
> to close.
>
>
>
>
>> -----Original Message-----
>> From: Marcos Caceres [mailto:marcosscaceres@gmail.com]
>> Sent: 04 February 2009 17:35
>> To: Priestley, Mark, VF-Group
>> Cc: Arthur Barstow; public-webapps
>> Subject: Re: Reminder: January 31 comment deadline for LCWD of
>> Widgets 1.0: Packaging & Configuration spec
>>
>> Hi Mark,
>> On Thu, Jan 29, 2009 at 6:29 PM, Priestley, Mark, VF-Group
>> <Mark.Priestley@vodafone.com> wrote:
>>>
>>> Hi Marcos, Art, All,
>>>
>>> Please find below Vodafone's comments on the Widgets 1.0: Packaging
>>> and Configuration specification. I have divided them into what I
>>> consider to be substantive comments and editorial comments.
>>>
>>> Thanks,
>>>
>>> Mark
>>>
>>>
>>>
>> ----------------------------------------------------------------------
>>> --
>>> ----------------------
>>> Substantive comments
>>>
>> ----------------------------------------------------------------------
>>> --
>>> ----------------------
>>> Step 5 Process the Digital Signatures
>>>
>>> We disagree with the stage 2, specifically "If the file entry is
>>> deemed by the [Widgets-DigSig] to be an invalid widget, then
>> a widget
>>> user agent must treat this widget as an invalid widget.", on
>> two grounds:
>>>
>>> (1) Because one signature is invalid it doesn't mean that all of the
>>> signatures are invalid;
>>> (2) Just because one signature or all signatures are invalid
>> does not
>>> mean that the widget should not be installed, only that it should
>>> _not_ be treated as a signed widget. The security policy of
>> the device
>>> might be configured not to install an unsigned widget or a
>> widget with
>>> an invalid signature but this should be dependent on the security
>>> policy implemented.
>>
>> Sorry, I think you might have misunderstood what I was trying
>> to say here (probably I did not write it clearly enough). This
>> assertion is here to deal with instances where the digital
>> signature deemed by the Widgets Dig Sig spec to be somehow
>> fully broken or completely non-conforming in such a way that
>> all processing must stop. I don't yet know if Widgets Dig Sig
>> will spit out such a result for any digsig it is processing,
>> but it seemed like a good idea to put this in here at the time.
>>
>> In other words, this is something that is controlled by the
>> Widgets Dig Sig spec. If it turns out that Widgets Dig Sig
>> never results in an invalid widget situation, then I will take
>> this out. I've created a red note in the spec that says
>> "Issue: [Widgets-DigSig] may never identify a widget package
>> as invalid" as a reminder that we need to sort this out.
>>
>> FWIW, I think step 5  is buggy and needs a rewrite (I've added
>> another issue to the spec stating as such). I'll need to work
>> with you to fix it as we progress the Dig Sig spec.
>>
>>> -----------------------------------------------
>>> Step 4 Locate Digital Signatures for the Widget
>>>
>>> I'm not sure whether the packaging and configuration
>> specification is
>>> the correct place to do this but IMHO there needs to be a statement
>>> that a files with a file name corresponding to the naming convention
>>> for digital signatures are not accessible from the widget once the
>>> widget is installed / instantiated. Failure to impose this
>> restriction
>>> will make it possible to include a signature and then reference it
>>> from the signed code, which presents a security hole.
>>
>> Good point. This seems like something that needs to be in the
>> yet to be written a widget runtime security spec.  I've added
>> an issue note to the spec so we don't forget about this.
>>
>> Just out of interest, can you present the nature of the security  
>> hole?
>> i.e., once an attacker has the signature, say, via an XSS
>> attack, what could they do with it?
>>
>>> -----------------------------------------------
>>> 7.10 The access Element
>>>
>>> The access element defines a network attribute as "A boolean
>> attribute
>>> that indicates that the widget might need to access network
>> resources
>>> as specified in [Widgets-Security]. "
>>>
>>> Based on this description we would like to make the following
>>> observations and suggestion:
>>>
>>> The access element contains security permissions that will
>> be used as
>>> hooks in the yet to be written [Widgets-Security] specification. The
>>> problem is that the permissions haven't yet been discussed in detail
>>> and so we may find that we want to represent additional
>> context other
>>> than a black and white "is network access required?". For
>> example, it
>>> may be the case that it is important from a security point
>> of view to
>>> know which bearer or protocol will be used, or to nest a set of
>>> domains/URLs with which the widget wants to communicate. I
>> do not have
>>> a strong view on what might be relevant here, and I am not
>> suggesting
>>> that it needs to be considered as part of the last call of the
>>> Packaging and Configuration spec, only that it is likely that the
>>> permission will need to be more complex when we look at it
>> from a security perspective.
>>
>> I think we better start this soon, then. My feeling is that we
>> will need some kind of <domain> access declarations, and I
>> would like to see them in the configuration document.
>>
>> __This has the potential to block progress of this specification.__
>>
>>> There is also the case in which the network permission may
>> be used to
>>> determine whether or not the user wants to install a widget,
>>
>> This sounds reasonable.
>>
>>> or by the
>>> widget user agent may want to indicate whether or not the widget can
>>> run when there is no available network connection. Some widgets may
>>> only operate when there is a network connection, whereas others may
>>> degrade gracefully.
>>
>> This sounds like something authors need to deal with, not user  
>> agents.
>>
>>> So to provide a degree of future-proofing we would like to suggest
>>> something like:
>>>
>>> <access>
>>>   <network use="true/false" required="true/false"/> </access>
>>
>> We might not need this at all, actually: If we go down the
>> declaring domain route, then network is off unless a domain is
>> declared.
>>
>>> (I realise that the "use" attribute in the above example is
>> a horrible
>>> name but I couldn't think of another word for access...There are
>>> probably also better ways of capturing the meaning - we open to
>>> suggested improvements)
>>
>> This needs further discussion.
>>
>>> Sorry for not raising this earlier but it has only become apparent
>>> when considering in more detail how the access element would be  
>>> used.
>>
>> No probs.
>>
>>>
>>>
>> ----------------------------------------------------------------------
>>> --
>>> ----------------------
>>> Editorial comments
>>>
>> ----------------------------------------------------------------------
>>> --
>>> ----------------------
>>> 6 Widget Resources
>>>
>>> First 5 bullets should say "and/or" rather than "or" ?
>>
>> "Zero and/or more" sounds weird to me (i.e., "Zero and more").
>> If you feel strongly about this, I will change it; otherwise,
>> I would prefer to leave it as is.
>>
>>> -----------------------------------------------
>>> 6.5 Content Localization
>>>
>>> "The container for localized content is a folder at the root of the
>>> widget whose the first five characters of the folder-name case
>>> insensitively match the string 'locales/'." Why the first five
>>> characters only?
>>
>> That was a mistake, the sentence now reads:
>> "The container for localized content is a folder at the root
>> of the widget whose folder-name case insensitively match the
>> string 'locales/'. A container for localized content may
>> contain zero or more localized folders."
>>
>>> Also sentence has an extra "the" in the middle, i.e. "whose
>> *the* first"
>>
>> fixed.
>>
>>> -----------------------------------------------
>>> 6.6 Start file and Default Start Files Sentence
>>>
>>> For consistency with other sections I suggest to add:
>>>
>>> "A default start file is a start file whose file-name case
>>> insensitively matches a file-name given in the first column of the
>>> default start files below and whose MIME type matches the MIME type
>>> given in the second column of the table."
>>>
>>> before the sentence starting: "A default start file is a start file
>>> that a widget user agent..."
>>
>> Ok, I think there was a more significant problem: I've defined
>> "custom start files" and "default start files". As a result, I
>> changed that whole section.
>>
>>> And then to combine the last two sentences before the default start
>>> files table to:
>>>
>>> "A widget user agent will attempt to locate a file entry whose
>>> file-name case insensitively matches one of the default start files
>>> based on the order they appear in the table below (from top
>> to bottom). "
>>
>> Can you please check that section again and let me know if the
>> rewrite is ok?
>>
>>> -----------------------------------------------
>>> 7.1 Namespace
>>>
>>> It seems a bit tough that an invalid configuration document
>> results in
>>> a invalid widget as the configuration document is optional. Also, if
>>> the configuration document in the localised folder is invalid, it
>>> could be the case that there is a valid configuration
>> document at the
>>> root of the widget.
>>>
>>> I don't have a strong opinion on this and have no objection
>> to leaving
>>> the text as it is, I just wondered if there was a reason why this
>>> approach had been taken?
>>
>> Although I agree that it's a bit cruel on developers, we made
>> this decision to make the behavior of configuration documents
>> predictable.
>> I feel pretty strongly that we should leave it as is.
>>
>>> -----------------------------------------------
>>> 7.2 Proprietary Extensions
>>>
>>> Should the "may" be a "should"? Otherwise, it could be
>> interpreted as
>>> suggesting that vendors may equally use other approaches?
>>
>> Right, fixed. This should, in fact, be a must (i.e., if you
>> want to extend, then you must use your own namespace).
>>
>>> -----------------------------------------------
>>> 7.9 The icon Element
>>>
>>> (disclaimer - I may well be talking rubbish here as the following
>>> comments are based on a _very_ basic understanding of graphics
>>> formats)
>>>
>>> The text says that if the icon is vector format then the height and
>>> width attributes will be used, however, isn't one the point of using
>>> vector graphics that they could be re-sized to fit the
>> available space.
>>
>> Yes and no. Beyond certain sizes (e.g., too little, too big),
>> the rendering engine may have undesirable effects on a design
>> (think, for example, of a really tiny font having anti-alias
>> applied to it:
>> because of sub-pixel interpolation, it becomes too blurry to
>> read. The same can happen with graphics, very thin lines can
>> vanish or become blurry, which can make a design look crappy).
>> In such cases, it may be desirable to use a bitmap.
>>
>>> Therefore shouldn't there be a statement saying that the widget user
>>> agent MAY ignore these values?
>>
>> No, the width and height attributes represent the _minimum_
>> size at which an image may be used. Then, the vector graphic
>> can behave in the manner you describe (i.e., can be used to
>> fill a rendering context larger than the width and height).
>>
>>> Equally should there be default sizes in case the attribute
>> is not used?
>>
>> Hmm... good point. I've added that as an issue in the relevant  
>> section.
>>
>>> In terms of raster graphics the text currently says "If the file
>>> pointed to by the src is a supported raster graphic, this
>> value may be
>>> ignored by the widget user agent." but shouldn't the "may" in this
>>> case be a "should"?
>>
>> Correct, but that "should" should be a "must". Fixed.
>>
>>> -----------------------------------------------
>>> 7.13 The feature Element
>>>
>>> In the sentence "The feature is used by an author to denote that, at
>>> runtime, a widget may require access to a feature." the use of "may
>>> require" is very slightly confusing given that the next attribute is
>>> "required". Suggest changing "require" to "try to" or "attempt to".
>>
>> Changed "require" to "attempt to".
>>
>>> Likewise in the definition of the name attribute in the sentence "A
>>> URI attribute that identifies a feature required by the widget at
>>> runtime (such as an API)." change "required by" to "that may
>> be used".
>>
>> Done.
>>
>>> -----------------------------------------------
>>> 8 Steps for Processing a Widget Resource
>>>
>>> The sentence "The steps for processing a widget resource
>> involves ten
>>> steps that a widget user agent must follow, in sequential order,
>>> responding accordingly if any of the steps result in an
>> error." could
>>> be slightly misleading as some of the steps are skipped depending on
>>> the processing in a preceding step. I'm not sure if this is
>> always in
>>> a response to an error?
>>
>> Ok, I changed it to: "The steps for processing a widget
>> resource involves ten steps that a user agent must follow, in
>> sequential order, responding accordingly if any of the steps
>> result in an error or if the specification asks for the user
>> agent to skip a step."
>>
>> Is that any better?
>>
>>> A minor comment on section 8 as a whole - some of the steps have an
>>> explicit link to go to the next step while others (like 9) don't. It
>>> would be nice if this was consistent.
>>
>> Ok, I checked every step and made sure things are consistent.
>> Once all the comments are done, I'll do another editorial
>> round to make sure everything is more consistent.
>>
>>> In addition, some of the algorithms, for example step 7,
>> could be made
>>> clearer by explicitly stating when to go to the next step (i.e. in
>>> case of success in 7.1 and 7.2).
>>
>> Ok, I did what you said for step 7 and Step 8. Can you let me
>> know which other ones need a rewrite?
>>
>>> Finally, in Step 6 there is a sentence "Else, remove the last subtag
>>> of the range and repeat this step 2.d. (e.g., if the range
>> ...". Just
>>> to be super clear perhaps "this step 2.d." could be change
>> to "and go
>>> to 2.d of this algorithm"
>>
>> Made the change you suggested.
>>
>> Very much appreciate Vodafone taking the time to conduct this review.
>>
>> Kind regards,
>> Marcos
>> --
>> Marcos Caceres
>> http://datadriven.com.au
>>
>
Received on Tuesday, 24 February 2009 22:21:50 GMT

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