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Re: Draft Blog Post on Cryptography API

From: Ryan Sleevi <sleevi@google.com>
Date: Mon, 8 Oct 2012 15:04:16 -0700
Message-ID: <CACvaWvZVXmv5F1MgdXg4W-TNU5WthpVLgoB2iOa4UuGNPss1Bg@mail.gmail.com>
To: Harry Halpin <hhalpin@w3.org>
Cc: "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Mon, Oct 8, 2012 at 1:29 PM, Harry Halpin <hhalpin@w3.org> wrote:
> On 10/08/2012 08:09 PM, Ryan Sleevi wrote:
>>
>> On Mon, Oct 8, 2012 at 10:54 AM, Harry Halpin <hhalpin@w3.org> wrote:
>>>
>>> On 10/08/2012 07:32 PM, Ryan Sleevi wrote:
>>>>
>>>> On Mon, Oct 8, 2012 at 10:22 AM, Harry Halpin <hhalpin@w3.org> wrote:
>>>>>
>>>>> As promised, here's a draft blog post to respond to some of the
>>>>> comments,
>>>>> and I'd like the WG to look at it before publishing on the W3C blog.
>>>>> Please
>>>>> feel free to make additions/subtractions/corrections. Note the
>>>>> provocative
>>>>> title :)
>>>>>
>>>>>     -harry
>>>>>
>>>>> ----
>>>>> Title: Re-igniting the Javscript Cryptography Flame War
>>>>>
>>>>> Recently, the W3C has released as a First Public Working Draft the Web
>>>>> Cryptography API [1], which defines a number of cryptographic
>>>>> primitives
>>>>> to
>>>>> be deployed across browsers and native Javascript environments. As has
>>>>> been
>>>>> discussed in a number of blog-posts [2], cryptography in Javascript on
>>>>> the
>>>>> Web is unsafe at best today, although technically the Web Crypto API is
>>>>> a
>>>>> WebIDL that could be bound to programming languages beyond Javascript.
>>>>> Even
>>>>> with excellent implementations such as the Stanford Javascript Crypto
>>>>> Library [3], browsers still have to download possibly untrusted
>>>>> Javascript
>>>>> cryptographic code in order to obtain basic cryptographic functionality
>>>>> not
>>>>> provided natively by Javascript.
>>>>
>>>> To be fair, I don't think this is where the contention is with regards
>>>> to JS security.
>>>
>>>
>>> That seems to be contention for lots of folks, as at best we reduce the
>>> security properties of JS crypto to TLS. Of course, this ignores the fact
>>> that digital signatures and many other things in Web apps are useful
>>> regardless. Hmmm...should I bring that out in the beginning?
>>>
>>> "obtain basic cryptographic functionality not provided natively by
>>> Javascript" -> " obtain basic cryptographic functionality not provided
>>> natively by Javascript such as digital signatures".
>>
>> Sorry, my point was that even with this API, there is still a
>> fundamental reliance on TLS to provide connection security (well,
>> outside of SysApps aka extensions). This API does not provide for a
>> replacement of TLS, since it's ultimately script delivered by a remote
>> server.
>
>
> I was in no way implying that we replaced TLS, but that safe code delivery
> is a problem (even with TLS, although all power to CA Transparency!).
>
>
>>
>> I think the primary "issue" with SJCL (and, again, it's a great API,
>> not to be mistaken here), that this API can resolve, is not about the
>> delivery of script (which is still an issue with this API), but about
>> secure key storage - and to a lesser degree, constant-time, vetted
>> operations.
>>
>> Randomness was addressed by WHATWG, but we could highlight it here
>> again if it matters.
>
>
>
> So, how about:
>
> "obtain basic cryptographic functionality not provided natively by
> Javascript" -> " obtain basic cryptographic functionality not provided
> natively by Javascript such as key storage".
>
>>
>> I just think the current wording suggests that it's a "delivery"
>> issue, which I don't think it is.
>
>
> I would note generic code-signing was a major issue for many folks.

Yes, but you still have to bootstrap the delivery of that code, which
is why it's turtles all the way down if we try to say we're solving
delivery.

I'm not denying that we can solve some of the delivery problems for
some of the use cases. I think Facebook's example/use case is an
excellent one we can solve, but the general "delivery" problem of
other scripts, say of Crypto.cat (over TLS or not) are ones we
cannot/should not solve.

(Short of something like
http://www.mozilla.org/projects/security/components/signed-scripts.html
which has its own issues).

I think my point is that this API does *nothing* for the "download
possibly untrusted Javascript cryptographic code" - we can't/aren't
solving the trust-in-JS issue. However, it does provide an abstraction
for key storage, so that *if* untrusted JS gets in, the worst it can
do is spoof during the time of the compromise, and *not* exfiltrate
the key itself.

Not to mention all the other (platform native) use cases we have,
ranging from "replacing the native plugins" (eg: Korean use cases) to
the OpenID Connect-et-al.

>
>>
>>>>> Yet is Javascript cryptography doomed on the Web? Much of the critique
>>>>> of
>>>>> Javascript cryptography boils down to a critique of current Web
>>>>> browsers,
>>>>> and as has been shown by the W3C and browser vendors - the Web Platform
>>>>> can
>>>>> evolve. Due to TLS, almost every web browser and operating system
>>>>> already
>>>>> contains well-verified and reviewed cryptographic algorithms. At its
>>>>> core,
>>>>> the Web Cryptography API will simply expose this functionality to
>>>>> WebApp
>>>>> developers, with a focus on essential features such as
>>>>> cryptographically
>>>>> strong random number generation, constant-time cryptographic
>>>>> primitives,
>>>>> and
>>>>> a secure keystore. Without these functions, Javascript web cryptography
>>>>> would be impossible.
>>>>>
>>>>> Yet we realize the Web Cryptography API is only a single component in
>>>>> building the emerging Web Security model of which the Web Cryptography
>>>>> API
>>>>> is only a single component.
>>>>
>>>> "is only a single component" appears twice here.
>>>
>>>
>>> Thanks for the catch! Again, trying to clarify we are not providing a
>>> magic
>>> bullet here, just a Crypto API.
>>>
>>>
>>>>> For example,  one open issue is whether or not
>>>>> applications using the Web Cryptography API also should be required to
>>>>> use
>>>>> CSP to prevent XSS attacks [4]. Indeed, should and can browser vendors
>>>>> and
>>>>> the W3C as a whole tackle the malleability of the browser Javascript
>>>>> run-time environment? Without a doubt these security considerations of
>>>>> utmost importance, and getting them right to enable cryptography on the
>>>>> Web
>>>>> will require holistic thinking about attack surfaces and threat models.
>>>>> There are a number of use-cases, such as checking digital signatures to
>>>>> out-of-band key provisioning, that our API hopes to enables by allowing
>>>>> key-based encryption and trust to be used in Web applications.
>>>>>
>>>>> One issue with the Web Cryptography API is that the Working Group
>>>>> decided
>>>>> to
>>>>> expose the low-level functionality first rather than aiming only for a
>>>>> high-level API aimed at the developer on the street who may not have a
>>>>> grasp
>>>>> of the finer details of cryptography. The Working Group did this on
>>>>> purpose
>>>>> after taking a survey of users [5], in order to allow experienced
>>>>> developers
>>>>> to build the functionality needed across the largest number of
>>>>> use-cases,
>>>>> but a "high-level" API that makes using cryptography easy for Web
>>>>> developers
>>>>> is still on our agenda. However, the Working Group decided to iron out
>>>>> the
>>>>> low-level details, in particular as regards keys and key storage,
>>>>> before
>>>>> moving to thinking about a higher-level and more simple API.
>>>>>
>>>>> A second issue is that the current Web Cryptography API exposes legacy
>>>>> cryptographic algorithms with known weaknesses such as those in  RSA
>>>>> PKCS#1
>>>>> v1.5, which was done in the draft to allow Web Application developers
>>>>> to
>>>>> create applications with interoperability with widely used applications
>>>>> such
>>>>> as GPG, SSH, and the like. These algorithms are not required to
>>>>> implement,
>>>>> but if implemented, we felt they should be uniformly specified across
>>>>> browsers. In our next iteration of the Web Cryptography API, we will
>>>>> label
>>>>> any algorithms with known weaknesses at our time of publication with
>>>>> sufficient warnings that the algorithm is not suitable to encrypt data
>>>>> and
>>>>> provide preferable alternatives.
>>>>
>>>> Did we have consensus for this? We had discussed, and it seemed like
>>>> opinions were mixed on this - how much should be labeled in the draft
>>>> and how much should be labeled elsewhere?
>>>
>>>
>>> I was under the impression we agreed that the request from CRF and others
>>> to
>>> label them was reasonable and to label them in the draft. I'm not sure
>>> where
>>> "elsewhere" would be. But yes, we have not yet of course decided on the
>>> labelling scheme.
>>
>> The example of "elsewhere" was the IRTF document (
>> http://tools.ietf.org/html/draft-irtf-cfrg-cipher-catalog-00 )
>>
>> With all respect to Zooko, the concern is that the wording more or
>> less matches his proposal, which is an outstanding issue at this time.
>>
>> An example of an alternative proposal was to list "Security
>> Considerations" on a per-algorithm basis, and to reference appropriate
>> external sources for more details. Such a solution is very different
>> than Zooko's, but functionally accomplishes the same goals, and is
>> what had been discussed prior to last week as being a workable
>> solution.
>>
>> So I don't think we've quite nailed down what "labeled" means yet.
>
>
> It was just not a concern of CRF, but also a concern raised by Dr. Rivest
> last time I was at MIT and by others at the W3C. Of course, once the interop
> angle was explained, they were much more sympathetic. So, we should say we
> will address these concerns by our next draft. In fact, perhaps before we go
> much further we should try to get consensus on what precisely we plan to do.
>
> So how about this text for the blog post, where we use the term "sufficient
> warning" rather than
>
> "In our next iteration of the Web Cryptography API, we will include
> sufficient warning to ensure that web developers do not mistakenly use
> cryptographic algorithms with known weaknesses for encryption. However,
> since cryptography is a moving field, we cannot guarantee that the security
> properties for the infinite future, only at the time of our publication."
>
> Is that sufficient?

"known weaknesses for encryption" -> "known weaknesses", since we're
not strictly talking about encryption here (it's just been the one
that has been on the top of everyone's minds)

Alternatively,

"In our next iteration of the Web Cryptography API, we will include
appropriate security considerations to try and ensure that web
developers do not mistakenly use cryptographic algorithms with known
flaws. However, as cryptography is a moving field, we cannot guarantee
that today's robust and secure solution will not be tomorrow's
security considerations." (or something to that effect)

>
>
>
>>
>>>> With every one of our algorithms, it's possible to use it
>>>> "insecurely", and the issues with PKCS#1 v1.5 are predominantly with
>>>> implementation issues, as opposed to fundamental algorithm issues
>>>> (although I realize that some will argue that *because* there can be
>>>> implementation issues, it's a fundamental algorithm issue)
>>>>
>>>> I'm hesitant to call this a firm commitment, if only because it's
>>>> unclear what we're committing to at this point.
>>>
>>>
>>> Yes, this is a hard point to phrase. However, I think the general point
>>> is
>>> that "Some of the algorithms can be used insecurely, but they are
>>> necessary
>>> for interoperability". Would that be a better way of phrasing it?
>>>
>>> So how about:
>>>
>>> "A second issue is that the current Web Cryptography API exposes legacy
>>> cryptographic algorithms that can be used and implemented insecurely, yet
>>> these are still needed in order to allow Web Application developers to
>>> create applications with interoperability with widely used applications
>>> such
>>> as..."
>>
>> Sounds reasonable.
>>
>>> "For our next iteration of the Web Cryptography API, we are considering
>>> labeling algorithms by their function, as well as possibly with known
>>> weaknesses at our time of publication and pointing to preferable
>>> alternatives for creating new secure protocols."
>>
>> Again, I think that gets us down the (reasonably) dangerous path of
>> trying to keep up to date with changes in cryptographic best practice.
>> I would rather avoid "suggestive" text entirely - and highlight known
>> issues at the time of publication.
>>
>> I think the real recommendation should be that web developers should
>> not be developing new secure protocols. This is not crypto-elitism,
>> this is security pragmatism. If we're going to recommend anything, I'd
>> rather recommend something like JOSE (which is to say, 'use the
>> high-level').
>>
>> But I don't know how committed we are to either normative or
>> informative recommendations.
>
>
> See above.
>
>>
>>>
>>>
>>>>> Is releasing this cryptography in Javascript to developers responsible?
>>>>> Of
>>>>> course, cryptography can be used for both great good and great harm.
>>>>> Yet
>>>>> given the current dangerously insecure state of Javascript cryptography
>>>>> and
>>>>> the fact that developers are already re-implementing cryptographic
>>>>> functions
>>>>> in Javascript, myself and others at the W3C thought that action should
>>>>> be
>>>>> taken. Yet who we're really interested is not what we think, but what
>>>>> you
>>>>> think.
>>>>
>>>> Is that what motivated the WG? This certainly didn't match my
>>>> understanding of at least what the WG was trying to accomplish in
>>>> chartering. What I qualify with is that this seems to make it out that
>>>> our goal is to solve "dangerously insecure state of Javascript
>>>> cryptography" - which sets a certain set of priorities to our work -
>>>> as opposed to perhaps other goals, such as enabling richer web
>>>> applications with secure key storage.
>>>
>>>
>>> I do not see the difference. Developers are already (see crypto.cat etc.)
>>> trying to make JS crypto apps, so an APi is necessary in order to enable
>>> secure key storage and other necessary components.  We could say instead
>>> "Given the fact that developers are already re-implementing  key-based
>>> cryptography in Javascript in order to create richer Web applications
>>> with
>>> key storage, my ..."
>>
>> I certainly can't speak to your goals, and leave you best to qualify
>> them however you see fit. My concern was and is simply that "others at
>> the W3C" may serve two interpretations. It may be seen to reflect the
>> goals of members (eg: the WG participants), who I think have a myriad
>> of different goals than trying to fix what /other/ developers are
>> doing. Or it may be seen to reflect what the administrative
>> arms/chairs/etc of the W3C see, which may be a different set of member
>> organizations.
>>
>> Either way, there's a number of reasons why participants have been
>> participating, and I'm not sure the current text reflects the goals of
>> all participants or fully qualifies that it's representing the opinion
>> of individuals/the W3C as an organization.
>>
>> This is really a minor point, to be fair, but hopefully it's clearer
>> now what my concern was.
>
>
> OK. Again, the point is that people re-implementing crypto in JS is
> generally a bad thing if well-verified crypto can be exposed to JS as an
> API. I'm happy to delete that above sentence.
>
>
>>
>>>
>>>> One could argue that, functionally, they're the same goal, but I fear
>>>> that how it's presented may set expectations for the set of problems
>>>> we SHOULD be solving.
>>>>
>>>>> The entire point of releasing a Working Draft is to get the wider input
>>>>> of
>>>>> the community before we set the API in stone by implementing it.
>>>>> Indeed,
>>>>> we
>>>>> purposefully released the API at an early stage, when many of the basic
>>>>> issues are still unresolved, in order to get community input. Indeed,
>>>>> most
>>>>> of the work of the Working Group has been on identifying the space of
>>>>> unresolved issues, ranging from how to determine where a key is stored
>>>>> and
>>>>> key naming. Many of these open issues are given in the fourteen open
>>>>> issues
>>>>> in the specification itself, with more in the issue-tracker [6]. What
>>>>> we
>>>>> really want is detailed comments about the space of design issues, in
>>>>> particular those currently listed as open issues. Also additional
>>>>> use-cases
>>>>> and development of current use-cases would be appreciated, which are
>>>>> currently being stored on our wiki [7].
>>>>>
>>>>>    So please take the time to carefully review the First Public Working
>>>>> Draft
>>>>> and send comments to the public-webcrypto@w3.org mailing list, where we
>>>>> will
>>>>> respond to you!
>>>>>
>>>>> [1]http://www.w3.org/TR/2012/WD-WebCryptoAPI-20120913/
>>>>> [2]http://www.matasano.com/articles/javascript-cryptography/
>>>>> [3]http://crypto.stanford.edu/sjcl/
>>>>> [4]http://www.w3.org/TR/CSP/
>>>>> [5]http://www.w3.org/2012/webcrypto/wiki/SurveyAnalysis
>>>>> [6]http://www.w3.org/2012/webcrypto/track
>>>>> [7]http://www.w3.org/2012/webcrypto/wiki/Use_Cases
>>>>>
>>>>>
>>>> I think overall, this is a great start, and thanks for taking the time
>>>> to draft this and get the word out. I apologize that I haven't offered
>>>> more concrete wording alternatives, and I think by and large, the
>>>> issues raised with the proposed text are minor. I just wanted to
>>>> highlight them in case you perhaps had an alternative way of wording.
>>>
>>>
>>> Thanks, and my suggested changes above. My goal here is to increase
>>> quality
>>> comments from the general public.
>>>
>>>> Cheers,
>>>> Ryan
>>>
>>>
>
Received on Monday, 8 October 2012 22:04:45 GMT

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