W3C home > Mailing lists > Public > public-webcrypto@w3.org > March 2014

Re: WebIDL usage for Algorithms

From: Mark Watson <watsonm@netflix.com>
Date: Mon, 17 Mar 2014 19:54:50 -0700
Message-ID: <CAEnTvdAzR+SJpOKF2Ui9ocF0CYnO4aS7zW3sjOT9d6EDvdqYFA@mail.gmail.com>
To: Ryan Sleevi <sleevi@google.com>
Cc: Boris Zbarsky <bzbarsky@mit.edu>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Mon, Mar 17, 2014 at 7:30 PM, Ryan Sleevi <sleevi@google.com> wrote:

>
>
>
> On Mon, Mar 17, 2014 at 6:55 PM, Boris Zbarsky <bzbarsky@mit.edu> wrote:
>
>> On 3/17/14 9:37 PM, Ryan Sleevi wrote:
>>
>>> Just to make sure - are you advocating for "any" as the type, on this
>>> basis, or are you still advocating for "object", for the reason below.
>>>
>>
>> I think using "object" here would be the right thing to do.
>>
>>
>>  I'm not sure I fully grok your concern here or what you're proposing as
>>> an alternative.
>>>
>>
>> If you look at the algorithm at https://dvcs.w3.org/hg/
>> webcrypto-api/raw-file/tip/spec/Overview.html#dfn-
>> SubtleCrypto-method-encrypt for example, it performs all the steps after
>> step 3 asynchronously (using what task source?).  Step 6 involves invoking
>> https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/
>> spec/Overview.html#algorithm-normalizing-rules (I assume; the actual
>> link in that step is broken), which can cause execution of arbitrary page
>> script.
>>
>> If it's not critical that this happen asynchronously, it would be best to
>> do this arbitrary script execution before returning from the encrypt()
>> call, to avoid introducing races.  If it _is_ critical that this happen
>> asynchronously, then we need to specify which task queue is used for the
>> task that calls into script.
>
>
> Yeah. The previous version of the spec was clear that there was a new
> (crypto) task queue, but this got inadvertently reverted.
>
> Algorithm *normalization*, as currently specified, could happen serially.
> This design itself was an artifact of the event-based system. The key event
> that needs to remain asynchronous is detection as to whether or not an
> algorithm is supported by the underlying implementation. In the previous
> (event-based) system, it had to make a distinction between a fast-failure
> path or not, but in the Promise system, we have a bit more flexibility to
> still reject later.
>
> This definitely all goes out the window if we allow JS to register its own
> polyfills as algorithms - as has been discussed in the past (eg: for
> allowing custom KDFs/digest operations). Of course, that's a "Version 3"
> kind of feature (where "Version 2" just deals with Streams API).
>
>
>>
>>
>>  The asynchronous nature is already going to be a problem for
>>> ArrayBuffers - which we MUST take a structured clone of the data BEFORE
>>> we can return the promise
>>>
>>
>> This is somewhat similar, yes.
>>
>>
>>  On a spec level, can we not simply state that you invoke the structured
>>> clone algorithm on /alg/, letting o be the internal object created from
>>> such clone. Then, at later points, as needed, you convert o to the IDL
>>> dictionary type D, then normalize over D?
>>>
>>
>> Even if you create a structured clone, as long as the result of the clone
>> operation is being created in the same global getting properties from it
>> can invoke arbitrary script.  Consider, for example:
>>
>>   Object.defineProperty(Object.prototype, "name", {
>>       get: function() { /* Now we get to do whatever we want */ }
>>     });
>>
>> and then passing an empty object literal (so {}) as the algorithm.  The
>> structured clone will create a new object with no properties in the same
>> global, and getting .name on it will invoke the getter defined on
>> Object.prototype.
>>
>> You could structured clone into a clean global, I guess.  Is that what
>> you're talking about here?  If so, can we guarantee that the clean global
>> will never leak out observably?
>>
>> -Boris
>>
>
> Yeah, I think we *could* get away with a clean global, since it's just
> used as a place-holder to defer IDL conversions, and never exposed.
>
> I'll try to put together a spec that attempts to *synchronously* handle
> the IDL conversion into the target/derived type prior to returning the
> promise, which should hopefully address this. It won't happen until after
> the LC version is published, unfortunately.
>
> Hi Ryan,

To do that in the synchronous section, we're going to need to look up the
correct target type for the ( algorithm, operation ) pair in the
synchronous section. Is that what you mean ? So, we would also detect
supported / unsupported algorithm / operation combinations here ?

[Boris - thanks for jumping in on this topic - I've learned a lot already]

...Mark
Received on Tuesday, 18 March 2014 02:55:19 UTC

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