W3C home > Mailing lists > Public > public-webappsec@w3.org > June 2013

Re: Content Security Policy

From: Bryan McQuade <bmcquade@google.com>
Date: Mon, 17 Jun 2013 13:36:31 -0400
Message-ID: <CADLGQyDE-nQLfMRRYFs0BwLAAa=pL_O9HybN5+4vGjwHnmnoPw@mail.gmail.com>
To: Joel Weinberger <jww@chromium.org>
Cc: Yoav Weiss <yoav@yoav.ws>, Neil Matatall <neilm@twitter.com>, Евнгений Яременко <w3techplayground@gmail.com>, "public-webappsec@w3.org" <public-webappsec@w3.org>
Does CSP support inline scripts and styles in statically served HTML files?
My impression was that nonce only works for dynamic serving. If that's the
case then IMO hashes are warranted to support the static case alone.

On Mon, Jun 17, 2013 at 1:22 PM, Joel Weinberger <jww@chromium.org> wrote:

> I'm not particularly against, hashes, but I'm naturally hesitant to add
> more constructs to CSP, especially since the use of nonces seem to
> completely overlap with the use cases for hashes. I think the concern about
> nonce abuse as Yoav pointed out are valid concerns, but I'd be hesitant to
> add a new construct just to cover that particular concern. Put differently,
> I don't see any dramatically different uses for hashes from nonces.
> --Joel
> On Mon, Jun 17, 2013 at 4:09 AM, Yoav Weiss <yoav@yoav.ws> wrote:
>> +1 for discussing it further.
>> The advantages I see:
>> * The author is authorizing a *specific* script/style and can do so using
>> static configuration
>>   - No need for a dynamic backend that changes the nonce for each
>> request..
>>   - This can simplify deployment, resulting in more people using it
>> * I'm afraid of authors abusing nonces, sending the same nonce over and
>> over as means to "bypass" CSP
>>   - Offering an alternative to nonce can reduce that risk
>> The complications I can think of:
>> * Make sure that either hashes don't break with small white-spaces
>> removals, text encoding changes, etc.
>>   - An alternative is tools that can give authors the resulting hash for
>> a specific script/style. (e.g. inside the Web inspector tools). That may be
>> more fragile, though.
>> All in all, I think hashes can make it easier for "copy&paste" authors to
>> integrate CSP. They can also make deployment of third party scripts easier.
>> On Sat, Jun 15, 2013 at 8:00 AM, Neil Matatall <neilm@twitter.com> wrote:
>>> This is the script-hash proposal. I would love it if we discussed this
>>> more as it has numerous benefits over a nonce as well as complications :)
>>> On Jun 15, 2013 1:11 AM, "Евнгений Яременко" <w3techplayground@gmail.com>
>>> wrote:
>>>> Is it possible to verify(whitelist) inline script block via checksum of
>>>> its logic(uniform) as alternative to "Nonce"?  ie send checksum of the
>>>> allowed script via header and if inlined script checksum is the same it's
>>>> allowed to execute.
Received on Monday, 17 June 2013 17:36:58 UTC

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