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Re: Agenda: <keygen> being destroyed when we need it

From: Alex Russell <slightlyoff@google.com>
Date: Fri, 11 Sep 2015 18:20:14 -0700
Message-ID: <CANr5HFXTsAPSCy5EFNzMbtkyKhsng0tbku6Hg-vWZ560b7nroQ@mail.gmail.com>
To: TAG List <www-tag@w3.org>
Cc: Wendy Selzer <wseltzer@w3.org>, Carvalho Melvin <melvincarvalho@gmail.com>, Tim Berners-Lee <timbl@w3.org>, Henry Story <henry.story@co-operating.systems>
Hi all,

Apologies for the late response to this thread. I'm not sure that the
conversation has created much mutual understanding. Perhaps it's worth
trying to consider to following aspects separately:

   - The implementer consensus regarding <keygen>
   - Questions regarding the origin model and global modification of user
   systems without user interaction
   - User and developer needs for key generation and storage

Given the current proposal to deprecate <keygen> in Blink [1], it seems
worth reiterating the broad consensus that <keygen>'s use of MD5 is
fundamentally broken [2]. Some in the thread seem to misunderstand the
impact of this brokenness, but rest assured, the only value a
<keygen>-created challenge could provide is fundamentally suspect. This is
in addition to long-standing objections by Microsoft that <keygen> isn't
fit for purpose for other reasons [3]. Implementers have also identified
core issues with <keygen>'s behavior that mean compatibility will suffer as
issues are fixed.

These concerns have reached a head with the proposal to deprecate. One
might imagine repairing <keygen>, but this works against the extensibility
principles the TAG encourages [4].

A more extensible solution would be an API form of key generation.
Interestingly, this now exists via Web Crypto (as was pointed out in the
original Blink thread by Ryan [1]). These keys are not directly generated
in the same key store used for client certificates, but page authors can
work with generated keys, even allowing users to import them into keystores.

Developers who want to persistent keys to the local system should
acknowledge that this is an operation that lives outside the Same Origin
Model. The inability to scope the use of keys added via <keygen> (via
addition to the effective keychain) creates a major hole in our one
workable security primitive. It's true that this isn't part of the <keygen>
spec, but compatibility requirements have caused this to be true in
practice. From an architectural perspective, this alone should be enough to
cause the TAG to recommend removal of <keygen> and replacement with a
better, origin-scoped alternative.

Lastly, I think it's important for us to take the need to generate keys
seriously. We can do this without holding onto poorly designed and
constructed features, however. I'd like to understand more deeply why key
generation via Web Crypto isn't functional. Perhaps we can discuss that
next week?


[2] http://www.kb.cert.org/vuls/id/836068
[3] https://lists.w3.org/Archives/Public/public-html/2009Sep/0043.html
[4] https://extensiblewebmanifesto.org/

On Sat, Sep 5, 2015 at 5:05 AM, Henry Story <
henry.story@co-operating.systems> wrote:

> > On 4 Sep 2015, at 14:54, Henry Story <henry.story@co-operating.systems>
> wrote:
> >
> >>
> >> On 2 Sep 2015, at 14:15, Wendy Seltzer <wseltzer@w3.org> wrote:
> >>
> >> On 09/02/2015 04:06 AM, Melvin Carvalho wrote:
> >>> On 1 September 2015 at 16:08, Tim Berners-Lee <timbl@w3.org> wrote:
> >>>
> >>>> Folks
> >>>>
> >>>> There is a strong move my Google chrome team followed by Firefox to
> remove
> >>>> the <keygen> tag from HTML5.   This has been done without an issue
> being
> >>>> raised in the WHATWG  or HTMLWG apparently.
> >>>>
> >>>> <keygen> is important because it allows authentication systems to be
> build
> >>>> in a distributed manner. It allows any Mom and Pop shop place to share
> >>>> public keys for people they trust.    For example, MIT uses it to
> create
> >>>> secure relationship with faculty and staff, and I use it for friends
> and
> >>>> family.
> >>>>
> >>>> Public key asymmetric crypto is generally so much stronger than the
> >>>> password-based authentication.  It requires certificate management
> code to
> >>>> be written.
> >>>>
> >>>
> >>> IMHO we need an area of the browser under a user's control
> >>
> >> That seems like a different, and more interesting requirement than
> >> "keygen."
> >>
> >> Keygen was a poorly designed, inconsistently implemented feature, that
> >> many sophisticated users and developers found confusing. If we can
> >> instead define what features we want to be able to build, and what they
> >> depend on that's not provided by WebCrypto, and think about how we can
> >> enable users to access these features without opening themselves up to
> >> be phished or tracked, that feels like a more productive avenue for
> >> discussion than "bring back keygen".
> >
> > I think this is much too harsh on keygen btw. What is happening may be
> > that the documentation in the HTML5 was not good enough at explaining how
> > it worked. After a discussion on the WhatWG where one key argument
> against
> > keygen turned out that it was insecure because of its use of MD5, and
> after an off
> > list pointer to what the aleged reason of the problem was I wrote a
> detailed
> > response to the WHATWG showing that MD5 has no effect on keygen, and
> > ansuggesting that improved wording of the spec may help diffuse this
> > misunderstanding.
> >
> >   https://github.com/whatwg/html/issues/102
> >
> > This did not stop the issue being closed within 15 minutes of my opening
> the
> > issue. ( and I seem to be filterd now on the WHATWG mailing list ).
> So yes the mail that referenced issue 102 linked to above was filtered and
> censored for reasons of "security". This is surreal. A decision for
> removing
> strong security from browsers is made on a mistaken understanding of how
> the
> feature works. Then showing that the alleged security hole is illusory is
> considered a potential security risk and is filtered. Here is the link to
> the
> mail:
> https://lists.w3.org/Archives/Public/public-whatwg-archive/2015Sep/0027.html
> I am sorry to mention it, but how can this not make one think of secret
> courts using secret evidence ( and even secret laws ) ? This requires
> everyone to completely trust the cryptography experts and makes it then
> impossible to bring to light the implicit assumptions that are guiding
> their thinking, and that would perhaps when brought out in the open allow
> new possibilities to emerge.
> Henry
> PS. I verified my position on the irrelevance of MD5 in keygen generated
> spkac with cryptography experts from openssl. It would be nice if some
> cryptography experts could at least confirm this here.
> >
> > Henry
> >
> >
> >>
> >> --Wendy
> >>
> >>
> >> --
> >> Wendy Seltzer -- wseltzer@w3.org +1.617.715.4883 (office)
> >> Policy Counsel and Domain Lead, World Wide Web Consortium (W3C)
> >> http://wendy.seltzer.org/        +1.617.863.0613 (mobile)
Received on Saturday, 12 September 2015 01:21:13 UTC

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