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

From: Melvin Carvalho <melvincarvalho@gmail.com>
Date: Tue, 15 Sep 2015 12:16:37 +0200
Message-ID: <CAKaEYhJnfERLYASwgcgFr4ECrTj_cqzgouo=3B=UWim=WGun2Q@mail.gmail.com>
To: Alex Russell <slightlyoff@google.com>
Cc: Henry Story <henry.story@co-operating.systems>, Wendy Seltzer <wseltzer@w3.org>, TAG List <www-tag@w3.org>, Tim Berners-Lee <timbl@w3.org>
On 12 September 2015 at 20:48, Alex Russell <slightlyoff@google.com> wrote:

>
> On 12 Sep 2015 12:27 am, "Melvin Carvalho" <melvincarvalho@gmail.com>
> wrote:
> >
> >
> >
> > On 12 September 2015 at 03:20, Alex Russell <slightlyoff@google.com>
> wrote:
> >>
> >>
> >> 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].
> >
> >
> > Certificates are not signed using MD5 here, but rather, a public key.
> The public key is later used to create a certificate on a server, using a
> hash such as sha2.
>
> SKPAC is used to generate a challenge. This relies on MD5. In
> proof-of-posession usecases, this challenge is a required to be
> trustworthy. Thanks to MD5, it isn't.
>
> >  I dont believe the attack outlined is usable here to compromise key
> material.
>
> In many keygen scenarios, this is immaterial. The challenge is suspect,
> which means POP can't be assured.
>
Thanks for articulating this so well.  I think it's fair to say that if
KEYGEN was invented today or improved, it would probably use a hash
function like SHA2.   However, in the case of asymmetric cryptography, a
public key is often useless without the private component.  For the
purposes of progress, could we continue (at least on this thread) with the
assumption that there is no immediate threat posed by KEYGEN + MD5.  (Happy
to discuss on another thread, tho)

> > If you have evidence to the contrary, it would be great to hear.  The
> same question was posed on the blink thread, and in each case, the proposer
> was unable to actually articulate an attack vector.
> >
> >>
> >> 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.
> >
> >
> > Thanks for pointing to microsoft's position from 2009.  In the mail,
> they propose some suggestions to improve the keygen widget, namely:
> >
> > - add key length parameter
> > - add expiry date parameter
> > - add the possibility of certificate generation
> > - add the possibility of non RSA keys
> >
> > These are all great suggestions and something similar was suggested on
> the blink thread, via an API.
> >
> > window.crypto.subtle.generateKey(
> > { name: "RSASSA-PKCS1-v1_5",
> >  modulusLength: 2048,
> >  publicExponent: new Uint8Array([1, 0, 1]),
> >  hash: {name: "SHA-256"},
> >  keystore: true                <------------------------That's an
> example. Even a PKCS#11 URI could be used!
> > },
> >
> > My own and other analysis of keys in the free and open source community
> show [1] that the vast majority of keys used today are 2048 bit RSA.
> Consistent with the functionality discussed by microsoft back in 2009.
> >
> > [1] https://blog.benjojo.co.uk/post/auditing-github-users-keys
> >
> >>
> >>
> >> 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?
> >
> >
> > Excellent suggestions.  Progress leading towards an API would be welcome
> in this area, but there were a number of calls to not completely deprecate
> keygen until the same functionality could be replaced with something else.
>
> I asked before and will again: why is it not workable for your uses to
> have Web Crypto generate key and have the page generate a download for the
> key file to be installed locally?
>
IMHO this could work, provided that the functionality offered could be
roughly agreed, as like for like.  I think more details would need to be
fleshed out, and there may be some interest in usability and user
experience, however this tends to be of quite a high standard in most
browsers.

>From an architectural POV you would want to ensure key material is under
the control of the user (cross origin) but insulated from potentially
malicious javascript (eg similar to location sharing).


> >> Regards
> >>
> >> [1]
> https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/pX5NbX0Xack
> >> [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 Tuesday, 15 September 2015 10:17:11 UTC

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