[whatwg] Hashing Passwords Client-side

Daniel Cheng dcheng at chromium.org
Thu Jun 16 14:39:26 PDT 2011

A variation of this idea has been proposed in the past but was largely seen
as undesirable--see
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2010-May/026254.html. In
general, I feel like the same objections are still true of this proposal.


On Thu, Jun 16, 2011 at 14:08, Tab Atkins Jr. <jackalmage at gmail.com> wrote:

> On Thu, Jun 16, 2011 at 12:59 PM, Sean Connelly <sean at pbwhere.com> wrote:
> > I've just joined the mailing list, and this is my first time in such an
> > environment, so I apologize ahead of time if I'm not using the list
> > correctly.
> Nope, you did pretty good.  You listed a problem, and then proposed a
> solution to it.  Most people forget to do that first part when they
> start posting.  ^_^
> > ## Problem Attempting to Solve:
> >
> > Websites commonly need to store login information for users.  Web
> developers
> > may naively store the password in non-secure ways (plain-text, md5 with
> no
> > salt, etc).  It has become common for hacker groups to target websites to
> > get a data-dump of all users/passwords, and using this information, try
> to
> > compromise accounts on other websites.
> >
> > One example below:
> >
> >
> http://arstechnica.com/security/news/2011/06/lulzsec-rampage-continues-62k-e-mails-and-passwords-cia-under-attack.ars
> Or, more concretely, you *never* actually need to store the password
> that someone is using.  Like, ever.  You should *always* immediately
> hash the password with a good cryptographic hash, and only store the
> hashed value.  The only thing you should ever need to do with the
> plaintext password is pass it to your hashing function, and then
> immediately forget it.
> However, a non-trivial number of servers don't do this, which is the
> source of constant security headaches.
> > ## Proposed Solution:
> >
> > Add an attribute to <input type="password"> called "hash".  For example:
> > <input type="password" hash="sha1" salt="something">
> >
> > This will indicate to the browser that it needs to hash the value locally
> > before sending it to the server.  This hash should include a
> site-specific
> > salt, so that the same password typed on two different sites will hash to
> > different values.  I propose the default salt to be the origin as an
> > string (protocol + host + port, ex: "http://example.com:80"), and the
> > default hash to be "none" (in order for backward compatibility).
> >
> > By hashing the password before transmitting to the host, the host is
> never
> > actually aware of the password typed by the user.  The host can treat it
> as
> > a normal password, and store it as it would normally store any other
> > password.  Authentication can still be performed because the host would
> > check to see if the hashes matched.
> >
> > In order to deal with migration correctly, the browser will also need to
> > communicate to the server that it correctly performed the hash.  I
> propose a
> > new header for the browser to send:
> >
> > X-Password-Hash: 1
> >
> > If the browser does not send this header, then the host should expect to
> > receive an unhashed, plain-text password.
> >
> > Each available hash function (sha1, sha2, etc), will have to be
> identified
> > in the spec, along with the format the hash should be transmitted in
> > (lower-case hex dump?).
> Personally, I'd prefer the information be transmitted via another
> (browser-synthesized) form input, as it's usually much easier to read
> form inputs than header values.
> (Also, X-* headers are an antipattern.  The X- prefix serves
> absolutely no purpose.  This is just a naming issue and irrelevant to
> your proposal; I just wanted to inform you in case you're ever
> directly responsible for naming a header in the future.)
> I like your idea for the default salt.  We might be able to hook off
> of slightly better concepts (use the origin directly?) but the idea is
> sound.
> For the @hash attribute, we should just specify a single hash for now,
> the strongest we believe we can rely on.  Then we can make it the
> default value, so utilizing this would be as simple as <input
> type=password hash>.  (You don't need a "none" value, since the lack
> of the attribute would indicate that.)  If this becomes inadequate in
> the future, we can just add more values.
> > ## Benefits:
> >
> > 1. Host never has access to actual password (as long as user has a modern
> > browser)
> > 2. If the host is compromised, hackers may be able to takeover the
> account
> > on the server, but will not be able to take over accounts on different
> > servers even if the user uses the same password (because the hackers will
> > only have access to the hashed password with site-specific salts)
> > 3. Plain-text passwords cannot be sniffed over HTTP
> > 4. Easy for webmasters to upgrade for additional security benefit
> For #3, you can still sniff the hashed password over HTTP, and then
> just submit that manually.  But point #2 mitigates the damage that
> would do, unlike the current state of affairs.
> > ## Disadvantages:
> >
> > 1. Host cannot validate password requirements (ex: 2 upper case, 2 lower
> > case, 2 special characters, password length, etc)
> This is a benefit, actually.  Password requirements are, nearly
> uniformly, absolutely horrendous for security in practice.
> > 2. Server-side code might be complicated for dealing with legacy,
> > non-hashing browsers
> Only for the transition period.  Afterwards, you can just ignore
> legacy browsers and store the passwords directly.  Those older
> browsers will just have security vulnerabilities.
> Of course, server-side frameworks can hide that for you.
> > ## Questions:
> >
> > 1. How to deal with the character encoding of the page correctly?  Should
> > everything be converted to UTF-8 before the hash is calculated?
> Javascript is utf-16 internally.  However, I'd recommend doing the
> hash with the string in utf-8.
> > 2. What level of access should JavaScript have?  Should it have access to
> > read the plain password, or should it only be able to read the hashed
> value?
> The .value property and the value actually submitted should be
> identical.  This indicates that, unless we add something extra, JS
> would only get the hashed value.
> Overall, I like the idea.  It seems like a pretty clueful addressing
> of the topic, and it directly addresses the problem that servers
> shouldn't ever remember passwords, but a lot of them do.  Finally, it
> puts the processor cost of good crypto-hashing on the client rather
> than the server, which is nice.  We can do a nice, expensive hash on
> the client without burdening the user, while an expensive hash *can*
> be a minor issue for busy servers.
> ~TJ

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