[cryptography] [SSL Observatory] Diginotar broken arrow as a tour-de-force of PKI fail

Ian G iang at iang.org
Mon Sep 5 19:35:30 EDT 2011


On 5/09/11 7:23 PM, Gervase Markham wrote:

> The thing which makes the entire system as weak as its weakest link is
> the lack of CA pinning.


Just a question of understanding:  how is the CA pinning information 
delivered to the browser?

(For those who don't know, I also had to look it up too :)  CA pinning 
is where a particular CA is the only one permitted to issue certs for a 
website.  I think, it's a very new feature, in some browsers only?)

>>    An HSM or smart card that does anything the PC that it's attached to tells
>>    it to is only slightly more secure than simply storing the key directly on
>>    the PC.  You need to do more to secure a high-value signing process than
>>    sprinkling smart card/HSM pixie dust around and declaring victory.
>
> This is true, but I'm not sure it's particularly relevant.

Well, what's relevant is whether the security processes are doing the 
job.  Evidence over the last year says no.  Why?

What Peter's saying is that there are signs that the processes are 
weaker than they appear.  One clue is when they go for expensive 
solutions rather than smart solutions, and declare it done.

> (Who claims
> that HSMs are magic pixie dust?)

CABForum, in BR15.6.  "CA must use a HSM" approx.

Monkey-see-monkey-do.  Which, amusingly, contradicts most of the rest of 
section 15 :)

>> Lack of breach disclosure requirements for CAs means that they'll cover
>> problems up if they can get away with it:
>
> Do you think that remains true?

We don't know.  There is no full disclosure mechanism, so we don't know 
what is disclosed and what not.  and even when the full disclosure 
mechanism is in place, we'll need 20 or so events to gain confidence in it.

Recall SB1386?  It actually didn't do anything until 2 years had passed. 
  Then someone paniced.  And attitudes shifted...

> Comodo didn't cover their problems up,

Have they released the full report of the issue?  Has Mozilla?

Or do we just know the headline, and what people have dug up against 
their best wishes?

You saw the chat on mozilla list, another CA declined to report, dressed 
up by lots of buts, ifs, maybes, not-us's and other rantings.

Non-disclosure is certainly in place.

> and are still in business. DigiNotar covered theirs up, and are not.
> Covering up is a massive business gamble, because if anyone finds the
> certs in the wild (as happened here), you are toast. Particularly given
> that browsers are deploying more technologies like pinning which makes
> this sort of attack easier to find, it would be a brave CA who covered a
> breach up after the lesson we had last week. You'd have to be pretty
> darn confident any misissued certs didn't get obtained by the attackers
> - and if they didn't get out, is there actually a problem?


What is of current concern is that CAs may now be "disclosing" to the 
vendors.  And calling that disclosure.

This is of concern for several reasons:  firstly, it likely puts the 
vendors in a very difficult position, even to the point of corrupting 
them.  Secondly, it creates a liability-shifting mechanism:  the broken 
CA can now point to this as its industry-standard disclosure mechanism 
(regardless of utility and user damages) which reduces its own 
liability, without a commensurate payment; and the vendor now has to 
take on the risk of suits.  Thirdly, it's being done in an ad hoc knee 
jerk fashion, again in secret, and there is no particular faith that the 
parties involved will be able to keep their interests of the table.

(For Mozilla alone, private disclosure goes against their principles.)

I'm not denying that disclosure to vendors may help.  But I have no 
faith in the risk managers at the other side to analyse that risk.

If you feel that they can do a good job, post their risk analysis.

Right, I thought so, they haven't done one.  All vendors are in breach 
of BR.  Doesn't auger well does it :)

>>    there's nothing protecting the user.  Even the most trivial checks by
>>    browsers would have caught the fake Google wildcard cert that started all
>>    this.
>
> What sort of "trivial checks" are you suggesting?

Perhaps CA pinning!  But in the browser :)


>>    Diginotar both passed audits in order to get on the browser gravy train and
>>    then passed a second level of auditing after the compromise was discovered.
>>    The auditors somehow missed that fact that the Diginotar site showed a two-
>>    year history of compromise by multiple hacking groups, something that a
>>    bunch of random commentators on blogs had no problem finding.
>
> I think there are definitely searching questions to ask of DigiNotar's
> auditors.

:)  and, any other CA audited by that organisation.  And any CA audited 
to that standard....

And ... wait, all of them!  Oops!

Short story -- you won't be able to blame the auditor for this.

Sure, you can embarrass them a lot!  But, it's pretty obvious on one 
reading of webtrust that it's a farce.  It's also pretty obvious reading 
BR that an audit would not have picked this up.

We could do it ten times over and it's still be the same thing.  Audit 
isn't up to solving this problem, it's only up to lifting the basic game 
of low-end CAs to some reasonable best-practices level at the governance 
side.

(Another sign that the processes aren't doing the job is that CABForum's 
solution is to add more audits.  We're up to 4, now, right?  WebTrust, 
BR, EV, vendor.  Would 5 do it?  6?)


>>    available.  There is no fallback.  Site owners who are concerned about the
>>    security of their users can't do anything, because the browser vendors have
>>    chosen to prevent them from employing any other option (I can't, for
>>    example, turn on TLS-PSK or TLS-SRP in my server, because no browsers
>>    support it - it would make the CAs look bad if it were deployed).
>
> Patches welcome? (Or did we reject them already? :-)

Yep, I'm afraid that's the case ;)

It's at the attitude level, not any particular patch.  Patches aren't 
welcome.  E.g., CA pinning was proposed in the mid-00s and people were 
told to go away.  And take their code with them...

I mean, we could be wrong.  But who's going to take the chance and spend 
a month on code, or a year, only to be told no?  Again?  Who's gonna 
bother to fight through the human-shield to get to the coders?

It's up to the vendors, really.  We wait and we watch and we groan.



iang



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