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How a Google Headhunter's E-Mail Revealed Massive Misuse of DKIM
concealment writes with a tale of how an email sent to a mathematician led to him discovering that dozens of high profile companies were using easily crackable keys to authenticate mail sent from their domains. From the article: "The problem lay with the DKIM key (DomainKeys Identified Mail) Google used for its google.com e-mails. DKIM involves a cryptographic key that domains use to sign e-mail originating from them – or passing through them – to validate to a recipient that the header information on an e-mail is correct and that the correspondence indeed came from the stated domain. When e-mail arrives at its destination, the receiving server can look up the public key through the sender's DNS records and verify the validity of the signature. Harris wasn't interested in the job at Google, but he decided to crack the key and send an e-mail to Google founders Brin and Page, as each other, just to show them that he was onto their game."
E-mail is an archaic protocol and easily broken.
Film at 11.
I'm surprise Mr. Harris wasn't accosted by lawyers or law enforcement. Huzzah for common sense.
How could he seriously think it was a headhunter challenge?
He is clearly lying or been living too much outside real world..
This is Obama, please vote for me. This email is from me, you can verify it using DKIM public keys.
Regards
Romney
It's possible that some of the short DKIM keys were due to concerns over compatibility with other systems. When you have a large heterogeneous environment like email, you sometimes get caught catering to the lowest common denominator.
DKIM keys can exceed the TXT DNS record limit or the UDP byte limit. Some software may not handle joining split TXT DNS records. Others may handle DNS over UDP but not handle TCP for long records.
News flash.
This was not a misuse of DKIM, or perhaps it was his own misuse in that he thinks DKIM validates the sender of an email. All it does is validate that the email originated from Google's mail servers, but it doesn't neccessarily mean that the address in the From: header wasn't spoofed before it was signed.
In any case, he found that Google (and others) are using an easily cracked 512 bit key, which they silently fixed with a 1024 bit key after he reported it to them by spoofing an email to appear as though it originated at Google.
There was no misuse, 512 bit keys are allowable under the DKIM spec, though they aren't recommended for long-lived keys.
So the reality is that, on top of being useless as an anti-spam mechanism, it now turns out to be even worse, and in fact vulnerable to malicious attacks. In other words, it's useless and uselesser.
I was heavily involved in a lot of the discussions surrounding SPF, DKIM and related "solutions" back in the early 2000s, and about the most that we could say about these "solutions" was that you could add a positive number to the score of an email in a weighting system if things checked out, but other than that, there was little to recommend them.
The world's burning. Moped Jesus spotted on I50. Details at 11.
Individual's sharp-mindedness against corporate stupidity. Happens all the time. I'm proud to be an individual having studied mathematics, even if I landed in IT later on...
Religous speak to God. Insane are spoken to by God. When all shut up, one can finally hear Shostakovich in peace
that Swordfish was a premonition — Hugh Jackman really does crack encryption...
Shame on Google for using a weak key, but also shame on this article for being more than a little hyperbolic.
If you, you know, actually read the standard, or even the Wikipedia page, you'll see that DKIM is not intended to be used as a signature mechanism in the same way as S/MIME or PGP. Rather, it's a means to assert responsibility for sending the message, it's done at the domain rather than user level, and verification results are intended to be used for message filtering, not for asserting that so-and-so actually signed the message.
Sure, the underlying technology is based on hashes, signatures, signature verification, and so on but that's because there's no other way to do it. The fact that DKIM allows for the application of relaxed interpretation of both message header and body data kinda tells you it's not intended to be used to provide an absolute assurance that what you got is authentic in every way.
DKIM is also not intended to be the ultimate source of information for filtering. Rather, DKIM results are supposed to be combined with other metrics to form an overall assessment of message validity. And that's a very good thing, since I get all sorts of spammy stuff that makes it through Google, including getting a legitimate DKIN signature attached. Other filtering mechanisms are needed to block such crap.
All that said, it's very disappointing to see yet another case where Google has seen fit to play fast and loose with standards. This is happening much too often.
Is it this guy's supposition that Brin and Page were using weak, crackable keys deliberately?
#DeleteChrome
I had until more recently been getting a bunch of "backscatter" hits to my gmail hosted account.
While the return message seemed legit, the email that supposedly went out from (an nonexistent account) at my domain was not.
I wonder if the spammers were already taking advantage of this vulnerability. I do notice that more recently I haven't got any of these.
Half the spam that makes it through my filters is DKIM-signed. Spammers use it to make the email look less bogus. Of course, that means that they have to use a real domain and hosting provider that they eventually lose — but domains are cheap, and changing hosts is no big deal.
Ru-oh!
I'd better take a closer look at the automatically generated DKIM keys for the several Google Apps domains I oversee....
This problem has been reported by the US-CERT (part of the US Department of Homeland Security [Insecurity?]) at http://www.kb.cert.org/vuls/id/268267. See that link for an authoritative report on the meaning of this problem and how to avoid it.
From the article, the line:
Harris thought there was no way Google would be so careless, so he concluded it must be a sly recruiting test to see if job applicants would spot the vulnerability.
That's exactly how I would think.
See if your intrusion is noticed.
"if ( it ain't broken, ||
the original coder has since left the company ||
no one has touched that header for four years ||
the code is abandoned without any "owner" in the company ||
it is living in a branch of source code deemed "legacy"){
don't fix it;
}
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
Instead, two days later, he noticed that Googleâ(TM)s cryptographic key had suddenly changed to 2,048 bits. And he got a lot of sudden hits to his web site from Google IP addresses.
So, googlers: How'd misc react to this? I can see all sorts of spoofing fun going on...
-B
Ash and Hickory, straight-grained and true, make excellent bludgeons, dandy for the cudgeling of vegetarians.
There's no way he seriously believed this was a sly test the recruiters were sending out to weed applicants. He's just saying that to cover his ass if Google actually peruses him legally for what he did.
But really though, all this system is for is for certifying that mail actually did come from a specific domain, not a specific sender. I'm not seeing the huge misuse here.
which they silently fixed with a 1024 bit key after he reported it to them...
From TFA:
Harris made sure the return path for the e-mails went to his own e-mail account, so that Brin and Page could ask him how heâ(TM)d cracked their puzzle. But Harris never got a response from the Google founders. Instead, two days later, he noticed that Googleâ(TM)s cryptographic key had suddenly changed to 2,048 bits. And he got a lot of sudden hits to his web site from Google IP addresses.(emphasis mine)
'The tyrant will always find pretext for his tyranny.' - Aesop's Fables
I hardly know what spam is anymore: since years, when I switched to GMail, I hardly get any spam. I'm always amazed when I see articles about the spam issue: "spam, do people still get *that*!?". I take it the more emails account you have (6 digits number of users at least), then it gets easier and easier to find and trash spam...
Do DKIM and/or SPF help get less spam? Less spoofed emails?
Isn't it a complete aberration that because 512 bits keys for DKIM were way too small that people do think that DKIM is useless? Apparently in less than 48 hours GMail's DKIM changed to 2048 bits keys.
Why exactly would DKIM be useless? Which problem does it solve? Which are its drawbacks? (IFF the keys are big enough)
Look at the photo. He does math in mirror writing!