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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."
He is clearly lying or been living too much outside real world..
He's a professional mathematician. That's a given.
Learning HOW to think is more important than learning WHAT to think.
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.
If the airplane's design allows you AS A REGULAR PASSENGER to do so, then yes.
The DKIM spec itself (RFC6376) says: "Signers MUST use RSA keys of at least 1024 bits for long-lived keys."
Keep in mind that RFC 6376 was issued in September of 2011. Prior versions did allow 512-bit keys, though they cautioned against them.
It's pretty unequivocal. Google just misconfigured their mailserver.
More likely, I think, is that Google failed to reconfigure their server. When Google started using DKIM, cracking 512-bit keys was significantly harder than it is now. The change is less due to increases in computing power (though that has helped) than it is to the availability of cloud-based compute clusters. Granted that it was always a little risky to use such small keys, it was much more reasonable than it is today.
So my guess is that it went down like this: A few years ago when Google implemented DKIM someone looked at RFC 4871's discussion of key sizes, which says:
... and thought "yeah, we can use 512-bit keys and change them occasionally, that will provide higher performance for less CPU load, and as the RFC says the security goals here really aren't that high". I imagine that the decision to implement DKIM at all may have been a tad controversial given the additional load it was going to place on the servers, so that 512-bit key usage may even have been an important design point. Then the "change them occasionally" bit got dropped on the floor.
Fast-forward a few years, the problem is discovered and fixed -- but this time the engineers decided to make sure it doesn't happen again and jumped to 2048-bit keys even if it required provisioning more capacity.
(Disclaimer: I work for Google, and do cryptographic security stuff for Google, but I don't have any more information than the rest of you about how all of this happened. The above is pure speculation based on my 15 years as a security consultant before joining Google. I saw lots of stuff just like it from the few companies I worked with who were actually quite good about security. And even more insanely stupid stuff from all the rest.)
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