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Saying that DKIM doesn't adequately verify an email is genuine ignores the point of DKIM which is to weed out emails that clearly aren't genuine. So Gmail can

by rsingel 14y ago

Saying that DKIM doesn't adequately verify an email is genuine ignores the point of DKIM which is to weed out emails that clearly aren't genuine. So Gmail can simply deadpool hundreds of fake paypal phishing emails. That doesn't mean the occasional one that gets through by fooling DKIM is authentic - but the security benefits exist. Unfortunately, in quibbling over the headline, which you are free to do, you argued that anti-spam has nothing to do with security. Simply put keeping most of the spam that purports to be from paypal.com out of an inbox is a security issue, even if a determined spammer can thwart dkim via dns shenanigans. US CERT seems to agree: http://www.kb.cert.org/vuls/id/268267 http://www.kb.cert.org/vuls/id/268267

tptacek 14y ago
What seems to be happening here is that you don't like the fact that I criticized the Wired headline, so you're moving the goalposts from "Massive Net Security Issue" to "Thing That Might Make It Harder For Google To Reject Spam". Then, when I point out that you're moving the goalposts, you respond by simply repeating the claim --- and then suggest that pointing out what DKIM actually is amounts to a "quibble". DKIM is one of many, many anti-spam mechanisms in place at Google (and presumably Yahoo). But of course, far fewer people would read and forward this Wired story if you had simply written "Mathematician Finds Weakness In One Google Anti-Spam Measure During Recruitment Attempt".
- reinhardt 14y ago
  Framing it as a mere anti-spam weakness rather than anti-phishing is kinda disingenuous.
  - tptacek 14y ago
    Here I'm just going to refer you to "Three Myths About DKIM", linked from the front page of the DKIM site: http://jl.ly/Email/threemyths.html http://jl.ly/Email/threemyths.html
    - Evbn 14y ago
      None of those myths talk about spoofing the sender domain. DKIM doesn't validate the From line. But where is the weakness in trusting that someone with Google's private key approved the entire content of a message that is signed with Google's key, and so, my trust in Google should extend to the content of that email?
      - tptacek 14y ago
        I already provided one specific example upthread: most domains people care about host applications with bugs that allow attackers to generate arbitrary mail from those domains. This is, please note, a very different problem than "being able to generate arbitrary mail under a specific signature". It is considerably easier to forge mail from BANKOFAMERICA.COM than it is to forge mail under the S/MIME signature of a specific Bank of America employee. Domains simply are not a meaningful security boundary. At no point in the life of the commercial Internet have they ever been. Yes, there are security mechanisms on the Internet that are simultaneously (a) important and (b) misguided enough to ignore this fact. Fortunately, the most important of them are in practice difficult to reliably and scalably exploit. This whole story is a tempest in a teacup. As Matthew Green said on Twitter: a 512 bit DKIM key says more about how little Google cares about DKIM than it does about any laxity on Google's part. Google is not lax about security. Since this thread is also dead, we'll have to wait until someone else tries to get to the top of the front page with a DKIM story to continue arguing about DKIM.
- rsingel 14y ago
  I know you are the resident curmudgeonly voice of security truthfulness on Hacker News, but it's really odd that you keep referring to anti-phishing measures as anti-spam, as if they have no relation whatsoever to security. DKIM plays a key role in keeping phishing e-mails out of the inboxes of hundreds of millions of people who have no idea what PGP or an e-mail header is. It's a standard, not just a Google feature. And if you'd read the story, you'd see that a number of companies fixed their weak crypto thanks to his efforts. But, of course, far fewer people would upvote your comments if you didn't diss everything with a tone of condescension.
  - tptacek 14y ago
    Ryan, I wrote: DKIM is an anti-spam mechanism. It does not authenticate the sender of an email message; to do that, use something like PGP. This is an interesting story, but it's not a story about a "massive net security hole". Mail on the Internet has always been spoofable. What else do you want me to say? Mail on the Internet is spoofable, with or without DKIM. I literally don't know what I can do to placate you at this point.

by rsingel 14y ago

tptacek 14y ago

What seems to be happening here is that you don't like the fact that I criticized the Wired headline, so you're moving the goalposts from "Massive Net Security Issue" to "Thing That Might Make It Harder For Google To Reject Spam". Then, when I point out that you're moving the goalposts, you respond by simply repeating the claim --- and then suggest that pointing out what DKIM actually is amounts to a "quibble". DKIM is one of many, many anti-spam mechanisms in place at Google (and presumably Yahoo). But of course, far fewer people would read and forward this Wired story if you had simply written "Mathematician Finds Weakness In One Google Anti-Spam Measure During Recruitment Attempt".

reinhardt 14y ago
Framing it as a mere anti-spam weakness rather than anti-phishing is kinda disingenuous.
- tptacek 14y ago
  Here I'm just going to refer you to "Three Myths About DKIM", linked from the front page of the DKIM site: http://jl.ly/Email/threemyths.html http://jl.ly/Email/threemyths.html
  - Evbn 14y ago
    None of those myths talk about spoofing the sender domain. DKIM doesn't validate the From line. But where is the weakness in trusting that someone with Google's private key approved the entire content of a message that is signed with Google's key, and so, my trust in Google should extend to the content of that email?
    - tptacek 14y ago
      I already provided one specific example upthread: most domains people care about host applications with bugs that allow attackers to generate arbitrary mail from those domains. This is, please note, a very different problem than "being able to generate arbitrary mail under a specific signature". It is considerably easier to forge mail from BANKOFAMERICA.COM than it is to forge mail under the S/MIME signature of a specific Bank of America employee. Domains simply are not a meaningful security boundary. At no point in the life of the commercial Internet have they ever been. Yes, there are security mechanisms on the Internet that are simultaneously (a) important and (b) misguided enough to ignore this fact. Fortunately, the most important of them are in practice difficult to reliably and scalably exploit. This whole story is a tempest in a teacup. As Matthew Green said on Twitter: a 512 bit DKIM key says more about how little Google cares about DKIM than it does about any laxity on Google's part. Google is not lax about security. Since this thread is also dead, we'll have to wait until someone else tries to get to the top of the front page with a DKIM story to continue arguing about DKIM.
rsingel 14y ago
I know you are the resident curmudgeonly voice of security truthfulness on Hacker News, but it's really odd that you keep referring to anti-phishing measures as anti-spam, as if they have no relation whatsoever to security. DKIM plays a key role in keeping phishing e-mails out of the inboxes of hundreds of millions of people who have no idea what PGP or an e-mail header is. It's a standard, not just a Google feature. And if you'd read the story, you'd see that a number of companies fixed their weak crypto thanks to his efforts. But, of course, far fewer people would upvote your comments if you didn't diss everything with a tone of condescension.
- tptacek 14y ago
  Ryan, I wrote: DKIM is an anti-spam mechanism. It does not authenticate the sender of an email message; to do that, use something like PGP. This is an interesting story, but it's not a story about a "massive net security hole". Mail on the Internet has always been spoofable. What else do you want me to say? Mail on the Internet is spoofable, with or without DKIM. I literally don't know what I can do to placate you at this point.