4 ms·

Are you saying that 1) anti-spam is not about about security and that 2) DKIM, even if properly implemented, doesn't make spoofing harder and security better?

by rsingel 14y ago

tptacek 14y ago
I'm saying that DKIM is an anti-spam mechanism, and that there are real ways to authenticate the actual sender of a message, like PGP or S/MIME. Calling a cracked DKIM key a "massive Internet security hole" is like calling a bug in SpamAssassin a "massive Internet security hole".
- rsingel 14y ago
  You didn't answer the questions. That's because you well know that anti-spam is security. Just because DKIM isn't foolproof, doesn't make it useless as a layer in anti-spam and security.
  - tptacek 14y ago
    You asked a question that had nothing to do with my comment, so I've declined to engage with you on that point. I'm not interested in litigating whether DKIM is "useless" or not. But I'm happy to continue backing up why this particular Wired headline is silly. DKIM is a cryptosystem backed by the insecure DNS. Mail has been spoofable since before RFC822. The whole idea behind phishing attacks is that you can't trust email. Nobody credible has ever suggested that DKIM resolves that problem; you will find no credible Internet security advice anywhere suggesting that a DKIM signature on a piece of email from Paypal or Chase means you should click on a link in that email and log into something.
    - 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.

Are you saying that 1) anti-spam is not about about security and that 2) DKIM, even if properly implemented, doesn't make spoofing harder and security better?

by rsingel 14y ago

Are you saying that 1) anti-spam is not about about security and that 2) DKIM, even if properly implemented, doesn't make spoofing harder and security better?

tptacek 14y ago

I'm saying that DKIM is an anti-spam mechanism, and that there are real ways to authenticate the actual sender of a message, like PGP or S/MIME. Calling a cracked DKIM key a "massive Internet security hole" is like calling a bug in SpamAssassin a "massive Internet security hole".

rsingel 14y ago
You didn't answer the questions. That's because you well know that anti-spam is security. Just because DKIM isn't foolproof, doesn't make it useless as a layer in anti-spam and security.
- tptacek 14y ago
  You asked a question that had nothing to do with my comment, so I've declined to engage with you on that point. I'm not interested in litigating whether DKIM is "useless" or not. But I'm happy to continue backing up why this particular Wired headline is silly. DKIM is a cryptosystem backed by the insecure DNS. Mail has been spoofable since before RFC822. The whole idea behind phishing attacks is that you can't trust email. Nobody credible has ever suggested that DKIM resolves that problem; you will find no credible Internet security advice anywhere suggesting that a DKIM signature on a piece of email from Paypal or Chase means you should click on a link in that email and log into something.
  - 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.