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How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

wired.com

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Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#61

Post by dfox »

mikeash wrote: post #54
Sami_Lehtinen wrote: post #24

Well, afaik key length isn't the problem. Weak algo is. I assume they use RSA, they should use ECC. 512 bits is more than enough. https://www.nsa.gov/business/programs/elliptic_curve.shtml

That doesn't make much sense. There are key lengths for which RSA is strong, and key lengths for which ECC is weak. ECC keys may be stronger at shorter lengths, but that hardly means that key length isn't the problem. After all, using a longer key would fix this problem.

Using ECC would solve this particular problem, because in both DKIM and DNSSEC usage of key lengths of 512 to 768 bits and not more are motivated by what can fit into one UDP DNS reply packet. Also for RSA signature size is equal to key length, and not some small multiple of security parameter and you don't want to expand messages by including large signature that might well be larger than actual payload.

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#62

Post by mikeash »

dfox wrote: post #61
mikeash wrote: post #54

Earlier quoted context omitted.

That doesn't make much sense. There are key lengths for which RSA is strong, and key lengths for which ECC is weak. ECC keys may be stronger at shorter lengths, but that hardly means that key length isn't the problem. After all, using a longer key would fix this problem.

Using ECC would solve this particular problem, because in both DKIM and DNSSEC usage of key lengths of 512 to 768 bits and not more are motivated by what can fit into one UDP DNS reply packet. Also for RSA signature size is equal to key length, and not some small multiple of security parameter and you don't want to expand messages by including large signature that might well be larger than actual payload.

Right. Either expanding the key length or using ECC would fix it. So saying the problem isn't one of those, but is only the other, doesn't make much sense to me.

ECC may even be a better solution, as you say, but that doesn't mean that the problem isn't also one of an insufficiently long key.

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#64

Post by rsingel »

tptacek wrote: post #49
rsingel wrote: post #43

Earlier quoted context omitted.

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.

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…

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

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#65

Post by jlgreco »

jere wrote: post #4

>But the government of Iran probably could, or a large group with sufficient computing resources could pull it off. Yes, I can see it now: Iran endures crushing sanctions in order to pursue spam email program.

The rule of thumb that I have heard, and seen played out, is that there are basically 3 tiers of who can factor what. governments or government sized companies (upper millions, or billions sized budgets), modestly sized companies / research projects (millions), or hobbyists. Each can handle about 256 bits more than the next, and the time for one to reach the capabilities of the other is somewhere between 5 to 10 years.

Hobbyists have been factoring 512bit keys on a whim for a few years now, so....

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#66

Post by tptacek »

rsingel wrote: post #64
tptacek wrote: post #49

Earlier quoted context omitted.

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…

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 t…

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".

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#67

Post by Aardwolf »

seanica wrote: post #9

“A 384-bit key I can factor on my laptop in 24 hours,” he says. “The 512-bit keys I can factor in about 72 hours using Amazon Web Services for $75. And I did do a number of those. Then there are the 768-bit keys. Those are not factorable by a normal person like me with my resources alone. But the government of Iran probably could, or a large group with sufficient computing resources could pull it off.” "But the gover…

That's your choice if you don't want to read information if it contains certain sentences. No need to tell the rest of the world about it.

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#68

Post by __alexs »

Erwin wrote: post #14
tptacek wrote: post #8

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.

Gmail (possibly Hotmail) put a little lock icon next to DKIM authenticated email from some senders, such as eBay & PayPal and outright reject unauthenticated emails from such domains. They've flaunted this feature in the past So if an authenticated PayPal email pops up in your Gmail inbox saying you must do this and that to unlock your account, you may be more likely to do so due to the legitimacy of DKIM.

Does that Padlock really have anything to do with DKIM or SPF? I thought it was just some magically hard coded thing for eBay and PayPal messages. My own DKIM signed messages certainly don't get it.

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#69

Post by borski »

tptacek wrote: post #29
Erwin wrote: post #14

Earlier quoted context omitted.

Gmail (possibly Hotmail) put a little lock icon next to DKIM authenticated email from some senders, such as eBay & PayPal and outright reject unauthenticated emails from such domains. They've flaunted this feature in the past So if an authenticated PayPal email pops up in your Gmail inbox saying you must do this and that to unlock your account, you may be more likely to do so due to the legitimacy of DKIM.

The reality is that people will act on "Paypal" mail that comes from "Payapal.ng". Let's not pretend that DKIM has much to do with that decision. I agree, though, that the little lock in the Gmail UI is misleading.

That UI affordance is actually incredibly frustrating for us, because we get that question a lot. Tons of people get confused by it.

Re: How a Google Headhunter’s E-Mail Unraveled a Massive Net Security Hole

#70

Post by [deleted] »

tptacek wrote: post #29
Erwin wrote: post #14

Earlier quoted context omitted.

Gmail (possibly Hotmail) put a little lock icon next to DKIM authenticated email from some senders, such as eBay & PayPal and outright reject unauthenticated emails from such domains. They've flaunted this feature in the past So if an authenticated PayPal email pops up in your Gmail inbox saying you must do this and that to unlock your account, you may be more likely to do so due to the legitimacy of DKIM.

The reality is that people will act on "Paypal" mail that comes from "Payapal.ng". Let's not pretend that DKIM has much to do with that decision. I agree, though, that the little lock in the Gmail UI is misleading.

[deleted]
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