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Ok Google: please publish your DKIM secret keys

blog.cryptographyengineering.com

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Re: Ok Google: please publish your DKIM secret keys

#111

Post by beagle3 »

LinuxBender wrote: post #36
hpoe wrote: post #18

So the author's central thesis essentially seems to boil down to that leaked emails were able to be cryptographically verified, because of DKIM and so we should prevent that so people can't use email to blackmail politicians? Ultimately I prefer the more information that we can get on politicians available. It seems to me that especially when an elected official has something they don't want others to know about that…

I am not a lawyer, but I do not believe that DKIM provides repudiation specific to an individual. DKIM provides evidence that email originated on an email provider. The users neither own nor control the server and user accounts get compromised all the time as well as fake accounts created all the time. Google battles this daily. DKIM might be one piece of information, used in combination with a client IP address and…

It is even weaker than that. DKIM keys themselves can be stolen - most servers don’t store them in HSMs (and HSMs are also not infallible).

Or factored - Debian had a bug 12 years ago that caused weak SSH keys, a similar thing could happen to DKIM key generation (or has happened, but not yet discovered).

Some study showed many RSA keys in the wild had a common factor. A weakness of this family might be discovered with DKIM keys.

It is supporting circumstantial evidence, not proof of identity.

Re: Ok Google: please publish your DKIM secret keys

#112

Post by ska »

baobabKoodaa wrote: post #108
tptacek wrote: post #87

Earlier quoted context omitted.

No, you have confused messaging cryptography with "all of cryptography".

You said "there is never a legitimate need to do X". I gave an example of a legitimate need to do X. Your rebuttal is that... I'm confused? Yeah, you're gonna have to be more specific than that if you want to convince anybody.

The point was that you pointed out a use case for some sort of cryptographic signing, not for (ab-) using DKIM for this purpose rather than what it was designed for.

I don't understand enough about all the issue to really know how I feel about it, but clearly there are trade-offs here that at least argue against expanding the scope.

Re: Ok Google: please publish your DKIM secret keys

#113

Post by toast0 »

speedgoose wrote: post #85

I doubt Google will publish old private keys that were not designed to become public later. I would guess that it's too dangerous or cumbersome to do the security analysis. What if someone realizes that Google uses a broken cryptographically secure pseudorandom number generator (CSPRNG) à la Debian ? Unlikely but the risks exists, so not going to happen in my opinion.

It's also quite possible that they simply deleted the private keys after cycling to new keys.

Re: Ok Google: please publish your DKIM secret keys

#114

Post by hashtagmarkup »

blendergeek wrote: post #32
hashtagmarkup wrote: post #28

Earlier quoted context omitted.

> The threat is not limited to politicians. Anyone (including you and your family members) could be blackmailed or otherwise publicly embarrassed. ... for what they actually did. You think the solution is allowing people to be blackmailed or otherwise publicly embarrassed for things they didn't do, while removing their ability to verify that they didn't do them?

No. Once DKIM keys are published, one can simply deny all emails published "from their account". We currently have a way for an attacker to prove an email's origin years after the fact.

Yes. We are saying the same thing.

Re: Ok Google: please publish your DKIM secret keys

#115

Post by avianlyric »

ivanhoe wrote: post #95
mschuster91 wrote: post #52

Earlier quoted context omitted.

> ... for what they actually did. Being gay is not a crime, and yet people can be blackmailed with it. It is very easy to open yourself up to blackmail by perfectly legitimate activities.

True, there are things that might ruin someone's life even though there's nothing bad about them, but the list of actual crimes and bad things that people do is WAY longer, and being able to prove it is definitely useful...

The same argument can be used to build a police state. But I suspect that you’re not in favour that either.

We shouldn’t be building technical systems that “trap” people, just because they might be doing something bad and might want to prove that one day.

Additionally you’re also ignoring the whole “people have the right, to not have their emails stolen” argument. DKIM signatures are only useful if the emails are stolen, are you trying to suggest that it’s ok to steal emails from people if they’re bad?

Re: Ok Google: please publish your DKIM secret keys

#116

Post by davewritescode »

mattbeckman wrote: post #77

As we head into the post-truth era, we already know videos are going to become far less trusted due to deep fake tech. Finding grains of truth through cryptography, like DKIM, is so refreshing that it hurts to think some people want to cripple it. The Hunter Biden email is a good example. I initially thought it was a garbage tabloid drop, but once I read Rob Graham's analysis, it felt very refreshing to have a real n…

The Hunter Biden email is a terrible example. It's very likely that what's been found on "Hunter Biden's" laptop is just hacked material which has been stuffed on a laptop to disguise the original source of the breach. In this case the DKIM signatures are being used to lend credibility to the story that the laptop was mysteriously left in repair shop, never to be reclaimed.

DKIM is not meant to validate conversations, it's meant to validate single messages for the purposes of spam prevention. Just because I can cryptographically validate selectively chosen messages from someone's mailbox, I don't have any proof that the conversation happened as presented.

There's a good reason why eliminating non-repudiation has been a goal of messaging protocols since OTR in 2004.

Re: Ok Google: please publish your DKIM secret keys

#117

Post by red_trumpet »

baobabKoodaa wrote: post #75
tptacek wrote: post #55

Earlier quoted context omitted.

Among messaging cryptographers, it's not even an argument. Serious secure messengers have been designed to avoid non-repudiation since OTR. Non-repudiation is a vulnerability: once counterparties have authenticated each other's messages, the legitimate need for authentication is gone; allowing random strangers to authenticate messages concedes information to them. Here, have a link, from 2004: https://otr.cypherpunks…

> once counterparties have authenticated each other's messages, the legitimate need for authentication is gone; allowing random strangers to authenticate messages concedes information to them. As you know, there are many legitimate needs to authenticate messages of strangers. For example, when you order products over the internet, an e-mail of your purchase is often the only proof of what was agreed in the purchase.…

> As you know, there are many legitimate needs to authenticate messages of strangers.

I agree with you here. However, EMail was never designed to do this. Eg if you order products over the internet, how do you know that your opposing party keeps their DKIM key safe?

Re: Ok Google: please publish your DKIM secret keys

#118

Post by thinkharderdev »

chimeracoder wrote: post #83
zajio1am wrote: post #73

Earlier quoted context omitted.

> Non-repudiation over time is a truly powerful property of DKIM'd email for a great many uses outside of blackmail. Exactly. If one enters into an contract using an e-mail, then DKIM can be used as a proof to the court of law that the contract was accepted by both sides.

> Exactly. If one enters into an contract using an e-mail, then DKIM can be used as a proof to the court of law that the contract was accepted by both sides. It would make a good TV drama plot, but courts don't work this way in real life. If that were the case, courts wouldn't be able to enforce contracts with wet signatures (which are straightforward to forge), or verbal contracts (which are valid contracts and regu…

Not to mention that DKIM only validates that en email was sent with particular content from a particular email address. It cannot ensure who was actually sitting at the keyboard composing the email.

Re: Ok Google: please publish your DKIM secret keys

#119

Post by mthoms »

ivanhoe wrote: post #91
blendergeek wrote: post #30

Earlier quoted context omitted.

> that so people can't use email to blackmail politicians? He mentions the politicians because those were high profile cases. This could be used against anybody, not just politicians. > It seems to me that especially when an elected official has something they don't want others to know about that it should be public knowledge. Is this true of everybody else as well? Should anybody be able to deny an email they sent i…

Other than whistleblowers and activists fighting the dictatorships (and they can work-around this), what is the case where not being able to prove who sent the email would be a good thing?

-- Example --

Dear Ivanhoe,

I regret to inform you that your HIV test came back positive. Please contact my office at your earliest convenience to arrange a follow up.

Sincerely, Your doctor

Re: Ok Google: please publish your DKIM secret keys

#120

Post by avianlyric »

zajio1am wrote: post #73
xbar wrote: post #25

I think this is a shameful argument. Non-repudiation over time is a truly powerful property of DKIM'd email for a great many uses outside of blackmail. Calling for the ability to remove it during the years 2016-2020 in order to "protect politicians from blackmail" is not only of deeply questionable value but of suspect motivation. Who is the author interested in protecting?

> Non-repudiation over time is a truly powerful property of DKIM'd email for a great many uses outside of blackmail. Exactly. If one enters into an contract using an e-mail, then DKIM can be used as a proof to the court of law that the contract was accepted by both sides.

If non-repudiation is important to you, then both parties should consent to it and use a platform that explicitly supports it.

It shouldn’t be sprung on people without consent. It would be like saying it’s fine to keep a recording from someone else’s webcam because it might prove a crime later.

There’s a reason why justice systems have statues of limitations. People should need to look over their shoulders for the rest of their lives because of one poorly written email.

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