Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Ok Google: please publish your DKIM secret keys

blog.cryptographyengineering.com

Post reply on HN
Print view View original

431–440 of 492 posts

Re: Ok Google: please publish your DKIM secret keys

#431

Post by Natanael_L »

beagle3 wrote: post #111
LinuxBender wrote: post #36

Earlier quoted context omitted.

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 wit…

Many DKIM keys uses outdated key generation defaults with 512 bit RSA keys. Google used to have such weak DKIM keys too in ~2012.

Re: Ok Google: please publish your DKIM secret keys

#432

Post by Natanael_L »

hashtagmarkup wrote: post #152
mthoms wrote: post #139

Earlier quoted context omitted.

Huh? No one (including yourself), have mentioned anything about "destruction of evidence" so far. If you care to enlighten me about how it's relevant I'm happy to listen.

By making the DKIM keys public, you are converting solid evidence of something that was said into something that was either really said, or someone else pretended that they said. Evidence was destroyed.

No, destruction of evidence involves things like making something impossible to analyze and evaluate. Publication of a key doesn't erase the original messages and does not make it impossible to look into their contents to try to establish authencity by external means. Causing ambiguity is not destruction of evidence.

Re: Ok Google: please publish your DKIM secret keys

#433

Post by Natanael_L »

yew wrote: post #393
tptacek wrote: post #390

Earlier quoted context omitted.

If you want to transfer assurance of the authenticity of an email to someone else, you can do so without DKIM; just sign a timestamp or something. The problem with current DKIM configurations is that it provides that assurance to everybody , including strangers who have no business having it. Which is why the ask here is for Google to do with DKIM what OTR does with MAC keys: burn them periodically, so that only peop…

That seems less usable for the average email recipient. Most people who need to prove authenticity to a third party (eg of politically sensitive or offensive messages) aren't techies. Too, it's easy to imagine not knowing you need proof until some time after you receive an email. If it isn't usable and enabled by default, it won't be used in practice - for the same reason almost nobody uses PGP.

It's already common to use unsigned documents in court, as long as you can show provenance is legit or if the counterparty is willing to acknowledge authencity.

In fact, it's quite common that the issue over unsigned documents in court is the interpretation, not authencity.

I think the issue of having to teach users how to opt in to signing emails in potentially controversial cases is preferable to having to teach them how to handle email communications that are permanently provable (for starters, never ever again leave out a quote and never ever write ambiguously).

Re: Ok Google: please publish your DKIM secret keys

#434

Post by Natanael_L »

patrec wrote: post #273
tptacek wrote: post #82

I know threads change over time, and it's dangerous to write a comment in response to the perceived gestalt of an HN thread, but, I have to say, it's pretty wild reading a thread on this site arguing so strenuously against the premise of secure messaging. In messaging cryptography, non-repudiability has for almost 2 decades been considered a vulnerability, not a feature. The OTR protocol[1] takes the step of publishi…

> To allow a stranger to authenticate a messages is to concede information to them, and avoiding concessions is the point of messaging cryptography. Whilst I agree with you that email messages should be repudiable , I have a feeling you're trying to pass something off as axiomatic that isn't. For example isn't a confidential business agreement basically exactly, by design, an authenticated non-repudiable message that…

Yes.

And they have much better mechanisms than DKIM available which they should use instead.

In fact, with reliance on DKIM you create the distorted incentive that one company might want to fake getting hacked to claim an email they sent is not authentic.

As a matter of fact, they might even be so sneaky as to send individual emails without DKIM signatures, with a policy set for the recipients to not reject those emails. Since most email clients do not display this discrepancy in a lack of a DKIM signature, the recipient might not notice and then the sender can later claim forgery.

So then let's not rely on something so unreliable if you need reliable authentication.

Re: Ok Google: please publish your DKIM secret keys

#435

Post by Natanael_L »

some_furry wrote: post #150
moyix wrote: post #131

Earlier quoted context omitted.

Has this kind of repudiation ever been tested in the real world? It's hard to imagine a court throwing out email evidence because it lacked a DKIM signature. And on a personal level seeing a chat transcript that had cryptographic non-repudiation would make me likely to believe it, but seeing one that lacked it would probably not weigh heavily in how I came to that determination.

> Has this kind of repudiation ever been tested in the real world? It's hard to imagine a court throwing out email evidence because it lacked a DKIM signature. They're more likely to ask their expert witness to testify about the evidence, and the deniability of the DKIM signature could be brought up by the expert witness as a reason to distrust the evidence. I wouldn't expect lawyers to discover this argument from fi…

I would expect any half decent prosecutor to focus on how the emails were acquired when a verifiable DKIM signature is missing. Then the defense doesn't even need to bring that argument up, just challenge the provenance of the evidence.

Re: Ok Google: please publish your DKIM secret keys

#436

Post by bambax »

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…

Well said. The article is interesting, but this is wrong:

> This is an amazing resource for journalists (...) But it doesn’t benefit you.

If it's an amazing resource for journalists it benefits me.

Re: Ok Google: please publish your DKIM secret keys

#437

Post by ianhawes »

cowsandmilk wrote: post #404
eloisius wrote: post #365

Earlier quoted context omitted.

That’s a false equivocation. Private citizens having “nothing to hide” in their personal lives is disimilar to public officials having nothing to hide in relation to their official duties. Blackmail related to embarrassing sexual proclivities or anything like that is unfortunate, but kindly asking politicians to be transparent isn’t a realistic answer. Of course they will use official channels and be transparent abou…

When John Podesta’s email was hacked, he was not a public official. He also was never up for election. In fact, none of the examples in the article were from people up for election.

Which is why we need a legal protection for the theft and publishing of stolen personal correspondence.

Re: Ok Google: please publish your DKIM secret keys

#438

Post by shinigami »

baobabKoodaa wrote: post #414
shinigami wrote: post #378

Earlier quoted context omitted.

So maybe digitally sign the contracts instead of unwillingly sign every single email you send?

Please explain how I can make a webshop like amazon digitally sign a contract?

Why do you need Amazon to digitally sign a contract?

Re: Ok Google: please publish your DKIM secret keys

#439

Post by shinigami »

tony101 wrote: post #381
shinigami wrote: post #266

Earlier quoted context omitted.

So... no need for DKIM

But you need to be able to prove the existence of the contract. Which DKIM would help with.

Then digitally sign it. Sign and scan it. Do not require signing every single email you send to protect 0,1% of them.

Re: Ok Google: please publish your DKIM secret keys

#440

Post by willyt »

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…

If a nation state adversary has hacked the DKIM keys from your email server, they can send fake emails signed with this key. So it doesn't prove that a high value target like a presidential candidate has actually typed and pressed send on that email, it just proves that the first SMTP server that routed the email has sent it.

Even google didn't bother to rotate their DKIM keys as recommended by the standard, so one wonders if the google keys are stored in a cage guarded by lasers and dogs or if there are copies on someones laptop somewhere and any sysadmin with a gambling problem or a secret affair could have leaked them to an unscrupulous journalist or a spy.

Post reply on HN