Discusses how to verify DKIM signatures in old emails, namely one of the Hunter Biden emails in the news
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Robert David Graham 2965177385
Merge pull request #5 from petertodd/timestamped-email
2 days ago
ots-timestamp Add timestamped email to prove Google was using those DKIM keys 11 months ago
20120113._domainkey.gmail.com.-TXT.txt first commit 11 months ago
Meeting for coffee.eml first commit 11 months ago
README.md Merge branch 'main' into patch-1 2 days ago
permission.png first commit 11 months ago
verify.py added offline Python tool from @stevecheckoway 11 months ago

README.md

hunter-dkim

This project validates that the "smoking gun" email from that NYPost story actually was a valid email sent 6 years ago. We know this because GMail cryptographically signed it with "DKIM".

This repository contains the original email, plus Google's DKIM key at the time the email was sent. This key is no longer provided by GMail's DNS servers, so you have to hack up a server yourself, such as using BIND9 as a resolver with a Response Policy Zone (RPZ).

Remember that while the email is validated, the context isn't. It's possible this reflects a secret meeting to conspire with Vice President Biden. Or, it's possible the guy attended one of the many Washington D.C. social functions whereby people shake hands with politicians and exchange pleasantries. As Richelieu is claimed to have said "Give me six words by the most honest of men and I'll find something to hang him by". Give me an email dump from the most honest of persons, and I'll pull one out of context to hang them in the court of social media.

As you would expect, many people try to challenge this. Many of them reflect misunderstandings, or people sending links to articles claiming "DKIM breaks" without having read or understood the article. There are three challenges, however. These are:

  • (Q) but we can't get the validation key from Google. (A) it's been archived all over the web, and thus is trustworthy
  • (Q) GMail verifies it's from that account, but not who controled that account (B) we see this account used by Pozharskyi elsewhere
  • (Q) The Date: field doesn't actually timestamp the message. (A) The signing key was valid from Jan-2012 to Oct-2015, giving a timestamp window when it must've been sent

These are described in more detail below.

FAQ

"What precisely was validated?"

What the signature in this email validates:

  • it was sent from this specific account, v.pozharskyi.ukraine@gmail.com, known to have been used by Vadym Pozharskyi, a Burisma board member
  • the intended recipient was to the account hbiden@rosemontseneca.com, known to have been used by Hunter Biden
  • that it was sent between 2012 and 2016
  • the Subject: and body have not been altered in any way

"How can I replicate this?"

There's a python script that'll do the validation for you within this repo.

If you run your own resolver, they all have ability to override certain records, so you can insert this one record (for 20120113._domainkey.gmail.com TXT) so that any tool will work, such as the DKIM Verifier add-on for Thunderbird. Google "Response Policy Zones for BIND9". That's what I first did.

Once you've replicated that the emails verify, try to change them and see if they still verify. Change then and change the signature. Hack away. Find some way that verification can happen with forged/altered emails.

"The entire email dump verified or just this one?"

I've only validated this one email. It's the only one sent to me.

Many can't be validated. They are sent from domains that don't use DKIM to sign outgoing emails. Others used DKIM when sent, but we can no longer find the public-keys that would authenticate them (it's been years).

"Can't signatures be faked, replayed, forged, or cheated?"

Not cryptographic signatures, at least, not in any practical/reasonable manner.

They use a mathematical trick of public-key crypto where a pair of matching keys are generated. Something signed with one, a private-key, can only be verified with the other, the public-key.

Public-key signatures it what underlies Bitcoin. If you could find a way to forge these signatures, you could instantly make billions of dollars.

The trick is you have to keep the private-key private. Bitcoin do sometimes get stolen when people break into a computer and steal the wallet's private-key. If somebody broke into GMail, they'd be able to forge signatures as well.

So many people ask this question. They know basic 'checksums', and know that if you change the contents you can just change the checksum to match. The step they don't undestand is that public-keys are involved, that without knowing the matching private-key, there's no way to adjust the signature to match the contents.

"Okay, you've verified the metadata, but couldn't the contents of the body of the email be changed?"

The signature covers both the metadata and the body. The slightest change to either invalidates the signature.

"Okay, you've verified the email contents, couldn't the metadata be spoofed, such as the real email being sent last month?"

The signature covers both the metadata and the body. Yes, some email metadata isn't covered by the signature, esoteric things like X-Received: headers. But the signature does cover the ones we care about: Date:, From:, To:, and Subject:.

"OKay, the email and metadata, but what about the envelope?"

Several people have cited this Wikipedia article that says that DKIM signatures do not encompass the message envelope. This is correct, but it doesn't mean what you might think it means.

It's like if somebody sent you a printed copy of this email. The address on the outside is unrelated to the contents -- it doesn't mean the contents aren't authenticated.

In any case, Google forces the two to be the same. If the email says From: a GMail account, and it was authenticated by GMail's DKIM key, then it came from an authenticated user of that account.

"Is it timestamped?"

The Date: field in the headers/metadata is included in the signature. DKIM verifies the contents of that field (that somebody didn't alter after signing), but not that it's the correct date. Any fraudulent information can be put here.

But the fraud would have to occur at the time the email was sent. And that time would have to be before October 2016, when GMail changed their DKIM signing keys.

Thus, it's effectively timestamped "some time after January 2012 and before October 2016".

In other words, we know it came from Vadym Pozharskyi, but he couldn't have sent it around a year later than the authenticated email headers claimed he sent it, like April 2016 instead of April 2015.

There are other timestamps in the email headers/metadata, but they aren't validated by DKIM, and hence, could be forged.

"How about very small changes? Couldn't they escape detection?"

It's like being a "little bit pregnant". If you changed the smallest thing, then the entire signatures fails -- and verification fails. It doesn't matter how small.

Well, except spaces. DKIM uses a "relaxed" verification scheme which allows, in certain circumstances, spaces to be added.

But even that isn't an issue here. This message used the "quoted printable" encoding, which means there's almost no place to add a space.

"But GMail's DNS servers no longer provide the public-key"

This is indeed a problem -- for most email domains that aren't GMail.

But in this case, because GMail is so popular, there are thousands of sources of the old key, including archives of old sites, log files from servers, and so on.

Thus, in theory the system only works when the domain in question is currently providing the public-key to validate signatures, but in practice we can know GMail's old key even if they don't provide it directly.

The proper key is one of the files in this project, but of course, I could be lying. You can verify this by googling the key, searching archives like Archive.org, or by specialty logging sites that have retained copies of the old key.

"My DKIM verifier can only fetch the key from a DNS server"

Yes, that's a problem. Other DKIM verification tools and libraries can grab the key from a file, so you could try that (like this one).

What I did instead was set up BIND9 as my DNS resolver, then configured a "Response Policy Zone" (RPZ) with this one record changed. This means that it'll provide live resolution for any other names, but overwrite the correct response (of "not found") with the old key that I retrieve from Internet websites.

Overriding certain records in a resolver this way is pretty common practice. If you manage your own DNS server already, you can easily update it to provide the correct public-key.

"What about this page that says DKIM can be fooled?"

A lot of confident Twitter "experts" proclaim that DKIM can be faked. They are just repeating rumors without understanding how. They also aren't reproducing this verification or demonstrating how this email specifically could've been faked.

The most common source they cite is the following web page to claim DKIM doesn't work:

https://noxxi.de/research/breaking-dkim-on-purpose-and-by-chance.html

None of it applies to this email. It does not apply because:

  • there are no duplicate metadata fields in the actual email
  • there isn't a length (l=) field in the actual email
  • the content-transfer-encoding field is included within the signature

Likewise, the following link about DKIM problems is invalid for the same reason:

https://www.zdnet.com/article/dkim-useless-or-just-disappointing/

The message doesn't have the issues described.

"So the Email is real, but the account could be fake, by someone claiming to be Pozharskyi."

Yup, that's possible. We've only proven a Vadym Pozharskyi sent the email, not that the Vadym Pozharskyi sent it. It's somebody who, in 2014, claimed to have been a "V. Pozharskyi from Ukraine".

DKIM proves only that the account indeed was v.pozharskyi.ukraine@gmail.com. You can create an account rob.graham.usa@gmail.com, and GMail will happily verify those outgoing messages without verifying the person sending them is actually named Robert Graham. In any event, even if it could verify a person's real name, it couldn't verify it's the same Robert Graham as myself.

Thus, we know the emails (based on DKIM) come from somebody claiming to be a Vadym Pozharskyi, but there's no way to prove it's our Vadym.

But, there are other sources that validate that he used this address. For example, there's this document from a Senate investigation showing him using that GMail address last year.

DKIM does verify the date (Date:). If it's somebody claiming to have been Pozharskyi claiming to have met Hunter's dad, then it's a conspiracy from 2014 not a conspiracy from 2020. It would mean somebody who knew intimate details about Hunter Biden sending him fake messages on the off chance that in a future election they would be able to hack into Hunter's email account to expose them.

Like the theory of them hacking into GMail to obtain the private-key, if the conspiracy was this sophisticated, they could do better emails. This one is lame.

"How did you see that secret metadata, in a debugger?"

In some cases, metadata in files like photographs require special tools. But emails are just text, even the metadata. You can open them in any text editor. Just click on this link and see for yourself.

"Short DKIM keys can be cracked."

When GMail first started DKIM signing, they used 1024 bit RSA keys. These are short enough that a nation state (like Russia) can crack them.

But since 2012, they've been using 2048 bit RSA keys, which even all the nation states working together cannot crack.

Note: that link is also yet another source verifying this key is the correct one.

"Did you get this email from the laptop? or was it sent to you?"

The email was sent to me by a journalist. This leads to two points.

The first is that validation of the email is solid regardless of source. We know it was an email sent by GMail from around that time by that named account. Doesn't matter where it came, we can know these facts.

The second is that even if I had a copy of the laptop drive, it's passed through so many hands on the way to me that it's untrustworthy. I mean, if you doubt the "laptop" story to begin, I don't think me having a copy could validate that their story is true.

I personally have many doubts about where this email came from, and the overall "narrative" they are trying to push. Regardless, I can validate the basic facts about this email.