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15 Aug 2016

VeraCrypt in the news

Very cool open-source project VeraCrypt is all over the news this week, it seems. First when they announced that they were going to perform a formal third-party code audit, and had come up with the funds to pay for it; and then today when they claimed their emails were being intercepted by a “nation-state” level actor.

The audit is great news, and once it’s complete I think we’ll have even more confidence in VeraCrypt as a successor to TrueCrypt (which suffered from a bizarre developer meltdown¹ back in 2014).

The case of the missing messages

However, I’m a bit skeptical about the email-interception claim, at least based on the evidence put forward so far. It may be the case – and, let’s face it, should be assumed – that their email really is being intercepted by someone, probably multiple someones. Frankly, if you’re doing security research on a “dual use” tool² like TrueCrypt and don’t think that your email is being intercepted and analyzed, you’re not participating in the same consensus reality as the rest of us. So, not totally surprising on the whole. Entirely believable.

What is weird, though, is that the evidence for the interception is that some messages have mysteriously disappeared in transit.

That doesn’t really make sense. It doesn’t really make sense from the standpoint of the mysterious nation-state-level interceptor, because making the messages disappear tips your hand, and it also isn’t really consistent with how most modern man-in-the-middle style attacks work. Most MITM attacks require that the attacker be in the middle, that is, talking to both ends of the connection and passing information. You can’t successfully do most TLS-based attacks otherwise. If you’re sophisticated enough to do most of those attacks, you’re already in a position to pass the message through, so why not do it?

There’s no reason not to just pass the message along, and that plus Occam’s Razor is why I think the mysteriously disappearing messages aren’t a symptom of spying at all. I think there’s a much more prosaic explanation. Which is not to say that their email isn’t being intercepted. It probably is. But I don’t think the missing messages are necessarily a smoking gun displaying a nation-state’s interest.

Another explanation

An alternative, if more boring, explanation to why some messages aren’t going through has to do with how Gmail handles outgoing email. Most non-Gmail mailhosts have entirely separate servers for incoming and outgoing mail. Outgoing mail goes through SMTP servers, while incoming mail is routed to IMAP (or sometimes POP) servers. The messages users see when looking at their mail client (MUA) are all stored on the incoming server. This includes, most critically, the content of the “Sent” folder.

In order to show you messages that you’ve sent, the default configuration of many MUAs, including Mutt and older versions of Apple Mail and Microsoft Outlook, is to save a copy of the outgoing message in the IMAP server’s “Sent” folder at the same time that it’s sent to the SMTP server for transmission to the recipient.

This is a reasonable default for most ISPs, but not for Gmail. Google handles outgoing messages a bit differently, and their SMTP servers have more-than-average intelligence for an outgoing mail server. If you’re a Gmail user and you send your outgoing mail using a Gmail SMTP server, the SMTP server will automatically communicate with the IMAP server and put a copy of the outgoing message into your “Sent” folder. Pretty neat, actually. (A nice effect of this is that you get a lot more headers on your sent messages than you’d get by doing the save-to-IMAP route.)

So as a result of Gmail’s behavior, virtually all Gmail users have their MUAs configured not to save copies of outgoing messages via IMAP, and depend on the SMTP server to do it instead. This avoids duplicate messages ending up in the “Sent” folder, a common problem with older MUAs.

This is all fine, but it does have one odd effect: if your MUA is configured to use Gmail’s SMTP servers and then you suddenly use a different, non-Google SMTP server for some reason, you won’t get the sent messages in your “Sent” box anymore. All it takes is an intermittent connectivity problem to Google’s servers, causing the MUA to fail over to a different SMTP server (maybe an old ISP SMTP or some other configuration), and messages won’t show up anymore. And if the SMTP server it rolls over to isn’t correctly configured, messages might just get silently dropped.

I know this, because it’s happened to me: I have Gmail’s SMTP servers configured as primary, but also have my ISPs SMTP set up in my MUA, because I have to use them for some other email accounts that don’t come with a non-port-25 SMTP server (and my ISP helpfully blocks outgoing connections on port 25). It’s probably not an uncommon configuration at all.

Absent some other evidence that the missing messages are being caused by a particular attack (and it’d have to be a fairly blunt one, which makes me think someone less competent than nation-state actors), I think it’s easier to chalk the behavior up to misconfiguration than to enemy action.

Ultimately though, it doesn’t really matter, because everyone ought to be acting as though their messages are going to be intercepted as they go over the wire anyway. The Internet is a public network: by definition, there’s no security guarantees in transit. If you want to prevent snooping, the only solution is end-to-end crypto combined with good endpoint hygiene.

Here’s wishing all the best to the VeraCrypt team as they work towards the code audit.

1: Those looking for more information on the TrueCrypt debacle can refer to this Register article or this MetaFilter discussion, both from mid-2014. This 2015 report may also be of interest. But as far as I know, the details of what happened to the developers to prompt the project’s digital self-immolation are still unknown and speculation abounds about the security of the original TrueCrypt.

2: “Dual use” in the sense that it is made available for use by anyone, and can be therefore used for both legitimate/legal and illegitimate/illegal purposes. I think it goes almost without saying that most people in the open-source development community accept the use of their software by bad actors as simply a cost of doing business and a reasonable trade-off for freedom, but this is clearly not an attitude that is universally shared by governments.

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