Or just don't use tools you don't understand enough to rely on in such a critical use case. My viewpoint is from a very developer's perspective, and rebels may not all possess the needed technical insight, but this looks like amateur hour. They must have trusted some technical person's advice in their organization, if they're a group, and you could be right that they were missing a sufficiently skilled CTO for such an operation.
Coups aren't a new invention, they were happening since people first organized into a society. Securing an organization is not a purely, or even primarily, a computer problem. Newest "encrypted" chatapp du jour is only a distraction, and should be at best treated as a shiny replacement for walkie-talkies. If someone is so stupid to base the security of their op on a chat app, frankly, they deserve to fail.
Not good enough, you still have metadata, which in this case is gold. "So you were messaging General X, while he was performing the coup. Would you like to tell us more about this, maybe during some waterboarding?"
Email addresses are not necessarily identifiable. Use a VPN or TOR and setup a Gmail account. Or maybe buy a prepay GSM card with 3G bandwidth included, and use it while moving through town.
Have you actually tried to set up an anonymous gmail account recently? Because I think you'll find that it is borderline impossible. Gmail's algorithms end up requiring SMS authentication when you're working over tor, which essentially deanonymizes you or requires the additional step of getting a burner phone for SMS; neither of which is good and probably will get you on all sorts of lists...
The barrier on PGP or GPG is EXTREMELY high for a bunch of normal people on various kinds of cell phones. I can see why someone found an app that someone thought was secure and everyone went with it.
If you read the alleged chat logs of how they coordinated the event, you will see that there was little coordination to begin with, regardless of the medium. If there had been proper planning, they first of all wouldn't have used a chat room, and they also wouldn't have used a tool that logs chats. This is not how military commanders instruct their troops in the field.
I'm really curious. What is the wise CTO's recommendation for a coup's way to securely message?
As one of the other commenters said, WhatsApp and Signal still rely on third parties to host the system. But doesn't Signal simply have each device generate a private key that it claims it never knows about so even if the Signal server were hacked it still wouldn't compromise existing keys?
PGP (or Keybase.io) seems like too much work for non-techies.
I'm not as familiar with Telegram.
In the end, could you do any better than a trusted third party providing a protocol it claims generates keys on your device and doesn't share them?
Oldie but goodie - Robert Heinleins 'Moon is a harsh mistress' gives anyone interested a nice introduction into coups, cells and other things conspiracy.
But before you go live, you don't know if your peer cells are real or just illusions set up to lure you into an ineffective attempt. With Gülen and AKP being such a narrow spectrum historically, changing sides is just a tiny shift in loyalty. It would be very easy to set up fake cells in that situation, it might even happen accidentally (formerly real cells not telling their peers about getting second thoughts).
But I fully agree with your subtext: it's not a technical problem.
Have the NSA design one for you through a front and have the Americans on your side (publicly or not).
It really depends on who you are trying to depose. I wouldn't trust any device if you were going against the interests of America / NATO, there are just too many opportunities for side channels. Likewise if it were using Chinese hardware against China. Assume you're compromised in either situation regardless of how secure your encryption seems to be.
Both WhatsApp and Signal allow verification of the keys. Signal will error out if you change devices - contacts must manually OK it to continue. I think WA has this too, maybe?
Signal also had some sort of work towards preventing contact list disclosure.
At a state level, there's also traffic analysis. If you find Target A then look at their traffic, you might be able to time-coordinate messages sent to other users. (Target->Signal Servers->Recipient)
Guess they could take the Signal source and run their own copy of it, too, eh? I'd also add a time-based auto-wipe function to Signal, which is useful if your are suddenly captured. Doing it by hand is tedious, so people don't. Signal doesn't do this because they don't want people to think it implements a secure remote wipe. But they should consider the problem of an activist having their phone recovered. If the app would delete on time, it'd mitigate some damage.
But remember that Turkey is a NATO ally, so you're up against the NSA, CIA and MI6 for starters (in addition to the fine intelligence service of Turkey).
So I would think that Signal would have to hand out all registered phone numbers in Turkey - a list which could be checked against all military personnel. Given that they've detained thousands of teachers, I don't think they'd be above detaining thousands of suspected troops, even at the risk of waterboarding loyalists.
You don't need an accurate list, just some help "short listing" people.
Similar issue with Tor - if you're in the military and your mobile device used Tor before/during the coup, you'd be on a watch-list (or shot).
The best op-sec is the terrorist/stay-behind/contras: small independent cells, with no knowledge or communication with each other. Obviously some plan is needed to set up a command and control structure when the coup is "won". I don't think there are any great solutions here, that also doesn't leak enough meta-data to get you tortured and killed in the event of a failed coup.
One way would be to use any standard messaging app, but bury the message in the noise. Make it look enough like normal communication and provide only as much signal to the people who need it and could fly under the radar long enough to pull it off.
A modern, digital scheme similar to this is called 'chaffing and winnowing' [2]. Both are steganography rather than encryption, but the intent is the same -- to communicate securely over an insecure channel.
OTR messaging is encrypted (only intended recipients can read your messages), authenticated (you can verify intended recipients identity), deniable (anyone can forge messages after a conversation to look like you sent them), and forward-secret (if you loose your keys, previous conversations aren't compromised).
Also, it is wise to communicate as little as possible. Chatter can be detected to see who are involved. It often doesn't matter what you said, if you were involved or engaged with the wrong people, you may find yourself zip-tied in a stress position.
The trouble with WhatsApp in practice in this coup is the coup guys messaged in larger groups and the messages are stored on the handset. Erdogan's guys only needed to get hold on one or two unlocked handsets to get the messages. (https://xkcd.com/538/). Something like snapchat where they disappear after a bit might have been better.
