Backdoor in encrypted chat apps

Alex, August 23, 2016 14:34
In Europe some intelligence agencies are worried they cannot catch criminals and terrorists now all popular chat apps are encrypting the messages. They demand a backdoor or a weakened encryption algorithm. Again the "every bit is important" and the "I have nothing to hide" sides are weighing in.
I belong to the every bit is important camp but I seem to be unable to convince people their data is important as well. I gladly leave that for others. What I want to do here is give the facts about the chat apps and why backdoors will not get the desired result.

International borders

Even if a law in country A demands a backdoor, chat app builder operating from country B will just ignore your law. You can think of blocking the service like Brazil is doing to Whatsapp but that will only trigger the launch of dozen of new apps in other countries.

Weakening encryption

This will allow man-in-the-middle attacks to sniff traffic at a lower cost than the current encryption standards. Criminals, IT professionals and later when the first incidents reach the news papers everybody will move to chat apps that claim not to have weakened their encryption. Users of weak or no encryption apps will be of no importance of law enforcement or just stupid and would have caught anyway.

Building in backdoors

No backdoor can be guaranteed to be only accessible by the government. Think TSA keys.

Key management

This is what currently is the best of the bad solutions: every chat app should provide one or more keys to the government(s), they will store it somewhere and when a judge has advised a chat discussion can be “unlocked” one of these keys should be used. I have heard people who I usually trust blindly when it comes to security talk about this solution as a serious candidate to keep encryption alive. I have three arguments why this will not work as intended.
  1. Governments have proven not to be able to protect sensitive data.
  2. The technology already exists. There will always be some guy on a campus making yet another encrypted chat app without handing over the main private keys.
  3. This will probably work inside the USA where all major chat apps are based and the largest intelligence agencies are but what if a country in Europe needs to decrypt a chat message? Will they get a copy of the keys? Will the NSA do the hard work for them? Will they to that for all countries even the ones with laws we think are cruel? What if North Korea wants a copy?
  4. The main argument is that a judge will decide if a message can be decrypted. This is where I want to focus my energy on. If a judge does so he will do so only if this concerns a possible terrorist, a major criminal or similar and sometimes a random person. Let law enforcement do their work with normal surveillance: hack the phone, use cameras to figure out the pin code of the phone, install malware on his PC etc. Yes, this will be more work, but the NSA will not be able to harvest all our chat messages forever and ever.

Let me know what you think! I am @hackpending on twitter.