End-to-End Crypto: Messaging and Chat

WhatsApp Messaging

As part of an ongoing series, we’re highlighting the benefits and advantages of various end-to-end encryption tools for messaging, file storage, and secret management.

Many data transfer techniques in use today leverage point-to-point encryption. This approach protects data from point A to B, then B to C, then C to D and so on. Points B and C in this scenario can potentially obtain data to which they’re not supposed to have access; this can be a big problem.

Conversely, data should be encrypted first at point A, then sent along through these intermediary points to its final destination. Only the recipient at point D -- the other “end” of the line -- should decrypt the data. The only way to truly protect the information being exchanged is to encrypt it on both ends of the exchange.

Messaging

The Internet is fast enough to present an illusion of direct peer-to-peer communication. In reality, there are often several parties in between that handle routing messages from one location to another. If messages are delivered in plain text, these parties can eavesdrop, impersonate the sender or recipient, or even manipulate data in transit.

Technology enabling secure communication from a client machine to a server (i.e. TLS encryption for secure web browsing) is already readily available. Let’s look at some options for creating secure communication from one person to another.

WhatsApp

WhatsApp is a secure alternative to SMS messaging that runs both on mobile devices (Android, iOS, and Windows Phone) and mainstream desktops. In addition to encrypting text chats, WhatsApp allows for video and audio messaging as well.

Beyond just encrypting the data sent between you and your contacts, WhatsApp goes further and uses unique encryption keys for each message. This way, even if someone is able to crack the key for a single message (a highly improbable event), they wouldn’t be able to read any other messages in the conversation.

There is nothing you need to do to activate security; WhatsApp enables its encryption model by default. What you will need to do, though, is verify your friends’ security codes (a unique identifier that verifies their device is what it says it is) through some channel other than WhatsApp.

WhatsApp has come under fire in the past for allowing these security codes to change somewhat transparently -- like when your friend gets a new phone. A new device will create a new key and it’s up to you to trust this new key before re-encrypting or re-sending any old messages.

Signal

Under the hood, WhatsApp uses Open Whisper System’s Signal Protocol (download whitepaper). That being said, the original publisher of the protocol also has their own secure messaging app for both Android and iOS: Signal. Like WhatsApp, Signal gives you both secure peer-to-peer text messaging and secure audio/video calling.

Signal can automatically delete messages after a specified interval through their “disappearing messages” feature, whether or not the recipient has read the messages.

The biggest difference between Signal and WhatsApp isn’t the technology they use -- they use the same communication protocols -- it’s in the pace of development. Signal has a smaller team and ships features at a more conservative pace. Facebook is the owner and primary financier of WhatsApp; this relationship means developers can ship new features very quickly.

Additionally, WhatsApp’s central focus is communication; Signal’s central focus is privacy. This impacts the decisions made by each team and the features they build into the app. As a result, WhatsApp collects account information and other metadata in order to better serve customers as a communication broker. Signal collects … just about nothing:

Unlike WhatsApp, Signal doesn’t store any message metadata. Cryptographer and Open Whisper Systems founder Moxie Marlinspike told me that the closest piece of information to metadata that the Signal server stores is the last time each user connected to the server, and the precision of this information is reduced to the day, rather than the hour, minute, and second. (Battle of the Secure Messaging Apps: How Signal Beats WhatsApp)

Enhanced privacy is the largest advantage of Signal. The disadvantage is a smaller user base with which to communicate. You’ll likely the need to convince your peers to install the app.

Allo

Google’s app, Allo, is a newer offering that delivers many of the same features as Signal and WhatsApp. Allo provides a smooth, intuitive alternative to traditional SMS for both Android and iOS. Unfortunately, the biggest trade-off Google has made is in valuing user-focused perks over security.

Instead of encrypting all messages by default, Allo requires you explicitly enable incognito mode to start an end-to-end encrypted chat. Enabling incognito mode will automatically encrypt messages as you send them; only the intended recipient can ever read them.

Google made the choice to go this route as many of the features and benefits of Allo require allowing their own services to read your messages. Allo itself is a chat system that learns about you the more you use it, presenting custom-tailored responses to help you communicate more quickly. Unfortunately, relegating end-to-end security to an afterthought makes Allo the weakest of the three messaging applications.

Is it enough?

Messaging and chat is just one form of communication that’s potentially subject to eavesdropping, impersonation, and manipulation. Tools like WhatsApp, Signal, and even Allo are all great ways to get started with secure, private communication. However, they are by no means the end of the road when it comes to personal privacy and data security.

Come back next week for a summary of the options available for protecting files with end-to-end encryption techniques.