computer science

TextSecure

TextSecure is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand TextSecure rather than just read about it. In short: TextSecure was an encrypted messaging application for Android that was developed from 2010 to 2015. It was a predecessor to Signal and the first application to use the Signal Protocol, which has since been implemented into WhatsApp and other applications.

Key takeaways

TextSecure belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect TextSecure to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TextSecure from memory before moving on to harder problems.

Reference excerpt

TextSecure was an encrypted messaging application for Android that was developed from 2010 to 2015. It was a predecessor to Signal and the first application to use the Signal Protocol, which has since been implemented into WhatsApp and other applications. TextSecure used end-to-end encryption to secure the transmission of text messages, group messages, attachments and media messages to other TextSecure users. TextSecure was first developed by Whisper Systems, who were later acqui-hired by Twitter. The application's source code was then released under a free and open-source software license. In 2013, TextSecure's development was picked up by an independent group called Open Whisper Systems, who merged it with an encrypted voice calling application called RedPhone and renamed the product as Signal.

History

Whisper Systems and Twitter (2010–2011) TextSecure started as an application for sending and receiving encrypted SMS messages. Its beta version was first launched on May 25, 2010, by Whisper Systems, a startup company co-founded by security researcher Moxie Marlinspike and roboticist Stuart Anderson. In addition to launching TextSecure, Whisper Systems produced a firewall, tools for encrypting other forms of data, and RedPhone, an application that provided encrypted voice calls. All of these were proprietary enterprise mobile security software. In November 2011, Whisper Systems announced that it had been acquired by Twitter. The financial terms of the deal were not disclosed by either company. The acquisition was done "primarily so that Mr. Marlinspike could help the then-startup improve its security". Shortly after the acquisition, Whisper Systems' RedPhone service was made unavailable. Some criticized the removal, arguing that the software was "specifically targeted [to help] people under repressive regimes" and that it left people like the Egyptians in "a dangerous position" during the events of the 2011 Egyptian revolution. Twitter released TextSecure as free and open-source software under the GPLv3 license in December 2011. RedPhone was also released under the same license in July 2012. Marlinspike later left Twitter and founded Open Whisper Systems as a collaborative Open Source project for the continued development of TextSecure and RedPhone.

Open Whisper Systems (2013–2015)

Open Whisper Systems' website was launched in January 2013. Open Whisper Systems started working to bring TextSecure to iOS in March 2013. In February 2014, Open Whisper Systems introduced the second version of their TextSecure Protocol (now Signal Protocol), which added group chat and push messaging capabilities to TextSecure. Toward the end of July 2014, Open Whisper Systems announced plans to unify its RedPhone and TextSecure applications as Signal. This announcement coincided with the initial release of Signal as a RedPhone counterpart for iOS. The developers said that their next steps would be to provide TextSecure instant messaging capabilities for iOS, unify the RedPhone and TextSecure applications on Android, and launch a web client. Signal was the first iOS app to enable easy, strongly encrypted voice calls for free. TextSecure compatibility was added to the iOS application in March 2015. Later that month, Open Whisper Systems ended support for sending and receiving encrypted SMS/MMS messages on Android. From version 2.7.0 onward, TextSecure only supported sending and receiving encrypted messages via the data channel. Reasons for this included:

Complications with the SMS encryption procedure: Users needed to manually initiate a "key exchange", which required a full round trip before any messages could be exchanged. In addition to this, users could not always be sure whether the receiver could receive encrypted SMS/MMS messages or not. Compatibility issues with iOS: Not possible to send or receive encrypted SMS/MMS messages on iOS due to the lack of APIs. The large amounts of metadata that inevitably arise and are uncontrollable when using SMS/MMS for the transportation of messages. Focus on software development: Maintaining SMS/MMS encryption and dealing with edge cases took up valuable resources and inhibited the development of the software. Open Whisper Systems' abandonment of SMS/MMS encryption prompted some users to create a fork named Silence (initially called SMSSecure) that is meant solely for the encryption of SMS and MMS messages. In November 2015, the RedPhone application was merged into TextSecure and it was renamed as Signal for Android.

Features

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with TextSecure

Start with the simplest possible case. Write down what TextSecure claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to TextSecure before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about TextSecure ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of TextSecure

In research: TextSecure appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses TextSecure in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: TextSecure is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2010 software, Cryptographic software, Formerly proprietary software, so understanding it makes those chapters shorter.
In everyday life: Look for TextSecure outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study TextSecure in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TextSecure means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain TextSecure out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TextSecure in simple terms?

Why does TextSecure matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study TextSecure?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on TextSecure.