Off-the-Record Messaging (OTR) & Encryption

Instructor: David Gloag
Everyone seems to use instant messaging these days. In this lesson, we'll take a look at off-the-record messaging, encryption, and how these technologies are related.

The Myriad of Messages

Texting, texting, texting - everyone seems to be doing it these days. Your kids text their friends from their cell phones, your significant others text you about various things, and colleagues instant message each other at work.

And why not? It's free on the Internet, using publicly available applications. It's also free on most cell phone usage plans, and a messaging application comes with your phone. But what if you need privacy? What if the conversation is too personal to make them available publicly?

The truth is that technology already exists to protect your conversations. These include off-the-record messaging, and encryption.


Encryption is a protection mechanism used to obscure information by changing its form. It is a mathematically-based process that uses a piece of secret information, called a key, to facilitate this change.

The key is known only to authorized parties, and introduces an element of randomness essential to the encryption's ability to resist attack. The algorithms used range in complexity from those that are considered simple, to some that are so complex they require custom hardware to calculate.

Encryption has one additional property that sets it apart from similar technologies; it is reversible. This means that a second application of the encryption algorithm can return the original information.

As you might imagine, this technology has a number of uses, ranging from protecting financial transactions to securing sensitive communications.

Off-the-Record Messaging

Off-the-record messaging (OTR) is a communications protocol used in instant messaging and chat applications created in 2004. It provides a couple of useful capabilities:

  • Encryption - the process of securing the information transmitted, and keeping it out of the hands of those with malicious intent.
  • Authentication - the process of ensuring that the author of the message is who you think it is. This ensures that someone can't impersonate someone else.
  • Confirmation - the process of ensuring that while the conversation is in process, the messages are authentic and were not tampered with.
  • Forward Protection - the process of ensuring that the loss of your secret key does not compromise any prior information sent.

OTR also features deniable authentication. While the conversation is in process, confirmation assures that the messages are authentic, but after the conversation is over, anyone could forge part of a message to make it look like it was said. As the messages don't have digital signatures, no one could prove that any certain message came from any certain person. This means the conversation can not be used in court or 'on-the-record'.

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