The popular IM+ app (free version, pro version) is offering their $4.99 “off-the-record” feature for just 99 cents until the end of tomorrow. Rather than using a single, proprietary messaging services, IM+ uses the OTR standard that can be used with many messaging services and across many devices.
On their Facebook page, the company details OTR.
First of all, OTR is end-to-end encryption, which means that message is encrypted on sender’s side and decrypted on receiver’s side.
This distinguishes OTR from other encryption methods. For example, almost every messenger (including IM+) uses SSL encryption to connect to its own server. But what happens then, when it connects to AOL, Facebook, ICQ or any other IM server? There is no guarantee that messages are encrypted there and on the way to your contact.
But if you use OTR, no matter how many servers are used to pass message from you to your contact – none of them is able to decrypt the message, it may be decrypted only on your contact’s smartphone or computer.
In short, it’s an encryption system that works with any service by creating encryption/decryption keys that only last for a short amount of time. As detailed on the Facebook post, Pidgin (for Windows) and Adium (for Mac) support OTR.