Secure Text Communication for the Tiger XS

Abstract: The option of communicating via SMS messages can be considered available in all GSM networks. It therefore constitutes a almost universally available method for mobile communication. The Tiger XS, a device for secure communication manufactured by Sectra, is equipped with an encrypted text message transmission system. As the text message service of this device is becoming increasingly popular and as options to connect the Tiger XS to computers or to a keyboard are being researched, the text message service is in need of upgrade. This thesis proposes amendments to the existing protocol structure. It thoroughly examines a number of options for source coding of small text messages and makes recommendations as to implementation of such features. It also suggests security enhancements and introduces a novel form of stegangraphy.