Within thesis we developed an application prototype of the safe communication across portable devices with Android operation system. Application offers safe sending and receiving of text messages along with the other multimedia content like images, videos and sound recordings. XML packets are used for transferring data. Text content is stored and transferred inside the packet, for other multimedia content the packet contains the identification number, which is used by the application to access the actual content, which is stored on external database and present it as part of the message. Apart from sending and receiving, application also offers safe storing for all content, which is stored in encrypted form.
Communication between devices is indirect. Message is transferred from the device, where the message was created, to the server system which sends the message to the devices, which are listed in the message as receivers. In case of offline devices, system holds the message and delivers the message when devices are online.
XMPP technology is used for transferring messages and HTTP requests are used for accessing and storing data in the external database. For protection are used symmetric encryption AES and asymmetric encryption RSA. For the integrity and authentication is used HMAC. Java language is used for the implementation of all necessary technologies.