AVR bootloader/firmware updater

I'm looking to have a developer develop a bootloader for the AVR Atmega 328 to provide the ability to update the firmware on the chip in the field. This will be accomplished by a PC application supplying the encrypted firmware over a serial connection. The AVR will boot up into bootloader mode, and accept and decrypt the firmware. Finally, it will flash the firmware. This job is 4 fold: * Develop a bootloader for the AVR Atmega328 * Develop a secure firmware file format to be streamed to the target device * Develop an application to download the firmware to the AVR. Otherwise, an Xmodem transfer could be used. * Also, an application must be designed to take a standard .hex file that a program compiled from AVR Studio into an encrypted firmware file for the bootloader to flash.