Theses Proposal

Theses Proposal Topic Title Submitted By

: Information Security : The Application of ATmega32 microcontroller in Secure communication over Telephone Line : Edi Permadi | Electrical Engineering 2005 | 002.2005.00005

Topic Discussion Now days, information means power. Sensitive information has to be passed through acknowledged client with no leakage. Hence, securing communication is becoming important to avoid eavesdropping. In addition, the avoidance of eavesdropping can be implemented as an embedded ciphering machine system through cryptography. The theses will concern with the application of an AVR microcontroller for the implementation of RC4 stream cipher in secure communication over Public Switched Telephone Network (PSTN). This implementation is intended for civilian use of secure communication such as banking transaction, managerial purposes and trade secret purposes. Public Switched Telephone network is a common and widely used communication channel. This communication channel is unsecure due to the absence of encryption as well as authentication. The implementation of secured communication channel is provided by encapsulating digitized and compressed voice through RC4 stream cipher with certain secret key agreed by those two parties. Secret key is distributed securely through Diffie-Hellman key exchange algorithm. A new session key is derived from user’s secret key with the assistance of Pseudo Random Number Generator (PRNG) and Environment Driven Random Number Generator (EDRNG) on each telephone call. RC4 is a well known, widely used and unpatented stream cipher algorithm invented by Ronald Rivest of MIT. RC4 is mainly used is Wireless Exchange Protocol (WEP) in wifi and other commercial hardware and software. The RC4 stream cipher is compact, simple and fast so that it can be directly adapted on 8-bit platform such as AVR ATMega32 microcontroller from Atmel. In addition, voice compression is done by using ADPCM method that stores differences of samples instead of samples itself. Prior to key exchange process, Diffie Hellman Key Exchange (DF-KEA) is a well known key secure key exchange algorithm that lays on the difficulty of factoring large prime number. The implementation of ciphering machine will be done as an embedded system. The embedded system will masquerade the ordinary telephone device with some additional security features buried inside. Each of those devices will contain: user interface, user interface and events handler, analog interface and crypto-RNG engine. The structural arrangement is shown below.

User interface is the part of embedded system that enables interactive process between user and embedded system. This part contains keypad, LCD, calling indicator and hook detection. This part is merely a group of user interface and has no dedicated microcontroller inside. The user interface and event handler module occupies the function of controlling keypad and LCD, displaying texts and images to LCD, providing user interface menu, character patterns, handling incoming calls, handling outgoing calls, detecting hooks activities as well as coordinating all modules to work together. This function is done by a single dedicated AVR microcontroller. The Crypto-RNG module is implemented as a dedicated AVR microcontroller that provides cryptographic functions (ciphering and deciphering), key exchange calculation and random number generation. The pseudo random number generator is calculated inside the microcontroller itself wile the true random number is sampled from environment through analog interface. The secret session key is generated in between 0 to (22048 – 1) therefore random generated number has to be in that margin also. In addition the key exchange has to be able to calculate the equation y = a b mod n where all parameters are in between 0 to (22048 – 1). The analog interface provides the pre amplification of conversation voices and external noise as random number source, A/D and D/A conversion and telephone line handling. For the sake of simplicity, the telephone line handling is done by another processor which is external modem. The communication between cipher machine and external modem is provided by AT command protocol through asynchronous serial line. In order to synchronize calling initiator and calling acceptor, the communication will be encapsulated by simple protocol that provides packet identification, frame identification and transmitted data itself and checksum.