An On-Line Signal Encryption Method REZA ZARE Department of electronics, Faculty of engineering University of Birjand IRAN Ali A. Pouyan, member IEEE Department of computer, Faculty of engineering University of Birjand IRAN Abstract: - On-line Signal Encryption (OSE) is an efficient free platform interrupt driven and on- line method for encrypting different types of signals (data). The proposed method is a variant-bit block cipher approach, which is independent of the platform. In this paper we have implemented; as a case study, the method based on 64-bit block ciphers on a 8-bit microprocessor. OSE needs three blocks of RAM, and block size depends on the selected specific block cipher method in the peer entities (sender and receiver). Key-Words: - encryption, on-line, block cipher, audio signal, interrupt driven, method 1 Introduction The National Institute of Standard and Technology (NIST) issued the first request for an encryption standard in 1972 and 1974. This led to the development of Data Encryption Standard (DES), the most arguably wide spread algorithm for encryption [1]-[3]. The major drawback of DES is the fixed 64-bit block length; as common in most well-known ciphers, which can open it up for attacking when large amount of data being encrypted under the smart key [4]. In 1997, NIST introduced Advanced Encryption Standard (AES) in response to the desire to replace DES [5]. Through a public call, NIST intended to review all submissions in order to eventually, develop an emergent encryption standard to replace DES. In addition to the block cipher, the announced criteria designed by NIST were larger block size, longer key length, reducing encryption and decryption time and flexibility. It does not convey that AES is an optimized standard for all of the above-mentioned criteria. One of the most outstanding submissions that meet the NIST criteria is Twofish [6]. It is a 128-bit block cipher with 128-, 192-, and 256-bit key and has implemented on different platforms. In OSE all the block cipher methods like DES, FEAL[7], LOKI [8], etc. can be utilized in order to establish an on- line connection between the communicating entities. We have implemented OSE based on Fast Encryption Algorithm (FEAL) on a 8-bit microprocessor. 2 On-Line Signal Encryption The so-called OSE method proposed in this paper, is an efficient block cipher on-line encryption method, which uses three blocks of RAM for encryption/de- encryption different types of data between communicating entities. The length of the blocks depends on the selected specific block cipher method. In the first entity (sender), the blocks consist of Sampling Block (SB), Encryption Block (EB) and Transmitting Block (TB). In the second entity (receiver), these blocks are Receiving Block (RB), De-encryption Block (DB) and Broadcasting Block (BB). Furthermore, the proposed method is an interrupt driven system in peer entities. 2.1 Sender The method works based on a series of periodic induced hardware interrupts (e.g., these interrupts can be generated by an oscillator). While CPU is engaged with encrypting EB, an interrupt signal occurs. By accepting the interrupt, a sample; say an 8-bit (byte) one, is taken from the input (e.g., an ADC) and stored in SB. Then, a byte is taken from Proceedings of the 10th WSEAS International Conference on COMMUNICATIONS, Vouliagmeni, Athens, Greece, July 10-12, 2006 (pp17-20)