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)

TB and delivered to a serial port for transmission. The RAM blocks in sender are shown in Figure 1.

Figure 1. RAM blocks in sender

It should be noted that when sampling block (SB) is filled with the taken samples and transmitting block (TB) is empty, CPU should already have finished the encryption process on EB. This enables CPU to copy the content of encryption block (EB) to TB for transmission and copy the content of SB to EB for encryption. Since the encryption process is time consuming, CPU should be fast enough to handle the entire procedure in terms of encryption stages. The flow diagram of the procedure is shown in Figure 2.

in te rru p t s e rv ic e ro u t in e

c o p y ((T B p o in te r)) to (s e ria l p o rt ) (T B p o in te r) = (T B p o in te r) + 1

c o p y (in p u t p o rt ) to ((S B p o in te r)) (S B p o in te r) = (S B p o in te r) + 1

(S B p o in te r) = la s t a d d re s s b y te o f S B ?

c o p y E B to T B c o p y S B to E B

(S B p o in te r) = firs t a d d re s s b y te o f S B (T B p o in te r) = firs t a d d re s s b y te o f T B

re tu rn fro m in te rru p t

N O

Y E S

Figure 2. Sender interrupt service routine

In Figure 2, SB and TB pointer denote the RAM addresses, which point to the objects that specify the addresses of the specific bytes in SB and TB, respectively. Therefore, (SB pointer) is the address of a designated byte in SB and ((SB pointer)) denotes the specific byte in SB. Analogously, ((TB pointer)) specify a byte in TB.

2.2 Receiver In receiver three blocks of RAM are considered as depicted in Figure 3.

Figure 3. RAM blocks in receiver

The receiver works based on interrupts. While CPU is engaged with de-encrypting (DB), a byte is received from the serial port and an interrupt signal; generated by the serial port controller, occurs. By accepting the interrupt, the received byte; is taken from the serial port and stored in RB. Then, a byte is taken from BB and delivered to the output port (e.g., a digital analog converter; DAC). The flow diagram of the receiver is shown in Figure 4. It should be noted that when receiving block (RB) is filled with the received bytes and broadcasting block (BB) is empty, CPU should already have finished the de-encryption process on de-encryption block (DB). This enables CPU to copy the content of DB to BB for transmission to output port and copy the content of RB to DB for de-encryption.

Proceedings of the 10th WSEAS International Conference on COMMUNICATIONS, Vouliagmeni, Athens, Greece, July 10-12, 2006 (pp17-20)

in te rru p t s e rv ic e ro u t in e

c o p y ((B B p o in te r)) to (o u tp u t p o rt ) (B B p o in te r) = (B B p o in te r) + 1

c o p y (s e ria l p o rt ) to ((R B p o in te r)) (R B p o in te r) = (R B p o in te r) + 1

(R B p o in te r) = la s t a d d re s s b y te o f R B ?

c o p y D B to B B c o p y R B to D B

(R B p o in te r) = firs t a d d re s s b y te o f R B (B B p o in te r) = firs t a d d re s s b y te o f B B

re tu rn fro m in te rru p t

N O

Y E S

Figure 4. Receiver interrupt routine 3 Empirical Results In this section the proposed on-line signal encryption method is implemented for on-line transmission of audio signals on a an8-bit microprocessor based on FEAL. The audio signals should be filtered first, in sender. Then these signals are sampled by an at least doubled band width of the filtered signals. The process of transmission-encryption/de-encryption-receiving is based on the flow diagrams of Figures 2 and 4. The block diagrams of sender and receiver are shown in Figure 5 and Figure 6, respectively.

Line Driver

Display Input

Output Serial PortOscillator (62.5 kHz)

RAMCPU

Address Decoder Oscillator

Sample& Hold

Amplifier Low-Pass-Filter

A/D convertor

ROM

MicMIC

Coaxial Cableint

Figure 5. Block diagram of sender

Line Receiver

Display Input

Serial PortOscillator (62.5 kHz)

RAMCPU

Address Decoder Oscillator

Low-Pass-FilterD/A convertor

ROM

Speaker

From Coaxial Cableint

Figure 6. Block diagram of receiver

4 Conclusion and Future Work In this paper we presented an On-line interrupt driven Encryption Method that can be implemented on different platforms and based on different encryption algorithms. Furthermore, it is a variant-bit block cipher method, which makes it very flexible in terms of application purposes. We have implemented the presented method on an8-bit microprocessor as a case study. The future trend of this research can be outlined as follows. The proposed method at this stage is based on a simplex mode (unidirectional). It can be extended to duplex mode. In terms of implementation the method has been tested on an 8-bit processor. Extending the trials to other types of processor can lead to significant results. In this paper, the implementation is based on FEAL, while applying other encryption algorithms like DES, Twofish, etc. can be investigated for probable better results. In terms of applicability, data compression can be applied on samples. This leads to a significant reduction in the size of transmitted data per unit of time. As a result, data compression reduces the maximum bandwidth in transmission medium and makes it possible to transmit data on ordinary telephone lines with 3 kHz bandwidth capacity. References: [1] W.E. Madryga, A High Performance Encryption

Algorithm, Computer Security: A Global Challenge, Elsevier Science Publishers, 1984, pp. 557-570.

[2] J. L. Massey, SAFER K-64: A byte-oriented block-ciphering algorithm, Fast software

Proceedings of the 10th WSEAS International Conference on COMMUNICATIONS, Vouliagmeni, Athens, Greece, July 10-12, 2006 (pp17-20)

encryption, Cambridge security workshop proceedings, Springer-Verlag, 1994, pp. 1-17.

[3] M. Matsui, Linear cryptanalysis method for DES cipher, Advances in cryptology EUROCRYPT ’93 proceedings, Springer-Verlag, 1994, pp. 386-397.

[4] M. J. Wiener, Efficient DES key search, TR-244, School of computer science, Carleton University, May 1994.

[5] National Institute of Standard and Technology,” Announcing request for candidate algorithm nominations for Advanced Encryption Standard (AES),” Federal register, Vol. 62, n. 117, 12 Sep 1997, pp. 48051-48058.

[6] B. Schneir et. al., Twofish: A 128-Bit Block Cipher, electronic paper located at the following URL, http://www.counterpane.com/twofish.html, June 1998.

[7] J. Miaguchi, The FEAL cipher fmily, Springer-Verlag, 1990, Advances in cryptology, pp. 627-638.

[8] L. Brown, J. Pieprzyk and J. Seberry, LOKI: cryptographic primitive for authentication and secrecy applications, Springer-Verlag, 1990, Advances in cryptology, pp. 229-236.

Proceedings of the 10th WSEAS International Conference on COMMUNICATIONS, Vouliagmeni, Athens, Greece, July 10-12, 2006 (pp17-20)