Real-time DSP Implementations of Voice Encryption Algorithms Cristina-Loredana Duta1, Laura Gheorghe2 and Nicolae Tapus1 1Department of Computer Science and Engineering, University Politehnica of Bucharest, Bucharest, Romania 2Research and Development Department, Academy of Romanian Scientists, Bucharest, Romania [email protected], {laura.gheorghe, nicolae.tapus}@cs.pub.ro Keywords: Digital Signal Processor, Voice Encryption, Blackfin Processor, TMS320C6X Processor, AES, RSA, NTRU. Abstract: In the last decades, digital communications and network technologies have been growing rapidly, which makes secure speech communication an important issue. Regardless of the communication purposes, military, business or personal, people want a high level of security during their conversations. In this context, many voice encryption methods have been developed, which are based on cryptographic algorithms. One of the major issues regarding these algorithms is to identify those that can ensure high throughput when dealing with reduced bandwidth of the communication channel. A solution is to use resource constrained embedded systems because they are designed such that they consume little system resources, providing at the same time very good performances. To fulfil all the strict requirements, hardware and software optimizations should be performed by taking into consideration the complexity of the chosen algorithm, the mapping between the selected architecture and the cryptographic algorithm, the selected arithmetic unit (floating point or fixed point) and so on. The purpose of this paper is to compare and evaluate based on several criteria the Digital Signal Processor (DSP) implementations of three voice encryption algorithms in real time. The algorithms can be divided into two categories: asymmetric ciphers (NTRU and RSA) and symmetric ciphers (AES). The parameters taken into consideration for comparison between these ciphers are: encryption, decryption and delay time, complexity, packet lost and security level. All the previously mentioned algorithms were implemented on Blackfin and TMS320C6x processors. Making hardware and software level optimizations, we were able to reduce encryption/decryption/delay time, as well as to reduce the energy consumed. The purpose of this paper is to determine which is the best system hardware (DSP platform) and which encryption algorithm is feasible, safe and best suited for real-time voice encryption. 1 INTRODUCTION There are two distinct approaches to achieve speech security: analogue scrambling and digital Security and privacy represent a fundamental issue ciphering. In the past, the researchers have been when transmitting information through insecure interested in speech scrambling because it uses small communication channels. bandwidth, has simple implementations and good There are many channels available for capabilities when dealing with asynchronous transmitting speech signals, for instance telephone transmission. networks and private or public radio communication The purpose of voice coders in digital systems. Speech signal can be represented in two telecommunication systems is to reduce the required forms: analogue and digital form. In analogue transmission bandwidth. Several vocoders have been representation, it is a waveform which describes the invented – LPC-10 (Linear Prediction Coding), frequency and amplitude of the signal. In digital CELP (Code Excited Linear Prediction), MELP form, it is the numeric representation of the analogue (Mixed Excitation Linear Prediction) and so on. In form, where the signal is composed of zeros and ones. general, secure communication systems are based on There are some situations when the information LPC techniques. The main reason is that LPC voice transmitted has to be confidential, such as diplomatic coding can ensure low bit rates and high voice and military communications during war and peace. intelligibility. Since speech has a lot of redundancy compared with Applications that use cryptographic algorithms written text, it becomes a very difficult task to provide often demand a set of strict requirements for security for it. implementations, such as low resource consumption, 439 Duta, C-L., Gheorghe, L. and Tapus, N. Real-time DSP Implementations of Voice Encryption Algorithms. DOI: 10.5220/0006208304390446 In Proceedings of the 3rd International Conference on Information Systems Security and Privacy (ICISSP 2017), pages 439-446 ISBN: 978-989-758-209-7 Copyright c 2017 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved ICISSP 2017 - 3rd International Conference on Information Systems Security and Privacy reduced number of logic gates and memory, and implementation of the system in detail. In Section 5 efficient power consumption. In this context, we present the results of the real-time designing implementations that fulfil all these implementations of the algorithms and a comparison requirements it’s a very challenging task and between them based on several criteria. The represents a wide area of research. conclusions and future work are summarized in More specifically, an implementation should be Section 6. fast enough to make sure that the execution of the cryptographic algorithms doesn’t slow down the system significantly. This can be achieved by 2 BACKGROUND hardware acceleration (because it has been demonstrated that software implementations cannot This section includes a brief description of the achieve the desired level of performance with implemented cryptographic algorithms: symmetric reasonable costs (Pedre, 2016) and (Joao, 2009)). cipher such as AES and asymmetric ciphers such as Regarding the available resources, only a small part RSA and NTRU, and the description of general of them are dedicated to cryptography, which makes aspects of DSP architectures used: Blackfin ADSP- implementing high-security algorithms very BF537 and TMS320C6711. complicated. Another important point for secure voice 2.1 Speech Scrambling Techniques communications is real-time processing. In this case, the aspect of framing of the incoming data becomes There are several types of analogue voice scrambling, an essential task. A good balance of the block size and which are described further on. all the parameters has to be found (short buffers can Time domain scrambling – the voice is being cause buffer overflow and large buffers can lead to recorded for some time and then is cut into small delays depending on the sampling rate). frames, which are transmitted in a different time Because the cryptographic algorithms are order, based on a secret code. The main disadvantage complex, they need to be implemented on flexible of this technique is the fact that the signal has the platforms in order to meet real-time requirements for same frequencies as before, which makes it easy to voice encryption. In this context, we have chosen for recover basic information. our implementations two DSP hardware platforms Frequency domain scrambling – the frequencies from Texas Instruments: Blackfin ADSP-BF537 and of the voice are being inverted. The main problem is TMS320C6711. that the fundamental characteristics of the voice In this paper, we study implementations of signal are not significantly changed which makes this cryptographic algorithms on existing embedded technique vulnerable. architectures. We took into consideration three Amplitude domain scrambling – the amplitude of algorithms, evaluate their performance (in terms of the signal is modified, but this doesn’t really change encryption/decryption/delay time), their complexity, the signal. packet loss, security level as well as their power Compared with analogue scrambling, digital consumption. We implemented symmetric and encryption is a much stronger method of protecting asymmetric algorithms on DSP platforms and speech communications. The main advantage is that explored how to make use of the existing architectural it doesn’t matter what kind of signal is being features to provide the best mapping between encrypted (text, video, voice and so on). Moreover, cryptographic processing and the target embedded there are little possibilities for cryptanalysis systems and how to reduce the energy consumption. compared to analogue scrambling. On the other side, We performed step by step optimizations in order to if the data is being corrupted, it will not be decrypted meet real time requirements with the purpose to correctly (degradation of voice quality) and if the data determine which encryption algorithm and which are lost, then the synchronization and communication hardware platform is best suited for real time secure will be lost. communications. Cryptographic algorithms can be classified based The remaining of the paper is organized as on the number of keys that are used in the follows. Section 2 presents a brief overview of the encryption/decryption process. Secret Key cryptographic algorithms and of the DSP platforms Cryptography (SKC) uses a single key for both considered in this paper. In Section 3 the related work encryption and decryption (AES, for example). is described. Section 4 includes our optimization Public Key Cryptography (PKC) uses one key for approach and experimental setup as well as the encryption and another for decryption and includes 440 Real-time DSP Implementations of Voice Encryption Algorithms algorithms such as: NTRU, RSA and Elliptic Curve 2.5 DSP Platforms Cryptography (ECC). Because intensive processing operations are 2.2 AES Block Cipher performed during