A new speech encryption algorithm based on dual shuffling Hénon chaotic map

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 11, No. 3, June 2021, pp. 2203~2210
ISSN: 2088-8708, DOI: 10.11591/ijece.v11i3.pp2203-2210  2203
Journal homepage: http://ijece.iaescore.com
A new speech encryption algorithm based on dual shuffling
Hénon chaotic map
Obaida M. Al-hazaimeh
Department of Computer Science and Information Technology, Al-Balqa' Applied University, Jordan
Article Info ABSTRACT
Article history:
Received May 21, 2020
Revised Sep 23, 2020
Accepted Oct 4, 2020
Over the past few decades, many algorithms have been proposed to improve
the performance of speech encryption over un-secure channel (i.e., Internet).
In this paper, the security level was enhanced using a dynamic dual chaotic
based on Hénon chaotic map. In the proposed algorithm, the speech elements
are shuffled in a random fashion. Moreover, when both Hénon state variables
are free to be used for shuffling the index is toggled randomly between them
according to toggle bit. After index shuffling each speech element is
modified with XOR operation between the original speech element value and
the key that is selected randomly from the updated key table. The same
chaotic map is used to initiate the empty or full table and provide new table
entries from the values that are already shuffled. The experimental results
show that the proposed crypto-system is simple, fast with extra random
toggling behavior. The high order of substitution make it sensitive to initial
condition, common cryptanalysis attacks such as linear and differential
attacks are infeasible.
Keywords:
Chaotic system
Cryptography
Hénon map
Speech signal
This is an open access article under the CC BY-SA license.
Corresponding Author:
Obaida M. Al-hazaimeh
Department of Computer Science and Information Technology
Al-Balqa' Applied University
Irbid 21163, Jordan
Email: dr_obaida@bau.edu.jo
1. INTRODUCTION
Multimedia data is one of the most fundamental forms of human communications. Today, security
and privacy are the two major requirements in the civilian and military applications to design and develop
robustness crypto-systems for multimedia data (i.e., speech) [1, 2]. Cryptography is a technique that holds
themultimedia data communications secure and incomprehensible to un-authorized access over the un-secure
channel (i.e., internet) and provide many security related services (i.e., non-repudiation, authentication, and
integrity) [3-5]. Generally, cryptography is classified into four categories as shown in Figure 1.
Most of the conventional cryptographic algorithms are built to protect the content test messages
which are not suitable for multimedia data (i.e., speech) during communication because it involves some
inherent features such as encryption and decryption process of speech is diﬀerent from that test messages,
and data redundancy [6]. In recent years, extensive studies have been observed in the research community to
apply a various algorithms based on chaos cryptographyto design a robustness crypto-system for multimedia
data due to it is desirable features such as non-linear, deterministic, aperiodicity, sensitivity to initial
conditions, and un-regular behaviours (i.e., random-like performance) [6-14], but unfortunately there are
fundamental drawbacks in these chaotic crypto-systems in terms of cryptanalysis attacks (i.e., low level of
security, and small key space) [15, 16]. In general, chaotic crypto-systems can be classified into three
categories based on their structure (i.e., analogue, or digital chaotic) each category represented by different

 ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 11, No. 3, June 2021 : 2203 - 2210
2204
equations (i.e., differential, and partial differential) [11, 17-19]. Figure 2 illustrated the classification of
chaotic systems with examples.
Figure 1. Classification of cryptology
Figure 2. Categories of chaotic system
In this paper we have used chaos based cryptography (i.e., chaotic cryptography) to propose a new
dynamic speech crypto-system using Hénon chaotic map to overcome the aforementioned drawbacks. The
rest of this paper including the introduction is organized into seven sections as follows: Section 2 provides an
overview of Hénon map. The next section i.e. section 3, describes the proposed algorithm. Section 4 presents
and discusses the experimental results. Section 5 elaborates the security and performance analyses of the
proposed speech crypto-system. A comparison with existing work (i.e., state-of-art) is given in section 6. The
last section, i.e. section 7, concludes the paper.
2. HÉNON MAP
In the late 1946's the "Hénon map" was developed as a simplified for Lorenz map and named after
its developer, M. Henon [18-20]. This chaotic map is a dynamical system (i.e., discrete-time) is presented by:
{
where, the control parameters for Hénon map are a and b. This map is chaotic when a = 1.4 and b = 0.3 (i.e.,
classical values). In (1) exhibits a strange attractor for other control parameters values (i.e., a, and b). The
chaotic attractor and the largest lyapunov exponent (i.e., maximum) of values for Hénon map are plotted in
Figures 3 and 4.

Int J Elec & Comp Eng ISSN: 2088-8708 
A new speech encryption algorithm based on dual shuffling Hénon chaotic map (Obaida M. Al-hazaimeh)
2205
Figure 3. Chaotic attractor Figure 4. The plot of largest lyapunov exponents
3. PROPOSED ALGORITHM
In the proposed crypt-system, Hénon map as an example, in (1) is selected to be used from the
chaotic maps in the encryption process. In Figure 5 (in Appendix) the block diagram of the proposed
encryption process is presented. The proposed speech crypt-system involves a series of sequential steps are
presented in Algortihm 1.
Algorithm 1: Encryption
1. Initialization. In this step, an empty cipher vector C and a flag vector F which has same length l of the
one dimensional plain speech frame , where j=132, represents the size of a 20-ms speech frame in
{ }each element is an 8-bit representation of the bit 0 (BIT-0: FF81) or the bit 1 (BIT-1:
007F) of the coder parameters which is codified on 8 bits. Finally, an empty key table is created with 0
initial pointer and toggle bit is also initiated to zero.
2. The input conditions are initiated as follow (Xn+1 = 1 + Yn – αXn2
, Yn+1 = βXn, with β = 0. 3 and
α = 1.4), and the Hénon map is iterated 100 times to eliminate the transient effect.
3. In this step, the Hénon map is iterated once, and the result is converted into speech frame index lj is
done based on (lj1= xn+1*1014
mod l, lj2=yn+1*1014
mod l).
4. Test the flag bit against both lj1and lj2, if both flag bit of the 8-bit index are true (1) (i.e., exists in step
3), so, go back to the previous step (i.e., step 3). If one of them is true, the other one will be used as
index for shuffling. If both flags are false, in this case the toggle bit is used to select between the two
indices and the toggle bit is inverted. Otherwise, the index with false flag either lj1orlj2 will be utilized as
new location for shuffling process.
5. Here, the key table is checked, if it is empty or all its contents are used (Key_P=0 or Key_P=table size),
then, a single iteration of Hénon map is performed to add a new entry to key table based on XOR
operation as follow: (lj1 = xn+1*1014
mod 132, lj2=yn+1*1014
mod 132, Key_T (Key_p+1) = lj1lj2).
6. As a next step, the current 8-bit speech element Bj is encrypted using key bit value and XOR operation,
then the result is stored in the cipher vector C(ljb) according to the shuffled location. After that, the
pointer of the key table is updated and the flag bit of the encrypted element is set to 1 based on ((Ci (ljb)
= Key_T (Key_P)Bj, Key_P=Key_P+1, F(ljb) = 1).
7. Repeat step 3 to complete encryption for all speech elements.
On the other hand, the ciphered speech elements need to receive the proposed crypto-system parameters
including the generated keys (i.e., secret) and follow Algorithm 1 (i.e., encryption steps) in reverse order for
decryption process.
4. EXPERIMENTAL RESULTS
In this paper, some subjective tests were conducted including several speech samples (i.e., TIMIT
database) with different sampling rate (i.e., 5000 samples/sec, and 8000 samples/sec) [21]. The obtained
results are presented in this sectionto demonstrate the efficiency (i.e., security level) of the proposed speech
encryption algorithm. The histograms of the input speech, ciphered speech, spectrogram (i.e., original speech,
ciphered, and decrypted), and the decrypted speech are presented in Figure 6. Our simulation is conducted on
LENOVO E320 with a 1.8 GHz core (TM) i5-8250U CPU, 1-TB hard disk, and 4-GB RAM with MATLAB
(R2013a)software.

 ISSN: 2088-8708
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(a) (b)
(c) (d)
(e) (f)
Figure 6. Histogram and Spectrogram analysis; (a) original speech, (b) spectrogram for original speech,
(c) ciphered speech, (d) spectrogram for ciphered speech, (e) decrypted speech, (f) spectrogram for decrypted
speech
5. SECURITY ANALYSIS
In general, the security analyses must be satisfied when a new chaotic crypto-system is proposed.
A perfect chaotic crypto-system should be robust against all kinds ofcryptanalysis attacks (i.e., brute-force,
statistical, etc) [22, 23]. Therefore, we have performed some security analyses to demonstrate the
effectiveness of the proposed algorithm (i.e., security level). In this paper, as an example, in (2) is used to
calculate the correlation coefficients.
∑( )( )
√ √ (2)
The security tests values for diﬀerent tests (i.e., correlation, ENT, DIEHARD, and NIST) are
calculated and listed in Table 1. Additionally, the excellent quality of the encrypted speech must be sensitive
in extreme way with respect to the secret keys [24, 25] to ensure the security procedure against brute-force
attacks. In the proposed algorithm, any small variation (i.e., bit flip) on the sensitivity factors (i.e., index
location, keys, and other encryption parameters) that would generate a decryption speech signals which is
completely different from the original signals as shown in Figure 7.

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Table 1. Security analysis
TESTS
Correlation Test
[22, 26]
Speech samples Original speech Encrypted speech DECISION
Speech_1 0.99016 0.000763 Statistical attacks - Secure
Speech _2 0.98126 0.000829
ENT Test
[27, 28]
Test Obtained value Theoretical value DECISION
Entropy 7.989896 Close to 8 Cryptanalysis attacks -Secure
Serial correlation 0.0000981 Close to 0
Chi-square coefficient 127.5007 Close to 127.5
DIEHARD Tests
[29, 30]
Success range p-value RESULT DECISION
0.01 - 0.99 Within the range Passed all tests Cryptanalysis attacks -Secure
NIST Tests
[24, 31]
Success range p-value RESULT DECISION
0.01 - 0.99 Within the range Passed all tests Cryptanalysis attacks -Secure
(a) (b)
(c)
Figure 7. Sensitivity analysis, (a) original speech, (b) decryption with incorrect index, (c) decryption with
incorrect key
6. COMPARISON WITH EXISTING WORKS
In this section, a comparison is made between the average time needed in our proposed speech
encryption algorithm with some of existing algorithms (i.e., advanced encryption standard) in both of
encryption and decryption processes (i.e., delay budget). To be more accurate, the proposed algorithm and
AES have been implemented and tested and evaluated in the same environment same platform and same
conditions (i.e., parameters). The results of that test are presented in Table 2. The line charts showing the
relationship between the proposed algorithm delay time and AES delay time in both cases (i.e., encryption,
and decryption) are shown in Figures 8 and 9 respectively.
It is clear from Table 2 the average time needed (i.e., delay time) to encrypt and decrypt the speech
packet using the proposed algorithm is much smaller than that in AES algorithm. The ratio is about 1:2 which
make the proposed algorithm is considered to be big for this type of application such as Internet speech
applications.

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Table 2. Time requirement
METHOD ENCRYPTION DECRYPTION
Trial No. Delay Trial No. Delay
AES 1 1.083813452 1 1.105283425
2 1.047655243 2 1.098274552
3 1.088726224 3 1.100422763
4 1.038455265 4 1.099819762
5 1.090726228 5 1.108687613
Average (ms) 1.069875282 Average (ms) 1.102497623
PROPOSED Trial No. Delay Trial No. Delay
1 0.43038297 1 0.58374982
2 0.41227197 2 0.60214912
3 0.41497785 3 0.54877941
4 0.39352131 4 0.60125153
5 0.64924367 5 0.54177679
Average (ms) 0.460079554 Average (ms) 0.575541334
Figure 8. Average time for encryption process
Figure 9. Average time for decryption process
7. CONCLUSION
In this paper we have achieved our objectives of proposing a new dynamic dual chaotic based on
Hénon chaotic map to enhance the multimedia data services (i.e., security level, reduces delay time). Our
methodology was divided into three processes: initialization for flag, Hénon map, key table, key pointer, and
toggle bit and encryption and decryption process. In the encryption process, the speech elements are shuffled
in a random fashion. Moreover, when both Hénon state variables are free to be used for shuffling the index is
toggled randomly between them according to toggle bit. After index shuffling each speech element is
modified with XOR operation between the original speech elements value and the key that is selected in a
random fashion from the updated key table. The same chaotic map is used to initiate the empty or full table
and provide new table entries from the values that are already shuffled. The experimental results show that
the cryptanalysis attacks such as linear and differential attacks are infeasible in the proposed crypto-system.
In addition, the delay budget (i.e., delay time) of the proposed crypto-system is made compare to AES (i.e.,
existing algorithms) and the results endorse that the proposed crypto-system has the lowest average delay
time, the ratio is about 1:2.

2209
APPENDIX
Figure 5. Block diagram
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BIOGRAPHY OF AUTHOR
Obaida M. Al-Hazaimeh received his BSc in Computer Science from Applied Science
University, Jordan in 2004 and MSc in Computer science from University Science Malaysia,
Malaysia, in 2006. He received his PhD degree in Network Security (Cryptography) from
Malaysia in 2010. He is an associate professor at department of computer science and
information technology, Al-Balqa' Applied University, Jordan. His main research interests are
cryptology, image processing, machine learning, and chaos theory. He has published more than
36 papers as author and Co-author in international refereed journals.

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