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<front>
<journal-meta>
<journal-id journal-id-type="pmc">CSSE</journal-id>
<journal-id journal-id-type="nlm-ta">CSSE</journal-id>
<journal-id journal-id-type="publisher-id">CSSE</journal-id>
<journal-title-group>
<journal-title>Computer Systems Science &#x0026; Engineering</journal-title>
</journal-title-group>
<issn pub-type="ppub">0267-6192</issn>
<publisher>
<publisher-name>Tech Science Press</publisher-name>
<publisher-loc>USA</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">36652</article-id>
<article-id pub-id-type="doi">10.32604/csse.2023.036652</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Article</subject>
</subj-group>
</article-categories>
<title-group>
<article-title>A Cross-Plane Color Image Encryption Algorithm Based on 1D-SLM</article-title><alt-title alt-title-type="left-running-head">A Cross-Plane Color Image Encryption Algorithm Based on 1D-SLM</alt-title><alt-title alt-title-type="right-running-head">A Cross-Plane Color Image Encryption Algorithm Based on 1D-SLM</alt-title>
</title-group>
<contrib-group>
<contrib id="author-1" contrib-type="author">
<name name-style="western"><surname>Wang</surname><given-names>Xiaohong</given-names></name>
</contrib>
<contrib id="author-2" contrib-type="author">
<name name-style="western"><surname>Wu</surname><given-names>Huiqing</given-names></name>
</contrib>
<contrib id="author-3" contrib-type="author">
<name name-style="western"><surname>Ma</surname><given-names>Yuying</given-names></name>
</contrib>
<contrib id="author-4" contrib-type="author" corresp="yes">
<name name-style="western"><surname>Huang</surname><given-names>Shuzhen</given-names></name><email>sdgc_whq@suet.edu.cn</email>
</contrib>
<aff id="aff-1"><institution>School of Artificial Intelligence, Shandong Vocational and Technical University of Engineering</institution>, <addr-line>Jinan, 250200</addr-line>, <country>China</country></aff>
</contrib-group><author-notes><corresp id="cor1"><label>&#x002A;</label>Corresponding Author: Shuzhen Huang. Email: <email>sdgc_whq@suet.edu.cn</email></corresp></author-notes>
<pub-date date-type="collection" publication-format="electronic"><year>2023</year></pub-date>
<pub-date date-type="pub" publication-format="electronic"><day>17</day><month>1</month><year>2023</year></pub-date>
<volume>46</volume>
<issue>1</issue>
<fpage>1093</fpage>
<lpage>1108</lpage>
<history>
<date date-type="received"><day>08</day><month>10</month><year>2022</year></date>
<date date-type="accepted"><day>15</day><month>11</month><year>2022</year></date>
</history>
<permissions>
<copyright-statement>&#x00A9; 2023 Wang et al.</copyright-statement>
<copyright-year>2023</copyright-year>
<copyright-holder>Wang et al.</copyright-holder>
<license xlink:href="https://creativecommons.org/licenses/by/4.0/">
<license-p>This work is licensed under a <ext-link ext-link-type="uri" xlink:type="simple" xlink:href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</ext-link>, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</license-p>
</license>
</permissions>
<self-uri content-type="pdf" xlink:href="TSP_CSSE_36652.pdf"></self-uri>
<abstract><p>With the rapid development of 5G technology, it has become fast and easy for people to transmit information on the Internet. Digital images can express information more intuitively, so transmitting information through images has excellent applications. This paper uses a new chaotic system called 1D-Sin-Logistic-Map (1D-SLM). 1D-SLM has two control parameters, which can provide larger parameter space, and the parameter space in the chaotic state is continuous. Through Lyapunov exponent analysis (LE), bifurcation diagrams analysis, spectral entropy analysis (SE), and 0-1 test, it is verified that 1D-SLM has complex dynamic behavior and is very suitable for cryptography. Compared with other 1D chaotic systems, the 1D-SLM has a larger Lyapunov exponent (LE) and spectral entropy (SE). For color image encryption algorithms, only relying on chaotic mapping is not enough to ensure security. So combined with 1D-SLM, we design a color image encryption algorithm, which is implemented by plane expansion, which reduces the correlation between the three channels of color images. The experimental results show that the proposed cross-plane color image encryption algorithm is safe and resistant to common attack methods.</p>
</abstract>
<kwd-group kwd-group-type="author">
<kwd>Chaos theory</kwd>
<kwd>chaotic system</kwd>
<kwd>1D-SLM</kwd>
<kwd>image encryption</kwd>
<kwd>information security</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<sec id="s1">
<label>1</label><title>Introduction</title>
<p>Digital images can express information more intuitively, so the transmission of information through images has great applications [<xref ref-type="bibr" rid="ref-1">1</xref>&#x2013;<xref ref-type="bibr" rid="ref-3">3</xref>]. The ensuing transmission process brings many security risks. Many image protection algorithms have been proposed nowadays [<xref ref-type="bibr" rid="ref-4">4</xref>&#x2013;<xref ref-type="bibr" rid="ref-8">8</xref>]. Chaos and cryptography have many similarities and connections [<xref ref-type="bibr" rid="ref-9">9</xref>&#x2013;<xref ref-type="bibr" rid="ref-11">11</xref>]. A chaotic system can generate a pseudo-random key stream with good performance, which is unpredictable and very suitable for cryptography [<xref ref-type="bibr" rid="ref-12">12</xref>&#x2013;<xref ref-type="bibr" rid="ref-14">14</xref>].</p>
<p>In order to design efficient and secure cryptosystems, image encryption algorithms combined with chaos have gradually become a hot field [<xref ref-type="bibr" rid="ref-15">15</xref>,<xref ref-type="bibr" rid="ref-16">16</xref>]. Kang et al. used two identical 4D chaotic systems to couple into an 8D chaotic system. The system has eight initial values and eight control parameters. The key stream of the cryptosystem is generated by this 8D chaotic system, and combined with 2D-VMD, a new image encryption method is proposed [<xref ref-type="bibr" rid="ref-17">17</xref>]. Yu et al. proposed a 6D fractional-order chaotic system called 6D-FMHNN. They studied this system&#x2019;s coexistence attractor characteristics and applied it to image encryption. The designed algorithm is secure and sensitive to secret keys [<xref ref-type="bibr" rid="ref-18">18</xref>]. Although high-dimensional chaotic systems have more control parameters and can provide a larger parameter space for cryptosystems, their keystream generation efficiency is not high [<xref ref-type="bibr" rid="ref-19">19</xref>&#x2013;<xref ref-type="bibr" rid="ref-21">21</xref>]. The low-dimensional chaotic system has smaller control parameters, and its key stream generation is efficient. However, the low-dimensional chaotic system has fewer control parameters. The cryptosystem is challenging to resist brute force attacks. This paper designs a new one-dimensional chaotic system called 1D-SLM. This chaotic system has two control parameters, an improvement on the Logistic map. The parameters corresponding to the chaotic region of 1D-SLM are continuous, and the chaotic region is wide, which is very suitable for the design of cryptographic systems.</p>
<p>For color image encryption algorithms, only relying on chaotic mapping is not enough to ensure security [<xref ref-type="bibr" rid="ref-22">22</xref>]. Zhou et al. used a one-dimensional chaotic system to generate multiple different key streams, using different signals to encrypt the three channels of the color image separately. The proposed encryption algorithm is simple and efficient [<xref ref-type="bibr" rid="ref-23">23</xref>]. Wang et al. used the hyperchaotic Lorenz system to generate the key stream of the cryptographic system. In order to enhance the security of the algorithm, they introduced the matrix semi-tensor product diffusion strategy. The encryption algorithm showed promising results on grayscale images. They extended this algorithm to color image encryption [<xref ref-type="bibr" rid="ref-24">24</xref>]. These algorithms encrypt the three channels of the plaintext image simultaneously, ignoring the correlation between the three channels. The attacker can obtain all the plaintext information by deciphering the content of one channel [<xref ref-type="bibr" rid="ref-25">25</xref>,<xref ref-type="bibr" rid="ref-26">26</xref>]. This paper proposes an encryption algorithm for the cross-plane, which treats the three channels as a whole, and the three channels interact with each other during encryption. This design structure increases the algorithm&#x2019;s security, can resist common attack methods, and ensures the security of color images during transmission.</p>
</sec>
<sec id="s2">
<label>2</label><title>Performance Analysis of the New Chaos System</title>
<sec id="s2_1">
<label>2.1</label><title>Existing One-Dimensional Chaotic Systems</title>
<p><xref ref-type="table" rid="table-1">Table 1</xref> gives some one-dimensional chaotic systems, including the analytic formulas and control parameters. In <xref ref-type="table" rid="table-1">Table 1</xref>, <inline-formula id="ieqn-1">
<mml:math id="mml-ieqn-1"><mml:msub><mml:mi>f</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math>
</inline-formula> is the initial value, <inline-formula id="ieqn-2">
<mml:math id="mml-ieqn-2"><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub></mml:math>
</inline-formula> is the iterative value. <italic>p</italic> and <italic>q</italic> are the control parameters.</p>
<table-wrap id="table-1"><label>Table 1</label>
<caption><title>Existing one-dimensional chaotic systems</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Name</th>
<th align="left">Expressions</th>
<th align="left">Parameters</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">Logistic map [<xref ref-type="bibr" rid="ref-27">27</xref>]</td>
<td align="left"><inline-formula id="ieqn-47">
<mml:math id="mml-ieqn-47"><mml:msub><mml:mi>f</mml:mi><mml:mrow><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>p</mml:mi><mml:mo>&#x22C5;</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula></td>
<td align="left"><italic>p</italic></td>
</tr>
<tr>
<td align="left">Cubic map [<xref ref-type="bibr" rid="ref-28">28</xref>]</td>
<td align="left"><inline-formula id="ieqn-48">
<mml:math id="mml-ieqn-48"><mml:msub><mml:mi>f</mml:mi><mml:mrow><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>p</mml:mi><mml:mo>&#x22C5;</mml:mo><mml:msubsup><mml:mi>f</mml:mi><mml:mi>n</mml:mi><mml:mn>3</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mi>p</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub></mml:math>
</inline-formula></td>
<td align="left"><italic>p</italic></td>
</tr>
<tr>
<td align="left">Sin map [<xref ref-type="bibr" rid="ref-29">29</xref>]</td>
<td align="left"><inline-formula id="ieqn-49">
<mml:math id="mml-ieqn-49"><mml:msub><mml:mi>f</mml:mi><mml:mrow><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>p</mml:mi><mml:mi>sin</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mi>&#x03C0;</mml:mi><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula></td>
<td align="left"><italic>p</italic></td>
</tr>
<tr>
<td align="left">1D-SMCLM [<xref ref-type="bibr" rid="ref-30">30</xref>]</td>
<td align="left"><inline-formula id="ieqn-50">
<mml:math id="mml-ieqn-50"><mml:msub><mml:mi>f</mml:mi><mml:mrow><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>p</mml:mi><mml:mi>sin</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mi>q</mml:mi><mml:mo>&#x22C5;</mml:mo><mml:mi>sin</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mi>&#x03C0;</mml:mi><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>&#x22C5;</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>+</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula></td>
<td align="left"><italic>p</italic> and <italic>q</italic></td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s2_2">
<label>2.2</label><title>New Chaos System 1D-Sin-Logistic-Map</title>
<p>The Logistic map has only one control parameter, the mapping range of the chaotic state is narrow, and the parameters are discontinuous. Therefore, we designed a new chaotic system named 1D-Sin-Logistic-Map (1D-SLM). The 1D-SLM is defined as,<disp-formula id="eqn-1"><label>(1)</label>
<mml:math id="mml-eqn-1" display="block"><mml:msub><mml:mi>f</mml:mi><mml:mrow><mml:mi>n</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>sin</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:msqrt><mml:mi>q</mml:mi></mml:msqrt><mml:mo>&#x22C5;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mi>p</mml:mi><mml:mo>&#x22C5;</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo>&#x22C5;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo stretchy="false">)</mml:mo><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>100</mml:mn><mml:mn>2</mml:mn></mml:msup><mml:mo>+</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">)</mml:mo><mml:mo>.</mml:mo></mml:math>
</disp-formula></p>
<p>In <xref ref-type="disp-formula" rid="eqn-1">Eq. (1)</xref>, <inline-formula id="ieqn-3">
<mml:math id="mml-ieqn-3"><mml:msub><mml:mi>f</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math>
</inline-formula> is the initial value, <inline-formula id="ieqn-4">
<mml:math id="mml-ieqn-4"><mml:msub><mml:mi>f</mml:mi><mml:mn>0</mml:mn></mml:msub><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula>. <inline-formula id="ieqn-5">
<mml:math id="mml-ieqn-5"><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub></mml:math>
</inline-formula> is the iterative value, <inline-formula id="ieqn-6">
<mml:math id="mml-ieqn-6"><mml:msub><mml:mi>f</mml:mi><mml:mi>n</mml:mi></mml:msub><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula>. <italic>p</italic> and <italic>q</italic> are control parameters, <inline-formula id="ieqn-7">
<mml:math id="mml-ieqn-7"><mml:mi>p</mml:mi><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:mo>+</mml:mo><mml:mi mathvariant="normal">&#x221E;</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula> and <inline-formula id="ieqn-8">
<mml:math id="mml-ieqn-8"><mml:mi>q</mml:mi><mml:mo>&#x2208;</mml:mo><mml:mo stretchy="false">(</mml:mo><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:mo>+</mml:mo><mml:mi mathvariant="normal">&#x221E;</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:math>
</inline-formula>.</p>
</sec>
<sec id="s2_3">
<label>2.3</label><title>Bifurcation Diagram of 1D-SLM</title>
<p>The bifurcation diagram reflects the trajectory of the nonlinear dynamic system from the periodic motion state to the chaotic motion state. The Bifurcation diagrams of 1D-SLM are shown in <xref ref-type="fig" rid="fig-1">Fig. 1</xref> under different parameter spaces. The Bifurcation diagrams of existing one-dimensional chaotic systems in <xref ref-type="table" rid="table-1">Table 1</xref> are shown in <xref ref-type="fig" rid="fig-2">Fig. 2</xref>. Compared with the Logistic map, Cubic map, Sin Map, and 1D-SMCLM, the 1D-SLM has a larger chaotic interval and more complex chaotic behavior.</p>
<fig id="fig-1">
<label>Figure 1</label>
<caption><title>Bifurcation diagrams of 1D-SLM</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-1.tif"/>
</fig><fig id="fig-2">
<label>Figure 2</label>
<caption><title>Bifurcation diagrams of existing one-dimensional chaotic systems</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-2.tif"/>
</fig>
</sec>
<sec id="s2_4">
<label>2.4</label><title>Lyapunov Exponents Analysis</title>
<p>Lyapunov exponents analysis is one of the most effective means of evaluating the dynamic behavior of nonlinear dynamical systems. The LE is defined as [<xref ref-type="bibr" rid="ref-31">31</xref>,<xref ref-type="bibr" rid="ref-32">32</xref>],<disp-formula id="eqn-2"><label>(2)</label>
<mml:math id="mml-eqn-2" display="block"><mml:mi>L</mml:mi><mml:mi>E</mml:mi><mml:mo>=</mml:mo><mml:munder><mml:mrow><mml:mo form="prefix">lim</mml:mo></mml:mrow><mml:mrow><mml:mi>t</mml:mi><mml:mo stretchy="false">&#x2192;</mml:mo><mml:mo>+</mml:mo><mml:mi mathvariant="normal">&#x221E;</mml:mi></mml:mrow></mml:munder><mml:mstyle displaystyle="true" scriptlevel="0"><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mi>t</mml:mi></mml:mfrac></mml:mrow><mml:munderover><mml:mo movablelimits="false">&#x2211;</mml:mo><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mi>n</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:munderover><mml:mrow><mml:mi>ln</mml:mi><mml:mo>&#x2061;</mml:mo><mml:mrow><mml:mo>|</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi>f</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">&#x2032;</mml:mi></mml:mrow></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>x</mml:mi><mml:mi>i</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow><mml:mo>|</mml:mo></mml:mrow></mml:mrow><mml:mo>.</mml:mo></mml:mstyle></mml:math>
</disp-formula></p>
<p>When the Lyapunov exponent is greater than 0, it means that in this parameter space, the system is in a chaotic state. The Lyapunov exponents of 1D-SLM are shown in <xref ref-type="fig" rid="fig-3">Fig. 3</xref>. The Lyapunov exponents of existing one-dimensional chaotic systems are shown in <xref ref-type="fig" rid="fig-4">Fig. 4</xref>. It can be seen from <xref ref-type="fig" rid="fig-3">Figs. 3</xref> and <xref ref-type="fig" rid="fig-4">4</xref> that the 1D-SLM shows the chaotic global state. Therefore, 1D-SLM can produce a keystream with excellent performance. Compared with other 1D chaotic systems, the 1D-SLM has a larger Lyapunov exponent, and the parameter space in the chaotic state is continuous.</p>
<fig id="fig-3">
<label>Figure 3</label>
<caption><title>Lyapunov exponents analysis of 1D-SLM</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-3.tif"/>
</fig><fig id="fig-4">
<label>Figure 4</label>
<caption><title>Lyapunov exponents analysis of existing one-dimensional chaotic systems</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-4.tif"/>
</fig>
</sec>
<sec id="s2_5">
<label>2.5</label><title>0&#x2013;1 Test</title>
<p>The 0&#x2013;1 test is a test algorithm that measures the presence of chaos in a time series. The 0&#x2013;1 test of 1D-SLM is shown in <xref ref-type="fig" rid="fig-5">Fig. 5</xref>. The 0&#x2013;1 test of existing one-dimensional chaotic systems is shown in <xref ref-type="fig" rid="fig-6">Fig. 6</xref>. <xref ref-type="fig" rid="fig-5">Figs. 5</xref> and <xref ref-type="fig" rid="fig-6">6</xref> show the motion state of 1D-SLM is a Boolean motion state. The Logistic map, Cubic map, Sin map, and 1D-SMCLM exhibit regular motion states in the same parameters. It shows that 1D-SLM can provide sequences with more complex dynamical behavior.</p>
<fig id="fig-5">
<label>Figure 5</label>
<caption><title>0&#x2013;1 test analysis of 1D-SLM</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-5.tif"/>
</fig><fig id="fig-6">
<label>Figure 6</label>
<caption><title>0&#x2013;1 test analysis of existing one-dimensional chaotic systems</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-6.tif"/>
</fig>
</sec>
<sec id="s2_6">
<label>2.6</label><title>Spectral Entropy Analysis</title>
<p>Spectral entropy reflects the energy of the signal. The greater the spectral entropy, the greater the signal&#x2019;s energy and the more complex the dynamic behavior of the signal. The spectral entropy of 1D-SLM and the Logistic map, Cubic map, Sin map, and 1D-SMCLM are shown in <xref ref-type="fig" rid="fig-7">Fig. 7</xref>. It can be seen from <xref ref-type="fig" rid="fig-7">Fig. 7</xref> that compared with the chaotic sequence generated by the Logistic map, Cubic map, Sin map, and 1D-SMCLM, the chaotic sequence generated by 1D-SLM has more potent energy, which indicates that the key stream generated by 1D-SLM has more complex dynamic behavior.</p>
<fig id="fig-7">
<label>Figure 7</label>
<caption><title>Spectral entropy of 1D-SLM and existing one-dimensional chaotic systems</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-7.tif"/>
</fig>
</sec>
</sec>
<sec id="s3">
<label>3</label><title>Encryption Algorithm</title>
<sec id="s3_1">
<label>3.1</label><title>Key Generation</title>
<p>The plaintext image is <italic>P</italic> (<inline-formula id="ieqn-9">
<mml:math id="mml-ieqn-9"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:math>
</inline-formula>), the <italic>R</italic> channel of the plaintext image is denoted as <inline-formula id="ieqn-10">
<mml:math id="mml-ieqn-10"><mml:msub><mml:mi>P</mml:mi><mml:mi>R</mml:mi></mml:msub></mml:math>
</inline-formula> (<inline-formula id="ieqn-11">
<mml:math id="mml-ieqn-11"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:math>
</inline-formula>), the <italic>G</italic> channel is denoted as <inline-formula id="ieqn-12">
<mml:math id="mml-ieqn-12"><mml:msub><mml:mi>P</mml:mi><mml:mi>G</mml:mi></mml:msub></mml:math>
</inline-formula> (<inline-formula id="ieqn-13">
<mml:math id="mml-ieqn-13"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:math>
</inline-formula>), and the <italic>B</italic> channel is denoted as <inline-formula id="ieqn-14">
<mml:math id="mml-ieqn-14"><mml:msub><mml:mi>P</mml:mi><mml:mi>B</mml:mi></mml:msub></mml:math>
</inline-formula> (<inline-formula id="ieqn-15">
<mml:math id="mml-ieqn-15"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:math>
</inline-formula>). Calculate the sum of the plaintext pixel values of each channel by<disp-formula id="eqn-3"><label>(3)</label>
<mml:math id="mml-eqn-3" display="block"><mml:mrow><mml:mo>{</mml:mo><mml:mrow><mml:mtable rowspacing="4pt" columnspacing="1em"><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mi mathvariant="normal">s</mml:mi><mml:mi mathvariant="normal">u</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>P</mml:mi><mml:mi>R</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mi mathvariant="normal">s</mml:mi><mml:mi mathvariant="normal">u</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>P</mml:mi><mml:mi>G</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mi mathvariant="normal">s</mml:mi><mml:mi mathvariant="normal">u</mml:mi><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>P</mml:mi><mml:mi>B</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mrow><mml:mo fence="true" stretchy="true" symmetric="true"></mml:mo></mml:mrow><mml:mo>.</mml:mo></mml:math>
</disp-formula></p>
<p>The key of the cryptosystem is <inline-formula id="ieqn-16">
<mml:math id="mml-ieqn-16"><mml:msub><mml:mi>K</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:mrow><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>K</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:mrow><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>K</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mrow><mml:msub><mml:mi>k</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:mrow></mml:mrow></mml:math>
</inline-formula>.</p>
</sec>
<sec id="s3_2">
<label>3.2</label><title>Cross-Plane for Color Images</title>
<p>Given the original initial value <inline-formula id="ieqn-17">
<mml:math id="mml-ieqn-17"><mml:msub><mml:mi>v</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula> and parameter <inline-formula id="ieqn-18">
<mml:math id="mml-ieqn-18"><mml:msub><mml:mi>p</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-19">
<mml:math id="mml-ieqn-19"><mml:msub><mml:mi>q</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula> of 1D-SLM. According to the secret key in Section 3.1, the new initial value and parameter are,<disp-formula id="eqn-4"><label>(4)</label>
<mml:math id="mml-eqn-4" display="block"><mml:msub><mml:mi>v</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi>v</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>p</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi>p</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>q</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>.</mml:mo></mml:math>
</disp-formula></p>
<p>The new initial value and parameters are brought into the 1D-SLM iteration to generate the key stream, discard the first 200 iterations of the initial value, denoted as <inline-formula id="ieqn-20">
<mml:math id="mml-ieqn-20"><mml:msub><mml:mi>X</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula> (<inline-formula id="ieqn-21">
<mml:math id="mml-ieqn-21"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:math>
</inline-formula>), definition<disp-formula id="eqn-5"><label>(5)</label>
<mml:math id="mml-eqn-5" display="block"><mml:mi>U</mml:mi><mml:mo>=</mml:mo><mml:mi>f</mml:mi><mml:mi>l</mml:mi><mml:mi>o</mml:mi><mml:mi>o</mml:mi><mml:mi>r</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mo>|</mml:mo><mml:mrow><mml:msub><mml:mi>X</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mo>|</mml:mo></mml:mrow><mml:mo stretchy="false">)</mml:mo><mml:mo lspace="thickmathspace" rspace="thickmathspace">mod</mml:mo><mml:mn>6</mml:mn><mml:mo>+</mml:mo><mml:mn>1.</mml:mn></mml:math>
</disp-formula></p>
<p>The rule for cross-plane for color images is<disp-formula id="eqn-6"><label>(6)</label>
<mml:math id="mml-eqn-6" display="block"><mml:mrow><mml:mo>{</mml:mo><mml:mrow><mml:mtable rowspacing="4pt" columnspacing="1em"><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>U</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>U</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>U</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>U</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>4</mml:mn></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>U</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>=</mml:mo><mml:mi>P</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>G</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>B</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>R</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd><mml:mtd columnalign="left"><mml:mrow><mml:msub><mml:mi>U</mml:mi><mml:mrow><mml:mi>l</mml:mi><mml:mo>,</mml:mo><mml:mi>w</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>6</mml:mn></mml:mrow></mml:mtd></mml:mtr></mml:mtable><mml:mo>.</mml:mo></mml:mrow><mml:mo fence="true" stretchy="true" symmetric="true"></mml:mo></mml:mrow></mml:math>
</disp-formula></p>
</sec>
<sec id="s3_3">
<label>3.3</label><title>Zigzag Scrambling</title>
<p>Concatenate the plaintext processed by cross-planes in Section 3.2 into a new plaintext P (<inline-formula id="ieqn-22">
<mml:math id="mml-ieqn-22"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mn>3</mml:mn><mml:mi>W</mml:mi></mml:math>
</inline-formula>), in the order of <inline-formula id="ieqn-23">
<mml:math id="mml-ieqn-23"><mml:msub><mml:mi>P</mml:mi><mml:mi>R</mml:mi></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-24">
<mml:math id="mml-ieqn-24"><mml:msub><mml:mi>P</mml:mi><mml:mi>G</mml:mi></mml:msub></mml:math>
</inline-formula>, and <inline-formula id="ieqn-25">
<mml:math id="mml-ieqn-25"><mml:msub><mml:mi>P</mml:mi><mml:mi>B</mml:mi></mml:msub></mml:math>
</inline-formula>. Perform zigzag scrambling on the new plaintext P to obtain the scrambled matrix S. The zigzag scrambling is shown in <xref ref-type="fig" rid="fig-8">Fig. 8</xref>.</p>
<fig id="fig-8">
<label>Figure 8</label>
<caption><title>Zigzag scrambling of 3&#x2009;&#x00D7;&#x2009;4</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-8.tif"/>
</fig>
</sec>
<sec id="s3_4">
<label>3.4</label><title>Diffusion</title>
<p>Given the original initial value <inline-formula id="ieqn-26">
<mml:math id="mml-ieqn-26"><mml:msub><mml:mi>v</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula> and parameter <inline-formula id="ieqn-27">
<mml:math id="mml-ieqn-27"><mml:msub><mml:mi>p</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-28">
<mml:math id="mml-ieqn-28"><mml:msub><mml:mi>q</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula> of 1D-SLM. According to the secret key in Section 3.1, the new initial value and parameter are,<disp-formula id="eqn-7"><label>(7)</label>
<mml:math id="mml-eqn-7" display="block"><mml:msub><mml:mi>v</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi>v</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>p</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi>p</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:msub><mml:mi>q</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>K</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>.</mml:mo></mml:math>
</disp-formula></p>
<p>The new initial value and parameters are brought into the 1D-SLM iteration to generate the key stream, discard the first 200 iterations of the initial value, denoted as <inline-formula id="ieqn-29">
<mml:math id="mml-ieqn-29"><mml:msub><mml:mi>X</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula> (<inline-formula id="ieqn-30">
<mml:math id="mml-ieqn-30"><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mn>3</mml:mn><mml:mi>W</mml:mi></mml:math>
</inline-formula>), definition<disp-formula id="eqn-8"><label>(8)</label>
<mml:math id="mml-eqn-8" display="block"><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mi>f</mml:mi><mml:mi>l</mml:mi><mml:mi>o</mml:mi><mml:mi>o</mml:mi><mml:mi>r</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mo>|</mml:mo><mml:mrow><mml:msub><mml:mi>X</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mo>|</mml:mo></mml:mrow><mml:mo stretchy="false">)</mml:mo><mml:mo lspace="thickmathspace" rspace="thickmathspace">mod</mml:mo><mml:mn>256.</mml:mn></mml:math>
</disp-formula></p>
<p>The diffusion process is<disp-formula id="eqn-9"><label>(9)</label>
<mml:math id="mml-eqn-9" display="block"><mml:mrow><mml:mo>{</mml:mo><mml:mrow><mml:mtable rowspacing="4pt" columnspacing="1em"><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>=</mml:mo><mml:mi>T</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>S</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>=</mml:mo><mml:mi>T</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>S</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo>=</mml:mo><mml:mn>2</mml:mn><mml:mo>&#x003A;</mml:mo><mml:mn>3</mml:mn><mml:mi>W</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>=</mml:mo><mml:mi>T</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>S</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>v</mml:mi><mml:mo>=</mml:mo><mml:mn>2</mml:mn><mml:mo>&#x003A;</mml:mo><mml:mi>L</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd columnalign="left"><mml:mrow><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>=</mml:mo><mml:mi>T</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>S</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo stretchy="false">]</mml:mo><mml:mo>&#x2295;</mml:mo><mml:mi>C</mml:mi><mml:mo stretchy="false">[</mml:mo><mml:mi>v</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>u</mml:mi><mml:mo>&#x2212;</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">]</mml:mo><mml:mo>.</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mrow><mml:mo fence="true" stretchy="true" symmetric="true"></mml:mo></mml:mrow></mml:math>
</disp-formula></p>
<p>Output the ciphertext <italic>C</italic>, and synthesize the ciphertext color image.</p>
</sec>
<sec id="s3_5">
<label>3.5</label><title>Decryption Algorithm</title>
<p>The decryption algorithm is shown in Algorithm 1.</p>
<fig id="fig-16">
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-16.tif"/>
</fig>
</sec>
</sec>
<sec id="s4">
<label>4</label><title>Performance Analysis</title>
<sec id="s4_1">
<label>4.1</label><title>Simulation Experiments</title>
<p>The visual analysis of the proposed algorithm is shown in <xref ref-type="fig" rid="fig-9 fig-10 fig-11">Figs. 9&#x2013;11</xref>. Visual analysis shows that, visually, the proposed algorithm is safe.</p>
<fig id="fig-9">
<label>Figure 9</label>
<caption><title>Visual analysis of Lena with the size of 512&#x2009;&#x00D7;&#x2009;512</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-9.tif"/>
</fig><fig id="fig-10">
<label>Figure 10</label>
<caption><title>Visual analysis of Airplane with the size of 512&#x2009;&#x00D7;&#x2009;512</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-10.tif"/>
</fig><fig id="fig-11">
<label>Figure 11</label>
<caption><title>Visual analysis of Baboon with the size of 512&#x2009;&#x00D7;&#x2009;512</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-11.tif"/>
</fig>
</sec>
<sec id="s4_2">
<label>4.2</label><title>Histogram Analysis</title>
<p>The histogram analysis of the proposed algorithm is shown in <xref ref-type="fig" rid="fig-12">Fig. 12</xref> [<xref ref-type="bibr" rid="ref-33">33</xref>]. Histogram analysis shows that the distribution of pixel values obtained by the proposed algorithm is uniform, and the algorithm has excellent security.</p>
<fig id="fig-12">
<label>Figure 12</label>
<caption><title>Histogram analysis</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-12.tif"/>
</fig>
</sec>
<sec id="s4_3">
<label>4.3</label><title>Differential Attack Analysis</title>
<p>A secure algorithm is sensitive to plaintext, and NPCR and UACI are two metrics for detecting plaintext sensitivity [<xref ref-type="bibr" rid="ref-34">34</xref>].<disp-formula id="eqn-10"><label>(10)</label>
<mml:math id="mml-eqn-10" display="block"><mml:mrow><mml:mrow><mml:mo>{</mml:mo> <mml:mtable columnalign='left'><mml:mtr><mml:mtd><mml:mi>N</mml:mi><mml:mi>P</mml:mi><mml:mi>C</mml:mi><mml:mi>R</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mrow><mml:mstyle displaystyle='true'><mml:msub><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:msub><mml:mrow><mml:mrow><mml:mo>{</mml:mo> <mml:mrow><mml:mtable columnalign='left'><mml:mtr columnalign='left'><mml:mtd columnalign='left'><mml:mrow><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:msub><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo stretchy='false'>(</mml:mo><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>j</mml:mi><mml:mo stretchy='false'>)</mml:mo><mml:mo>&#x2260;</mml:mo><mml:msub><mml:mi>c</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo stretchy='false'>(</mml:mo><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>j</mml:mi><mml:mo stretchy='false'>)</mml:mo></mml:mrow></mml:mtd></mml:mtr><mml:mtr columnalign='left'><mml:mtd columnalign='left'><mml:mrow><mml:mn>0</mml:mn><mml:mo>,</mml:mo><mml:msub><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo stretchy='false'>(</mml:mo><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>j</mml:mi><mml:mo stretchy='false'>)</mml:mo><mml:mo>=</mml:mo><mml:msub><mml:mi>c</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo stretchy='false'>(</mml:mo><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>j</mml:mi><mml:mo stretchy='false'>)</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mrow> </mml:mrow></mml:mrow></mml:mstyle></mml:mrow><mml:mrow><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:mrow></mml:mfrac></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mi>U</mml:mi><mml:mi>A</mml:mi><mml:mi>C</mml:mi><mml:mi>I</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mi>L</mml:mi><mml:mo>&#x00D7;</mml:mo><mml:mi>W</mml:mi></mml:mrow></mml:mfrac><mml:mstyle displaystyle='true'><mml:munder><mml:mo>&#x2211;</mml:mo><mml:mrow><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:munder><mml:mrow><mml:mfrac><mml:mrow><mml:mo>&#x007C;</mml:mo><mml:mi>c</mml:mi><mml:mn>1</mml:mn><mml:mo stretchy='false'>(</mml:mo><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>j</mml:mi><mml:mo stretchy='false'>)</mml:mo><mml:mo>&#x2212;</mml:mo><mml:mi>c</mml:mi><mml:mn>2</mml:mn><mml:mo stretchy='false'>(</mml:mo><mml:mi>i</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mi>j</mml:mi><mml:mo stretchy='false'>)</mml:mo><mml:mo>&#x007C;</mml:mo></mml:mrow><mml:mrow><mml:mn>255</mml:mn></mml:mrow></mml:mfrac></mml:mrow></mml:mstyle></mml:mtd></mml:mtr></mml:mtable></mml:mrow><mml:mo>.</mml:mo></mml:mrow></mml:math>
</disp-formula></p>
<p>For a image with the size of 512&#x2009;&#x00D7;&#x2009;512, when the value of NPCR is <inline-formula id="ieqn-31">
<mml:math id="mml-ieqn-31"><mml:mo stretchy="false">[</mml:mo><mml:mn>99.5893</mml:mn><mml:mi mathvariant="normal">&#x0025;</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>100</mml:mn><mml:mi mathvariant="normal">&#x0025;</mml:mi><mml:mo stretchy="false">]</mml:mo></mml:math>
</inline-formula>, and the value of UACI is <inline-formula id="ieqn-32">
<mml:math id="mml-ieqn-32"><mml:mo stretchy="false">[</mml:mo><mml:mn>33.3730</mml:mn><mml:mi mathvariant="normal">&#x0025;</mml:mi><mml:mo>,</mml:mo><mml:mtext>&#x00A0;</mml:mtext><mml:mn>33.5541</mml:mn><mml:mi mathvariant="normal">&#x0025;</mml:mi><mml:mo stretchy="false">]</mml:mo></mml:math>
</inline-formula>, at this point, it indicates that the algorithm is sensitive to plaintext. The test results of NPCR and UACI are shown in <xref ref-type="table" rid="table-2">Table 2</xref>. The results of the differential attack show that the algorithm is sensitive to plaintext.</p>
<table-wrap id="table-2"><label>Table 2</label>
<caption><title>Differential attack analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left" colspan="2">Image</th>
<th align="left">NPCR (&#x0025;)</th>
<th align="left">Pass (Y/N)</th>
<th align="left">UACI (&#x0025;)</th>
<th align="left">Pass (Y/N)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" rowspan="3">Lena</td>
<td align="left">R</td>
<td align="left">99.6059</td>
<td align="left">Y</td>
<td align="left">33.4427</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">99.5914</td>
<td align="left">Y</td>
<td align="left">33.4700</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">99.6120</td>
<td align="left">Y</td>
<td align="left">33.4747</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left" rowspan="3">Airplane</td>
<td align="left">R</td>
<td align="left">99.5960</td>
<td align="left">Y</td>
<td align="left">33.4068</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">99.6219</td>
<td align="left">Y</td>
<td align="left">33.4579</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">99.6158</td>
<td align="left">Y</td>
<td align="left">33.4020</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left" rowspan="3">Baboon</td>
<td align="left">R</td>
<td align="left">99.6025</td>
<td align="left">Y</td>
<td align="left">33.4966</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">99.6070</td>
<td align="left">Y</td>
<td align="left">33.4701</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">99.6120</td>
<td align="left">Y</td>
<td align="left">33.5190</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left" rowspan="3">Peppers</td>
<td align="left">R</td>
<td align="left">99.6082</td>
<td align="left">Y</td>
<td align="left">33.6462</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">99.5964</td>
<td align="left">Y</td>
<td align="left">33.4047</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">99.6067</td>
<td align="left">Y</td>
<td align="left">33.5091</td>
<td align="left">Y</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_4">
<label>4.4</label><title>NIST for Ciphertext and Plaintext</title>
<p>The NIST effectively checks whether the data has randomness [<xref ref-type="bibr" rid="ref-35">35</xref>&#x2013;<xref ref-type="bibr" rid="ref-37">37</xref>]. The NIST test results of ciphertext and plaintext are shown in <xref ref-type="table" rid="table-3">Table 3</xref>. NIST test results show that the ciphertext has terrific randomness.</p>
<table-wrap id="table-3"><label>Table 3</label>
<caption><title>NIST for ciphertext and plaintext</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Sub-tests</th>
<th align="left">Plaintext</th>
<th align="left">Pass (Y/N)</th>
<th align="left">Ciphertext</th>
<th align="left">Pass (Y/N)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">Frequency</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.2932</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">FFT</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.0027</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Block Frequency</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.0164</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Longest Run</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.0618</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Overlapping Template</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.1995</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Approximate Entropy</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.2589</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Rank</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.1137</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Non-Overlapping Template</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.5595</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Cumulative Sums</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.4145</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Random Excursions</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.3504</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Linear Complexity</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.3711</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Runs</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.2277</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Serial</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.1516</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Random Excursions Variant</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.5341</td>
<td align="left">Y</td>
</tr>
<tr>
<td align="left">Universal</td>
<td align="left">0</td>
<td align="left">N</td>
<td align="left">0.2589</td>
<td align="left">Y</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_5">
<label>4.5</label><title>Adjacent Pixel Correlation Analysis</title>
<p>A secure encryption algorithm can reduce ciphertext&#x2019;s horizontal, vertical, and diagonal adjacent pixel correlations. Otherwise, the algorithm can be easily cracked by statistical attacks. The adjacent pixel correlation analysis of the algorithm is shown in <xref ref-type="fig" rid="fig-13">Fig. 13</xref>.</p>
<fig id="fig-13">
<label>Figure 13</label>
<caption><title>Correlation analysis of Baboon</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-13.tif"/>
</fig>
<p>The quantitative results of the correlation analysis of the proposed algorithm are shown in <xref ref-type="table" rid="table-4">Table 4</xref>. The correlation analysis shows that the correlation of the plaintext image in the three directions is very high. The correlation of the ciphertext image in the three directions is very high, close to 0 (theoretical value). Therefore, the proposed encryption algorithm has good security.</p>
<table-wrap id="table-4"><label>Table 4</label>
<caption><title>Correlation coefficients analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="center" rowspan="2">Image</th>
<th align="center" rowspan="2"></th>
<th align="center" colspan="3">Plaintext</th>
<th align="center" colspan="3">Ciphertext</th>
</tr>
<tr>
<th align="left">H</th>
<th align="left">V</th>
<th align="left">D</th>
<th align="left">H</th>
<th align="left">V</th>
<th align="left">D</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" rowspan="3">Lena</td>
<td align="left">R</td>
<td align="left">0.9797</td>
<td align="left">0.9893</td>
<td align="left">0.9696</td>
<td align="left">&#x2212;0.0001</td>
<td align="left">&#x2212;0.0012</td>
<td align="left">&#x2212;0.0019</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">0.9689</td>
<td align="left">0.9823</td>
<td align="left">0.9554</td>
<td align="left">0.0014</td>
<td align="left">&#x2212;0.0003</td>
<td align="left">&#x2212;0.0004</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">0.9325</td>
<td align="left">0.9574</td>
<td align="left">0.9180</td>
<td align="left">&#x2212;0.0027</td>
<td align="left">&#x2212;0.0005</td>
<td align="left">&#x2212;0.00006</td>
</tr>
<tr>
<td align="left" rowspan="3">Airplane</td>
<td align="left">R</td>
<td align="left">0.9726</td>
<td align="left">0.9568</td>
<td align="left">0.9343</td>
<td align="left">&#x2212;0.00009</td>
<td align="left">&#x2212;0.0006</td>
<td align="left">0.0017</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">0.9576</td>
<td align="left">0.9676</td>
<td align="left">0.9324</td>
<td align="left">0.0025</td>
<td align="left">&#x2212;0.0038</td>
<td align="left">0.0005</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">0.9639</td>
<td align="left">0.9352</td>
<td align="left">0.9145</td>
<td align="left">&#x2212;0.0010</td>
<td align="left">&#x2212;0.0015</td>
<td align="left">0.0017</td>
</tr>
<tr>
<td align="left" rowspan="3">Baboon</td>
<td align="left">R</td>
<td align="left">0.9230</td>
<td align="left">0.8659</td>
<td align="left">0.8543</td>
<td align="left">0.0008</td>
<td align="left">&#x2212;0.0013</td>
<td align="left">0.0030</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">0.8654</td>
<td align="left">0.7650</td>
<td align="left">0.7347</td>
<td align="left">&#x2212;0.0009</td>
<td align="left">&#x2212;0.0024</td>
<td align="left">0.0025</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">0.9072</td>
<td align="left">0.8807</td>
<td align="left">0.8397</td>
<td align="left">&#x2212;0.0016</td>
<td align="left">0.0008</td>
<td align="left">&#x2212;0.0020</td>
</tr>
<tr>
<td align="left" rowspan="3">Peppers</td>
<td align="left">R</td>
<td align="left">0.9635</td>
<td align="left">0.9663</td>
<td align="left">0.9563</td>
<td align="left">0.0022</td>
<td align="left">&#x2212;0.0013</td>
<td align="left">&#x2212;0.0006</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">0.9810</td>
<td align="left">0.9817</td>
<td align="left">0.9685</td>
<td align="left">0.0009</td>
<td align="left">&#x2212;0.0027</td>
<td align="left">0.0022</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">0.9663</td>
<td align="left">0.9662</td>
<td align="left">0.9476</td>
<td align="left">&#x2212;0.0013</td>
<td align="left">0.0002</td>
<td align="left">&#x2212;0.0005</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_6">
<label>4.6</label><title>R, G, B Correlation Analysis</title>
<p>A safe algorithm requires a slight correlation between adjacent pixels and a small correlation between the three channels. The correlation analysis between the three channels of the proposed algorithm is shown in <xref ref-type="table" rid="table-5">Tables 5</xref> and <xref ref-type="table" rid="table-6">6</xref>. The results of correlation analysis show that the proposed algorithm can reduce not only the correlation of adjacent pixels but also the correlation between different channels, and the attacker cannot obtain the information of the remaining channels from one channel.</p>
<table-wrap id="table-5"><label>Table 5</label>
<caption><title>Plaintext correlation between R, G, and B</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Image</th>
<th align="left">(R, G)</th>
<th align="left">(R, B)</th>
<th align="left">(G, B)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">Lena</td>
<td align="left">0.8785</td>
<td align="left">0.6763</td>
<td align="left">0.9104</td>
</tr>
<tr>
<td align="left">Airplane</td>
<td align="left">0.9211</td>
<td align="left">0.8410</td>
<td align="left">0.9378</td>
</tr>
<tr>
<td align="left">Baboon</td>
<td align="left">0.3565</td>
<td align="left">0.1236</td>
<td align="left">0.8071</td>
</tr>
<tr>
<td align="left">Peppers</td>
<td align="left">0.2748</td>
<td align="left">0.3951</td>
<td align="left">0.8377</td>
</tr>
</tbody>
</table>
</table-wrap><table-wrap id="table-6"><label>Table 6</label>
<caption><title>Ciphertext correlation between R, G, and B</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Image</th>
<th align="left">(R, G)</th>
<th align="left">(R, B)</th>
<th align="left">(G, B)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">Lena</td>
<td align="left">&#x2212;0.0013</td>
<td align="left">0.0006</td>
<td align="left">0.0031</td>
</tr>
<tr>
<td align="left">Airplane</td>
<td align="left">0.0005</td>
<td align="left">0.0007</td>
<td align="left">&#x2212;0.0007</td>
</tr>
<tr>
<td align="left">Baboon</td>
<td align="left">0.0010</td>
<td align="left">0.0004</td>
<td align="left">&#x2212;0.0041</td>
</tr>
<tr>
<td align="left">Peppers</td>
<td align="left">&#x2212;0.0026</td>
<td align="left">&#x2212;0.0004</td>
<td align="left">0.0006</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_7">
<label>4.7</label><title>Information Entropy Analysis</title>
<p>The information entropy is defined as<disp-formula id="ueqn-1">
<mml:math id="mml-ueqn-1" display="block"><mml:mi>H</mml:mi><mml:mo>=</mml:mo><mml:munderover><mml:mo movablelimits="false">&#x2211;</mml:mo><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mn>255</mml:mn></mml:mrow></mml:munderover><mml:mrow><mml:mi>p</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>g</mml:mi><mml:mi>i</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow><mml:msub><mml:mi>log</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mstyle displaystyle="true" scriptlevel="0"><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:mi>p</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>g</mml:mi><mml:mi>i</mml:mi></mml:msub><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:mfrac></mml:mrow><mml:mo>.</mml:mo></mml:mstyle></mml:math>
</disp-formula></p>
<p>Information entropy is an index to analyze the randomness of image information distribution. The higher the information entropy, the more chaotic the information.</p>
<p>The information entropy analysis of the proposed algorithm is shown in <xref ref-type="table" rid="table-7">Table 7</xref>. The local information entropy reflects the degree of local confusion of the image [<xref ref-type="bibr" rid="ref-38">38</xref>]. When the value of local information entropy is between 7.9015 and 7.9034, it indicates that the local information of the image has good randomness. The local information entropy is shown in <xref ref-type="table" rid="table-7">Table 7</xref>. The information entropy analysis results show that the information entropy of the ciphertext is close to the theoretical value, indicating that the algorithm has a good encryption effect.</p>
<table-wrap id="table-7"><label>Table 7</label>
<caption><title>Information entropy analysis and Local information entropy</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left" colspan="2">Image</th>
<th align="left">IE of plaintext</th>
<th align="left">IE of ciphertext</th>
<th align="left">Local information entropy</th>
<th align="left">Pass or No Pass</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" rowspan="3">Lena</td>
<td align="left">R</td>
<td align="left">7.2530</td>
<td align="left">7.9993</td>
<td align="left">7.9021</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">7.5951</td>
<td align="left">7.9993</td>
<td align="left">7.9026</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">6.9685</td>
<td align="left">7.9994</td>
<td align="left">7.9022</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left" rowspan="3">Airplane</td>
<td align="left">R</td>
<td align="left">6.7177</td>
<td align="left">7.9992</td>
<td align="left">7.9019</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">6.8055</td>
<td align="left">7.9993</td>
<td align="left">7.9030</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">6.2139</td>
<td align="left">7.9993</td>
<td align="left">7.9026</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left" rowspan="3">Baboon</td>
<td align="left">R</td>
<td align="left">7.7066</td>
<td align="left">7.9993</td>
<td align="left">7.9025</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">7.4752</td>
<td align="left">7.9993</td>
<td align="left">7.9029</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">7.7522</td>
<td align="left">7.9993</td>
<td align="left">7.9018</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left" rowspan="3">Peppers</td>
<td align="left">R</td>
<td align="left">7.3388</td>
<td align="left">7.9994</td>
<td align="left">7.9023</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">G</td>
<td align="left">7.5183</td>
<td align="left">7.9993</td>
<td align="left">7.9031</td>
<td align="left">Pass</td>
</tr>
<tr>
<td align="left">B</td>
<td align="left">7.0583</td>
<td align="left">7.9993</td>
<td align="left">7.9023</td>
<td align="left">Pass</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_8">
<label>4.8</label><title>Key Analysis</title>
<p>The key space of a cryptographic system is at least greater than <inline-formula id="ieqn-33">
<mml:math id="mml-ieqn-33"><mml:msup><mml:mn>2</mml:mn><mml:mrow><mml:mn>100</mml:mn></mml:mrow></mml:msup></mml:math>
</inline-formula> that to meet the conditions for resisting brute force attacks. The keys in this paper include <inline-formula id="ieqn-34">
<mml:math id="mml-ieqn-34"><mml:msub><mml:mi>v</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-35">
<mml:math id="mml-ieqn-35"><mml:msub><mml:mi>p</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-36">
<mml:math id="mml-ieqn-36"><mml:msub><mml:mi>q</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-37">
<mml:math id="mml-ieqn-37"><mml:msub><mml:mi>v</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-38">
<mml:math id="mml-ieqn-38"><mml:msub><mml:mi>p</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-39">
<mml:math id="mml-ieqn-39"><mml:msub><mml:mi>q</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-40">
<mml:math id="mml-ieqn-40"><mml:msub><mml:mi>K</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-41">
<mml:math id="mml-ieqn-41"><mml:msub><mml:mi>K</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
</inline-formula>, <inline-formula id="ieqn-42">
<mml:math id="mml-ieqn-42"><mml:msub><mml:mi>K</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>
</inline-formula>. If the computational precision of the computer is <inline-formula id="ieqn-43">
<mml:math id="mml-ieqn-43"><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msup></mml:math>
</inline-formula>, the size of the key space of the proposed algorithm is,<disp-formula id="ueqn-2">
<mml:math id="mml-ueqn-2" display="block"><mml:mi>K</mml:mi><mml:mo>=</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>28</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>28</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>28</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>28</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msup><mml:mo>&#x00D7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msup><mml:mo>=</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mn>168</mml:mn></mml:mrow></mml:msup><mml:mo>&#x2248;</mml:mo><mml:msup><mml:mn>2</mml:mn><mml:mrow><mml:mn>558</mml:mn></mml:mrow></mml:msup><mml:mo>.</mml:mo></mml:math>
</disp-formula></p>
<p>The designed algorithm is strong enough to resist brute-force attacks.</p>
<p>A highly sensitive key is a necessary condition for an encryption algorithm. This section tests the key sensitivity of the proposed algorithm, with the initial key set to <inline-formula id="ieqn-44">
<mml:math id="mml-ieqn-44"><mml:msub><mml:mi>v</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mn>0.985612</mml:mn></mml:math>
</inline-formula>, <inline-formula id="ieqn-45">
<mml:math id="mml-ieqn-45"><mml:msub><mml:mi>p</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mn>10.36985</mml:mn></mml:math>
</inline-formula>, <inline-formula id="ieqn-46">
<mml:math id="mml-ieqn-46"><mml:msub><mml:mi>q</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:mn>11.23654</mml:mn></mml:math>
</inline-formula>. The key sensitivity analysis is shown in <xref ref-type="fig" rid="fig-14">Fig. 14</xref>. Key sensitivity analysis shows that the key of the proposed algorithm is sensitive. Calculate the difference between the images in <xref ref-type="fig" rid="fig-14">Fig. 14</xref> using NPCR and UACI shown in <xref ref-type="table" rid="table-8">Table 8</xref> [<xref ref-type="bibr" rid="ref-35">35</xref>,<xref ref-type="bibr" rid="ref-36">36</xref>].</p>
<fig id="fig-14">
<label>Figure 14</label>
<caption><title>Key sensitivity analysis</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-14.tif"/>
</fig><table-wrap id="table-8"><label>Table 8</label>
<caption><title>NPCR and UACI of key sensitivity analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">NPCR (&#x0025;) and UACI (&#x0025;)</th>
<th align="left"><xref ref-type="fig" rid="fig-14">Fig. 14a</xref></th>
<th align="left"><xref ref-type="fig" rid="fig-14">Fig. 14b</xref></th>
<th align="left"><xref ref-type="fig" rid="fig-14">Fig. 14c</xref></th>
<th align="left"><xref ref-type="fig" rid="fig-14">Fig. 14d</xref></th>
</tr>
</thead>
<tbody>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-14">Fig. 14a</xref></td>
<td align="left">0</td>
<td align="left">32.2304</td>
<td align="left">32.2352</td>
<td align="left">32.2123</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-14">Fig. 14b</xref></td>
<td align="left">99.5924</td>
<td align="left">0</td>
<td align="left">33.4445</td>
<td align="left">33.4585</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-14">Fig. 14c</xref></td>
<td align="left">99.6063</td>
<td align="left">99.6138</td>
<td align="left">0</td>
<td align="left">33.4996</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-14">Fig. 14d</xref></td>
<td align="left">99.6081</td>
<td align="left">99.6105</td>
<td align="left">99.6200</td>
<td align="left">0</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_9">
<label>4.9</label><title>Robustness Analysis</title>
<p>The image will be interfered with by noise during transmission [<xref ref-type="bibr" rid="ref-39">39</xref>]. A safe algorithm should have good resistance to this attack. The robustness analysis of the algorithm is shown in <xref ref-type="fig" rid="fig-15">Fig. 15</xref>. The PSNR is generally used to measure the restoring ability of images. The results of MSE are shown in <xref ref-type="table" rid="table-9">Table 9</xref>. The results of PSNR are shown in <xref ref-type="table" rid="table-10">Table 10</xref>.</p>
<fig id="fig-15">
<label>Figure 15</label>
<caption><title>Robustness analysis</title></caption>
<graphic mimetype="image" mime-subtype="tif" xlink:href="CSSE_36652-fig-15.tif"/>
</fig><table-wrap id="table-9"><label>Table 9</label>
<caption><title>MSE of robustness analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Images</th>
<th align="left">MSE</th>
<th align="left">Images</th>
<th align="left">MSE</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-15">Figs. 15a</xref> and <xref ref-type="fig" rid="fig-15">15d</xref></td>
<td align="left">11413</td>
<td align="left"><xref ref-type="fig" rid="fig-15">Fig. 15d</xref> and original image</td>
<td align="left">2750</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-15">Figs. 15b</xref> and <xref ref-type="fig" rid="fig-15">15e</xref></td>
<td align="left">10789</td>
<td align="left"><xref ref-type="fig" rid="fig-15">Fig. 15e</xref> and original image</td>
<td align="left">1461</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-15">Figs. 15c</xref> and <xref ref-type="fig" rid="fig-15">15f</xref></td>
<td align="left">10270</td>
<td align="left"><xref ref-type="fig" rid="fig-15">Fig. 15f</xref> and original image</td>
<td align="left">305</td>
</tr>
</tbody>
</table>
</table-wrap><table-wrap id="table-10"><label>Table 10</label>
<caption><title>PSNR of robustness analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Images</th>
<th align="left">PSNR (dB)</th>
<th align="left">Images</th>
<th align="left">PSNR (dB)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-15">Figs. 15a</xref> and <xref ref-type="fig" rid="fig-15">15d</xref></td>
<td align="left">7.5565</td>
<td align="left"><xref ref-type="fig" rid="fig-15">Fig. 15d</xref> and original image</td>
<td align="left">13.7367</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-15">Figs. 15b</xref> and <xref ref-type="fig" rid="fig-15">15e</xref></td>
<td align="left">7.8006</td>
<td align="left"><xref ref-type="fig" rid="fig-15">Fig. 15e</xref> and original image</td>
<td align="left">16.4833</td>
</tr>
<tr>
<td align="left"><xref ref-type="fig" rid="fig-15">Figs. 15c</xref> and <xref ref-type="fig" rid="fig-15">15f</xref></td>
<td align="left">8.0148</td>
<td align="left"><xref ref-type="fig" rid="fig-15">Fig. 15f</xref> and original image</td>
<td align="left">23.2832</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_10">
<label>4.10</label><title>Time Analysis</title>
<p>Efficiency analysis is an important index to evaluate the practicability of an algorithm [<xref ref-type="bibr" rid="ref-40">40</xref>,<xref ref-type="bibr" rid="ref-41">41</xref>]. The efficiency analysis of the proposed algorithm is shown in <xref ref-type="table" rid="table-11">Table 11</xref>. Experimental environment, Matlab R2019a, Windows 11, Intel i3-10105. Efficiency analysis shows that the proposed algorithm has excellent performance and is more practical.</p>
<table-wrap id="table-11"><label>Table 11</label>
<caption><title>Time analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Algorithms</th>
<th align="left">Size</th>
<th align="left">Time (s)</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">Proposed</td>
<td align="left">512&#x2009;&#x00D7;&#x2009;512&#x2009;&#x00D7;&#x2009;3</td>
<td align="left"><bold>0.9856</bold></td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-42">42</xref>]</td>
<td align="left">512&#x2009;&#x00D7;&#x2009;512&#x2009;&#x00D7;&#x2009;3</td>
<td align="left">1.4597</td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-43">43</xref>]</td>
<td align="left">512&#x2009;&#x00D7;&#x2009;512&#x2009;&#x00D7;&#x2009;3</td>
<td align="left">1.3053</td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-44">44</xref>]</td>
<td align="left">512&#x2009;&#x00D7;&#x2009;512&#x2009;&#x00D7;&#x2009;3</td>
<td align="left">1.2122</td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-45">45</xref>]</td>
<td align="left">512&#x2009;&#x00D7;&#x2009;512&#x2009;&#x00D7;&#x2009;3</td>
<td align="left">1.2271</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s4_11">
<label>4.11</label><title>Comparative Analysis</title>
<p>In this section, the proposed algorithm is compared with some classical algorithms, and the comparison results are shown in <xref ref-type="table" rid="table-6">Table 6</xref>. The values in <xref ref-type="table" rid="table-12">Table 12</xref> are averages. The comparison results show that our algorithm is more secure than the algorithm in Ref. [<xref ref-type="bibr" rid="ref-42">42</xref>], algorithm in Ref. [<xref ref-type="bibr" rid="ref-43">43</xref>], algorithm in Ref. [<xref ref-type="bibr" rid="ref-44">44</xref>], and algorithm in Ref. [<xref ref-type="bibr" rid="ref-45">45</xref>].</p>
<table-wrap id="table-12"><label>Table 12</label>
<caption><title>Comparative analysis</title></caption>
<table><colgroup><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/><col align="left"/>
</colgroup>
<thead>
<tr>
<th align="left">Algorithms</th>
<th align="left">IE</th>
<th align="left">Horizontal</th>
<th align="left">Vertical</th>
<th align="left">Diagonal</th>
<th align="left">Keyspace</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">Proposed</td>
<td align="left"><bold>7.9993</bold></td>
<td align="left"><bold>0.0014</bold></td>
<td align="left"><bold>0.0007</bold></td>
<td align="left"><bold>0.0008</bold></td>
<td align="left"><bold>2<sup>588</sup></bold></td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-42">42</xref>]</td>
<td align="left">7.5618</td>
<td align="left">&#x2212;0.0107</td>
<td align="left">&#x2212;0.0079</td>
<td align="left">&#x2212;0.0014</td>
<td align="left">2<sup>232</sup></td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-43">43</xref>]</td>
<td align="left">7.9993</td>
<td align="left">0.0034</td>
<td align="left">&#x2212;0.0008</td>
<td align="left">&#x2212;0.0010</td>
<td align="left">2<sup>512</sup></td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-44">44</xref>]</td>
<td align="left">7.9993</td>
<td align="left">0.0038</td>
<td align="left">0.0024</td>
<td align="left">0.0020</td>
<td align="left">2<sup>512</sup></td>
</tr>
<tr>
<td align="left">Algorithm in Ref. [<xref ref-type="bibr" rid="ref-45">45</xref>]</td>
<td align="left">7.9973</td>
<td align="left">0.0060</td>
<td align="left">0.0146</td>
<td align="left">0.0384</td>
<td align="left">2<sup>189</sup></td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
</sec>
<sec id="s5">
<label>5</label><title>Conclusion</title>
<p>In this paper, a new chaotic system, 1D-SLM, is proposed. This system has two control parameters that give the cryptosystem a larger key space. It is verified that the key stream generated by 1D-SLM has strong energy and can generate a key stream with excellent performance that is very suitable for cryptography by the Lyapunov exponent, bifurcation graph analysis, and spectral entropy analysis. We propose a new image encryption algorithm based on 1D-SLM. This encryption algorithm combines the three channels of the color image to encrypt simultaneously. In other words, during the encryption process, the three channels of the color image are interactive. This design structure reduces the correlation between image channels. Through performance analysis, it is verified that the proposed algorithm has good performance. Comparative analysis shows that the proposed algorithm has excellent security.</p>
</sec>
</body>
<back>
<sec><title>Funding Statement</title>
<p>This research was supported by the <funding-source>National Natural Science Foundation of China</funding-source> (<award-id>61802212</award-id>).</p>
</sec>
<sec sec-type="COI-statement"><title>Conflicts of Interest</title>
<p>The authors declare that they have no conflicts of interest to report regarding the present study.</p>
</sec>
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