📄 des算法图解.htm
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<h3
style="margin-left:84.5pt;text-indent:-42.0pt;mso-list:l9 level3 lfo15;
tab-stops:list 84.5pt"><font
color="#FF0000" size="5"><b><span lang="EN-US">2.1.2<span style="font-style: normal; font-variant: normal; font-family: Times New Roman"></span></span><span style="mso-spacerun: yes"> </span><span lang="EN-US">DES加密算法</span></b></font></h3>
<p class="MsoNormalIndent"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">假定明文</span><span lang="EN-US">m</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">和密钥</span><span lang="EN-US">k</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">都是</span><span lang="EN-US">64</span><span style="font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">比特的</span><span lang="EN-US">0</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">，</span><span lang="EN-US">1</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">符号串。设</span></p>
<p align="center" class="MsoNormalIndent"
style="text-align:center"><span lang="EN-US">m=m<sub>1</sub>m<sub>2</sub>……m<sub>64</span></sub></p>
<p align="center" class="MsoNormalIndent"
style="text-align:center"><span lang="EN-US">k=k<sub>1</sub>k<sub>2</sub>……k<sub>64</span></sub></p>
<p align="center" class="MsoNormalIndent"
style="text-align:center"><span lang="EN-US">m<sub>i</sub>,k<sub>i</sub>=0</span><span style="font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">或</span><span lang="EN-US">1<span style="mso-tab-count:2">
</span>i=1,2,……,64</span></p>
<p class="MsoNormalIndent"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">说明：密钥</span><span lang="EN-US">k</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">只有</span><span lang="EN-US">56</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">比特有效，</span><span lang="EN-US">k<sub>8</sub>,k<sub>16</sub>,k<sub>24</sub>,k<sub>32</sub>,k<sub>40</sub>,k<sub>48</sub>,k<sub>56</sub>,k<sub>64</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman""></sub>这</span><span lang="EN-US">8</span><span style="font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"">位是奇偶校验位，在算法中不起作用。</span></p>
<p class="MsoNormalIndent"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">加密过程表达如下：</span></p>
<p class="MsoNormalIndent"><span lang="EN-US">DES(m)=IP<sup>-1</span><span style="font-family:宋体;mso-hansi-font-family:"Times New Roman""></sup>·</span><span lang="EN-US">T<sub>16</span><span style="font-family:宋体;mso-hansi-font-family:
"Times New Roman""></sub>·</span><span lang="EN-US">T<sub>15</span><span style="font-family:宋体;mso-hansi-font-family:"Times New Roman""></sub>·</span><span lang="EN-US">……T<sub>2</span><span style="font-family:宋体;mso-hansi-font-family:
"Times New Roman""></sub>·</span><span lang="EN-US">T<sub>1</span><span style="font-family:宋体;mso-hansi-font-family:"Times New Roman""></sub>·</span><span lang="EN-US">IP(m)</span></p>
<p class="MsoNormalIndent"
style="margin-left:0cm;mso-list:l0 level1 lfo16;
tab-stops:list 39.0pt 91.5pt"><span lang="EN-US">1．IP</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">是初始变换，</span><span lang="EN-US">IP<sup>-1</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman""></sup>是它的逆变换。实际上是将明文</span><span lang="EN-US">m</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"">中的字符按照事先规定的次序重新排列。二者满足</span><span lang="EN-US">IP</span><span style="font-family:宋体;mso-hansi-font-family:"Times New Roman"">·</span><span lang="EN-US">IP<sup>-1</sup>=I</span><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">。</span></p>
<p class="MsoNormalIndent"
style="margin-left:0cm;mso-list:l0 level1 lfo16;
tab-stops:list 39.0pt 91.5pt"><span lang="EN-US">2．DES</span><span style="font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"">迭代过程。</span></p>
<p class="MsoNormalIndent" style="text-indent:0cm"><span lang="EN-US"> <o:p> </o:p> </span></p>
<p class="MsoNormalIndent" style="text-indent:0cm"><span lang="EN-US"> <o:p> </o:p> </span></p>
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<p class=MsoNormal align=center style='text-align:center'><span
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<p class=MsoNormal align=center style='text-align:center'><span
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<p class=MsoNormal align=center style='text-align:center'><span
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"Times New Roman"'>迭代</span><span lang=EN-US>16</span><span
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<p class=MsoNormal align=center style='text-align:center'><span
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<span lang="EN-US"> <o:p> </o:p> </span><br clear="all" style="mso-ignore:vglayout">
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<p class="MsoNormalIndent"><span style="font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"">每一次迭代过程如下：</span></p>
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