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POGCM Multiplication Implementation
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  1. POGCM Multiplication Implementation
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    copied!<p>I am puting up a C code for the Multiplication of block (Alogrithm 1) in the GCM SP-800-38D document <a href="http://www.google.com.ng/url?sa=t&amp;rct=j&amp;q=GCM%20sp%20800%2038d&amp;source=web&amp;cd=1&amp;ved=0CFYQFjAA&amp;url=http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf&amp;ei=n162T4bRDsnL0QXjiqW0Cg&amp;usg=AFQjCNEElGcj_hAkPTB-5voW5YxfN7iocg&amp;cad=rja" rel="nofollow">here</a>. Page 11-12.</p> <p>Having completed the code, I want to see if there are any way I can test the code. You can find attached below the code I have put up. Note that instead of the 128 bit block, I used a 24 bit block just for testing purposed. I will appreciate any suggestions where necessary.</p> <pre><code>void BLK_MUL (u8 *val_1,u8 *val_2, u8 *out_val) { u8 xdata R_val = 0xE1; u8 xdata Z_val[3],V_val[3]; u8 mask_b = 0x80; u16 i; u8 j; bit rnd; for(j=0;j&lt;3;j++,++val_2) { Z_val[j]=0x00; V_val[j]=*val_2; } for(i=0;i&lt;24;i++) { if (*val_1 &amp; mask_b) { for(j=0;j&lt;3;j++) Z_val[j]^=V_val[j]; } if (!(V_val[2] &amp; 0x01)) {//if LSB of V_val is 0 for(j=0;j&lt;3;j++) { //V_val = rightshift(V_val) if (j!=0) if (V_val[2-j] &amp; 0x01) V_val[3-j] |= 0x80; V_val[2-j]&gt;&gt;=1; } } else {//if LSB of V_val is 1 for(j=0;j&lt;3;j++) {//V_val = rightshift(V_val) if (j!=0) if (V_val[2-j] &amp; 0x01) V_val[3-j] |= 0x80; V_val[2-j]&gt;&gt;=1; } V_val[0]^=R_val; //V_val = rightshift(V_val) ^ R } if(mask_b &amp; 0x01) { val_1++; rnd=1;} mask_b &gt;&gt;= 1; if (rnd) { mask_b=0x80; rnd=0; } } STR_CPY(out_val,Z_val,3); return ; } void main() { code unsigned char val_1[3] ={ 0x2b,0x7e,0x15 }; code unsigned char val_2[3] ={ 0x39,0x25,0x84 }; unsigned char out[3]; BLK_MUL (val_1,val_2,out); return; } </code></pre>
 

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