<?php
/************************************************************************
+----------------------------------------------------------------------+
| ioc.php -> Index of Coincidence |
+----------------------------------------------------------------------+ |
| |
| (c) 2002 by M.Abdullah Khaidar (khaidarmak@yahoo.com) |
| |
| This program is free software. You can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2 of the License. |
| |
+----------------------------------------------------------------------+
************************************************************************/
include "main.php";
$TITLE="Index of Coincidence";
$HEADTITLE="Index of Coincidence";
top();
echo "<form name=\"Form\" action=\"ioc.php\" method=\"post\">\n";
echo "Enter text you want to calculate:<br>\n";
echo "<textarea name=\"plain\" cols=40 rows=7 class=\"txtcolor\">\n";
if ($plain){
$plain=filter($plain);
$plain=check_length($plain);
echo $plain;
}
echo "</textarea><br><br>\n";
echo "Key Length:";
echo "<select name=\"keylength\" width=200 class=\"txtcolor\">\n";
for($i=1;$i<=$MAXKEYLENGTH;$i++){
if ($i==$keylength){
echo "<option value=$i selected>$i</option>\n";
}else{
echo "<option value=$i>$i</option>\n";
}
}
echo "</select>\n";
echo "<br><br>";
echo "<input type=\"submit\" name=\"process\" value=\"Calculate\" class=\"txtcolor\"> \n";
echo "</form>\n";
if ($process=="Calculate"){
$plain=filter($plain);
$plain=check_length($plain);
for($i=0;$i<26;$i++){
for($j=1;$j<=$keylength;$j++){
$freq[$i][$j]=0;
}
}
for($i=0;$i<strlen($plain);$i=$i+$keylength){
$pblock=substr($plain,$i,$keylength);
for($m=1;$m<=$keylength;$m++){
$p=substr($pblock,$m-1,1);
$p=decimal($p);
$freq[$p][$m]++;
}
}
for($m=1;$m<=$keylength;$m++){
$sum=0;
$n=0;
for($p=0;$p<26;$p++){
$sum=$sum + $freq[$p][$m]*($freq[$p][$m]-1);
$n=$n+$freq[$p][$m];
}
if($n==1||$n==0){
$ioc[$m]="division by zero";
}else{
$ioc[$m]=$sum/($n*($n-1));
}
}
echo "Index of coincidence with m=$keylength:<br>";
for($m=1;$m<=count($ioc);$m++){
echo number_format($ioc[$m],3)."<br>";
}
}
bottom();
?>
