Member Avatar for thirsty.soul

Hello Everyone Help needed, Has anyone implemented frequency analysis attack on caesar cipher in PHP and predicting the possible key for it. it should input the cipher text and predict the key using frequency analysis chart.

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  • 3 Hours Discussion Span
  • Latest Post Latest Post by cereal
Member Avatar for thirsty.soul

this breaks but i want to do frequency analysis attack on it.

<?php

error_reporting(0);
$do=$_REQUEST["do"];
if($do=="break"){
    $alpha=array(
    array("0","A"),array("1","B"),array("2","C"),
    array("3","D"),array("4","E"),array("5","F"),
    array("6","G"),array("7","H"),array("8","I"),
    array("9","J"),array("10","K"),array("11","L"),
    array("12","M"),array("13","N"),array("14","O"),
    array("15","P"),array("16","Q"),array("17","R"),
    array("18","S"),array("19","T"),array("20","U"),
    array("21","V"),array("22","W"),array("23","X"),
    array("24","Y"),array("25","Z")
    );  // $alpha[20][1]= words    $alpha[20][0]=numbers
    $text=$_REQUEST["text"];
    $text_len=strlen($text);
    for($h=1; $h<26; $h++){
        for($i=0; $i<$text_len; $i++){
        $chr=$text[$i];
            for($j=0; $j<=24; $j++){ // search the arry for char
                if($alpha[$j][1]==$chr){
                        $res=($h+$alpha[$j][0])%25;
                        echo($alpha[$res][1]);
                }else if($chr==" "){
                        echo(" "); // replace spaces
                }
            }
        }echo("<br />");
                echo("===================================================================");
                echo("<br />");
    }
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Caesar Cipher Manual Breaking</title>
<link href="style.css" rel="stylesheet" type="text/css" />
</head>

<body><center>
<form id="form1" name="form1" method="post" action="<?php echo($_SERVER['PHP_SELF']); ?>?do=break">
  <p><strong>Caesar Cipher Manual Breaking</strong> <br />
    <br />
    Cipher
    <textarea name="text" id="text" cols="45" rows="5"></textarea>
  <br />
  </p>
  <p>
    <input type="submit" name="button" id="button" value="Break" />
  </p>
</form>
<p><a href="Caesar-Cipher-Encrypt.php">CaesarCipher Encrypt</a> &nbsp;|&nbsp; <a href="Caesar-Cipher-Decrypt.php">CaesarCipher Decrypt</a> &nbsp;| &nbsp;<a href="Caesar-Cipher-Breaking.php">CaesarCipher Manual Break</a></p>
<br />
</center>
</body>
</html>
Member Avatar for cereal

Hi,

I don't understand what it should do your script, tested with a ciphered string and prints only ====. If you are searching for character frequency, then look at count_chars():

For example:

<?php

$message    = 'pda sknhz eo behhaz sepd oaynapo wjz iuopaneao fqop swepejc pk xa zeoykranaz';
$stats      = count_chars($message, 1);
$chars      = array_map('chr', array_keys($stats));
$frequency  = array_combine($chars, array_values($stats));

arsort($frequency);
print_r($frequency);

returns:

Array
(
    [ ] => 12
    [a] => 9
    [e] => 7
    [p] => 7
    [o] => 7
    [z] => 5
    [n] => 4
    [s] => 3
    [k] => 3
    [h] => 3
    [j] => 2
    [w] => 2
    [d] => 2
    [y] => 2
    [b] => 1
    [u] => 1
    [x] => 1
    [r] => 1
    [i] => 1
    [f] => 1
    [q] => 1
    [c] => 1
)

Example taken from: https://www.khanacademy.org/computing/computer-science/cryptography/ciphers/e/caesar_cipher_frequency_analysis

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