Tabula Recta Generator

By | December 24, 2010

Inspired by the Lifehacker article of “How to Write Down and Encrypt Your Passwords with an Old-School Tabula Recta” I have thrown together my own web-based Tabula Recta generator.

This is a just a quick proof of concept. I don’t shift the characters but generate a random character from a limited character set (abcdefghijklmnopqrstuvwxys0123456789!@#$%^&*()+_-{}|;<>?) using the mt_rand PHP function. I also only use lowercase alpha characters for this test.

Feel free to use and print out.

Generate Tabula Recta

**UPDATE**

After I posted this and thought about it I for the life of me don’t know why I just didn’t post the code. So here it is. Very simplified, but a good starting point to build on possibly if someone is interested in taking it further.

<table style="border: 1px solid black;;font-family: verdana;font-size:16pt"
cellpadding="0" cellspading="0">
<tr>
<td style="border: 1px solid black">&nbsp;</td><?php
function rand_char($chars = 'abcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()+_-{}|;<>?ABCDEFGHIJKLMNOPQRSTUVWXYZ')
{
$string = '';
for ($i = 0; $i < 1; $i++)
{
$pos = rand(0, strlen($chars)-1);
$string .= $chars{$pos};
}
return $string;
}
$letterarray = array('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't' ,'u', 'v', 'w', 'x', 'y','z');
$count = count($letterarray);
for ($i = 0; $i < $count; $i++) {
echo "<td style='border: 1px solid black;font-weight:900' width='30' align='center'>".$letterarray[$i]."</td>";
}
echo "</tr>";
for ($i = 0; $i < $count; $i++) {
echo "<tr><td style='border: 1px solid black;font-weight:900' align='center'>".$letterarray[$i]."</td>";
for($s=0; $s < $count; $s++)
{
echo "<td style='border: 1px solid black' align='center'>".rand_char()."</td>";
}
echo "</tr>";
}
?>
</tr>
</table>

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6 thoughts on “Tabula Recta Generator

  1. annonymous

    Is the random number generator you used cryptographically secure?

    1. Kelly Martinez Post author

      No. Using the PHP function mt_rand from a limited set of ASCII characters. mt_rand is not cryptographically secure (see discussion of mt_rand on PHP.net).

      This randomness would have to be generated using the CryptoAPI or OpenSSL.

      However, for normal everyday password I find it pretty secure.

  2. youseph

    I notice you don’t have uppercase letters and the example show on the Lifehacker has both upper and lower case letters. Any plans to add that?

    1. Kelly Martinez Post author

      Threw this together as a quick and dirty test. Added uppercase for you though. However, still only using a limited ASCII character set (abcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()+_-{}|;?ABCDEFGHIJKLMNOPQRSTUVWXYZ)

      Thanks for the feedback! 🙂

  3. Stewart

    Something I based on the same article. Very neat.

    This one exports the data into a text file for import into a spreadsheet.

    ‘, ‘<');

    $numChars = array_merge($chars, $numbers);

    $all = array_merge($numChars, $symbols);

    for ($i = 0; $i <= 5; $i++) {
    shuffle($all);
    }

    $rand = array_rand($all, 26);

    for ($y = 0; $y <= 25; $y++) {

    for ($x = 0; $x

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