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What now follows is an example of how to use the Mcrypt encryption function that is part of the PHP scripting language. In order to use Mcrypt with PHP you will need to include the mcrypt library files by editing the php.ini file accordingly.

If you need a primer in what the Mcrypt function is capable of performing I suggest you check out http://us.php.net/manual/en/book.mcrypt.php as I will only be providing an example on how to use the encryption and decryption functionality.

The encryption function used is simply called - mcrypt_encrypt
The decryption function used is simply called - mcrypt_decrypt

Here's an example PHP script that performs both the encryption and decryption function in the same script so you can see it at work.


<?php
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CBC);
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
$key = hash ("md5", "It's all just apples and oranges.");
$text = "The quick brown fox jumps over the lazy dog.";
echo "<p><b>Initialization Vector Size = </b>" .$iv_size." characters</p&gt";
echo "<p><b>Initialization Vector = </b>" .$iv ."</p>";
echo "<p><b>KEY (Password Used after MD5 Hash) = </b>" .$key. "</p>";
echo "<p><b>Plain Text String Length = </b>" .strlen($text) . " characters</p>";
echo "<p><b><u>Plain Text = </u></b><font color='blue'>" .$text."</font></p>";
$crypttext = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_CBC, $iv);
echo "<p><b>Encrypted Text String Length = </b>".strlen($crypttext) . " characters</p>";
echo "<p><b><u>Encrypted Text = </u></b><font color='red'>".$crypttext ."</font></p>";
echo "<i>The Mcrypt_decrypt function pads out the RETURN STRING (decrypttext) with null characters '\0' to pad to the same block size as (crypttext), which is in this case 64 characters in length.</i><br>";
$decrypttext = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $crypttext, MCRYPT_MODE_CBC, $iv);
$decrypted = rtrim($decrypttext, "\0");
echo "<p><b>Decrypted Text (decrypttext) = </b>" .$decrypttext . " - <i>With the nulls used to pad still present. These need to be trimmed off.</i></p>";
echo "<p><b>Decrypted Text (decrypttext) = </b>" .$decrypted . " - <i>With the nulls used to pad out the blocksize of the encrypted text removed.</i></p>";
?>


And here is the what the script returns:

Initialization Vector Size = 32 characters

Initialization Vector = $pÍ£Ûö¹Ôe¤º¨yr ízkO½Z6¨“szö

KEY (Password Used after MD5 Hash) = c54dcf123bf2548c7cdb862ef36e87e0

Plain Text String Length = 44 characters

Plain Text = The quick brown fox jumps over the lazy dog.

Encrypted Text String Length = 64 characters

Encrypted Text = ٍPKàoB,ãU0šÎmÑç{ÛîêPnëkèu¸–…ê`~ì÷Ni‡dݝ¹!ò×V@ˆKWH„õ„Ò
The Mcrypt_decrypt function pads out the RETURN STRING (decrypttext) with null characters '�' to pad to the same block size as (crypttext), which is in this case 64 characters in length.

Decrypted Text (decrypttext) = The quick brown fox jumps over the lazy dog.�������������������� - With the nulls used to pad still present. These need to be trimmed off.

Decrypted Text (decrypttext) = The quick brown fox jumps over the lazy dog. - With the nulls used to pad out the blocksize of the encrypted text removed.

As you step through the script (top) compare the output above for a self explanatory view of the results of each line. A basic understanding of PHP should be all that is required to grasp what is happening here.

Enjoy!