Question

mcrypt function - decrypting variable ?

Asked by: andyw27


I have the following code, I'm looking for how I would decrypt the variable $encrypted_data;

<?php

   $key = "this is a secret key";
   $input = "http://www.google.com";

   $td = mcrypt_module_open('tripledes', '', 'ecb', '');
   $iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
   mcrypt_generic_init($td, $key, $iv);
   $encrypted_data = mcrypt_generic($td, $input);
   mcrypt_generic_deinit($td);
   mcrypt_module_close($td);
   
?>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Untitled Document</title>
</head>

<body>

<?php echo $encrypted_data; ?>

</body>
</html>

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Asked On
2007-01-07 at 12:53:49ID22114047
Tags

mcrypt

,

php

,

decrypt

Topic

PHP Scripting Language

Participating Experts
3
Points
500
Comments
3

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Answers

 

by: slyongPosted on 2007-01-07 at 14:24:27ID: 18263427

http://au.php.net/manual/en/function.mcrypt-decrypt.php

at the bottom of the pages:

<?php
$text = "boggles the inivisble monkey will rule the world";
$key = "This is a very secret key";

$iv_size = mcrypt_get_iv_size(MCRYPT_XTEA, MCRYPT_MODE_ECB);
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
echo strlen($text) . "<br>";

$enc = mcrypt_encrypt(MCRYPT_XTEA, $key, $text, MCRYPT_MODE_ECB, $iv);
echo strlen($enc) . "<br>";
 
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
$key = "This is a very secret key";
$text = "Meet me at 11 o'clock behind the monument.";
echo strlen($text) . "<br>";

$crypttext = mcrypt_decrypt(MCRYPT_XTEA, $key, $enc, MCRYPT_MODE_ECB, $iv);
echo "$crypttext<br>";
?>

 

by: hernst42Posted on 2007-01-08 at 01:45:04ID: 18265604

Decrypting should work as written in http://de3.php.net/manual/en/function.mdecrypt-generic.php:

  /* Open module, and create IV */
   $td = mcrypt_module_open('tripledes', '', 'ecb', '');
   $key = substr($key, 0, mcrypt_enc_get_key_size($td));
   $iv_size = mcrypt_enc_get_iv_size($td);
   $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

   /* Initialize encryption handle */
   if (mcrypt_generic_init($td, $key, $iv) != -1) {
       $p_t = mdecrypt_generic($td, $c_t);

       /* Clean up */
       mcrypt_generic_deinit($td);
       mcrypt_module_close($td);
   }

 

by: mensuckPosted on 2007-01-08 at 07:37:06ID: 18267444

Here's a couple of functions (they add gzip compress and hex conversion to make the string transport safe)

<?php

// super secret key

define ( 'SYS_KEY', 'my_secret_key' );

// string to protect

$string = 'protect me';

// usage

// encrypt string

$str = encrypt_string ( $string );

// show the encrypted string

echo "encrypted string\r\n<br />\r\n" . $str . "\r\n<br />\r\n";

// decrypt string

$str = decrypt_string ( $str );

echo "decrypted string\r\n<br />\r\n" . $str . "\r\n<br />\r\n";

/* the functions */

/*
* protect a string
*/

function encrypt_string ( $str )
{
      $obj = mcrypt_create_iv ( mcrypt_get_iv_size ( MCRYPT_XTEA, MCRYPT_MODE_ECB ), MCRYPT_RAND );

      return bin2hex ( gzcompress ( mcrypt_encrypt ( MCRYPT_XTEA, SYS_KEY, $str, MCRYPT_MODE_ECB, $obj ), 9 ) );
}

/*
* decode a protected string
*/

function decrypt_string ( $str )
{
      $str = @gzuncompress ( @pack ( 'H*', $str ) );

      $obj = @mcrypt_create_iv ( @mcrypt_get_iv_size ( MCRYPT_XTEA, MCRYPT_MODE_ECB ), MCRYPT_RAND );

      return @mcrypt_decrypt ( MCRYPT_XTEA, SYS_KEY, $str, MCRYPT_MODE_ECB, $obj );
}

?>


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