PHP: mdecrypt_generic - Manual

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MCVE mcrypt_ofb

Last updated: Sat, 27 Jan 2007

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# mdecrypt_generic

(PHP 4 >= 4.0.2, PHP 5)

mdecrypt_generic -- Decrypt data

## Description

string mdecrypt_generic ( resource td, string data )

This function decrypts data. Note that the length of the returned string can in fact be longer then the unencrypted string, due to the padding of the data.

Пример 1. mdecrypt_generic() example

`<?php
/* Data */
$key = 'this is a very long key, even too long for the cipher';
$plain_text = 'very important data';
/* Open module, and create IV */
$td = mcrypt_module_open('des', '', '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) {
/* Encrypt data */
$c_t = mcrypt_generic($td, $plain_text);
mcrypt_generic_deinit($td);
/* Reinitialize buffers for decryption */
mcrypt_generic_init($td, $key, $iv);
$p_t = mdecrypt_generic($td, $c_t);
/* Clean up */
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
}
if (strncmp($p_t, $plain_text, strlen($plain_text)) == 0) {
echo "ok\n";
} else {
echo "error\n";
}
?>`

The above example shows how to check if the data before the encryption is the same as the data after the decryption. It is very important to reinitialize the encryption buffer with mcrypt_generic_init() before you try to decrypt the data.

The decryption handle should always be initialized with mcrypt_generic_init() with a key and an IV before calling this function. Where the encryption is done, you should free the encryption buffers by calling mcrypt_generic_deinit(). See mcrypt_module_open() for an example.

See also mcrypt_generic(), mcrypt_generic_init(), and mcrypt_generic_deinit().

add a note User Contributed Notes
mdecrypt_generic
php at pcwize dot com
12-Oct-2006 02:59
`Just confirming the .DLL issues. With 4.3.4 you need the older .DLL. I'm guessing any version of PHP4 needs the older .DLL. With PHP5 you need the newer one.`
drew at expressdynamics dot com
05-Jul-2005 10:07
`On Win32 systems with PHP 5, you must use the newer libmcrypt.dll file, otherwise mdecrypt_generic will not work.`
robbie [at] averill [dot] co [dot] nz
24-Mar-2005 03:15
`I have noticed that sometimes when the binary ciphertext is longer than the plaintext, the decrypted plaintext can have some little boxes/squares next to it as 'padding'. I also noticed that you can't cut and paste them to be able to edit them out, but i did find a solution.
Just call rtrim() around the string and it removes them.`
jon@jonroig dot com
07-Apr-2004 07:29
`Here's a bit of encrypt/decrypt code.
If you're using this on the win32 platform, BEWARE! The latest DLL (19-Jan-2004) contains a bug that keeps mdecrypt_generic from functioning. Nearly drove me over the edge... The 30-Dec-2002 version seems to work with no trouble.
<?
$key = "this is a secret key";
$input = "Let us meet at 9 o'clock at the secret place.";
$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($td);
echo "Encrypt: ".$encrypted_data;
echo "<br><br>";
$td = mcrypt_module_open('tripledes', '', 'ecb', '');
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
$key = substr($key, 0, mcrypt_enc_get_key_size($td));
mcrypt_generic_init($td, $key, $iv);
$decrypted_data = mdecrypt_generic($td, $encrypted_data);
echo "Decrypt: ".$decrypted_data;
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
?>`
add a note
MCVE mcrypt_ofb

Last updated: Sat, 27 Jan 2007
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