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Last updated: Thu, 21 Aug 2003

LIII. Mcrypt Encryption Functions


This is an interface to the mcrypt library, which supports a wide variety of block algorithms such as DES, TripleDES, Blowfish (default), 3-WAY, SAFER-SK64, SAFER-SK128, TWOFISH, TEA, RC2 and GOST in CBC, OFB, CFB and ECB cipher modes. Additionally, it supports RC6 and IDEA which are considered "non-free".


These functions work using mcrypt. To use it, download libmcrypt-x.x.tar.gz from here and follow the included installation instructions. Windows users will find all the needed compiled mcrypt binaries here.

If you linked against libmcrypt 2.4.x or higher, the following additional block algorithms are supported: CAST, LOKI97, RIJNDAEL, SAFERPLUS, SERPENT and the following stream ciphers: ENIGMA (crypt), PANAMA, RC4 and WAKE. With libmcrypt 2.4.x or higher another cipher mode is also available; nOFB.


You need to compile PHP with the --with-mcrypt[=DIR] parameter to enable this extension. DIR is the mcrypt install directory. Make sure you compile libmcrypt with the option --disable-posix-threads.

Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Table 1. Mcrypt configuration options

For further details and definition of the PHP_INI_* constants see ini_set().

Resource Types

This extension has no resource types defined.

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

Mcrypt can operate in four block cipher modes (CBC, OFB, CFB, and ECB). If linked against libmcrypt-2.4.x or higher the functions can also operate in the block cipher mode nOFB and in STREAM mode. Below you find a list with all supported encryption modes together with the constants that are defines for the encryption mode. For a more complete reference and discussion see Applied Cryptography by Schneier (ISBN 0-471-11709-9).

  • MCRYPT_MODE_ECB (electronic codebook) is suitable for random data, such as encrypting other keys. Since data there is short and random, the disadvantages of ECB have a favorable negative effect.

  • MCRYPT_MODE_CBC (cipher block chaining) is especially suitable for encrypting files where the security is increased over ECB significantly.

  • MCRYPT_MODE_CFB (cipher feedback) is the best mode for encrypting byte streams where single bytes must be encrypted.

  • MCRYPT_MODE_OFB (output feedback, in 8bit) is comparable to CFB, but can be used in applications where error propagation cannot be tolerated. It's insecure (because it operates in 8bit mode) so it is not recommended to use it.

  • MCRYPT_MODE_NOFB (output feedback, in nbit) is comparable to OFB, but more secure because it operates on the block size of the algorithm.

  • MCRYPT_MODE_STREAM is an extra mode to include some stream algorithms like WAKE or RC4.

Some other mode and random device constants:





MCRYPT_RAND (integer)

Mcrypt ciphers

Here is a list of ciphers which are currently supported by the mcrypt extension. For a complete list of supported ciphers, see the defines at the end of mcrypt.h. The general rule with the mcrypt-2.2.x API is that you can access the cipher from PHP with MCRYPT_ciphername. With the libmcrypt-2.4.x and libmcrypt-2.5.x API these constants also work, but it is possible to specify the name of the cipher as a string with a call to mcrypt_module_open().


  • MCRYPT_ARCFOUR_IV (libmcrypt > 2.4.x only)

  • MCRYPT_ARCFOUR (libmcrypt > 2.4.x only)






  • MCRYPT_DES_COMPAT (libmcrypt 2.2.x only)

  • MCRYPT_ENIGMA (libmcrypt > 2.4.x only, alias for MCRYPT_CRYPT)


  • MCRYPT_IDEA (non-free)

  • MCRYPT_LOKI97 (libmcrypt > 2.4.x only)

  • MCRYPT_MARS (libmcrypt > 2.4.x only, non-free)

  • MCRYPT_PANAMA (libmcrypt > 2.4.x only)

  • MCRYPT_RIJNDAEL_128 (libmcrypt > 2.4.x only)

  • MCRYPT_RIJNDAEL_192 (libmcrypt > 2.4.x only)

  • MCRYPT_RIJNDAEL_256 (libmcrypt > 2.4.x only)


  • MCRYPT_RC4 (libmcrypt 2.2.x only)

  • MCRYPT_RC6 (libmcrypt > 2.4.x only)

  • MCRYPT_RC6_128 (libmcrypt 2.2.x only)

  • MCRYPT_RC6_192 (libmcrypt 2.2.x only)

  • MCRYPT_RC6_256 (libmcrypt 2.2.x only)



  • MCRYPT_SAFERPLUS (libmcrypt > 2.4.x only)

  • MCRYPT_SERPENT(libmcrypt > 2.4.x only)

  • MCRYPT_SERPENT_128 (libmcrypt 2.2.x only)

  • MCRYPT_SERPENT_192 (libmcrypt 2.2.x only)

  • MCRYPT_SERPENT_256 (libmcrypt 2.2.x only)

  • MCRYPT_SKIPJACK (libmcrypt > 2.4.x only)

  • MCRYPT_TEAN (libmcrypt 2.2.x only)


  • MCRYPT_TRIPLEDES (libmcrypt > 2.4.x only)

  • MCRYPT_TWOFISH (for older mcrypt 2.x versions, or mcrypt > 2.4.x )

  • MCRYPT_TWOFISH128 (TWOFISHxxx are available in newer 2.x versions, but not in the 2.4.x versions)



  • MCRYPT_WAKE (libmcrypt > 2.4.x only)

  • MCRYPT_XTEA (libmcrypt > 2.4.x only)

You must (in CFB and OFB mode) or can (in CBC mode) supply an initialization vector (IV) to the respective cipher function. The IV must be unique and must be the same when decrypting/encrypting. With data which is stored encrypted, you can take the output of a function of the index under which the data is stored (e.g. the MD5 key of the filename). Alternatively, you can transmit the IV together with the encrypted data (see chapter 9.3 of Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of this topic).


Mcrypt can be used to encrypt and decrypt using the above mentioned ciphers. If you linked against libmcrypt-2.2.x, the four important mcrypt commands (mcrypt_cfb(), mcrypt_cbc(), mcrypt_ecb(), and mcrypt_ofb()) can operate in both modes which are named MCRYPT_ENCRYPT and MCRYPT_DECRYPT, respectively.

Example 1. Encrypt an input value with TripleDES under 2.2.x in ECB mode

$key = "this is a secret key";
$input = "Let us meet at 9 o'clock at the secret place.";

$encrypted_data = mcrypt_ecb (MCRYPT_3DES, $key, $input, MCRYPT_ENCRYPT);
This example will give you the encrypted data as a string in $encrypted_data.

If you linked against libmcrypt 2.4.x or 2.5.x, these functions are still available, but it is recommended that you use the advanced functions.

Example 2. Encrypt an input value with TripleDES under 2.4.x and higher in ECB mode

    $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);
This example will give you the encrypted data as a string in $encrypted_data. For a full example see mcrypt_module_open().

Table of Contents
mcrypt_cbc -- Encrypt/decrypt data in CBC mode
mcrypt_cfb -- Encrypt/decrypt data in CFB mode
mcrypt_create_iv --  Create an initialization vector (IV) from a random source
mcrypt_decrypt -- Decrypts crypttext with given parameters
mcrypt_ecb -- Encrypt/decrypt data in ECB mode
mcrypt_enc_get_algorithms_name -- Returns the name of the opened algorithm
mcrypt_enc_get_block_size -- Returns the blocksize of the opened algorithm
mcrypt_enc_get_iv_size -- Returns the size of the IV of the opened algorithm
mcrypt_enc_get_key_size -- Returns the maximum supported keysize of the opened mode
mcrypt_enc_get_modes_name -- Returns the name of the opened mode
mcrypt_enc_get_supported_key_sizes -- Returns an array with the supported keysizes of the opened algorithm
mcrypt_enc_is_block_algorithm_mode -- Checks whether the encryption of the opened mode works on blocks
mcrypt_enc_is_block_algorithm -- Checks whether the algorithm of the opened mode is a block algorithm
mcrypt_enc_is_block_mode -- Checks whether the opened mode outputs blocks
mcrypt_enc_self_test -- This function runs a self test on the opened module
mcrypt_encrypt -- Encrypts plaintext with given parameters
mcrypt_generic_deinit --  This function deinitializes an encryption module
mcrypt_generic_end -- This function terminates encryption
mcrypt_generic_init -- This function initializes all buffers needed for encryption
mcrypt_generic -- This function encrypts data
mcrypt_get_block_size -- Get the block size of the specified cipher
mcrypt_get_cipher_name -- Get the name of the specified cipher
mcrypt_get_iv_size --  Returns the size of the IV belonging to a specific cipher/mode combination
mcrypt_get_key_size -- Get the key size of the specified cipher
mcrypt_list_algorithms -- Get an array of all supported ciphers
mcrypt_list_modes -- Get an array of all supported modes
mcrypt_module_close --  Close the mcrypt module
mcrypt_module_get_algo_block_size -- Returns the blocksize of the specified algorithm
mcrypt_module_get_algo_key_size -- Returns the maximum supported keysize of the opened mode
mcrypt_module_get_supported_key_sizes -- Returns an array with the supported keysizes of the opened algorithm
mcrypt_module_is_block_algorithm_mode -- This function returns if the the specified module is a block algorithm or not
mcrypt_module_is_block_algorithm -- This function checks whether the specified algorithm is a block algorithm
mcrypt_module_is_block_mode -- This function returns if the the specified mode outputs blocks or not
mcrypt_module_open -- Opens the module of the algorithm and the mode to be used
mcrypt_module_self_test -- This function runs a self test on the specified module
mcrypt_ofb -- Encrypt/decrypt data in OFB mode
mdecrypt_generic -- Decrypt data

add a note add a note User Contributed Notes
Mcrypt Encryption Functions
20-Oct-2003 11:42 is a good place for learning more.
04-Oct-2003 04:03
DEBIAN users: avoid mcrypt installation headaches.
to add mcrypt support to an existing php installation, get root and run

apt-get install php4-mcrypt

restart your webserver, and voil?
steve@itemfront dot ltd dot uk
29-Sep-2003 07:17
Just spent a while getting mcrypt support working with php. Used libmcrypt version 2.5.7 with php 4.3.3. Out of the box it just won't work. Configure as follows:


  ./configure --disable-posix-threads --enable-dynamic-loading

php: ( as you can see, it's built for a SunONE server, but that's the easy bit to configure! )

./configure  --with-nsapi=/usr/iplanet/servers --enable-sigchld --with-ldap --with-zlib-dir=/usr/lib --with-mcrypt=<srcdir>/libmcrypt-2.5.7

hth, steve
herowekker at hotmail dot com
31-Jul-2003 07:55
mcrypt_ecb with base64_decode gave some problems, i found out that it had to be chopped to work:

paul at xmill dot com
06-Nov-2002 02:25
The statement that use of the 'generic' functions is 'recommended' in 2.4+ should probably be 'required'.  Having like many others struggled with a "mcrypt module initialization failed" error even when phpinfo() showed mcrypt installed and all its algorithms loaded, I found that:

$key = mcrypt_ecb (MCRYPT_3DES, $magic, $input, MCRYPT_ENCRYPT);

fails, but

$td = mcrypt_module_open (MCRYPT_TripleDES, "", MCRYPT_MODE_ECB, "");
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size ($td), MCRYPT_RAND);
mcrypt_generic_init ($td, $magic, $iv);
$key = mcrypt_generic ($td, $input);
mcrypt_generic_end ($td);

works fine.  You can't leave out the creation of the IV to the right length, even though ECB doesn't use it (happily, because I want it repeatable).
scott at boothcreek dot com
28-Mar-2002 05:28
If you are using ECB mode to encrypt it does not seem to use the iv (initialization vector) for much of anything, given the same key it will always decrypt it no matter what the iv is.  If you use CBC mode you must decrypt with the same iv that you encrypted with.

 If you use a different iv before decrypting, your decrypt will not work.  IMHO it seems better to use CBC mode than ECB as ECB will always encrypt to the same cipher text given the same plain text  (leaving you open to know plaintext attacks).  CBC uses the random iv which means text encrypts to different things.  You probably could get the same effect from using random keys in ECB mode.

Read that in the Schneier book - Applied Cryptography (ISBN 0-471-11709-9)  This book is a must for anyone seriously using any type of encryption.
pawelNOSPAM at rsc dot pl
03-Aug-2001 08:37
If you compiled mcrypt and php without problem, but phpinfo() shows there are no supported ciphers and modes, try to change mode to 755 on libdirs (/usr/local/libmcrypt, /usr/local/libcrypt).
mountie at paygate dot net
10-Feb-2000 09:21
the encrypted result data maybe binary data and It make errors in sql query.
so use the base64_encode/base64_decode function with mcrypt()
try below


nsayer at quack dot kfu dot com
30-Jun-1999 09:31
For a practical example suitable for encrypting and
validating cookies or passing secure messages,
go to

 Last updated: Thu, 21 Aug 2003
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