## Encryption Filters

mcrypt.* and mdecrypt.* provide symmetric encryption and decryption using libmcrypt. Both sets of filters support the same algorithms available to mcrypt extension in the form of mcrypt.ciphername where `ciphername` is the name of the cipher as it would be passed to mcrypt_module_open(). The following five filter parameters are also available:

mcrypt filter parameters
Parameter | Required? | Default | Sample Values
--- | --- | --- | ---
mode | Optional | cbc | cbc, cfb, ecb, nofb, ofb, stream
algorithms_dir | Optional | ini_get('mcrypt.algorithms_dir') | Location of algorithms modules
modes_dir | Optional | ini_get('mcrypt.modes_dir') | Location of modes modules
iv | Required | N/A | Typically 8, 16, or 32 bytes of binary data. Depends on cipher
key | Required | N/A | Typically 8, 16, or 32 bytes of binary data. Depends on cipher

Example#1 Encrypting file output using 3DES

`<?php
$passphrase = 'My secret';
/* Turn a human readable passphrase
* into a reproducable iv/key pair
*/
$iv = substr(md5('iv'.$passphrase, true), 0, 8);
$key = substr(md5('pass1'.$passphrase, true) .
md5('pass2'.$passphrase, true), 0, 24);
$opts = array('iv'=>$iv, 'key'=>$key);
$fp = fopen('secert-file.enc', 'wb');
stream_filter_append($fp, 'mcrypt.tripledes', STREAM_FILTER_WRITE, $opts);
fwrite($fp, 'Secret secret secret data');
fclose($fp);
?>`

Example#2 Reading an encrypted file

`<?php
$passphrase = 'My secret';
/* Turn a human readable passphrase
* into a reproducable iv/key pair
*/
$iv = substr(md5('iv'.$passphrase, true), 0, 8);
$key = substr(md5('pass1'.$passphrase, true) .
md5('pass2'.$passphrase, true), 0, 24);
$opts = array('iv'=>$iv, 'key'=>$key);
$fp = fopen('secert-file.enc', 'rb');
stream_filter_append($fp, 'mdecrypt.tripledes', STREAM_FILTER_WRITE, $opts);
$data = rtrim(stream_get_contents($fp));
fclose($fp);
echo $data;
?>`