CodeIgniter User Guide Version 2.1.2

Encryption Class

The Encryption Class provides two-way data encryption. It uses a scheme that either compiles the message using a randomly hashed bitwise XOR encoding scheme, or is encrypted using the Mcrypt library. If Mcrypt is not available on your server the encoded message will still provide a reasonable degree of security for encrypted sessions or other such "light" purposes. If Mcrypt is available, you'll be provided with a high degree of security appropriate for storage.

Setting your Key

A key is a piece of information that controls the cryptographic process and permits an encrypted string to be decoded. In fact, the key you chose will provide the only means to decode data that was encrypted with that key, so not only must you choose the key carefully, you must never change it if you intend use it for persistent data.

It goes without saying that you should guard your key carefully. Should someone gain access to your key, the data will be easily decoded. If your server is not totally under your control it's impossible to ensure key security so you may want to think carefully before using it for anything that requires high security, like storing credit card numbers.


Your key can be either stored in your application/config/config.php, or you can design your own storage mechanism and pass the key dynamically when encoding/decoding.



Message Length


Initializing the Class

Like most other classes in CodeIgniter, the Encryption class is initialized in your controller using the $this->load->library function:


Once loaded, the Encrypt library object will be available using: $this->encrypt


Performs the data encryption and returns it as a string. Example:

$msg = 'My secret message';

$encrypted_string = $this->encrypt->encode($msg);

You can optionally pass your encryption key via the second parameter if you don't want to use the one in your config file:

$msg = 'My secret message';
$key = 'super-secret-key';

$encrypted_string = $this->encrypt->encode($msg, $key);


Decrypts an encoded string. Example:

$encrypted_string = 'APANtByIGI1BpVXZTJgcsAG8GZl8pdwwa84';



$msg = 'My secret message';
$key = 'super-secret-key';

$encrypted_string = $this->encrypt->decode($msg, $key);


Permits you to set an Mcrypt cipher. By default it uses MCRYPT_RIJNDAEL_256. Example:


Please visit for a list of available ciphers.

If you'd like to manually test whether your server supports Mcrypt you can use:

echo ( ! function_exists('mcrypt_encrypt')) ? 'Nope' : 'Yup';


Permits you to set an Mcrypt mode. By default it uses MCRYPT_MODE_CBC. Example:


Please visit for a list of available modes.


SHA1 encoding function. Provide a string and it will return a 160 bit one way hash. Note: SHA1, just like MD5 is non-decodable. Example:

$hash = $this->encrypt->sha1('Some string');

Many PHP installations have SHA1 support by default so if all you need is to encode a hash it's simpler to use the native function:

$hash = sha1('Some string');

If your server does not support SHA1 you can use the provided function.

$this->encrypt->encode_from_legacy($orig_data, $legacy_mode = MCRYPT_MODE_ECB, $key = '');

Enables you to re-encode data that was originally encrypted with CodeIgniter 1.x to be compatible with the Encryption library in CodeIgniter 2.x. It is only necessary to use this method if you have encrypted data stored permanently such as in a file or database and are on a server that supports Mcrypt. "Light" use encryption such as encrypted session data or transitory encrypted flashdata require no intervention on your part. However, existing encrypted Sessions will be destroyed since data encrypted prior to 2.x will not be decoded.

Why only a method to re-encode the data instead of maintaining legacy methods for both encoding and decoding? The algorithms in the Encryption library have improved in CodeIgniter 2.x both for performance and security, and we do not wish to encourage continued use of the older methods. You can of course extend the Encryption library if you wish and replace the new methods with the old and retain seamless compatibility with CodeIgniter 1.x encrypted data, but this a decision that a developer should make cautiously and deliberately, if at all.

$new_data = $this->encrypt->encode_from_legacy($old_encrypted_string);
Parameter Default Description
$orig_data n/a The original encrypted data from CodeIgniter 1.x's Encryption library
$legacy_mode MCRYPT_MODE_ECB The Mcrypt mode that was used to generate the original encrypted data. CodeIgniter 1.x's default was MCRYPT_MODE_ECB, and it will assume that to be the case unless overridden by this parameter.
$key n/a The encryption key. This it typically specified in your config file as outlined above.