Encryption Library


DO NOT use this or any other encryption library for user password storage! Passwords must be hashed instead, and you should do that via PHP’s own Password Hashing extension.

The Encryption Library provides two-way data encryption. To do so in a cryptographically secure way, it utilizes PHP extensions that are unfortunately not always available on all systems. You must meet one of the following dependencies in order to use this library:

  • OpenSSL (and PHP 5.3.3)
  • MCrypt (and MCRYPT_DEV_URANDOM availability)

If neither of the above dependencies is met, we simply cannot offer you a good enough implementation to meet the high standards required for proper cryptography.

Using the Encryption Library

Initializing the Class

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


Once loaded, the Encryption library object will be available using:


Default behavior

By default, the Encryption Library will use the AES-128 cipher in CBC mode, using your configured encryption_key and SHA512 HMAC authentication.


AES-128 is chosen both because it is proven to be strong and because of its wide availability across different cryptographic software and programming languages’ APIs.

However, the encryption_key is not used as is.

If you are somewhat familiar with cryptography, you should already know that a HMAC also requires a secret key and using the same key for both encryption and authentication is a bad practice.

Because of that, two separate keys are derived from your already configured encryption_key: one for encryption and one for authentication. This is done via a technique called HMAC-based Key Derivation Function (HKDF).

Setting your encryption_key

An encryption key is a piece of information that controls the cryptographic process and permits a plain-text string to be encrypted, and afterwards - decrypted. It is the secret “ingredient” in the whole process that allows you to be the only one who is able to decrypt data that you’ve decided to hide from the eyes of the public. After one key is used to encrypt data, that same key provides the only means to decrypt it, so not only must you chose one carefully, but you must not lose it or you will also lose access to the data.

It must be noted that to ensure maximum security, such key should not only be as strong as possible, but also often changed. Such behavior however is rarely practical or possible to implement, and that is why CodeIgniter gives you the ability to configure a single key that is to be used (almost) every time.

It goes without saying that you should guard your key carefully. Should someone gain access to your key, the data will be easily decrypted. 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 encryption key must be as long as the encyption algorithm in use allows. For AES-128, that’s 128 bits or 16 bytes (charcters) long. You will find a table below that shows the supported key lengths of different ciphers.

The key should be as random as possible and it must not be a regular text string, nor the output of a hashing function, etc. In order to create a proper key, you must use the Encryption library’s create_key() method

// $key will be assigned a 16-byte (128-bit) random key
$key = $this->encryption->create_key(16);

The 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 encrypting/decrypting.

To save your key to your application/config/config.php, open the file and set:

$config['encryption_key'] = 'YOUR KEY';

You’ll notice that the create_key() method outputs binary data, which is hard to deal with (i.e. a copy-paste may damage it), so you may use bin2hex(), hex2bin() or Base64-encoding to work with the key in a more friendly manner. For example:

// Get a hex-encoded representation of the key:
$key = bin2hex($this->encryption->create_key(16));

// Put the same value in your config with hex2bin(),
// so that it is still passed as binary to the library:
$config['encryption_key'] = hex2bin(<your hex-encoded key>);

Supported encryption ciphers and modes


The terms ‘cipher’ and ‘encryption algorithm’ are interchangeable.

Portable ciphers

Because MCrypt and OpenSSL (also called drivers throughout this document) each support different sets of encryption algorithms and often implement them in different ways, our Encryption library is designed to use them in a portable fashion, or in other words - it enables you to use them interchangeably, at least for the ciphers supported by both drivers.

It is also implemented in a way that aims to match the standard implementations in other programming languages and libraries.

Here’s a list of the so called “portable” ciphers, where “CodeIgniter name” is the string value that you’d have to pass to the Encryption library to use that cipher:

Cipher name CodeIgniter name Key lengths (bits / bytes) Supported modes
AES-128 / Rijndael-128 aes-128 128 / 16 CBC, CTR, CFB, CFB8, OFB, ECB
AES-192 aes-192 192 / 24 CBC, CTR, CFB, CFB8, OFB, ECB
AES-256 aes-256 256 / 32 CBC, CTR, CFB, CFB8, OFB, ECB
DES des 56 / 7 CBC, CFB, CFB8, OFB, ECB
TripleDES tripledes 56 / 7, 112 / 14, 168 / 21 CBC, CFB, CFB8, OFB
Blowfish blowfish 128-448 / 16-56 CBC, CFB, OFB, ECB
CAST5 / CAST-128 cast5 88-128 / 11-16 CBC, CFB, OFB, ECB
RC4 / ARCFour rc4 40-2048 / 5-256 Stream


Because of how MCrypt works, if you fail to provide a key with the appropriate length, you might end up using a different algorithm than the one configured, so be really careful with that!


In case it isn’t clear from the above table, Blowfish, CAST5 and RC4 support variable length keys. That is, any number in the shown ranges is valid, although in bit terms that only happens in 8-bit increments.


Even though CAST5 supports key lengths lower than 128 bits (16 bytes), in fact they will just be zero-padded to the maximum length, as specified in RFC 2144.


Blowfish supports key lengths as small as 32 bits (4 bytes), but our tests have shown that only lengths of 128 bits (16 bytes) or higher are properly supported by both MCrypt and OpenSSL. It is also a bad practice to use such low-length keys anyway.

Driver-specific ciphers

As noted above, MCrypt and OpenSSL support different sets of encryption ciphers. For portability reasons and because we haven’t tested them properly, we do not advise you to use the ones that are driver-specific, but regardless, here’s a list of most of them:

Cipher name Driver Key lengths (bits / bytes) Supported modes
AES-128 OpenSSL 128 / 16 CBC, CTR, CFB, CFB8, OFB, ECB, XTS
AES-192 OpenSSL 192 / 24 CBC, CTR, CFB, CFB8, OFB, ECB, XTS
AES-256 OpenSSL 256 / 32 CBC, CTR, CFB, CFB8, OFB, ECB, XTS
Rijndael-128 MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
Rijndael-192 MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
Rijndael-256 MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
GOST MCrypt 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
Twofish MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
CAST-128 MCrypt 40-128 / 5-16 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
CAST-256 MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
Loki97 MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
SaferPlus MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
Serpent MCrypt 128 / 16, 192 / 24, 256 / 32 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
XTEA MCrypt 128 / 16 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
RC2 MCrypt 8-1024 / 1-128 CBC, CTR, CFB, CFB8, OFB, OFB8, ECB
RC2 OpenSSL 8-1024 / 1-128 CBC, CFB, OFB, ECB
Camellia-128 OpenSSL 128 / 16 CBC, CFB, CFB8, OFB, ECB
Camellia-192 OpenSSL 192 / 24 CBC, CFB, CFB8, OFB, ECB
Camellia-256 OpenSSL 256 / 32 CBC, CFB, CFB8, OFB, ECB
Seed OpenSSL 128 / 16 CBC, CFB, OFB, ECB


If you wish to use one of those ciphers, you’d have to pass its name in lower-case to the Encryption library.


You’ve probably noticed that all AES cipers (and Rijndael-128) are also listed in the portable ciphers list. This is because drivers support different modes for these ciphers. Also, it is important to note that AES-128 and Rijndael-128 are actually the same cipher, but only when used with a 128-bit key.


CAST-128 / CAST-5 is also listed in both the portable and driver-specific ciphers list. This is because OpenSSL’s implementation doesn’t appear to be working correctly with key sizes of 80 bits and lower.


RC2 is listed as supported by both MCrypt and OpenSSL. However, both drivers implement them differently and they are not portable. It is probably worth noting that we only found one obscure source confirming that it is MCrypt that is not properly implementing it.

Encryption modes

Different modes of encryption have different characteristics and serve for different purposes. Some are stronger than others, some are faster and some offer extra features. We are not going in depth into that here, we’ll leave that to the cryptography experts. The table below is to provide brief informational reference to our more experienced users. If you are a beginner, just stick to the CBC mode - it is widely accepted as strong and secure for general purposes.

Mode name CodeIgniter name Driver support Additional info
CBC cbc MCrypt, OpenSSL A safe default choice
CTR ctr MCrypt, OpenSSL Considered as theoretically better than CBC, but not as widely available
CFB cfb MCrypt, OpenSSL N/A
CFB8 cfb8 MCrypt, OpenSSL Same as CFB, but operates in 8-bit mode (not recommended).
OFB ofb MCrypt, OpenSSL N/A
OFB8 ofb8 MCrypt Same as OFB, but operates in 8-bit mode (not recommended).
ECB ecb MCrypt, OpenSSL Ignores IV (not recommended).
XTS xts OpenSSL Usually used for encrypting random access data such as RAM or hard-disk storage.
Stream stream MCrypt, OpenSSL This is not actually a mode, it just says that a stream cipher is being used. Required because of the general cipher+mode initialization process.

Message Length

It’s probably important for you to know that an encrypted string is usually longer than the original, plain-text string (depending on the cipher).

This is influenced by the cipher algorithm itself, the IV prepended to the cipher-text and the HMAC authentication message that is also prepended. Furthermore, the encrypted message is also Base64-encoded so that it is safe for storage and transmission, regardless of a possible character set in use.

Keep this information in mind when selecting your data storage mechanism. Cookies, for example, can only hold 4K of information.

Configuring the library

For usability, performance, but also historical reasons tied to our old Encrypt Class, the Encryption library is designed to use repeatedly the same driver, encryption cipher, mode and key.

As noted in the “Default behavior” section above, this means using an auto-detected driver (OpenSSL has a higher priority), the AES-128 ciper in CBC mode, and your $config['encryption_key'] value.

If you wish to change that however, you need to use the initialize() method. It accepts an associative array of parameters, all of which are optional:

Option Possible values
driver ‘mcrypt’, ‘openssl’
cipher Cipher name (see Supported encryption ciphers and modes)
mode Encryption mode (see Encryption modes)
key Encryption key

For example, if you were to change the encryption algorithm and mode to AES-256 in CTR mode, this is what you should do:

                'cipher' => 'aes-256',
                'mode' => 'ctr',
                'key' => '<a 32-character random string>'

Note that we only mentioned that you want to change the ciper and mode, but we also included a key in the example. As previously noted, it is important that you choose a key with a proper size for the used algorithm.

There’s also the ability to change the driver, if for some reason you have both, but want to use MCrypt instead of OpenSSL:

// Switch to the MCrypt driver
$this->encryption->initialize(array('driver' => 'mcrypt'));

// Switch back to the OpenSSL driver
$this->encryption->initialize(array('driver' => 'openssl'));

Encrypting and decrypting data

Encrypting and decrypting data with the already configured library settings is simple. As simple as just passing the string to the encrypt() and/or decrypt() methods:

$plain_text = 'This is a plain-text message!';
$ciphertext = $this->encryption->encrypt($plain_text);

// Outputs: This is a plain-text message!
echo $this->encryption->decrypt($ciphertext);

And that’s it! The Encryption library will do everything necessary for the whole process to be cryptographically secure out-of-the-box. You don’t need to worry about it.


Both methods will return FALSE in case of an error. While for encrypt() this can only mean incorrect configuration, you should always check the return value of decrypt() in production code.

How it works

If you must know how the process works, here’s what happens under the hood:

  • $this->encryption->encrypt($plain_text)
    1. Derive an encryption key and a HMAC key from your configured encryption_key via HKDF, using the SHA-512 digest algorithm.
    2. Generate a random initialization vector (IV).
    3. Encrypt the data via AES-128 in CBC mode (or another previously configured cipher and mode), using the above-mentioned derived encryption key and IV.
    4. Prepend said IV to the resulting cipher-text.
    5. Base64-encode the resulting string, so that it can be safely stored or transferred without worrying about character sets.
    6. Create a SHA-512 HMAC authentication message using the derived HMAC key to ensure data integrity and prepend it to the Base64 string.
  • $this->encryption->decrypt($ciphertext)
    1. Derive an encryption key and a HMAC key from your configured encryption_key via HKDF, using the SHA-512 digest algorithm. Because your configured encryption_key is the same, this will produce the same result as in the encrypt() method above - otherwise you won’t be able to decrypt it.
    2. Check if the string is long enough, separate the HMAC out of it and validate if it is correct (this is done in a way that prevents timing attacks agains it). Return FALSE if either of the checks fails.
    3. Base64-decode the string.
    4. Separate the IV out of the cipher-text and decrypt the said cipher-text using that IV and the derived encryption key.

Using custom parameters

Let’s say you have to interact with another system that is out of your control and uses another method to encrypt data. A method that will most certainly not match the above-described sequence and probably not use all of the steps either.

The Encryption library allows you to change how its encryption and decryption processes work, so that you can easily tailor a custom solution for such situations.


It is possible to use the library in this way, without setting an encryption_key in your configuration file.

All you have to do is to pass an associative array with a few parameters to either the encrypt() or decrypt() method. Here’s an example:

// Assume that we have $ciphertext, $key and $hmac_key
// from on outside source

$message = $this->encryption->decrypt(
                'cipher' => 'blowfish',
                'mode' => 'cbc',
                'key' => $key,
                'hmac_digest' => 'sha256',
                'hmac_key' => $hmac_key

In the above example, we are decrypting a message that was encrypted using the Blowfish cipher in CBC mode and authenticated via a SHA-256 HMAC.


Note that both ‘key’ and ‘hmac_key’ are used in this example. When using custom parameters, encryption and HMAC keys are not derived like the default behavior of the library is.

Below is a list of the available options.

However, unless you really need to and you know what you are doing, we advise you to not change the encryption process as this could impact security, so please do so with caution.

Option Default value Mandatory / Optional Description
cipher N/A Yes Encryption algorithm (see Supported encryption ciphers and modes).
mode N/A Yes Encryption mode (see Encryption modes).
key N/A Yes Encryption key.
hmac TRUE No Whether to use a HMAC. Boolean. If set to FALSE, then hmac_digest and hmac_key will be ignored.
hmac_digest sha512 No HMAC message digest algorithm (see Supported HMAC authentication algorithms).
hmac_key N/A Yes, unless hmac is FALSE HMAC key.
raw_data FALSE No Whether the cipher-text should be raw. Boolean. If set to TRUE, then Base64 encoding and decoding will not be performed and HMAC will not be a hexadecimal string.


encrypt() and decrypt() will return FALSE if a mandatory parameter is not provided or if a provided value is incorrect. This includes hmac_key, unless hmac is set to FALSE.

Supported HMAC authentication algorithms

For HMAC message authentication, the Encryption library supports usage of the SHA-2 family of algorithms:

Algorithm Raw length (bytes) Hex-encoded length (bytes)
sha512 64 128
sha384 48 96
sha256 32 64
sha224 28 56

The reason for not including other popular algorithms, such as MD5 or SHA1 is that they are no longer considered secure enough and as such, we don’t want to encourage their usage. If you absolutely need to use them, it is easy to do so via PHP’s native hash_hmac() function.

Stronger algorithms of course will be added in the future as they appear and become widely available.

Class Reference

class CI_Encryption
  • $params (array) – Configuration parameters

CI_Encryption instance (method chaining)

Return type:


Initializes (configures) the library to use a different driver, cipher, mode or key.


        array('mode' => 'ctr')

Please refer to the Configuring the library section for detailed info.

encrypt($data[, $params = NULL])
  • $data (string) – Data to encrypt
  • $params (array) – Optional parameters

Encrypted data or FALSE on failure

Return type:


Encrypts the input data and returns its ciphertext.


$ciphertext = $this->encryption->encrypt('My secret message');

Please refer to the Using custom parameters section for information on the optional parameters.

decrypt($data[, $params = NULL])
  • $data (string) – Data to decrypt
  • $params (array) – Optional parameters

Decrypted data or FALSE on failure

Return type:


Decrypts the input data and returns it in plain-text.


echo $this->encryption->decrypt($ciphertext);

Please refer to the Using custom parameters secrion for information on the optional parameters.

  • $length (int) – Output length

A pseudo-random cryptographic key with the specified length, or FALSE on failure

Return type:


Creates a cryptographic key by fetching random data from the operating system’s sources (i.e. /dev/urandom).

hkdf($key[, $digest = 'sha512'[, $salt = NULL[, $length = NULL[, $info = '']]]])
  • $key (string) – Input key material
  • $digest (string) – A SHA-2 family digest algorithm
  • $salt (string) – Optional salt
  • $length (int) – Optional output length
  • $info (string) – Optional context/application-specific info

A pseudo-random key or FALSE on failure

Return type:


Derives a key from another, presumably weaker key.

This method is used internally to derive an encryption and HMAC key from your configured encryption_key.

It is publicly available due to its otherwise general purpose. It is described in RFC 5869.

However, as opposed to the description in RFC 5869, this implementation doesn’t support SHA1.


$hmac_key = $this->encryption->hkdf(

// $hmac_key is a pseudo-random key with a length of 64 bytes