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PHP Implementation of AES-128 Encryption Utilizing the Mcrypt Library's Rijndael-128 Algorithm

Posted on Saturday, June 5, 2010 at 8:11PM by Jack Servedio

Storing sensitive personal data may seem like a frightening idea, especially when a single compromise can completely ruin a company. However, you can safely store sensitive information reliably by strictly adhering to the PCI DSS Standards. However, no matter how much money you spend on your infrastructure or how much time you spend tightening your policies, they are all useless without properly encrypting your data. Now don't get me wrong, hardening your servers and having air tight policies are essential, but your encryption algorithm is the key to ensuring that even if your infrastructure is compromised, your customers' sensitive information is never accessed.

The pinnacle of encryption algorithms is Advanced Encryption Standard (AES). AES is the only public encryption algorithm that has been approved by the National Security Agency (NSA) to store and transfer Secret and Top-Secret sensitive information. To learn more about AES and how it works, you can read a comprehensive overview on Wikipedia's Advanced Encryption Standard. However, due to the fact that PHP's Mcrypt Library doesn't have AES built in, we will implement AES-128 utilizing the Rijndael-128 encryption algorithm, which is interchangeable AES. You may have heard of AES-256, which is more secure than AES-128, and be wondering why we aren't using the Rijndael-256 encryption method in the Mcrypt Library, which would seem logical. However, Rijndael-256 doesn't actually mean it is using a 256 bit key like you may think, 256 actually describes the block size data is broken down to.

Our implementation will utilize an initialization vector with a 128-bit key using the CFB Mode. After the data is encrypted, it will be stored in Base 64 along with the Initialization Vector. When encrypting and decrypting, the Initialization Vector and Key are needed. When storing encrypted data in a database, the Initialization Vector is stored along with the encrypted data prefixed by the Initialization Vector, in base 64. The mode can be changed from CFB to ECB or CBC by passing a mode parameter. ECB is the default meant for small amounts of data such as credit card numbers. CBC should be used when encrypting larger amounts of data, such as files and CFB should be used for small amounts of data such as streams.

// Class: AES-128 Implementation Utilizing Mcrypt's Rijndael-128 Algorithm
    // File: AES128.class.php
    // Author: Jack Servedio -
    // Published: July 2, 2010
    // Current: v1.00 (2010-07-02)
    /* About This Class
            - PHP 4 >= 4.3.0, PHP 5
            - PHP Mcrypt library
        This class implements AES-128 Encryption utilizing the PHP Mcrypt Library with the Rijndael-128 Algorithm. This encryption method uses an Intialization Vector as "seed" along with a 128-bit key. The encrypted data is stored in Base 64 prepended by the Initialization Vector also in Base 64.
        Copyright 2010 Jack Servedio
class AES128 {
//Private Member Variables
private $key$iv$data$mode$encrypted_data$encrypted_string;
        //Instantiates the Object and allows the 128-bit Encryption Key to be passed as a parameter. If a 128-bit key (32 Hex Characters) isn't supplied, or is too short, it will be padded '\0' to fill 128-bits.
        //Mode can also be set by passing ECB, CFB, or CBC
public function AES128$key ""$mode "ECB" ) {
//Sets key member variable from string passed through the parameter key
$this->key $key;
//Sets Encryption Mode from mode parameter
switch( $mode ) {
$this->mode MCRYPT_MODE_ECB;
$this->mode MCRYPT_MODE_CFB;
$this->mode MCRYPT_MODE_CBC;
$this->mode MCRYPT_MODE_ECB;
//Method to Generate and Set the Initialization Vector
private function generate_iv() {
//Generates a Random Initialization Vector for the Rijndael Cipher using the System Random Generator
$this->iv mcrypt_create_ivmcrypt_get_block_sizeMCRYPT_RIJNDAEL_128$this->mode ), MCRYPT_RAND );
//Method to Encrypt Data
        //Encrypts the data passed through the data parameter in Rijndael-128 algorithm in CFB mode and returns the encrypted data in base 64 encoding prefixed by the initialization vector
public function encrypt$data ) {
//Set data member variable with string passed through the data parameter
$this->data $data;

//Generate Initialization Vector using the generate_iv method

//Encrypt Data to AES-128 Standards in CFB Mode
$this->encrypted_data mcrypt_encryptMCRYPT_RIJNDAEL_128$this->key$this->data$this->mode$this->iv );

//Create Storage Encryption String from Base 64 Encrypted Data prefixed by Base 64 IV
$this->encrypted_string base64_encode$this->iv ) . base64_encode$this->encrypted_data );
//Returns the Encrypted String
return $this->encrypted_string;

//Method to Decrypt Encrypted Data
        //Decrypts Encrypted data passed through encrypted_string variable by separating the IV and Encrypted Data using the Rijndael-128 algorithm in CFB mode and returns the plain text
public function decrypt$encrypted_string ) {
//Set Encryption String member variable from encrypted string parameter
$this->encrypted_string $encrypted_string;

//Separate Base 64 Encoded Initialization Vector from Encrypted Data
$b64_iv substr$this->encrypted_string024 );
$b64_data substr$this->encrypted_string24 );

//Decode the Base 64 Initialization Vector and set Member Variable
$this->iv base64_decode$b64_iv );
//Decode the Base 64 Encrypted Data and set Member Variable
$this->encrypted_data base64_decode$b64_data );

//Decrypt Encrypted Data using Key and Initialization Vector with the Rijndael-128 algorithm in CFB mode and set member variable
$this->data mcrypt_decryptMCRYPT_RIJNDAEL_128$this->key$this->encrypted_data$this->mode$this->iv);
//Return plain text decrypted
return $this->data;
//Method to Set Key Member Variable
public function set_key$key ) {
$this->key $key;
//Method to Get Encrypted String
public function get_encrypted_string() {
//Return Encrypted String Member Variable if its not Null
if( $this->encrypted_string != (null) )
//If Null, Return False
//Method to get plaintext data
public function get_data() {
//Return decrypted plain text if member variable isn't null
if( $this->data != (null) )
//If null, return false
//Method to get Initialization Vector Base 64 Encoded
public function get_iv() {
//Return Initialization Vector Base 64 Encoded if member variable isn't null
if( $this->iv != (null) )
//If null, return false
//Method to get Encrypted Data Base 64 Encoded
public function get_encrypted_data() {
$this->encrypted_data != (null) )

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