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File: aes128encrypter.php

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File: aes128encrypter.php
Role: Class source
Content type: text/plain
Description: Class source
Class: AES128 Encrypter
Encrypt and decrypt data with AES 128
Author: By
Last change:
Date: 4 years ago
Size: 2,658 bytes
 

Contents

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<?php

/**
Requirements:
 - a initial string from which I create a key ($string)
 - for decryption:
   - given a base64 encoded string to be decrypted -> return clear text
 - for encryption:
   - given a clear Text -> return a base64 encoded string
 - every object is instanziated by the initial string:
   var encObj = new sswEncrypter($string);
   var aClearText = encObj.decrypt(base64encodedString);
   var aBase64EncodedString = encObj.encrypt(aClearText);
*/

class AES128encrypter
{
    public
$key;
   
    function
__construct($string)
    {
       
$this->key = pack('H*',md5($string));
    }
   
    private function
pkcs5_pad ($text, $blocksize) {
       
$pad = $blocksize - (strlen($text) % $blocksize);
        if(
$pad == 0) {
           
$pad = $blocksize;
        }
        return
$text . str_repeat(chr($pad), $pad);
    }

    function
encrypt($clearText,$ivStr = NULL)
    {
       
$key = $this->key;
       
$key_size = strlen($key);
       
// text has to be divisible by block size, thus a possibile padding is added
       
$plaintext = $this->pkcs5_pad($clearText,mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC));
       
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
       
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
        if(
$ivStr != NULL) {
            for(
$i = 0; $i<$iv_size && $i<strlen($ivStr); $i++) {
               
$iv[$i] = $ivStr[$i];
            }
        }
       
$ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key,
                        
$plaintext, MCRYPT_MODE_CBC, $iv);
       
# prepend the IV for it to be available for decryption
       
$ciphertext = $iv . $ciphertext;
       
$ciphertext_base64 = base64_encode($ciphertext);
        return
$ciphertext_base64;
    }

    function
decrypt($base64EncodedStr)
    {
       
$sKey = $this->key;
       
$ciphertext_dec = base64_decode($base64EncodedStr);
       
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
       
# retrieves the IV, iv_size should be created using mcrypt_get_iv_size()
       
$iv_dec = substr($ciphertext_dec, 0, $iv_size);
   
       
# retrieves the cipher text (everything except the $iv_size in the front)
       
$ciphertext_dec = substr($ciphertext_dec, $iv_size);
       
$plaintext_dec = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $sKey,
                       
$ciphertext_dec, MCRYPT_MODE_CBC, $iv_dec);
       
// and now remove the padding (possible)
       
$dec_s = strlen($plaintext_dec);
       
$padding = ord($plaintext_dec[$dec_s-1]);
       
$plaintext_dec = substr($plaintext_dec, 0, -$padding);
        return
$plaintext_dec;
    }

    function
getIV($base64EncodedStr) {
       
$ciphertext_dec = base64_decode($base64EncodedStr);
       
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
       
# retrieves the IV, iv_size should be created using mcrypt_get_iv_size()
       
$iv_dec = substr($ciphertext_dec, 0, $iv_size);

        return
$iv_dec;
    }

}

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