Question

I need to communicate with a asp platform that uses the aspEncrypt from persits.
Can anyone provide an example how to decode a string with PHP and mcrypt that was created via the aspEncrypt routines.

An example page of aspEncrypt is available at this link:
http://support.persits.com/encrypt/demo_text.asp

So if I use the text “Test” and the key “test” it provides an base64 encoded string. I need a php example that convert this encoded string back to the text “Test” with usage of key “test”.

Answer 1

This is how i finally solved it:

Expectation:

• Key is known
• IV is known (in my case, first 32 characters of encoded data)
• Encrypted Text is known

In my special case all received data hex encoded.
This means IV and encrypted text.

function decrypt($sString, $sIv, $sKey, $iCipherAlg) {       
   $sDecrypted = mcrypt_decrypt($iCipherAlg, $sKey, $sString, MCRYPT_MODE_CBC, $sIv);
    return trim($sDecrypted);
}

function hex2bin($sData) {
    $iLen = strlen($sData);
    $sNewData = '';
    for($iCount=0;$iCount<$iLen;$iCount+=2) {
        $sNewData .= pack("C",hexdec(substr($sData,$iCount,2)));
    }
    return $sNewData;
} 

$sKey = 'this is my key';
// first 32 chars are IV
$sIv = hex2bin(substr($sEncodedData, 0, 32));
$sEncodedData = substr($sEncodedData, 32);
$sEncodedRaw = hex2bin($sEncodedData);
$sDecrypted = decrypt($sEncodedRaw, $sIv, $sKey, MCRYPT_RIJNDAEL_128);

A corresponding encryption works like that:

$sIv = mcrypt_create_iv(mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC), MCRYPT_RAND);
$sKey = 'this is my key';
$sContent = 'a lot of content';
$sEncrypted = bin2hex(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $sKey, $sContent, MCRYPT_MODE_CBC, $sIv));
$sFullEncodedText = bin2hex($sIv) . $sEncrypted;