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i tried to encrypt a text in as3crypto via the demo app.

now i am trying to decrypt the crypted text via php but it seems that the text is not properly decrypted. has anyone know how to properly decrypt it via PHP? or am I doing it wrong? please enlighten me...

here's the scenario:

  1. encrypt this in http://crypto.hurlant.com/demo/:

    encryption: AES

    mode: CBC

    padding: none

    key: 11918f8bcd112e92744125008722050c

    text: Lorem ipsum dolor sit amet, consectetur adipiscing elit. In ut massa nec purus laoreet posuere quis vitae tortor.

    initialize vector: leave it blank

  2. press encrypt. select base64 and copy the cipher text.

  3. make a php script that has these codes and run it:

    $cipher = MCRYPT_RIJNDAEL_128;

    $mode = MCRYPT_MODE_CBC;

    $key = "11918f8bcd112e92744125008722050c";

    $cipher = "PLACE CIPHER TEXT HERE...";

    $data = base64_decode($cipher);

    echo mcrypt_decrypt($cipher, $key, $data, $mode);

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2 Answers

up vote 0 down vote accepted

the issue probably lies in your key. While you can feed a hex string to as3crypto and it will know what do to with it, mcrypt_decrypt will interpret each character as it's underlying ASCII value (like a = 97) instead of it's hexadecimal value (a = 10). Use the hex2bin method to convert the hex string into a byte string, and your decryption should probably work fine.

also, an issue may rest with different ideas of a default IV (initialization vector) between as3crypto and php. Since you are using CBC mode, you should be specifying an IV, just as a good security practice. also be aware of the potential pitfalls similar to those with your key, of specifying a hex string in as3 and needing to convert it in php.

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i will keep that in mind Peter, will try your suggestions first –  gptimajo Mar 20 '13 at 5:26
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This would work:

PHP code:

//notice that $key and $iv length must be 16 chars long! ex: 1234567890123456
function decrypt($data,$key,$iv)

    $decr= mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, base64_decode($data), MCRYPT_MODE_CBC, $iv);    
    return $decr;   

And here is AS3 code

private function encrypt(input:String,decrKey:String,decrIV:String):String
    var inputBA:ByteArray=Hex.toArray(Hex.fromString(input));        
    var key:ByteArray = Hex.toArray(Hex.fromString(decrKey));                
    var pad:IPad = new NullPad();
    var aes:ICipher = Crypto.getCipher("aes-cbc", key, pad);
    var ivmode:IVMode = aes as IVMode;
    ivmode.IV = Hex.toArray(Hex.fromString(decrIV));            

    return Base64.encodeByteArray( inputBA);
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