How to decrypt with as3crypto string encrypted with by aes-256-ecb?

Question

String is encrypted with php as here. It can be decrypted by this with parameters: Rijndael-256, ECB and Base64. But it cannot be decrypted by my ActionScript code:

var text:String = "Some data";
var key:ByteArray = new ByteArray();
key.writeUTFBytes("SomePassword");
key.position = key.length;
for (var i:int = key.length; i < 256 / 8; i++) {
    key.writeByte(0);
}
var pad:IPad = new NullPad();
var cipher:ICipher = Crypto.getCipher("aes-256-ecb", key, pad);
var data:ByteArray = Base64.decodeToByteArray(text);
cipher.decrypt(data);
trace(data.toString());

UPD:

"It cannot be decrypted" means I get wrong plain text.

In php plain text is encrypted by aes-256-ecb firstly. Then it is encoded by Base64. In ActionScript these stepsarw being done in reverse order.

UPD2:

Test for encoding-decoding:

var key:ByteArray = new ByteArray();
key.writeUTFBytes("Some password");
key.position = key.length;
for (var i:int = key.length; i < 256 / 8; i++) {
    key.writeByte(0);
}
trace(key.toString());
var data:ByteArray = new ByteArray();//plain text
data.writeUTFBytes("Hello, my dear World! Hello, the Sun! Hello, the Moon! Hello! Hello! Hello!");
var pad:IPad = new NullPad();
var cipher:ICipher = Crypto.getCipher("aes-256-ecb", key, pad);
trace(data.toString());//trace plain text
cipher.encrypt(data);
trace(data.toString());//trace encrypted text
cipher.decrypt(data);
trace(data.toString());//trace decrypted text

The output after halting at cihper.encrypt(data) is:

Some password
Hello, my dear World! Hello, the Sun! Hello, the Moon! Hello! Hello! Hello!
[Fault] exception, information=Error: Error #2030: End of file found.

UPD3:

It works right with PKCS5 padding:

var pad:IPad = new PKCS5();
var cipher:ICipher = Crypto.getCipher("aes-256-ecb", key, pad);
pad.setBlockSize(cipher.getBlockSize());

Output is:

Some password
Hello, my dear World! Hello, the Sun! Hello, the Moon! Hello! Hello! Hello!
$ú^{±àÙ[pm|x¿9¡ÃZsI D¾`©4¾þÂõ,J
('èfÑk1ôì&ªQƆfbÇåòþ§VµÄs   ¦p<iÿ
Hello, my dear World! Hello, the Sun! Hello, the Moon! Hello! Hello! Hello!

UPD4:

For data gotten from php (as here) code with PKCS5 padding running halts here. And with Null padding it doesn't halts but decrypted data is wrong.

"*it cannot be decrypted*" is not a good error description. Do you get the wrong plaintext? Do you get an error? — Duncan Jones, Dec 05 '12 at 08:44
This means the implementation of algorithm is different in PHP and AS3Crypto. Try another algorith, like rc4 or BlowFish. — alxx, Dec 05 '12 at 18:02
Try to encrypt the same string with same pass in PHP and AS3Crypto, what you will get? — alxx, Dec 05 '12 at 18:03

score 2 · Accepted Answer · answered Dec 06 '12 at 21:57

2

Quoting the code in your last post:

return trim(
    base64_encode(
        mcrypt_encrypt(
            MCRYPT_RIJNDAEL_256,
            $sSecretKey, $sValue, 
            MCRYPT_MODE_ECB, 
            mcrypt_create_iv(
                mcrypt_get_iv_size(
                    MCRYPT_RIJNDAEL_256, 
                    MCRYPT_MODE_ECB
                ), 
                MCRYPT_RAND)
            )
        )
    );

MCRYPT_RIJNDAEL_256 isn't AES. MCRYPT_RIJNDAEL_128 is. Rijndael has variable block sizes. AES is a subset of Rijndael with fixed block sizes.

The number after MCRYPT_RIJNDAEL_* is referring to the block size. So MCRYPT_RIJNDAEL_256 is Rijndael with a 256-bit block size. MCRYPT_RIJNDAEL_128 is Rijndael with a 128-block size, aka AES.

Also, if you're going to use MCRYPT_MODE_ECB I'd replace the mcrypt_create_iv() call with an empty string of a bunch of null bytes. ECB as a block mode does not use an IV.

Finally, my own personal recommendation, since this is all very counter intuitive with mcrypt, is to use phpseclib, a pure PHP AES implementation.

answered Dec 06 '12 at 21:57

neubert

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So I can't decrypt RIJNDAEL_256_ECB by as3crypto? – user1826684 Dec 07 '12 at 00:41
But phpseclib offers AES-256-ECB. – user1826684 Dec 07 '12 at 00:43
Decrypting RIJNDAEL_256_ECB with as3crypto is probably not possible. – neubert Dec 07 '12 at 00:51
As for phpseclib's offering AES-256-ECB... both AES and Rijndael support variable key sizes. Only Rijndael supports variable block sizes as well. – neubert Dec 07 '12 at 00:52
Will using of MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB for PHP and aes-128-ecb for as3crypto (with 128-bit keys for both) solve the problem? – user1826684 Dec 07 '12 at 01:12

How to decrypt with as3crypto string encrypted with by aes-256-ecb?

1 Answers1