i have this on my php code:
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB); $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND); $key = \"bla\";
I bet, you're stumbling upon a padding issue. I addressed this topic in three SO answers, so you likely find the solution in one of those answers:
Difference in PHP encryption from iOS and .NET
AES Encrypt in C#, decrypt in PHP
DES Encryption in PHP and C#