I am trying to apply PKCS7 padding to my PHP code. I derived my code from this gist
https://gist.github.com/Halama/5956871
The blocksize is expected to be 16 bytes. The data is "password" with a length of 8 bytes. After getting the pad, it will append it at the end of the data to be encrypted.
$blockSize = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, $thisMCRYPT_MODE_CBCmode);
$pad = $blockSize - (strlen($data) % $blockSize);
$data = $data . str_repeat(chr($pad), $pad);
The problem is there are (a lot) of instances that where the data fails to decrypt it.
Provided below are base64 encoded sample data. The first 16 bytes of the decoded sample represents the IV
working: cjg1RYWxlc8bDH2de43t0bv1ug36i8ayjWDQTela938= (pad length: 8)
not working: 9wWI+MyYj5ZVj2sC4xr7EgOsgNSoeTZW1yM8ddmqg18= (pad length: 122)
The pad length mentioned above is retrieved using this
$pad = ord($data[strlen($data) - 1]);
I am using mcrypt_enrypt to encrypt the string "password". The key I am using for mcrypt is
lGbsVE+qVO1P2ue0iCjrTPMU5hKX9aHE7r1aUUeqFag=
solved it. the "+" signs in the base64 encoded data is being converted to spaces when transported through http thus resulting into different values.
What I did is the client encoded the binary data to base64 and passed it through urlencode() function. The PHP side handled the data by using rawurldecode so it will ignore the "+" signs.