Decryption on PHP have problems after 16 digits - php

Question

I am doing AES encryption on ios End, and i the base64 encode that string and send over to php end. On the php end, i have following code:
<?php
$key = 'a16byteslongkey!';
$data = base64_decode('LsCH4nvvGPKN67v94Ig9BweQgOk9rtDdK7ZugeJkTS8=');
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
$iv = substr($data, 0, $iv_size);
function aes256_cbc_decrypt($key, $data, $iv) {
if(32 !== strlen($key)) $key = hash('SHA256', $key, true);
if(16 !== strlen($iv)) $iv = hash('MD5', $iv, true);
$data = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $data, MCRYPT_MODE_ECB, $iv);
$padding = ord($data[strlen($data) - 1]);
return substr($data, 0, -$padding);
}
$result = aes256_cbc_decrypt($key,$data,$iv);
var_dump($result);
?>
But when i run this code i get this "anil.mnd#gmail.cA���u�" . I should have got anil.mnd#gmail.com. I get only first 16 characters correct.
I am new to encryption so not have much idea what is wrong.

Answer 1

I am new to encryption so not have much idea what is wrong.
If you're new and want something that "just works", use defuse/php-encryption instead of trying to write it yourself.
If you're up for the challenge, however, keep reading:
Your code is unreadable. Let's add some whitespace.
$key = 'a16byteslongkey!';
$data = base64_decode('LsCH4nvvGPKN67v94Ig9BweQgOk9rtDdK7ZugeJkTS8=');
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
$iv = substr($data, 0, $iv_size);
function aes256_cbc_decrypt($key, $data, $iv)
{
if (32 !== strlen($key)) {
$key = hash('SHA256', $key, true);
}
if (16 !== strlen($iv)) {
$iv = hash('MD5', $iv, true);
}
$data = mcrypt_decrypt(
MCRYPT_RIJNDAEL_128,
$key,
$data,
MCRYPT_MODE_ECB,
$iv
);
$padding = ord($data[strlen($data) - 1]);
return substr($data, 0, -$padding);
}
$result = aes256_cbc_decrypt($key,$data,$iv);
var_dump($result);
Specific problems:
You're using MCRYPT_MODE_ECB for a function named aes256_cbc (have you seen the penguin?)
When I switch that out, I get invalid data.
Your encryption method is also probably broken, since changing your IV to "\x00\x00"... makes it decrypt.
Specific recommendations:
Please, please, PLEASE consider using well-studied cryptography code instead of writing it yourself.
strlen() and substr() are brittle. See: function overloading.
Use a real key derivation function, not a hash function.
Your IV (and keys, for that matter) should be generated from a cryptographically secure pseudo-random number generator, such as random_bytes().
Use authenticated encryption.