Decrypted string is sometimes not same as encrypted source - php

Question

class Auth extends MySQLi {
public function aes_enc($encrypt, $mc_key, $iv) {
$passcrypt = trim(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, substr($mc_key, 0, 32), trim($encrypt), MCRYPT_MODE_CBC, $iv));
return $passcrypt;
}
public function aes_dec($decrypt, $mc_key, $iv) {
$decrypted = trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_128, substr($mc_key, 0, 32), trim($decrypt), MCRYPT_MODE_CBC, $iv));
return $decrypted;
}
public function salt() {
return str_shuffle('abcdefghijklmnoprsquvzyx0123456789-.,;:_<>');
}
public function iv() {
return mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC), MCRYPT_RAND);
}
}
And on test.php, following code:
<?
require('Auth.php');
$Auth = new Auth;
$str = "verygudlongpassword";
for ($i = 0; $i < 1000; $i++) {
$salt = sha1($Auth->salt());
$iv = $Auth->iv();
$enc = $Auth->aes_enc($str, $salt, $iv);
$dec = $Auth->aes_dec($enc, $salt, $iv);
if ($str != $dec) {
echo $salt . "<br>\n";
}
}
?>
Sometimes, $dec != $str. Why is this happening? I am not even saving anything into DB atm, so it's not that.
Thanks for help.
i dont really have anything more to say, but site isnt letting me post. (nvm that part)

Answer 1

After reviewing your code and playing with it locally. It would appear that your decryption leaves some whitespace on the decrypted text. I removed the trim() function from all locations except the return value from aes_dec() and the code now encrypts/decrypts your string successfully 1000 times.
So it would seem trimming was the problem and the solution.
class Auth extends MySQLi {
public function aes_enc($encrypt, $mc_key, $iv)
{
$passcrypt = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, substr($mc_key, 0, 32), $encrypt, MCRYPT_MODE_CBC, $iv);
return $passcrypt;
}
public function aes_dec($decrypt, $mc_key, $iv)
{
$decrypted = trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_128, substr($mc_key, 0, 32), $decrypt, MCRYPT_MODE_CBC, $iv));
return $decrypted;
}
public function salt()
{
return str_shuffle('abcdefghijklmnoprsquvzyx0123456789-.,;:_<>');
}
public function iv()
{
return mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC), MCRYPT_RAND);
}
}
$Auth = new Auth;
$str = "verygudlongpassword";
for ($i = 0; $i < 1000; $i++) {
$salt = sha1($Auth->salt());
$iv = $Auth->iv();
$enc = $Auth->aes_enc($str, $salt, $iv);
$dec = $Auth->aes_dec($enc, $salt, $iv);
if ($str != $dec) {
echo "Decryption failed!<br>\n";
} else {
echo "Decryption success! String: $dec<br>\n";
}
}