PHP JSON Decode erroring with valid JSON

Question

I am trying to decode a simple JSON string and the format to make it look correct. I actually copied the string and decode is with the same algorithm but without all the extra code and it worked fine.

print_r(json_decode('{"user_id":1,"issused":"2016-02-24 04:40:17","expire":"2016-03-02 04:40:17"}'));

That worked. But when I do

$hash = Hash::salt(32);
$issused = date('Y-m-d H:i:s');
$expire = date('Y-m-d H:i:s', strtotime('+1 week'));
$data = array('user_id' => 1, 'issused' => $issused, 'expire' =>     $expire);
$encrypt = Cipher::encrypt(json_encode($data), $hash);
$decrypt = Cipher::decrypt($encrypt, $hash);
echo $encrypt;
echo "<br><br>";
echo $decrypt;
echo "<br><br>";
print_r(json_decode($decrypt));

Where $decrypted is the valid formated JSON that I posted above. When I used:

echo json_last_erro();

It gave me an output of 3 which is JSON_ERROR_CTRL_CHAR

Any idea why this isn't being decoded correctly?

EDIT Here is how I am encrypting data.

class Cipher {
public static function encrypt($string, $hash) {
    $size = mcrypt_get_iv_size(MCRYPT_BLOWFISH, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($size, MCRYPT_RAND);
    $encrypted = mcrypt_encrypt(MCRYPT_BLOWFISH, $hash, utf8_encode($string), MCRYPT_MODE_ECB, $iv);
    //$encoded = urlencode($encrypted);
    $encoded = base64_encode($encrypted);
    return $encoded;
}

public static function decrypt($string, $hash) {
    //$decoded = urldecode($string);
    $decoded = base64_decode($string);
    $size = mcrypt_get_iv_size(MCRYPT_BLOWFISH, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($size, MCRYPT_RAND);
    $decrypted = mcrypt_decrypt(MCRYPT_BLOWFISH, $hash, $decoded, MCRYPT_MODE_ECB, $iv);
    return $decrypted;
}

}

Here how I am creating the salt.

public static function salt($length) {
    return mcrypt_create_iv($length); //base64_encode(openssl_random_pseudo_bytes($length));
}

what is the library that you have used for generating salt and encrypt data. There is causing because of character encoding mismatching. — shrish
– shrish, Commented Feb 24, 2016 at 4:47
Extract an example, as per guidelines, and state exactly where things go wrong. Note that volatile things like the date are not suitable for an example, as they change and require human interpretation. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Feb 24, 2016 at 6:44
I am using mcrypt to encrypt a json string and the same mcrypt to decode it — Kurieita
– Kurieita, Commented Feb 24, 2016 at 11:42
does your Cipher code work - is Cipher::decrypt(Cipher::encrypt("test", $hash), $hash)) === "test" true ? (for all possible strings) — birdspider
– birdspider, Commented Feb 24, 2016 at 12:19

Bill Croft · Accepted Answer · 2016-02-24 22:18:33Z

2

The extra control characters (\0) are due to the cypher block padding. From the mcrypt_decrypt docs

data

The data that will be decrypted with the given cipher and mode. If the size of the data is not n * blocksize, the data will be padded with '\0'.

You can pad the input for the block size yourself in the encrypt and then remove the extra padding in decrypt() or you can trim the trailing zero bytes from the decoded message doing the below.

$decrypt = trim($decrypt, "\0");

answered Feb 24, 2016 at 22:18

Bill Croft

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