How to create two way encode/decode methods using use-specific key - PHP?

Question

I need two functions/methods, one to encode, one to decode. This is not for storing passwords. Each user will have a specific key/salt to encode the data.

This is how I would like it to work:

function encode($str, $key) {
    // something fancy
}

function decode($str, $key) {
    // something fancy
}

$key = $logged_in_user->get_key();
$plain = 'abc abc 123 123';
$encoded_data = encode($plain, $key);
// some_fancy_encrypted_data_that_is_really_cooooool
$decoded_data = decode($encoded_data, $key);
// abc abc 123 123

Another thing is that every time I use this function it needs to return the same thing every time I use the encode function with the same user key.

How would I do this??

Colettecoleus

So have you looked at mcrypt (php.net/manual/en/mcrypt.examples.php) at all? And drop the hash tag, because you say you don't want a hash – Anasarca

I have a small class that can do what you need, but the real question is why you feel the need to individually encrypt each user's data independently. It is generally assumed that once an attacked can see your stored data they can also see your source code which invalidates most uses of internal encryption, as well-intentioned as they might be. – Richmal

@Richmal In some cases it's useful if the key used to encrypt/decrypt the data cannot be found anywhere (and only belongs to the user). I'm pretty sure that LastPass does this as well. – Gumdrop

@Richmal Because it is not for the user, but for messages between users. So on the database it is not plain text data. – Colettecoleus

@MarkBaker I have, but even with the same key, every time the output is different. – Colettecoleus

Answer 1

$myVarIWantToEncodeAndDecode

Define key (salt, broth etc..): $key = "#&$sdfdfs789fs7d";

To encode:

$encoded = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $myVarIWantToEncodeAndDecode, MCRYPT_MODE_CBC, md5(md5($key))));

To decode:

$decoded = rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($encoded), MCRYPT_MODE_CBC, md5(md5($key))), "\0");

Note: mcrypt_decrypt has been DEPRECATED as of PHP 7.1.0. Relying on this function is highly discouraged.

Reportage

hmm.. This seems to work, but the data I am getting back from decoding the string is A”·fµŒ”÷Óÿ‰Zvÿ“õE¥‰¬DõØ&Hå§. What's wrong? – Colettecoleus

So it decodes and encodes right? What are you encoding? plain text? encoded data should look something like this: VXHE0iM0bMXQecCAKYAzYZjy4gbctqLGQHYvW2cFhaE= – Reportage

I am encoding just "abc abc 123 123" – Colettecoleus

Alright fixed it. Now it's working, thanks for the help. @Reportage – Colettecoleus

When i run this on foreach loop, only the first iteration works, all the other iteration gives illegal decoded string. – Mullinax

@JaganK Post the question with the code sample and link to this comment – Reportage

Sweet, simple, one liner. Thanks a ton!! Cheers!! +1 :) – Gastroscope

mcrypt_encrypt / _decode are deprecated. Use openssl_encrypt / _decrypt instead. php.net/manual/en/function.openssl-encrypt.php – Luciana

Answer 2

Use openssl_encrypt instead of mcrypt_encrypt

mcrypt_encrypt DEPRECATED as of PHP 7.1.0 and REMOVED as of PHP 7.2.0.

So, Try this..

function encrypt_decrypt($string, $action = 'encrypt')
{
    $encrypt_method = "AES-256-CBC";
    $secret_key = 'AA74CDCC2BBRT935136HH7B63C27'; // user define private key
    $secret_iv = '5fgf5HJ5g27'; // user define secret key
    $key = hash('sha256', $secret_key);
    $iv = substr(hash('sha256', $secret_iv), 0, 16); // sha256 is hash_hmac_algo
    if ($action == 'encrypt') {
        $output = openssl_encrypt($string, $encrypt_method, $key, 0, $iv);
        $output = base64_encode($output);
    } else if ($action == 'decrypt') {
        $output = openssl_decrypt(base64_decode($string), $encrypt_method, $key, 0, $iv);
    }
    return $output;
}
 
echo "Your Encrypted password is = ". $pwd = encrypt_decrypt('spaceo', 'encrypt');
echo "Your Decrypted password is = ". encrypt_decrypt($pwd, 'decrypt');

Yang