Best way to use PHP to encrypt and decrypt passwords? [duplicate]

Answer 1

You should not encrypt passwords, instead you should hash them using an algorithm like bcrypt. This answer explains how to properly implement password hashing in PHP. Still, here is how you would encrypt/decrypt:

$key = 'password to (en/de)crypt';
$string = ' string to be encrypted '; // note the spaces

To Encrypt:

$iv = mcrypt_create_iv(
    mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC),
    MCRYPT_DEV_URANDOM
);

$encrypted = base64_encode(
    $iv .
    mcrypt_encrypt(
        MCRYPT_RIJNDAEL_128,
        hash('sha256', $key, true),
        $string,
        MCRYPT_MODE_CBC,
        $iv
    )
);

To Decrypt:

$data = base64_decode($encrypted);
$iv = substr($data, 0, mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC));

$decrypted = rtrim(
    mcrypt_decrypt(
        MCRYPT_RIJNDAEL_128,
        hash('sha256', $key, true),
        substr($data, mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC)),
        MCRYPT_MODE_CBC,
        $iv
    ),
    "\0"
);

---

Warning: The above example encrypts information, but it does not authenticate the ciphertext to prevent tampering. You should not rely on unauthenticated encryption for security, especially since the code as provided is vulnerable to padding oracle attacks.

See also:

• https://stackoverflow.com/a/30189841/2224584
• https://stackoverflow.com/a/30166085/2224584
• https://stackoverflow.com/a/30159120/2224584

Also, don't just use a "password" for an encryption key. Encryption keys are random strings.

---

Demo at 3v4l.org:

echo 'Encrypted:' . "\n";
var_dump($encrypted); // "m1DSXVlAKJnLm7k3WrVd51omGL/05JJrPluBonO9W+9ohkNuw8rWdJW6NeLNc688="

echo "\n";

echo 'Decrypted:' . "\n";
var_dump($decrypted); // " string to be encrypted "

Answer 2

This will only give you marginal protection. If the attacker can run arbitrary code in your application they can get at the passwords in exactly the same way your application can. You could still get some protection from some SQL injection attacks and misplaced db backups if you store a secret key in a file and use that to encrypt on the way to the db and decrypt on the way out. But you should use bindparams to completely avoid the issue of SQL injection.

If decide to encrypt, you should use some high level crypto library for this, or you will get it wrong. You'll have to get the key-setup, message padding and integrity checks correct, or all your encryption effort is of little use. GPGME is a good choice for one example. Mcrypt is too low level and you will probably get it wrong.