PHP Manual: Encrypted Storage Model

Encrypted Storage Model

SSL/SSH protects data travelling from the client to the server: SSL/SSH does not protect persistent data stored in a database. SSL is an on-the-wire protocol.

Once an attacker gains access to your database directly (bypassing the webserver), stored sensitive data may be exposed or misused, unless the information is protected by the database itself. Encrypting the data is a good way to mitigate this threat, but very few databases offer this type of data encryption.

The easiest way to work around this problem is to first create your own encryption package, and then use it from within your PHP scripts. PHP can assist you in this with several extensions, such as Mcrypt and Mhash, covering a wide variety of encryption algorithms. The script encrypts the data before inserting it into the database, and decrypts it when retrieving. See the references for further examples of how encryption works.

Hashing

In the case of truly hidden data, if its raw representation is not needed (i.e. will not be displayed), hashing should be taken into consideration. The well-known example for hashing is storing the cryptographic hash of a password in a database, instead of the password itself.

In PHP 5.5 or newer password functions provide a convenient way to hash sensitive data and work with these hashes. In PHP 5.3.7+ » password_compat library can also be used.

password_hash is used to hash a given string using the strongest algorithm currently available and password_verify checks whether the given password matches the hash stored in database.

Example #1 Hashing password field


<?php

// storing password hash
$query  = sprintf("INSERT INTO users(name,pwd) VALUES('%s','%s');",
            pg_escape_string($username),
            password_hash($password, PASSWORD_DEFAULT));
$result = pg_query($connection, $query);

// querying if user submitted the right password
$query = sprintf("SELECT pwd FROM users WHERE name='%s';",
            pg_escape_string($username));
$row = pg_fetch_assoc(pg_query($connection, $query));

if ($row && password_verify($password, $row['pwd'])) {
    echo 'Welcome, ' . htmlspecialchars($username) . '!';
} else {
    echo 'Authentication failed for ' . htmlspecialchars($username) . '.';
}

?>

In older versions of PHP this can be achieved using crypt function.

Example #2 Hashing password using crypts


<?php

// storing password hash
// $random_chars retrieved e.g. using /dev/random
$query  = sprintf("INSERT INTO users(name,pwd) VALUES('%s','%s');",
            pg_escape_string($username),
            pg_escape_string(crypt($password, '$2a$07$' . $random_chars . '$')));
$result = pg_query($connection, $query);

// querying if user submitted the right password
$query = sprintf("SELECT pwd FROM users WHERE name='%s';",
            pg_escape_string($username));
$row = pg_fetch_assoc(pg_query($connection, $query));

if ($row && crypt($password, $row['pwd']) == $row['pwd']) {
    echo 'Welcome, ' . htmlspecialchars($username) . '!';
} else {
    echo 'Authentication failed for ' . htmlspecialchars($username) . '.';
}

?>