PHP: Generating Random Passwords Example

Sometimes security dictates that users may not be allowed to choose their own passwords. In these cases you need some way to quickly generate them. Even if you do not have a requirement for random passwords, you will still often need to generate initial passwords for users, or use them when someone has lost his password and needs a new temporary one.

The following code gives an example of a function that lets you specify an arbitrary length of characters, and it generates a random password for you containing only lowercase letters, uppercase letters, and numbers.

<?php
// A function that accepts a parameter to specify a length, and then returns
// a random password with characters and letters
function random_password($length = 8) {
    // Declare a blank string to start from
    $pass = '';

    // Now loop for as many times as the length
    for ($i = 0; $i < $length; $i++) {
        // For this character, first give an equal chance of upper,lower,num
        switch (rand(0,2)) {
            case 0:
                // Generate a Number from 0 to 9
                $pass .= rand(0,9);
                break;
            case 1:
                // Generate a letter from A to Z via ascii values 65 to 90
                $pass .= chr(rand(65,90));
                break;
            default:
                // Instead use a letter from a to z, via ascii 97 to 122
                $pass .= chr(rand(97,122));
        }
    }

    // Return that password!
    return $pass;
}

// Test this, echo out a batch of 10 passwords, from 1 to 10 characters long
echo "<ol>\n";
foreach (range(1,10) as $l) {
    $tmp = random_password($l);
    echo "<li>{$tmp}</li>\n";
}
echo "</ol>\n";
?>

At the heart of this code is a switch statement that gives a random one-in-three chance of each character being lowercase, uppercase, or a number. It then randomly picks the appropriate type of character via generating ASCII values and converting them with chr(). By first randomly choosing which of the three types is used, we evenly distribute them throughout. Otherwise, because there are more letters than digits, digits would rarely appear.

Hope it helps.