PHP Random Password Generation Tutorial

We can already setup the basics for the random password generating function. We'll call the function randomStr as it basicly generates a random string of letters and numbers.

function randomStr( parameters ) {
function code
}

The parameters for the function are the data the funcion needs. In this case our function needs a charset ( the characters to choose randomly from to create the password ) and the length of the password ( the amount of characters to choose randomly ).

function randomStr($length, $charset) {
function code
}

What I usually do for the charset as parameter is to give it a default value. This way the default charset is used when no other charset is provided, but it does offer the posibility to offer an alternative charset.

function randomStr($length, $charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
01234567890123456789") {
function code
}

Now let's write the basic function code. It basicly needs to define a variable $str which will contain the output ( random password ) in the end. We also need a for loop to add random characters to this $str variable for the amount of times as set in $length. And of course the function needed to return the random password created in $str, so we add the line return $str to the end of the function.

function randomStr($length, $charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
01234567890123456789") {
$str = "";
for($i=0;$i<$length;$i++) {
add random character of $charset to $str.
}
return $str;
}

Now all we need to do more is write the code to add a random charater to $str inside of the for loop ( which repeats it $length amount of times ).

The first method to pick a random character is to pick one from the charset from a random position. We can use the PHP function mt_rand to generate a random position. We set the min. value for the random number to 0 ( =first position in charset ) and the max. value for the random number to the length of the charset minus 1 ( =last position in charset ).

$pos = mt_rand(0, strlen($charset)-1);

Now we got a random position and so a random character to pick from the charset. All we need to do now is pick that character at that position and add it to $str ( the output random password ).

$pos = mt_rand(0, strlen($charset)-1);
$str .= $charset[$pos];

That's all! We written the code to add a random character to the password ($str) in just 2 lines of code. Now let's put it together with our function . We need to put it inside of the for loop that's repeated $length amount of times.

function randomStr($length, $charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
01234567890123456789") {
$str = "";
for($i=0;$i<$length;$i++) {
$pos = mt_rand(0, strlen($charset)-1);
$str .= $charset[$pos];
}
return $str;
}

Another way to pick a random character is to shuffle the charset using the PHP function str_shuffle. This way we can pick the first character of the charset as it will be a different one each time we shuffle the charset.

$charset = str_shuffle($charset);
$str .= $charset[0];

This method may even be easier than the previous one, however both just consist of 2 lines of code. We here shuffled $charset and then picked the first character out of it and added it to $str. That's all there's to do. Now we can merge this with the function as well, and we'll have another random password generating function that does exactly the same!

function randomStr($length, $charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
01234567890123456789") {
$str = "";
for($i=0;$i<$length;$i++) {
$charset = str_shuffle($charset);
$str .= $charset[0];
}
return $str;
}