password-generator

password-generator

#!/usr/bin/env php
<?php

	function dev_rand( $min=0, $max=-1 )
	{
		if( -1 == $max ) { $max=getrandmax(); } #can't use a function as a default value
		$range = $max-$min+1; #+1 to be inclusive
		$file="/dev/random"; ##urandom is the faster/less random variant
		$handle=fopen($file,"rb");
		if( false == $handle ) { throw new Exception("Unable to open ".$file); }
		$byte = fgetc($handle);  ##TODO: get the right number of bits according to $range; 2nd parm $length = ⌈log₂($range)/8⌉ # (bits to represent range)/8 = (bytes to represent range)
		fclose($handle);
		$raw = (double) ord($byte); # $byte is a one-byte char; ord($byte) is the byte value of the encoded char as an int
		$scaled = $range * $raw / 256; # since $r is one byte, it has a range of 256; $scaled ∈[0,$range)
		$result = $min + $scaled;
		return (int) $result;
	}

	function password_2009() { return password_bits(48); }  ## I estimated 48-bits as sufficient (but did not record sources)
	function password_2012() { return password_bits(72); }  ## I was using 13-chars in 2012 (but did not record sources)
	function password_2019() { return password_bits(100); } ## 18-chars = 100-bits, re https://discourse.codinghorror.com/t/password-rules-are-bullshit/5033/91

	## I estimated and ~5.6bits/character with these character options (somewhat based on wikipedia and possibly other sources)
	function password_bits( $bits=100 ) { return password_chars( ceil($bits/5.6) ); }

	## Generate ~n-character password using upper- lower- and numerals
	function password_chars( $chars=18 )
	{
		$pickfrom="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"; #alphanumeric only
		#$pickfrom="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_%@!$&*~"; #alphanumeric and "special" characters
		$password="";
		for( $n=0; $n<$chars; $n++ ) {
			$i = dev_rand( 0, strlen($pickfrom)-1 );
			$c = $pickfrom[$i];
			$password .= $c;
		}
		return $password;
	}

	function password_default() { return password_2019(); }

	if( __FILE__ == realpath($argv[0]) ) #if this file was executed directly
	{ print "".password_default()."\n"; }
?>