How to programmatically build an APR1-MD5 using PHP

Question

Much like this question I want to generate an htpasswd file entry from PHP. However it needs to be the APR1 (Apache) style, as mentioned in the original answer (The answer did not show how to implement the APR1 style), to work with mod_dav_svn.

I can't seem to find a working implementation that will create the password.

I found this (I forget where now):

function crypt_apr1_md5($plainpasswd) {
    $salt = substr(str_shuffle("abcdefghijklmnopqrstuvwxyz0123456789"), 0, 8);
    $len = strlen($plainpasswd);
    $text = $plainpasswd.'$apr1$'.$salt;
    $bin = pack("H32", md5($plainpasswd.$salt.$plainpasswd));
    for($i = $len; $i > 0; $i -= 16) { $text .= substr($bin, 0, min(16, $i)); }
    for($i = $len; $i > 0; $i >>= 1) { $text .= ($i & 1) ? chr(0) : $plainpasswd{0}; }
    $bin = pack("H32", md5($text));
    for($i = 0; $i < 1000; $i++) {
        $new = ($i & 1) ? $plainpasswd : $bin;
        if ($i % 3) $new .= $salt;
        if ($i % 7) $new .= $plainpasswd;
        $new .= ($i & 1) ? $bin : $plainpasswd;
        $bin = pack("H32", md5($new));
    }
    for ($i = 0; $i < 5; $i++) {
        $k = $i + 6;
        $j = $i + 12;
        if ($j == 16) $j = 5;
        $tmp = $bin[$i].$bin[$k].$bin[$j].$tmp;
    }
    $tmp = chr(0).chr(0).$bin[11].$tmp;
    $tmp = strtr(strrev(substr(base64_encode($tmp), 2)),
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
    "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
    return "$"."apr1"."$".$salt."$".$tmp;
}

But it doesn't generate a working password. I think this might be something to do with the version of apache but am not sure. (I am running on CENTOS 5)

Answer 1

It turns out I made a mistake and this function does in fact create working APR1 htpasswd entries. They do look different to the ones Apache creates but they do work.

Answer 2

Look for existing components that do it on sites like phpclasses.org. One example: http://www.phpclasses.org/browse/package/5066.html.

Answer 3

This might be a bit hacky, but have you considered using the exec() function to call the command that generates the htpasswd ?

Answer 4

Thanks you! It works like a charm.

Just a small comment: The salt can also contain "./" and "A..Z" besides "a..z0..9", so it is the same string as the 'translate-to' string in the last line. And sometimes you want to set the salt in addition, to create reproducable results, like:

function crypt_apr1_md5( $plainpasswd, $salt = '' ) {
$translateTo = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
if ( $salt == '' ) { $salt = substr(str_shuffle($translateTo), 0, 8); }

...

$tmp = strtr(strrev(substr(base64_encode($tmp), 2)), "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/", $translateTo);
return '$apr1$'.$salt.'$'.$tmp;
}

Answer 5

See on this:

1:   private function crypt_apr1_md5($plainpasswd) { </br>
7:   for($i = $len; $i > 0; $i >>= 1) { $text .= ($i & 1) ? chr(o) : $plainpasswd{0}; } </br>
16:  $tmp = ''; </br>