Hello, i'm trying to port a function from PHP to Perl, a following function: in PHP:

function md5_decrypt($enc_text, $password, $iv_len = 16)
{
    $enc_text = base64_decode($enc_text);
    $n = strlen($enc_text);
    $i = $iv_len;
    $plain_text = '';
    $iv = substr($password ^ substr($enc_text, 0, $iv_len), 0, 512);
    while ($i < $n) {
        $block = substr($enc_text, $i, 16);
        $plain_text .= $block ^ pack('H*', md5($iv));
        $iv = substr($block . $iv, 0, 512) ^ $password;
        $i += 16;
    }
    return preg_replace('/\\x13\\x00*$/', '', $plain_text);
}
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i wrote in perl:

use MIME::Base64;
use Digest::MD5 qw(md5 md5_hex md5_base64);
use strict;
sub md5_decrypt
{
my $iv_len = 16;
    my $enc_text = decode_base64(shift);
    my $password = shift;
    my $n = length($enc_text);
    my $i = $iv_len;
    my $plain_text;
    my $iv = substr(($password ^ substr($enc_text, 0, $iv_len)), 0, 51
+2);

    while ($i < $n) {
        my $block = substr($enc_text, $i, 16);
        $plain_text .= $block ^ pack('H*', md5_hex($iv));
        $iv = substr($block . $iv, 0, 512) ^ $password;
        $i += 16;
    }
    #$plain_text =~ s/\x13\x00*$//;
    return $plain_text;
}
[download]

perl function gives me a different and wrong result decrypting this hash, for example md5_decrypt('XHnhcRzMuo63RqqZmbxW1nQKXqVMm48eXMS6oh9wmBdg9pfXhAmNQEvR+luaVVzk', 'test'); should return 'very secret string', but it doesn't