GooglePageRankChecksum.cpp

/*

Google PageRank checksum algorithm

The Google PageRank functionality in Google Toolbar works by querying Google's server for information on the PageRank of a specific page.
This might seem easy enough to implement in your own program/website, but the problem is that the toolbar calculates a checksum on the 
page URL before querying the server, and the server only responds if the checksum is correct. Fortunately the checksum algorithm was
reverse engineered from Google Toolbar 7. I was provided the hand decompiled version of the algorithm in C from a friend. Then I went

ahead and rewrote it in PHP for web development usage. You can find both versions below.

As an example, the query URL for the page 'http://en.wikipedia.org/wiki/Cypherpunk' is :
http://toolbarqueries.google.com/tbr?client=navclient-auto&features=Rank&q=info:http://en.wikipedia.org/wiki/Cypherpunk&ch=783735859783

Any other query with a checksum other than 783735859783 will result in a '403 forbidden' response.

*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
char fch(uint csm)
{
    int a, b, c, t;
 
    a = csm % 10;
    t = 1;
    b = csm / 10;
    while(b) {
        c = b % 10;
        if(t)
            c = c / 5 + (c * 2) % 10;
        b /= 10;
        a += c;
        t ^= 1;
    }
 
    a = 10 - a % 10;
    if(a == 10)
        return '0';
     
    if(t)
        return '0' + (a & 1 ? a + 9 : a) / 2;
 
    return '0' + a;
}
 
uint checksum(char *str)
{
    int a, b, c, d, e;
    char *p;
 
    if(*str == '\0')
        return 0x1000;
 
    p = str;
    a = 5381;
    while(*p)
        a += (a << 5) + *p++;
     
    p = str;
    b = 0;
    while(*p)
        b = (b << 6) + (b << 16) - b + *p++;
 
    a = ((a >> 6) & 0x3ffffc0) | ((a >> 2) & 0x3f);
    c = ((a >> 4) & 0x3ffc00) | (a & 0x3ff);
    d = ((c >> 4) & 0x3c000) | (c & 0x3fff);
    c = (((d & 0x3c0) << 4) | (d & 0x3c)) << 2;
    a = b & 0x0f0f;
    e = b & 0x0f0f0000;
    b = ((d & 0xffffc000) << 4) | (d & 0x3c00);
 
    return (b << 10) | c | a | e;
}
 
#define PR_SERVER "http://toolbarqueries.google.com/tbr?client=navclient-auto&features=Rank&q=info:"
 
int main(int argc, char *argv[])
{
    uint csm;
 
    if(argc < 2) {
        fprintf(stderr, "usage: %s link\n",
            argv[0] ? argv[0] : "gchecksum");
        return EXIT_FAILURE;
    }
     
    csm = checksum(argv[1]);
    printf(PR_SERVER "%s&ch=7%c%u\n", argv[1], fch(csm), csm);
     
    return EXIT_SUCCESS;
}

GooglePageRankCheckSum.php

<?php

function fch($csm)
{
    if($csm < 0)
        $csm += 4294967296.0;
 
    $a = (int)fmod($csm, 10);
    $t = 1;
    $b = (int)($csm / 10);
    while($b) {
        $c = $b % 10;
        if($t)
            $c = (int)($c / 5) + ($c * 2) % 10;
        $b = (int)($b / 10);
        $a += $c;
        $t ^= 1;
    }
     
    $a = 10 - $a % 10;
    if($a == 10)
        return ord('0');
     
    if($t)
        return ord('0') + (int)(($a & 1 ? $a + 9 : $a) / 2);
 
    return ord('0') + $a;
}
 
function checksum($str)
{
    if(strlen($str) == 0)
        return 0x1000;
         
    /* the floating point hacks are due to PHP's bugs when handling integers */
 
    $a = 5381.0;
    for($i = 0; $i < strlen($str); $i++)
        $a = fmod($a + ($a * 32) + ord($str[$i]), 4294967296.0);
    if($a > 2147483647.0)
        $a -= 4294967296.0;
    $a = (int)$a;
 
    $b = 0.0;
    for($i = 0; $i < strlen($str); $i++)
        $b = fmod(($b * 64) + ($b * 65536) - $b + ord($str[$i]), 4294967296.0);
    if($b > 2147483647.0)
        $b -= 4294967296.0;
    $b = (int)$b;
     
    $a = (($a >> 6) & 0x3ffffc0) | (($a >> 2) & 0x3f);
    $c = (($a >> 4) & 0x3ffc00) | ($a & 0x3ff);
    $d = (($c >> 4) & 0x3c000) | ($c & 0x3fff);
    $c = ((($d & 0x3c0) << 4) | ($d & 0x3c)) << 2;
    $a = $b & 0x0f0f;
    $e = $b & 0x0f0f0000;
    $b = (($d & 0xffffc000) << 4) | ($d & 0x3c00);
 
    return ($b << 10) | $c | $a | $e;
}
 
$PR_SERVER = "http://toolbarqueries.google.com/tbr?client=navclient-auto&features=Rank&q=info:";
 
$page = "http://en.wikipedia.org/wiki/Cypherpunk";
$csm = checksum($page);
printf($PR_SERVER . "%s&ch=7%c%u\n", $page, fch($csm), $csm);
 
?>