Trying to digitally sign via HMAC-SHA1 with PHP

Question

I'm trying to setup some Google Maps Premier API action, and to do so, I need to sign my URLs to authenticate. If you go down to Signature examples, there is some Python, C# and Java code to show you how to do the signature via HMAC-SHA1. There is also an example so that I can to test my PHP implementation. However, I just can't seem to get it to work.

Here's my code:

$key = "vNIXE0xscrmjlyV-12Nj_BvUPaw=";

$data = "/maps/api/geocode/json?address=New+York&sensor=false&client=clientID";

$my_sign = hash_hmac("sha1", $data, base64_decode($key));
$my_sign = base64_encode($my_sign);

$valid_sign = "KrU1TzVQM7Ur0i8i7K3huiw3MsA=";

When, I run this, I get a signature of:

ZDRlNGMwZjIyMTA1MWM1Zjk0Nzc4M2NkYjlmNDQzNDBkYzk4NDI4Zg==

Which totally doesn't match.

Things I have thought about:

1. The key is in Modified URL encoded format, so changing - and _ to + and / also doesn't work
2. The Python example code does indeed work, so this is a valid example.
3. Completely rewriting our code-base in python instead of PHP (I inherited it).

Answer 1

You have 2 problems at least,

1. The Google uses special URL-safe Base64. Normal base64_decode doesn't work.
2. You need to generate the SHA1 in binary.

Try this,

$key = "vNIXE0xscrmjlyV-12Nj_BvUPaw=";
$data = "/maps/api/geocode/json?address=New+York&sensor=false&client=clientID";
$my_sign = hash_hmac("sha1", $data, base64_decode(strtr($key, '-_', '+/')), true);
$my_sign = strtr(base64_encode($my_sign), '+/', '-_');

Answer 2

A php example is available at http://gmaps-samples.googlecode.com/svn/trunk/urlsigning/UrlSigner.php-source