PHP Amazon File upload Signature

Without having your code to view it's hard to help but here is some example code that you might find helpful:

class myS3Helper{
public function getSignedImageLink($timeout = 1800, $my_aws_secretkey, $my_aws_key)
{

    $now = new Zend_Date(); //Gives us a time object that is set to NOW
    $now->setTimezone('UTC'); //Set to UTC a-la AWS requirements
    $now->addSecond($timeout); //set the time in the time object to a point in the future
    $expirationTime = $now->getTimestamp(); //returns unix timestamp representation of the time.

    $signature = urlencode(
            base64_encode(
                    hash_hmac(
                            'sha1', $this->_generateStringToSign($expirationTime),
                            $my_aws_secretkey, 
                            true
                            )
                    )
            );

    //Yes - this is ugly but hopefully readable 
    $url = 'https://';
    $url .= Zend_Service_Amazon_S3::S3_ENDPOINT; //e.g s3.amazonaws.com
    $url .= $this->_getImagePath(); //e.g /mybucket/myFirstCar.jpg
    $url .='?AWSAccessKeyId=' . $my_aws_key;
    $url .='&Signature=' . $signature; //signature as returned by below function
    $url .='&Expires=' . $expirationTime;

    return $url;


}

protected function _generateStringToSign($expires)
{   

    $string = "GET\n"; //Methods
    $string .= "\n";
    $string .= "\n";
    $string .= "$expires\n"; //Expires
    $string .= $this->_getImagePath();

    return $string;
}