sample.js

<script src="http://crypto-js.googlecode.com/svn/tags/3.1.2/build/rollups/hmac-sha1.js"></script>
<script src="http://crypto-js.googlecode.com/svn/tags/3.1.2/build/components/enc-base64-min.js"></script>
<script type="text/javascript">

    function CalculateSig(stringToSign, privateKey){
        var hash = CryptoJS.HmacSHA1(stringToSign, privateKey);
        var base64 = hash.toString(CryptoJS.enc.Base64);
        return encodeURIComponent(base64);
    }

    var d = new Date,
         expiration = 3600 // 1 hour,
         unixtime = parseInt(d.getTime() / 1000),
         future_unixtime = unixtime + expiration,
         publicKey = "1234",
         privateKey = "abcd",
         method = "GET",
         route = "forms/1/entries";

    stringToSign = publicKey + ":" + method + ":" + route + ":" + future_unixtime;
    sig = CalculateSig(stringToSign, privateKey);
    console.log(sig);
</script>

sample.php

<?php
function calculate_signature($string, $private_key) {
    $hash = hash_hmac("sha1", $string, $private_key, true);
    $sig = rawurlencode(base64_encode($hash));
    return $sig;
}

$api_key = "1234";
$private_key = "abcd";
$method  = "GET";
$route    = "forms/1/entries";
$expires = strtotime("+60 mins");
$string_to_sign = sprintf("%s:%s:%s:%s", $api_key, $method, $route, $expires);
$sig = calculate_signature($string_to_sign, $private_key);
var_dump($sig);
?>

sample.rb

  def request_params
    expires = (DateTime.now + 1.hour).to_i
    public_key = '1234'
    route = 'forms/1/entries'
    method = 'GET'
    private_key = 'abcd'
    string = "#{public_key}:#{method}:#{route}:#{expires}"
    hmac = OpenSSL::HMAC.digest('sha1', string, private_key)
    signature = CGI.escape(Base64.encode64(hmac))
    
    base_url = 'http://mydomain.com/gravityformsapi/'
    url= "#{base_url}#{route}/?api_key=#{public_key}&signature=#{signature}&expires=#{expires}"
  end