gistfile1.js

var util = require('util'),
  	crypto = require('crypto');

function getSharedSignature(bucket, path) {
	var now = new Date().getTime();
	var expires = Math.round((now + 10 * 365 * 24 * 3600 * 1000) / 1000); // Ten years
	var cannonicalPath = util.format("/%s/%s", bucket, path);
	var stringToSign = util.format("GET\n\n\n%s\n%s", expires, cannonicalPath);

	var signature = crypto.createHmac("sha1", process.env.AWS_ACCESS_SECRET).update(stringToSign).digest("base64");
	var data = { expiration: expires, signature: signature,  key: process.env.AWS_ACCESS_KEY };

	return data;
};

// Aca se pone el path del archivo (1 o más)
var files = ['jbmdarling/1370188055324.docx', 'jbmdarling/1370260785584.pdf', 'jbmdarling/1370260747955.pdf', 'jbmdarling/1370200977600.pdf'];

for (var i in  files) {
	var filePath = files[i];
	var root = 'https://s3.amazonaws.com/upload.mural.ly';
	var path = [ root, filePath ].join('/');

	var cred = getSharedSignature('upload.mural.ly', filePath);
	var query = "?AWSAccessKeyId=" + cred.key + "&Signature=" + encodeURIComponent(cred.signature) + "&Expires=" + cred.expiration;
	var link =  path + query;

	console.log(link);
}