Signature—This is an optional parameter and has no default value. A signature is created by using the request type, domain, the URI, and a sorted string of every parameter in the request (except the Signature parameter itself) with the following format <parameter>=<value>&. Once properly formatted, you create a base64-encoded HMAC_SHA256 signature using your AWS secret key. For a detailed example of this process, see Example REST Requests.

Timestamp—This is a required parameter if you include the Signature parameter. Otherwise it is optional. There is no default value. The time stamp you use in the request must be a dateTime object, with the complete date plus hours, minutes, and seconds (for more information, go to http://www.w3.org/TR/NOTE-datetime).This is a fixed -length subset of the format defined by ISO 8601, represented in Universal Time (GMT): YYYY-MM-DDThh:mm:ssZ (where T and Z are literals).

	Note
	Currently you are not required to send the Signature parameter until August 15, 2009. A request without a Signature parameter will still go through. However such a request will not be authenticated.

	Important
	If you are using .NET you must not send overly specific time stamps, due to different interpretations of how extra time precision should be dropped. To avoid overly specific time stamps, manually construct dateTime objects with no more than millisecond precision.