What is "Signature" or "Timestamp" for the Amazon ecommerce web service?

Question

Register for Amazon Web Services.

Then try the following URL:

http://ecs.amazonaws.com/onca/xml?Service=AWSECommerceService&Operation=ItemLookup&AWSAccessKeyId=YOURKEY

If you have my experience you'll see:

<Error>
  <Code>AWS.MinimumParameterRequirement</Code>
    <Message>
      Your request should have atleast 1 of the following parameters: Signature, Timestamp.
    </Message>
</Error>

What is this trying to tell me? What are "Signature" and "Timestamp" parameters?

This is a n00b problem of some sort, but finding the answer is not obvious. I Googled for "MinimumParameterRequirement". I looked at http://docs.amazonwebservices.com/AWSEcommerceService/2007-01-17 and http://s3.amazonaws.com/awsdocs/ECS/20080819/QRC-AAWS-2008-08-19.pdf and http://docs.amazonwebservices.com/AWSEcommerceService/2007-01-17/ApiReference/ErrorCodesAndMessages.html.

In fact, even a link to the latest API doc for ecommerce would be nice. Is 2008-08-19 the latest?

Answer 1

Well here's the signature parameter: http://docs.amazonwebservices.com/AmazonFPS/latest/FPSAdvancedGuide/index.html?APPNDX_GeneratingaSignature.html

It's a hash of the other parameters. Strange that they give lots of examples without it and claim that those examples work.