Once you have registered as an Amazon Associate, you will need a key pair, consisting of an access Key ID and a secret key. The Product Advertising API uses the Amazon Web Services infrastructure for generating key pairs, as well as for other Product Advertising API resources. You can get your keys at
http://aws-portal.amazon.com/gp/aws/developer/account/index.html?action=access-key.
Once you have obtained your key pair, you can make calls to the Product Advertising API in all Amazon locales.