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For all operation with Amazon services(S3, EC2, SimpleDB) You need to sign all resquest with HMAC-SHA-1 Signature( http://en.wikipedia.org/wiki/HMAC , http://docs.amazonwebservices.com/AWSFWS/latest/DeveloperGuide/index.html?SummaryOfAuthentication.html ). I'm working under asp.net backend and there is no problems. Problem is in the iPhone application. iPhone developer says that there is no way to use HMAC-SHA-1 encoding, and he have no rigths to implement his own algorithm. As programmer I cannot understand why there can be a problem. So I want too know is iPhone developer right? I've never coded for iPhone, so I don't even where to search such an information. Source: Tips4all