Android : Signature doesn't match in REST API

I have used a code for creating a bucket on amazon.. I don't want to use Amazon SDK available as it makes my android code very heavy,therefore tryng to write REST API.

I found the code here REST API

I have used true keys. But I get this error

403 Error: AccessDenied

SignatureDoesNotMatchThe request signature we calculated does not match the signature you provided. Check your key and signing method.

please help.