Question

I’m going to write a program can post and read messages from SQS with authentication and I’ve read the document from here
Link: Query Request Authentication

I have successfully written the process which post a message to specified queue follow by the document. But I always get 403 error when I try to receive message from queue. And I found the signature string rules are different for POST and GET methods.

the signature string is:

GET\n
sqs.us-east-1.amazonaws.com\n
/<My Account Id>/<Queue Name>\n
AWSAccessKeyId=<My Access Key>
&Action=ReceiveMessage
&MaxNumberOfMessages=10
&VisibilityTimeout=600
&AttributeName=All
&Expires=2012-04-01T11%3A29%3A24Z
&SignatureMethod=HmacSHA1
&SignatureVersion=2
&Version=2011-10-01

and the url is

https://sqs.us-east-1.amazonaws.com/<My Account Id>/<Queue Name>?
Action=ReceiveMessage
&MaxNumberOfMessages=10
&VisibilityTimeout=600&AttributeName=All
&Version=2011-10-01
&Expires=2012-04-01T11%3A29%3A24Z
&Signature=<BASE64 encoded HmacSHA1 digist with signature string and my security key>
&SignatureVersion=2
&SignatureMethod=HmacSHA1
&AWSAccessKeyId=<My Access Key>

And I always get the 403 forbidden error:

<ErrorResponse xmlns="http://queue.amazonaws.com/doc/2011-10-01/">
  <Error>
    <Type>Sender</Type> 
    <Code>SignatureDoesNotMatch</Code>
    <Message>
      The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details.
    </Message>
    <Detail/>
  </Error>
  <RequestId>16f6e910-62e6-4259-8c09-0358b84cbe60</RequestId>
</ErrorResponse>

Is there anyone can tell me how can I deal with it? Thanks a lot

Answer 1

The error message tells you that the signature is being calculated wrong. This is really tough to debug. I spent hours on it the first time I tried it. There’s an example signed SQS request at http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/MakingRequests_MakingQueryRequestsArticle.html. You should put those parameters in your program, calculate the signature, and try finding bugs into your program creates the same signature.

Specific problems I had, and fixes for them included:

• Sorting the query parameters correctly. They must be in ascending order when creating the string to sign. Your example URL does not show them in order. Did you sort them differently when creating the string to sign?
• URI encoding properly. Every parameter must be URI encoded in the string to sign. Your sample URL does have URI encoding, so this probably isn’t your issue. But make sure you’re not double-encoding.
• Padding the base64 signature. At least some AWS services insist that the signature be a multiple of four characters long. Two-thirds of the time a base64 encoding will be too short, and need one or two equal signs appended to it. Most base64 encoding libraries do that for you, but not all.

Of course, the easiest thing is to use somebody else’s library to make the requests, but what’s the fun in that? Good luck debugging this.