How secure are Amazon AWS Access keys

Question

I want to offer presigned urls to my s3 buckets with an expiry date. The .net sdk nicely generates these urls, but looking at them makes me worry a little:

https://s3.amazonaws.com/upload_youtipit/myfile?AWSAccessKeyId=**MYACCESSKEY**&Expires=1317924047&response-content-disposition=attachment;filename=feedback.jpg&response-content-type=image/jpeg&Signature=podKJSrNeFel6%2B0aOneb342H5GA%3D

Why does it need to put my (public) AWSAccessKey in the Url? Shouldn't this be kept a bit more confidential? I know its not the secret, but I still don't feel comfortable exposing it in public.

How likely is it that, somebody who has my public key, can guess/brute force my private key?

Answer 1

The Access Key ID is not a secret and does not need protecting.

In fact, you can give expiring URLs to random strangers if you want them to access an S3 object. They can see the access key in that URL, but can't do anything with it that you have not authorized.

reference: http://docs.amazonwebservices.com/AWSSecurityCredentials/1.0/AboutAWSCredentials.html#AccessKeys