Amazon S3 : access without Secret Key

Question

I am developing an iOS app which saves picture in an Amazon S3 server. Unfortunately, the owner of the server prefers not to give me his secret key. Instead, he generates and provides me with a signature he says I can use to upload a file.

The problem is that I cannot find a way to perform that. Especially with the Amazon S3 sample "S3Uploader".

Do you have any idea about that ?

Thanks in advance

Answer 1

The secret key is only needed to calculate the signature, so if you already have a signature you don't need it. You do however need the access key id (so that amazon knows which secret key to use to validate the signature).

I had a quick look at the iOS sdk docs and it doesn't look like they provide a way to short-circuit the signature calculation process. Uploading a file is easy though, you just make a PUT request:

PUT /ObjectName HTTP/1.1
Host: BucketName.s3.amazonaws.com
Date: date
Authorization: signatureValue
Content-Length: 1234

There are details of extra headers you can use in the documentation.

Another workflow is that instead of providing you with signature values, the remote service could use the amazon STS api to return temporary credentials authorised only to upload files to the specified bucket. If you go this route then you would be able to just use the SDK provided by amazon.