[peedy]

As making a policy involves no communication with Amazon, I used to just create a policy on the fly for every upload request that said "allow upload to this specific key(path)". The key would be unique to every upload request. Once the upload is done, I'd just start processing the upload and move it where it belongs.

Thus, in plaintext you'd have to put only your AccessID and a policy which would expire after a few minutes.

EDIT: typo