How is it useless? If the digest you provide is found, then you know the data hasn't been changed. Sure, that's the only bit of information you get, but in a l

How is it useless? If the digest you provide is found, then you know the data hasn't been changed. Sure, that's the only bit of information you get, but in a lot of cases that's the only one you need. It doesn't guarantee your data can't be changed, no. What guarantees that is your contact with Amazon.