http://z7735okcy6gggduobp6vjfcgwz4ss5eeduww7iw2agjmfgpjlnquezqd.onion/article/pseudonymous_memberships
A change in the hash means that the file has been altered, making it practically impossible to find another
file with different content that would produce the same hash. Thus, we can include the hashes of private data
in a contract. The data will remain private until we reveal the original file.
Unfortunately, that's not enough to keep data really safe.