above over the whole file in this way if any byte of the message file is corrupted in transmission it will be discovered the file is then encrypted using an asymmetrical cryptosystem under the user 39 s private key effectively signing the file finally identifying information is added to the now doubly encrypted file and the file is encrypted again u2014 this time under the storage facility 39 s public key now observe the properties of the file thus created the file is secure nobody but the storage facility can open the outer wrapper the file is anonymous to casual observers there is no identifying information outside of the outer wrapper the file is signed the storage facility can open the outer wrapper and discover an identifier of the party who claims to have created the file the signature is irrefutable and cannot be repudiated the storage facility can look up the public key of the party claiming to be the author of the file and can attempt to open the middle wrapper inside they will find an encrypted file and a hash of the file if the calculated hash matches the given hash then the photograph without question belongs to that party even after two wrappers have been removed the picture is still secret the.