Immutability of medical data

The first line of defense is offered by zero-knowledge encryption itself. It is easier to defend data integrity when a potential attacker doesn't know what to change since everything is encrypted in the first place.

The second line is offered by redundant storage nodes and saved medical data checksums on patient devices support immutability. If anything is changed, a user will know.

The final line of defense is to find out which node was changed. All storage nodes would provide cryptographic proofs to patients, by writing hashes in the EOS blockchain. Patients would be able to independently verify that the provided proof was really there with a blockchain receipt. That way, if the checksum verification fails, the compromised storage node can be easily identified and replaced.

To reduce the number of hashes, aggregation into a Merkle tree will be used. Clients receive a blockchain receipt which they can use to independently verify the blockchain proof .