Great article from Brian Deery:
Never loose your child’s birth certificate
Readers have asked us: how we can secure private data publicly on a blockchain and also keep it private? Specifically, how would Factom “never lose your child’s birth certificate?” It would be foolish to publish private data, such as a birth certificate, on a blockchain where the whole world can read it. However, if you only publish a hash of the data, it does not prevent the loss of data, it only gives a reference point to see if it changed. This is a great question and core to the ideas around data management on the blockchain.
When we talk about all the wonderful things that can now be done with a blockchain, it takes a little thinking outside the box. As Henry Ford said, “If I had asked people what they wanted, they would have said faster horses.” Blockchains can change the way we do things, not what we do. Our claim would be confusing if you thought of birth certificates from the perspective of the 20th century; sheets of paper issued by a certificate authority, like a government.
What probably comes to mind is a mere hash of a digital certificate on the blockchain. “If I delete my copy, how is the hash going to retrieve my document?” As many of you know, hashes are one way, you cannot derive the original content from a hash. Conversely, things like a birth certificate should not be published on a blockchain because then anyone could read them. So how does one create a record that can never be lost?
(...)
https://www.factom.com/never-loose-your-childs-birth-certificate/