Can we protect a Private Blockchain with a Public Blockchain and how

Question

I read somewhere that Private Blockchain has the risk of 51% attack, while Public Blockchain is pretty safe. So, my question is - can we protect private chain with public chain? Can we go around it the following way -  Save block height and block hash, every 100 block. We save 1,101,201... block height and hash on public chain, and we verify it. But it still has risk, before 101 block is protected, 2-99 blocks still have risk. Is there any better way to solve it?

Answer 1

I have recently reviewed Exonum framework  and its Anchoring feature is similar to what you have made.But, I believe the way do it is the correct way. You may either store hash of your Nth block or just store hash every day (or hour) in public chain. You may also look at the possibility to encrypt your data inside a public blockchain. This way you can benefit of the extra security of the public blockchain.