I have just finished reading the paper Purely P2P Crypto-Currency With Finite Mini-Blockchain by J.D. Bruce. While I got the impression, that the rolling blockchain as an idea might work, I was left wondering about one detail in the proposal.
It seems to me that the proof-chain fails to live-up to it's purpose:
Bruce suggests that it would be sufficient to keep the proof-of-work solutions of the blocks as a proof-chain. Yet, how could one verify the proof-chain if all the block data has been discarded as suggested? Wouldn't it be possible to replace any blockhash in the proof-chain with another valid blockhash and start a competing mini-blockchain from that point?
That way an attacker could spend any amount of time on the mini-blockchain and just insert it into the proof-chain whenever it is sufficiently long.
Am I missing something? Why would the proposal work as intended by the author? Or is it actually "broken"?