> The parties don't have to be trusted.

Actually, zwenger was right. Without a proof of work, they do.

What's a blockchain? It's a data structure with a cryptographically strong CRC mechanism. But there's nothing stopping me from writing a new set of data into a new chain and passing it off as the original.

Sure, you may notice, but you can't prove my new chain is forged. I'll say the backup chain you're using as proof is the forgery...

It takes a proof of work to make the chain effectively uneditable. (Uneditable without paying for the work, which has been selected to be too expensive to be practical.)