How do you Blockchain anything?
It depends on the block chain. But, in the majority of cases, you aren't "blockchain'ing" the actual utility bill. That's a misconception. What you're relying on is the fact that if you take your digital utility bill, feed it into a function, and maybe feed the result of that function into another function, you can reduce your original utility bill down, let's stay it was 12kb originally, to a much smaller string that's only 40 bytes. What you can do with this smaller string is verify that you have the same bill, at a later date. That's about it. If you fed the same utility bill through the same functions, you should get the same result. However, if the utility bill has even one extra period or comma, then the output of that function will be radically different. And you can know for certain that it has been tampered with in some way. That's the idea at least. They call it proof-of-existence.I would have called it a tamper-proof. In Bitcoin, and it may work differently in other block chains, there is a small allocation of space for arbitrary data in transactions. I believe it's 40-80 bytes. Bitcoin stores transactions in the block chain, at a certain time - forever. If you were to add a little bit of extra info to a transaction, it would get stored and timestamped too. Most of these services that are "blockchain'ing" data are "piggy backing" on top of a regular bitcoin transaction to store this proof-of-existence string. So, they send a tiny amount of bitcoin with their data to store - it gets saved. All they have to do is remember the transaction's id, in order to look it up later. Now, they can check it at a later date. And the Bitcoin network doesn't really worry about it. They allow some arbitrary data, and focus on moving bitcoins around. You see how that's useful? You have a string that you want to rely on to determine if something else has changed. That string isn't useful, if it can also potentially change, so we store it into the Bitcoin block chain where we can be reasonably certain that it will remain unchanged, forever. Giving us the ability to prove that, at a certain time, a document had a certain state. If you check the current state against the proof, and it's different, you can know that some time between the timestamp and now, changes were made.