[jonprins]

Am I completely missing a key part of bitcoin, then? My understanding was the 'pointless tasks' were actually the verifications of previous transactions. And to make such a system verifiable, several nodes in the network must hash out the same blocks the same way.

[nhaehnle]

It depends on what you mean by verifying the transactions. Checking the signature of the transactions, to prove that the transaction was in fact issued by whoever owns the coins being sent, is only a negligible part of the computation.

The actual pointless task is to try to find a type of hash collision, to be specific: find a plaintext containing hashes of the transactions to be committed such that the hash of this plaintext starts with a bunch of zeroes. The more initial zeroes you require, the higher is the difficulty. (The plaintext is allowed to contain a small arbitrary nonce. So miners just cycle through all the possible nonces, computing hashes, until they find one that starts with a bunch of zeroes.)

It's conceivable that one could somehow mix the transaction data into a problem of bioinformatics, but I don't know so much about that. The problem is that, as far as I'm aware, some hash of the transactions to be committed must be part of the input of the "pointless" problem.

[eli]

Yes, that's my understanding. But it doesn't require that the tasks are "pointless" -- just that they are hard to compute, but relatively easy to verify.

There are lots of problems in bioinformatics and physics that are hard to compute and easily divided into chunks. Find one that also has easily verifiable results and you've got a pretty good candidate.

[jonprins]

But the problems being chunked up in bitcoins are the actual bitcoin transactions, thus churning them is not pointless. It strengthens the system.

[wccrawford]

The 'pointless tasks' are the mining of the original coins. There are additional tasks for verifying the validity of the transactions of coins as well, but they take much less processing power.