How to overthrow the GPU Oligarchs

The strength of this project was meant to be its distributedness.

But now, it seems that an increasingly small and exclusive elite has taken charge of coin/block generation. It’s dominated by specialists who have access to wholesale means of production and secret, proprietary GPU code.

The average user no longer has a fighting chance and has given up generating blocks altogether.

What does this remind me of? That’s right, bitcoin is becoming like the physical money economy, where a small number of central banks now guarantee the trustworthiness of paper money.

There are two problems: One, the possibility of market manipulation, and more importantly, if only a handful of people do most of the proof of work, what is the point of a decentralized currency in the first place? It weakens us, because a powerful attacker would only need to bribe a few people to gain more than 50% of khash/s.

To stop this, I suggest the following:

1. Add more hash functions that must be solved in addition to SHA-2. The more, the better. The function ecosystem should include functions with very different requirements, eg. some that require lots of memory, some that can’t be paralellized, some that require lots of disk space,… Also, function parameters that change randomly every time difficulty changes. This would take away some advantage from people who are highly specialized at solving just one hash function.

2. Pooled block generation. For instance, if 100 users join a pool and one block is solved, the 50 coins are distributed among those users. This would encourage amateur users to start generating again.

Can you tell more about this: “they have to do weird things with extraNonce, which increases the size of the block header”.

Can you tell more about it: “they have to do weird things with extraNonce, which increases the size of the block header”.

When you generate, you calculate hashes of the block header. Hashing more data is slower than hashing less data, so the block header is critically of a fixed size for everyone, with one exception. After every hash attempt, you increment the Nonce header field, but since this field is only 32 bytes long, it overflows a lot. Whenever it overflows, you increment the variable-size extraNonce field. The larger extraNonce gets, the slower generating will get. It doesn’t get significantly large with normal incrementing, though.

If you have a lot of computers and they’re all working on the same block with the same public key, then they’re all very likely to be hashing the same block at the same time, which is pointless. To fix this, each computer is given a unique extraNonce modifier value. This might be very large to prevent collisions, and it therefore slows down hashing.

Undoubtedly you could design a pooling system without this flaw, but it’d be more difficult.

I see that m0mchil’s getwork is doing something with extraNonce. I don’t know how bad that implementation is, but it theoretically must be slower than a client without it (all things being equal; clearly adding GPU support will improve performance).

If you have a lot of computers and they’re all working on the same block with the same public key, then they’re all very likely to be hashing the same block at the same time, which is pointless. To fix this, each computer is given a unique extraNonce modifier value. This might be very large to prevent collisions, and it therefore slows down hashing.

In a centralized system, the server could simply keep a list of extraNonces in active use and give out the lowest free one. Then you would avoid collisions without requiring more than one unique extraNonce per client. A 3-byte extraNonce would be sufficient for millions of clients. Note that clients of realistic performance do not really need the extraNonce to handle nonce overflow today, since such overflows happen less frequently than the periodic nTime updates (but this is not considered by the standard client today, which updates the extraNonce more liberally).

I’m just getting into this whole bitcoin thing. It seems to me already, though, that getting great results from bitcoin mining would require a server farm, super computer, etc; worrying about individuals taking advantage of their GPUs or crypto accelerators is probably pointless. What can 30000 khash/s really get you? Maybe around the equivalent of $1.50 per day at current difficulty levels? Not really a very efficient means of recouping the cost of an expensive gaming rig.

I’d be much more concerned about what somebody with a botnet might be capable of.

I’d be much more concerned about what somebody with a botnet might be capable of.

So what if a botnet generate all these bitcoins? He’ll be able to move markets for his money. Big deal.

Quote from: lzsaver on October 01, 2010, 8:49:47 PM UTC

Can you tell more about it:

“they have to do weird things with extraNonce, which increases the size of the block header”. When you generate, you calculate hashes of the block header. Hashing more data is slower than hashing less data, so the block header is critically of a fixed size for everyone, with one exception.This is the point of confusion.  extraNonce is not part of the block header, it is part of the first transaction.  It does not slow down your hashing.  It does not change the size of the header.

We need to be vigilant and nip in the bud any misconception that the contents of your block slows down your hash speed.  It doesn’t.

extraNonce never needs to be very big.  We could reset it every second whenever the time changes if we wanted.  Worst case, if you didn’t want to keep track of incrementing it, extraNonce could be 4 random bytes and the chance of wasting time from collision would be negligible.

Separate machines are automatically collision proof because they have different generated public keys in the first transaction.  That also goes for each thread too.

Quote from: chrisdbc on October 03, 2010, 8:08:33 PM UTC

I’d be much more concerned about what somebody with a botnet might be capable of.

So what if a botnet generate all these bitcoins? He’ll be able to move markets for his money. Big deal.

It’s certainly a big deal to steal other’s resources to generate bitcoins.

It’s certainly a big deal to steal other’s resources to generate bitcoins.

Look, it’s still true without the bitcoin part.

Quote It’s certainly a big deal to steal other’s resources to generate bitcoins.

Look, it’s still true without the bitcoin part.

I suspect it’s more profitable to run a email scam than to generate bitcoin.