Subject: [Bitcoin-development] ASIC-proof mining

From: Andy Parkins <[email-masked]>
Date: Fri, 04 Jul 2014 11:27:51 +0100

Hello,

I had a thought after reading Mike Hearn's blog about it being impossible to 
have an ASIC-proof proof of work algorithm.

Perhaps I'm being dim, but I thought I'd mention my thought anyway.

It strikes me that he's right that it's impossible for any algorithm to exist 
that can't be implemented in an ASIC.  However, that's only because it's 
trying to pick an algorithm that is CPU bound.  You could protect against ASCI 
mining (or rather, make it irrelevant that it was being used) by making the 
algorithm IO-bound rather than CPU-bound.

For example, what if the proof-of-work hash for a block were no longer just 
"hash of block", which contains the hash of the parent block, but instead were 
hash of 

   [NEW_BLOCK] [ALL_PREVIOUS_BLOCKS] [NEW_BLOCK]

[ALL_PREVIOUS_BLOCKS] is now 20GB (from memory) and growing.  By prefixing and 
suffixing the new block, you have to feed every byte of the blockchain through 
the hashing engine (the prefix prevents you caching the intermediate result).  
Whatever bus you're using to feed your high speed hashing engine, it will 
always be faster than the bus -- hence you're now IO-bound, not CPU-bound, and 
any hashing engine will, effectively, be the same.

I'm making the assumption that SHA-256 is not cacheable from the middle 
outwards, so the whole block-chain _has_ to be transferred for every hash.

Apologies in advance if this is a stupid idea.

Andy
-- 
Dr Andy Parkins
[email-masked]