[bitcoin-dev] BIP proposal: Inhibiting a covert attack on the Bitcoin POW function

David Vorick david.vorick at gmail.com
Thu Apr 6 12:13:23 UTC 2017

> Another thing that could be done is increase the number of times SHA256 is
> performed... but now we are really talking about altering the PoW
> algorithm.  Correct me if I'm wrong: The more number of times its
> performed, the less any patent-able pre or post calculation
> skipping/caching have an effect on efficiency.

The more complex that the PoW algorithm is, the more likely it is that
someone finds a unique and special method for optimizing it that they are
able to patent. And the more difficult it is to create specialized hardware
to run that algorithm, meaning that there will be fewer players who are
able to do so profitably (higher fixed costs).

If you want to talk about changing the PoW algorithm, you really want to be
looking to simplify it so that it's more obvious (not that you can ever be
completely sure) that there are no hidden or unexpected optimizations that
someone could patent.

We can even do a lot better than SHA. Cryptographic hash functions need to
be collision resistant, and collision resistance is the property that
usually breaks. Preimage resistance and partial preimage resistance (and
second preimage resistance) is generally easier to protect - to the best of
our knowledge, md5 would actually still be a secure PoW function today.

It's bitterly ironic to me that so much research and effort has been put
into making asic-resistant PoW algorithms when in the long run
asic-resistance only leads to problems like these - single parties who have
found significant optimizations and not shared them, completely destroying
any chance of a level playing field and giving themselves a centralized
monopoly - a result that is supremely unhealthy for the rest of the
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