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From: David Vorick <david.vorick@gmail.com>
Date: Thu, 6 Apr 2017 08:13:23 -0400
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To: praxeology_guy <praxeology_guy@protonmail.com>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary=001a114a4c868f145f054c7e6f29
Subject: Re: [bitcoin-dev] BIP proposal: Inhibiting a covert attack on the
 Bitcoin POW function
Precedence: list

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>
> 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
community.

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote"><blo=
ckquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #c=
cc solid;padding-left:1ex"><div>Another thing that could be done is increas=
e the number of times SHA256 is performed... but now we are really talking =
about altering the PoW algorithm.=C2=A0 Correct me if I&#39;m wrong: The mo=
re number of times its performed, the less any patent-able pre or post calc=
ulation skipping/caching have an effect on efficiency.</div></blockquote><d=
iv><br></div><div>The more complex that the PoW algorithm is, the more like=
ly it is that someone finds a unique and special method for optimizing it t=
hat they are able to patent. And the more difficult it is to create special=
ized hardware to run that algorithm, meaning that there will be fewer playe=
rs who are able to do so profitably (higher fixed costs).<br><br></div><div=
>If you want to talk about changing the PoW algorithm, you really want to b=
e looking to simplify it so that it&#39;s more obvious (not that you can ev=
er be completely sure) that there are no hidden or unexpected optimizations=
 that someone could patent.<br><br></div><div>We can even do a lot better t=
han SHA. Cryptographic hash functions need to be collision resistant, and c=
ollision resistance is the property that usually breaks. Preimage resistanc=
e and partial preimage resistance (and second preimage resistance) is gener=
ally easier to protect - to the best of our knowledge, md5 would actually s=
till be a secure PoW function today.<br><br></div><div>It&#39;s bitterly ir=
onic to me that so much research and effort has been put into making asic-r=
esistant PoW algorithms when in the long run asic-resistance only leads to =
problems like these - single parties who have found significant optimizatio=
ns and not shared them, completely destroying any chance of a level playing=
 field and giving themselves a centralized monopoly - a result that is supr=
emely unhealthy for the rest of the community.<br></div></div></div></div>

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