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Date: Thu, 12 Jul 2018 22:10:16 +0200
From: Solar Designer <solar@...nwall.com>
To: announce@...ts.openwall.com
Subject: [openwall-announce] yespower 1.0.0 - a proof-of-work (PoW) focused fork of yescrypt

Hi,

For historical reasons, multiple CPU mining focused cryptocurrencies use
yescrypt 0.5'ish as their proof-of-work (PoW) scheme.  With this
announcement, we introduce a separate project for the PoW use case:
yespower.  Thus, rather than misuse yescrypt 1.0+ for PoW, those and
other projects needing a PoW scheme are advised to use yespower 1.0+.

You can download yespower 1.0.0 from its new homepage:

http://www.openwall.com/yespower/

yespower is a proof-of-work (PoW) focused fork of yescrypt.  While
yescrypt is a password-based key derivation function (KDF) and password
hashing scheme, and thus is meant for processing passwords, yespower is
meant for processing trial inputs such as block headers (including
nonces) in PoW-based blockchains.

On its own, yespower isn't a complete proof-of-work system.  Rather, in
the blockchain use case, yespower's return value is meant to be checked
for being numerically no greater than the blockchain's current target
(which is related to mining difficulty) or else the proof attempt
(yespower invocation) is to be repeated (with a different nonce) until
the condition is finally met (allowing a new block to be mined).  This
process isn't specific to yespower and isn't part of yespower itself
(rather, it is similar in many PoW-based blockchains and is to be
defined and implemented externally to yespower) and thus isn't described
in here any further.


	Why or why not yespower?

Different proof-of-work schemes in existence vary in many aspects,
including in friendliness to different types of hardware.  There's
demand for all sorts of hardware (un)friendliness in those - for
different use cases and by different communities.

yespower in particular is designed to be CPU-friendly, GPU-unfriendly,
and FPGA/ASIC-neutral.  In other words, it's meant to be relatively
efficient to compute on current CPUs and relatively inefficient on
current GPUs.  Unfortunately, being GPU-unfriendly also means that
eventual FPGA and ASIC implementations will only compete with CPUs, and
at least ASICs will win over the CPUs (FPGAs might not because of this
market's peculiarities - large FPGAs are even more "over-priced" than
large CPUs are), albeit by far not to the extent they did e.g. for
Bitcoin and Litecoin.

There's a lot of talk about "ASIC resistance".  What is (or should be)
meant by that is limiting the advantage of specialized ASICs.  While
limiting the advantage at KDF to e.g. 10x and at password hashing to
e.g. 100x (talking orders of magnitude here, in whatever terms) may be
considered "ASIC resistant" (as compared to e.g. 100,000x we'd have
without trying), similar improvement factors are practically not "ASIC
resistant" for cryptocurrency mining where they can make all the
difference between CPU mining being profitable and not.  There might
also exist in-between PoW use cases where moderate ASIC advantage is OK,
such as with non-cryptocurrency and/or private/permissioned blockchains.

Thus, current yespower may be considered either a short-term choice
(valid until one of its uses provides sufficient perceived incentive to
likely result in specialized ASICs) or a deliberate choice of a pro-CPU,
anti-GPU, moderately-pro-ASIC PoW scheme.  It is also possible to
respond to known improvements in future GPUs/implementations and/or to
ASICs with new versions of yespower that users would need to switch to.


	yespower versions.

yespower includes optimized and specialized re-implementation of the
obsolete yescrypt 0.5 (based off its first submission to Password
Hashing Competition back in 2014) now re-released as yespower 0.5, and
brand new proof-of-work specific variation known as yespower 1.0.

yespower 0.5 is intended as a compatible upgrade for cryptocurrencies
that already use yescrypt 0.5 (providing a few percent speedup), and
yespower 1.0 may be used as a further upgrade or a new choice of PoW by
those and other cryptocurrencies and other projects.

There are many significant differences between yespower 0.5 and 1.0
under the hood, but the main user visible difference is yespower 1.0
greatly improving on GPU-unfriendliness in light of improvements seen in
modern GPUs (up to and including NVIDIA Volta) and GPU implementations
of yescrypt 0.5.  This is achieved mostly through greater use of CPUs'
L2 cache.

The version of algorithm to use is requested through parameters,
allowing for both algorithms to co-exist in client and miner
implementations (such as in preparation for a cryptocurrency hard-fork
and/or supporting multiple cryptocurrencies in one program).


	Further detail.

Please refer to the documentation included inside the yespower release
tarball for guidance on parameter selection, benchmarks and performance
tuning, how to build yespower from source and test it, how to integrate
yespower in a program, and more.

Alexander

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