phc-discussions - Asymmetric proof-of-work based on the Generalized Birthday problem

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Date: Tue, 29 Sep 2015 11:28:52 +0200
From: Dmitry Khovratovich <khovratovich@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Asymmetric proof-of-work based on the Generalized Birthday problem

Dear all,

we have recently developed a memory-hard proof-of-work, which is based on
the well known Generalized Birthday problem: given a list of binary vectors
X_1,X_2,..X_N and number k find i1,i2,..ik such that
X_i1 + X_i2 +.. + X_ik =0.

The non-trivial algorithm for it was developed by Wagner in 2001 and has
been studied extensively since then.

Our proof-of-work is tunable for time, memory, and time-memory tradeoff
independently, and verification is instant. Uniquely, by varying k  any
tradeoff resilience level can be chosen (e.g., one may require that the
time grows as 4-th power of the memory reduction).

 For example, the proof for 700-MB memory is 148 bytes long. The
implementation exists but is not optimized.

In our paper we explore in details all the related time-space tradeoffs,
compare the scheme to existing alternatives, discuss its implementations on
ASICs and GPUs, and estimate its performance and bandwidth requirements.

The full paper is available at http://eprint.iacr.org/2015/946

Comments are welcome.
-- 
Best regards,
Alex Biryukov
Dmitry Khovratovich

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