Title: Hardening Stratum, the Bitcoin Pool Mining Protocol,
Abstract: Stratum, the de-facto mining communication protocol used by blockchain based
cryptocurrency systems, enables miners to reliably and efficiently fetch jobs
from mining pool servers. In this paper we exploit Stratum's lack of encryption
to develop passive and active attacks on Bitcoin's mining protocol, with
important implications on the privacy, security and even safety of mining
equipment owners. We introduce StraTap and ISP Log attacks, that infer miner
earnings if given access to miner communications, or even their logs. We
develop BiteCoin, an active attack that hijacks shares submitted by miners, and
their associated payouts. We build BiteCoin on WireGhost, a tool we developed
to hijack and surreptitiously maintain Stratum connections. Our attacks reveal
that securing Stratum through pervasive encryption is not only undesirable (due
to large overheads), but also ineffective: an adversary can predict miner
earnings even when given access to only packet timestamps. Instead, we devise
Bedrock, a minimalistic Stratum extension that protects the privacy and
security of mining participants. We introduce and leverage the mining cookie
concept, a secret that each miner shares with the pool and includes in its
puzzle computations, and that prevents attackers from reconstructing or
hijacking the puzzles. We have implemented our attacks and collected 138MB of
Stratum protocol traffic from mining equipment in the US and Venezuela. We show
that Bedrock is resilient to active attacks even when an adversary breaks the
crypto constructs it uses. Bedrock imposes a daily overhead of 12.03s on a
single pool server that handles mining traffic from 16,000 miners.