[cryptography] A secret sharing consensus protocol (or leader election protocol)

Tony Arcieri tony.arcieri at gmail.com
Thu Jul 18 23:57:24 EDT 2013


Has there been any work with combining Shamir-style secret sharing with
consensus protocols like Paxos and Raft (or leader election protocols like
Omega Meets Paxos)?

The idea would be to have a network of n peers, who share a secret where
t=2 shares are required to reassemble the original secret. This secret is
used to sign new values when a group consensus is reached via a Paxos-like
protocol.

In this scheme, a "proposer" would give its secret share, along with a
proposed new value, to "acceptor" nodes, who can reassemble the entire
secret. If they accept the new value, they can sign it with the secret,
then immediately erase it. If we use a deterministic signature algorithm
like Ed25519, every acceptor taking part in the consensus protocol can
produce the same signed version of the proposed new value. They can then
continue with the consensus protocol's accept phase. The result will be a
quorum on a signed value (or a consensus failure if quorum can't be
reached, of course)

Let's assume a malicious entity gains control of one and only one of the
nodes. They are now able to propose new values, so they can manipulate the
peer network by proposing malicious values which will get accepted by the
rest of the group.

However, they do not *immediately* learn the private key. They would only
learn the private key if any other node were to propose a value which
contained their secret share.

-- alternatively --

Secret sharing could be combined with a leader election protocol. In this
scheme, the leader and only the leader would learn the shared secret. All
proposed values would have to be approved and signed by the leader.

I'm not sure I like this as much though. The leader is a single point of
failure, and an attacker could maliciously force a leader election through
e.g. DoS, having compromised only one other host directly.

-- 
Tony Arcieri
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