A newly-proposed relay protocol could reduce the “transaction bandwidth” used up by bitcoin nodes by up to 75%.
Called Erlay, the proposed protocol alters the way transactions are
relayed so that they use significantly less bandwidth, an important
resource for the nodes that make up the network. The authors include The
University of British Columbia researcher Gleb Naumenko as well as two
bitcoin development heavy-weights: Greg Maxwell and Pieter Wuille.
The way bitcoin works is that nodes across the world tie together to
form a network. Under the hood, once a transaction is broadcast, it
ripples through this vast network of hardware.
Erlay changes up how the announcement of these transactions is performed. As Naumenko described in a bitcoin dev email announcing the new proposal:
“The main idea is that instead of announcing every
transaction to every peer, announcements are only sent directly over a
small number of connections (only 8 outgoing ones). Further relay is
achieved by periodically running a set reconciliation protocol over
every connection between the sets of withheld announcements in both
directions.”
The results, according to Naumenko: “We save half of the bandwidth a
node consumes, allow increasing connectivity almost for free, and, as a
side effect, better withstand timing attacks. If outbound peer count
were increased to 32, Erlay saves around 75% overall bandwidth compared
to the current protocol.”
One important result of this new protocol, the researchers argue, is
that by reducing how much bandwidth this process takes, nodes can
increase the number of connections they hold with other nodes.
Eclipse attack
As low-level and technical as it sounds, it’s important research,
particularly as it relates to the security of the network itself.
The security of bitcoin depends at least partly on connections
between nodes. This new protocol could make room for more connections,
and the more connected a node is, the more “hardened” it is against
network attacks.
Naumenko described one such attack to CoinDesk: “The most trivial
example is Eclipse attack, when a target node gets isolated from the
longest chain, because all its connections are established with an
attacker. In this case, an attacker, for example, can make a target node
believe that they paid that target node (show shorter chain with that
[transaction] in), without actually submitting transactions to the
longest chain.”
How this attack could impact bitcoin is described in more detail in a 2015 research paper.
So, if the protocol is so important for the security of bitcoin,
what’s next? Will it be added to Bitcoin Core, the most-popular software
implementation of bitcoin?
“A couple weeks ago I chatted with several Bitcoin Core contributors
and the feedback was generally positive, although they requested more
experiments. Now, as those experiments are added, I would give more time
for everybody to familiarize themselves with new technical bits,”
Naumenko told CoinDesk.
As a rule, new technology isn’t added to bitcoin unless the most
active contributors to the software, as well as the wider ecosystem that
actually operates the nodes (and, unlike miners, don’t receive any kind
of built-in subsidy or compensation), agrees with it.
“We received positive signals from the community, which encourages us
to continue working on the implementation,” he added. If the community
continues to like it, then: “The protocol should become part of one of
the future major releases (hopefully, the next one).”
Fiber optics image via Shutterstock
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