How could the Bitcoin protocol be modified so that pruned nodes could still participate in BIP 37 SPV?

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According to Jameson Lopp (https://www.coindesk.com/spv-support-billion-bitcoin-users-sizing-scaling-claim/), allowing pruned nodes to advertise that they support BIP 37 would be impossible without "extensive protocol changes." What changes would make this possible?

Ian MathWiz

Posted 2018-01-17T22:44:38.847

Reputation: 101

Answers

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Pruned peers do not have the full blockchain history and therefore have only limited value for SPV clients.

With Bitcoin Core 0.16, pruned peers will announce its service via NODE_NETWORK_LIMITED (see BIP159 https://github.com/bitcoin/bips/blob/master/bip-0159.mediawiki). BIP159 is a non consensus change.

This will allow SPV clients to connect to pruned peers. But, since they only signal for the last 288 blocks, SPV/BIP37 clients interested to load history older then 1 day of blocks would still require to connect to traditional peers.

In future, pruned nodes may have a way to signal how many blocks they will keep on disk (without adding a fingerprinting vulnerability).

Not to forget is that BIP37 is a controversial concept. It has significant privacy downsides (see Jonas Nicks research).

A far better concept is "Client side filtering". See the upcoming BIP: https://github.com/bitcoin/bips/pull/636

Jonas Schnelli

Posted 2018-01-17T22:44:38.847

Reputation: 5 465