To: Bitcoin development mailing list <bitcoin-dev@lists.linuxfoundation.org>
From: Jonas Schnelli <dev@jonasschnelli.ch>
Message-ID: <56D41D71.80503@jonasschnelli.ch>
Date: Mon, 29 Feb 2016 11:29:05 +0100
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Subject: [bitcoin-dev] Fast bootstrapping with a pre-generated UTXO-set
	database
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Hi

I’ve been thinking around a solution to reduce nodes bootstrap time
(IBD) as well as a way to reduce the amount of bandwidth/network usage
per node.
Not sure if this idea was/is already discussed, haven’t found anything
in a quick research.


==Title==
Fast bootstrapping with a pre-generated UTXO-set database.

==Abstract==
This documents describes a way how bitcoin nodes can bootstrap faster
by loading a pre-generated UTXO-set datafile with moderate reduction
of the security model.

==Specification==
Bitcoin-core or any other full node client will need to provide a
feature to "freeze" the UTXO-set at a specified height (will require a
reindex). The frozen UTXO-set – at a specific height – will be
deterministic linearized in a currently not specified
data-serializing-format.
Additionally, a serialized form of the current chain-index (chain
containing all block-headers) up to the specified height will be
appended to the pre-generated UTXO-set-datafile.
The datafile will be hashed with a double SHA256.

The corresponding hash will be produced/reproduced and signed (ECDSA)
by a group of developers, ideally the same group of developers who are
also signing deterministic builds (binary distribution).

Full node client implementations that supports bootstrapping from a
pre-generated UTXO-set, need to include...
1.) a set of pubkeys from trusted developers
2.) the hash (or hashes) of the pre-generated UTXO-set-datafile(s)
3.) n signatures of the hash(es) from 2) from a subset of developers
defined in 1)

To guarantee the integrity of developers pubkeys & signatures, methods
like the current gitian build, used in bitcoin-core, must be used.

New nodes could download a copy of the pre-generated UTXO-set, hash
it, verify the hash against the allowed UTXO-sets, verify the ECDSA
signatures from various developers, and continue bootstrapping from
the specified height if the users accepts the amount of valid signatures
.

Sharing of the pre-generated UTXO-set can be done over CDNs,
bit-torrent or any other file hosting solution. It would also be
possible to extend the bitcoin p2p layer with features to
distribute/share a such pre-generated UTXO-set, in chunks and with the
according hashes to detect invalidity before downloading the whole
content (but would probably end up in something very similar to
bit-torrent).


- ----------------------
</jonas>
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