on the crypto
Lightning Network creator Tadge Dryja worked on a new design for a lighter Bitcoin full node. Last week, Dryja and a team of programmers released a first version of the Utreexo software as part of MIT's Digital Currency Initiative (DCI).
Utreexo specifically addresses the size of the "state" of a complete node, which shows updated information on who owns how many bitcoins. Utreexo reduces the size of the state from about four gigabytes to less than one kilobyte. This could be a big step forward, but has not yet been fully implemented.
A "super-pruned knot"
Currently, full Bitcoin nodes contain all transactions ever made, clocked at around 200 GB. Full "pruned" nodes are able to reduce the size of the transaction history to a minimum of half a gigabyte.
But this is not about storing Bitcoin's Unspent Transaction Output (UTXO), which collects the amount of bitcoins - here the quotation in real time - linked to each bitcoin address. This batch of data takes up just under 4 GB of data.
This UTXO state has grown rapidly over time and is likely to continue to grow, making full node execution more difficult. This is where Utreexo comes in. With the help of sophisticated new encryption, this large state can be replaced with a small cryptographic proof that takes up much less storage space.
"Utreexo is a new hash-based dynamic accumulator that allows you to represent millions of unspent outputs in a kilobyte - small enough to be written on a sheet of paper," explains Dryja on the MIT DCI website.
SPV demanding
Trying to lighten Bitcoin's knots is far from a new idea. Simplified Payment Verification (SPV) is probably the most popular version of a light node, used by Electrum and other wallets. Utreexo is similar to SPV in that it hardly requires the storage space of a full node computer.
But SPV nodes don't preserve user privacy and are more sensitive to attack than Utreexo nodes. Since Utreexo offers these security benefits, Dryja hopes that it can escape SPV's dominance in space (as long as writing the Utreexo software goes as expected). But it also claims that it is difficult to completely replace SPV, since SPV is even easier to perform.
Forward but with caution
"There are still many known bugs and inefficiencies in the code, but we are improving it quickly," writes Dryja. In the end, it will be necessary to make the Utreexo node compatible with the nodes already running on the Bitcoin network.
To do this, you will need to modify Bitcoin Core, the most popular Bitcoin node software. But this could be dangerous. Utreexo is "a significant rethinking of how Bitcoin works, which changes the consent code," writes Dryja.
“It is therefore likely that it will be difficult to insert the Utreexo code in Bitcoin Core, and with good reason. We want to make sure we don't introduce problems into a system that manages so much money, "said Dryja.
