<p>This is approximately how Bitcoin full nodes already work, though with one important change.</p>
<hr />
<p>Bitcoin, at the protocol level, has no notion of addresses, and doesn't work in an &quot;account&quot; based fashion, for privacy reasons. Instead, it uses a &quot;UTXO model&quot; (unspent transaction output). The idea that the state of ledger is a set of UTXOs, which you can think of as &quot;coins&quot;. Every transaction consumes certain specific, referenced coins in their entirety, and then creates new coins whose combined value does not exceed the consumed coins' value. Each coin has an identifier, an amount, and a locking script which determines the conditions under which it can be spent (as a simplification, you can think of locking scripts and addresses as the same thing). However, coins all have their own identity, and are not identified by their script/address. In order to create a transaction, you have to specify exactly which coins you're spending. The address just controls what signature is expected to sign for it, but there is no balance per address at the protocol level, just coins.</p>
<p>The reason for this UTXO model is privacy: account based models (where the rule is that sending accounts have sufficient funds available) encourage reuse, because reusing the same account is cheaper (both economically and computationally) than creating new accounts for each receipt. Such reuse is horrible for privacy, as it makes it trivial to link transactions of the same user together. In general, we want a system where acting in a more private manner is not more expensive than not doing so. In a UTXO model, reusing addresses is just as costly as using a new address for each receipt, satisfying that property (there are of course other privacy leaks too, not covered by address reuse).</p>
<hr />
<p>So, with that out of the way, the equivalent of the &quot;address: balance&quot; list you imagine, is actually a &quot;coin: value, script&quot; list, and it is called the &quot;UTXO set&quot;.</p>
<p>Bitcoin full nodes actually do not use the blockchain for anything during validation. They download all blocks, check them against the UTXO set (e.g. checking that all coins consumed by the transactions in the block still exist), then update the UTXO set (removing spent coins, and adding newly created coins), and then move on to the next block. Some nodes do keep the block after processing around, but it's just so that they can provide to other nodes who ask for it; they don't use it for validation of future blocks, that just needs the UTXO set. So-called pruned nodes don't keep blocks around after validation.</p>
<p>The current UTXO set is a few GB when stored on disk, and that is the minimum needed to run a node. It is far lower than storing the whole blockchain, which is a few hundred GB.</p>
<p>Now, in order to fully validate without trusting their peers, nodes do need to download and process all blocks, so that they can build up the UTXO set. It's in theory possible to just get the UTXO set from another node, but that does involve trusting that that UTXO set is correct. There is no P2P protocol for doing so, though there is ongoing work (called &quot;assumeutxo&quot;) to permit something along these lines.</p>

CC BY-SA 4.0
2023-07-23T21:30:45.883Z
2023-07-23T21:30:45.883Z
Pieter Wuille
<p>It seems like theoretically new blocks could be determined from the list of addresses and the amounts possessed by each address, where maintaining the blockchain would be optional and mostly for scanning for errors, etc.</p>
<pre><code>address amount
address amount
...
address amount
</code></pre>
<p>(If an address possessed zero coins, it wouldn't be included in the db)</p>
<p>Do any wallets currently implement anything like that?</p>
<p>Or do tx verification proofs require summing all the txs of an address?</p>
<p>--</p>
<p>Additionally, if not possible with BTC, is there a crypto network where it's possible to participate in consensus verification without the ledger, and mostly a db of addresses and amounts possessed?</p>

CC BY-SA 4.0
2023-07-24T13:46:29.520Z
Hey Bryan, after seeing your two questions, I’m wondering whether you are falling into the [XY problem](https://meta.stackexchange.com/q/66377/232061). Is it possible that you are asking about the _attempted solutions_ for your problem, rather than your _actual problem_? What are you trying to do?
Murch
CC BY-SA 4.0
2023-07-24T18:11:53.757Z
@Murchisonstrike, aspirationally, I'm searching for a climate friendly online monetary network (with offline tx signing) that has nearly zero possibility of immutable bad (or illegal) media being inscribed and distributed.
Bryan Grace
CC BY-SA 4.0
2023-07-24T21:03:25.840Z
A worthy endeavor, although one that seems to still elude us—at least if we wish to retain censorship resistance and a flexible scripting system.
Murch
CC BY-SA 4.0
2023-07-24T21:16:15.043Z
In case it isn’t obvious to you yet, I think it’s also fair to point out that a fair bit of work is going towards leveraging the on-chain Bitcoin transactions to facilitate a multitude of payments in trust-minimized distributed higher layer systems which use the base layer for arbitration and contract enforcement. As that scales up, perhaps the energy investment at the base layer becomes more palatable.
Murch
<wallet><consensus><voting>
Is there a way to participate in bitcoin consensus (tx, block, mining, etc.) verification without downloading the ledger?
Bryan Grace
# Is there a way to participate in bitcoin consensus (tx, block, mining, etc.) verification without downloading the ledger?

(Asked by: username_0 on 2023-07-23)

It seems like theoretically new blocks could be determined from the list of addresses and the amounts possessed by each address, where maintaining the blockchain would be optional and mostly for scanning for errors, etc.

```
address amount
address amount
...
address amount

```

(If an address possessed zero coins, it wouldn't be included in the db)

Do any wallets currently implement anything like that?

Or do tx verification proofs require summing all the txs of an address?

--

Additionally, if not possible with BTC, is there a crypto network where it's possible to participate in consensus verification without the ledger, and mostly a db of addresses and amounts possessed?

**Tags:** wallet, consensus, voting

> **Comments:**
> **username_1**: Hey username_0, after seeing your two questions, I’m wondering whether you are falling into the [XY problem](https://meta.stackexchange.com/q/66377/232061). Is it possible that you are asking about the _attempted solutions_ for your problem, rather than your _actual problem_? What are you trying to do?  
> **username_0**: @Murchisonstrike, aspirationally, I'm searching for a climate friendly online monetary network (with offline tx signing) that has nearly zero possibility of immutable bad (or illegal) media being inscribed and distributed.  
> **username_1**: A worthy endeavor, although one that seems to still elude us—at least if we wish to retain censorship resistance and a flexible scripting system.  
> **username_1**: In case it isn’t obvious to you yet, I think it’s also fair to point out that a fair bit of work is going towards leveraging the on-chain Bitcoin transactions to facilitate a multitude of payments in trust-minimized distributed higher layer systems which use the base layer for arbitration and contract enforcement. As that scales up, perhaps the energy investment at the base layer becomes more palatable.  

---

## 1 answers

### Answer by username_2 on 2023-07-23. Score: 7 | Accepted answer

This is approximately how Bitcoin full nodes already work, though with one important change.

---

Bitcoin, at the protocol level, has no notion of addresses, and doesn't work in an "account" based fashion, for privacy reasons. Instead, it uses a "UTXO model" (unspent transaction output). The idea that the state of ledger is a set of UTXOs, which you can think of as "coins". Every transaction consumes certain specific, referenced coins in their entirety, and then creates new coins whose combined value does not exceed the consumed coins' value. Each coin has an identifier, an amount, and a locking script which determines the conditions under which it can be spent (as a simplification, you can think of locking scripts and addresses as the same thing). However, coins all have their own identity, and are not identified by their script/address. In order to create a transaction, you have to specify exactly which coins you're spending. The address just controls what signature is expected to sign for it, but there is no balance per address at the protocol level, just coins.

The reason for this UTXO model is privacy: account based models (where the rule is that sending accounts have sufficient funds available) encourage reuse, because reusing the same account is cheaper (both economically and computationally) than creating new accounts for each receipt. Such reuse is horrible for privacy, as it makes it trivial to link transactions of the same user together. In general, we want a system where acting in a more private manner is not more expensive than not doing so. In a UTXO model, reusing addresses is just as costly as using a new address for each receipt, satisfying that property (there are of course other privacy leaks too, not covered by address reuse).

---

So, with that out of the way, the equivalent of the "address: balance" list you imagine, is actually a "coin: value, script" list, and it is called the "UTXO set".

Bitcoin full nodes actually do not use the blockchain for anything during validation. They download all blocks, check them against the UTXO set (e.g. checking that all coins consumed by the transactions in the block still exist), then update the UTXO set (removing spent coins, and adding newly created coins), and then move on to the next block. Some nodes do keep the block after processing around, but it's just so that they can provide to other nodes who ask for it; they don't use it for validation of future blocks, that just needs the UTXO set. So-called pruned nodes don't keep blocks around after validation.

The current UTXO set is a few GB when stored on disk, and that is the minimum needed to run a node. It is far lower than storing the whole blockchain, which is a few hundred GB.

Now, in order to fully validate without trusting their peers, nodes do need to download and process all blocks, so that they can build up the UTXO set. It's in theory possible to just get the UTXO set from another node, but that does involve trusting that that UTXO set is correct. There is no P2P protocol for doing so, though there is ongoing work (called "assumeutxo") to permit something along these lines.


---

