<p>UTXO is short for "Unspent Transaction Output". You can imagine the UTXO set as a set of tuples of the form <code>(txid, index)</code>. Transactions remove items from that list by claiming the outputs and add new items by allocating the bitcoins from claimed outputs to new outputs. Basically the whole of Bitcoin boils down to agreeing on what the current UTXO looks like, as it tells you how many bitcoins are owned by each address at any time.</p>

<p>The UTXO Proof Peter was talking about is a way for a node, that does not store an entire copy of the UTXO set, namely a DHT node, to validate transactions. This is done by querying other nodes in the DHT and retrieving the parts of the UTXO that is needed in order to validate the transaction.</p>

<p>Notice that, while there are some ideas on how to implement this, there currently is no prototype.</p>

CC BY-SA 3.0
2014-01-14T14:50:43.623Z
Isn't the UTXO actually a `(txid, index) -> (value, script)` mapping? This lets the client retrieve `(value, script)` for transaction validation without reading the blockchain. If you're going to read the blockchain anyways, you could just index `txid -> blockid`.
kaoD
CC BY-SA 3.0
2014-01-16T20:00:24.400Z
Yes, this does not actually involve the blockchain and the format of a UTXO key-value pair is as you describe a `(txid, index) -> (value, script)` map. Or if you prefer a set then it's a set of `(txid, index, value, script)` tuples.
cdecker
CC BY-SA 3.0
2013-12-15T13:52:49.537Z
2013-12-15T13:52:49.537Z
cdecker
<p><a href="http://www.youtube.com/watch?v=4d3LA8KpdMQ" rel="nofollow">This video</a> discusses how off chain transactions can be accomplished as an alternative to increasing the block size.</p>

<p>At the 21:25 marker he discusses "UTX 0 Proofs".  What is that?</p>

<offline><off-chain>
What is a UTX 0 Proof? (as discussed in this video)
makerofthings7
# What is a UTX 0 Proof? (as discussed in this video)

(Asked by: username_0 on 2013-12-15)

[This video](http://www.youtube.com/watch?v=4d3LA8KpdMQ) discusses how off chain transactions can be accomplished as an alternative to increasing the block size.

At the 21:25 marker he discusses "UTX 0 Proofs". What is that?

**Tags:** offline, off-chain


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## 1 answers

### Answer by username_1 on 2013-12-15. Score: 1

UTXO is short for "Unspent Transaction Output". You can imagine the UTXO set as a set of tuples of the form `(txid, index)`. Transactions remove items from that list by claiming the outputs and add new items by allocating the bitcoins from claimed outputs to new outputs. Basically the whole of Bitcoin boils down to agreeing on what the current UTXO looks like, as it tells you how many bitcoins are owned by each address at any time.

The UTXO Proof Peter was talking about is a way for a node, that does not store an entire copy of the UTXO set, namely a DHT node, to validate transactions. This is done by querying other nodes in the DHT and retrieving the parts of the UTXO that is needed in order to validate the transaction.

Notice that, while there are some ideas on how to implement this, there currently is no prototype.

> **Comments:**
> **username_2**: Isn't the UTXO actually a `(txid, index) -> (value, script)` mapping? This lets the client retrieve `(value, script)` for transaction validation without reading the blockchain. If you're going to read the blockchain anyways, you could just index `txid -> blockid`.  
> **username_1**: Yes, this does not actually involve the blockchain and the format of a UTXO key-value pair is as you describe a `(txid, index) -> (value, script)` map. Or if you prefer a set then it's a set of `(txid, index, value, script)` tuples.  

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