<blockquote>
  <p>Is my understanding correct please?</p>
</blockquote>

<p>The only nit above is the total amount of data is increased a little - so little that it can be ignored.</p>

<blockquote>
  <p>Does it mean that for old-fashioned Nodes who don’t look at Witness side-chain, they can only verify transactions up to the SegWit implementation, and will have to reject new blocks because they won't find a valid signature within the new blocks?</p>
</blockquote>

<p>Wrong. SegWit outputs look like AnyoneCanSpend outputs to legacy nodes (AnyoneCanSpend = P2SH address that can be spent without a signature - you just have to know the script to spend it.) While new nodes understand the "<a href="https://github.com/bitcoin/bips/blob/master/bip-0142.mediawiki#specification" rel="nofollow noreferrer">Witness Program</a>" and verify witness signatures, legacy nodes think it's just a usual AnyoneCanSpend script. Hence, they accept transactions that spend Witness addresses.</p>

CC BY-SA 3.0
2018-02-11T15:32:26.157Z
2018-02-11T15:32:26.157Z
MCCCS
<p>Can someone please help to confirm my understanding of SegWit ?</p>

<p>My understanding:</p>

<ul>
<li>Originally, signatures are included in each block alongside each transaction, these signatures can be read by nodes to prove validity of each transactions.</li>
<li>With SegWit, signatures are omitted from the blocks, but instead recorded in a side-chain called Witness blockchain.</li>
<li>Whoever wants to verify a transaction can refer to the corresponding signature from the Witness side-chain</li>
<li>The total amount of data remains the same, but since we now have two separate chains running in parallel, the size of each block is effectively doubled.</li>
</ul>

<p>Questions:</p>

<ul>
<li>Is my understanding correct please?</li>
<li>Does it mean that for old-fashioned Nodes who don’t look at Witness side-chain, they can only verify transactions up to the Segwit implementation, and will have to reject new blocks because they won't find a valid signature within the new blocks?</li>
<li>In that case, how is it a soft-fork? Since all nodes will be forced to upgrade in order to operate. (by here I am sure I am wrong somewhere..)</li>
<li>Finally, do miners and nodes now keep both chains and when they broadcast the new block, they also broadcast the new Witness block?</li>
</ul>

<p>Thank you very much.</p>

<segregated-witness><soft-fork><anyone-can-spend>
Trying to understand SegWit
kfp22
# Trying to understand SegWit

(Asked by: username_0 on 2018-02-11)

Can someone please help to confirm my understanding of SegWit ?

My understanding:

* Originally, signatures are included in each block alongside each transaction, these signatures can be read by nodes to prove validity of each transactions.
* With SegWit, signatures are omitted from the blocks, but instead recorded in a side-chain called Witness blockchain.
* Whoever wants to verify a transaction can refer to the corresponding signature from the Witness side-chain
* The total amount of data remains the same, but since we now have two separate chains running in parallel, the size of each block is effectively doubled.

Questions:

* Is my understanding correct please?
* Does it mean that for old-fashioned Nodes who don’t look at Witness side-chain, they can only verify transactions up to the Segwit implementation, and will have to reject new blocks because they won't find a valid signature within the new blocks?
* In that case, how is it a soft-fork? Since all nodes will be forced to upgrade in order to operate. (by here I am sure I am wrong somewhere..)
* Finally, do miners and nodes now keep both chains and when they broadcast the new block, they also broadcast the new Witness block?

Thank you very much.

**Tags:** segregated-witness, soft-fork, anyone-can-spend


---

## 1 answers

### Answer by username_1 on 2018-02-11. Score: 1 | Accepted answer

> Is my understanding correct please?

The only nit above is the total amount of data is increased a little - so little that it can be ignored.

> Does it mean that for old-fashioned Nodes who don’t look at Witness side-chain, they can only verify transactions up to the SegWit implementation, and will have to reject new blocks because they won't find a valid signature within the new blocks?

Wrong. SegWit outputs look like AnyoneCanSpend outputs to legacy nodes (AnyoneCanSpend = P2SH address that can be spent without a signature - you just have to know the script to spend it.) While new nodes understand the "[Witness Program](https://github.com/bitcoin/bips/blob/master/bip-0142.mediawiki#specification)" and verify witness signatures, legacy nodes think it's just a usual AnyoneCanSpend script. Hence, they accept transactions that spend Witness addresses.


---

