<blockquote>
<p>Can we prune the witness area to save space</p>
</blockquote>
<p>You can so do today already, with a pruned node. It precludes the ability to let other post-segwit nodes synchronize from you, and loses the ability to audit which participant(s) spent coins in case of a multisig. Other than that, it's perfectly feasible today; it's not done because it's much easier to prune everything past a certain point (rather than just witness data).</p>
<blockquote>
<p>and turn old transactions into a proper anyone can spend?</p>
</blockquote>
<p>That is unrelated, and would require a hard fork. Without witness data, no pre-hardfork post-segwit node will be able to synchronize.</p>
<p>From comments:</p>
<blockquote>
<p>Good idea. And soft fork in a new postsegwit area for postquantum sigs.</p>
</blockquote>
<p>You don't need a post-segwit area for that. Segwit v0 and v1 use ECDSA and Schnorr/BIP340 signatures respectively, but v2 or other future versions could be introduced that use post-quantum signatures.</p>

CC BY-SA 4.0
2023-07-12T17:57:05.150Z
> Without witness data, no pre-hardfork post-segwit node will be able to synchronize. ... I doubt this is the case. As the quantum computer can feed garbage signatures to pre-hardfork post-segwit node and cause bugs anyway.
Hcomber
CC BY-SA 4.0
2023-07-12T17:59:03.473Z
That would require the quantum computer to forge PoW (as the witness data is committed to by PoW), which very likely remains nontrivial even with powerful quantum computers (you get the sqrt() Grover's quantum speedup, but not the polynomial Shor speedup).
Pieter Wuille
CC BY-SA 4.0
2023-07-09T13:35:21.473Z
2023-07-09T14:29:42.590Z
2023-07-09T14:29:42.590Z
Pieter Wuille
<p>Assuming a quantum computer gets deployed. ECDSA doesn't prove anything anymore. Can we prune the witness area to save space and turn old transactions into a proper anyone can spend?</p>

CC BY-SA 4.0
2023-07-09T12:32:00.457Z
If ECDSA is broken, aren't pre-segwit transactions also vulnerable? What would this gain?
RedGrittyBrick
CC BY-SA 4.0
2023-07-09T12:34:55.827Z
it would prune storage (save unnecessarily occupied disk space) after the point when segwit gained traction. It will also prune the ordinal spam
Hcomber
CC BY-SA 4.0
2023-07-09T12:35:59.193Z
Why not prune everything  vulnerable to a break of ECDSA?
RedGrittyBrick
CC BY-SA 4.0
2023-07-09T12:37:08.410Z
Good idea. And soft fork in a new postsegwit area for postquantum sigs.
Hcomber
<quantum-computing><witness-data>
Asumming a quantum computer gets deployed. Is it safe to prune the witness area and make blocks 1MB again?
Hcomber
# Asumming a quantum computer gets deployed. Is it safe to prune the witness area and make blocks 1MB again?

(Asked by: username_0 on 2023-07-09)

Assuming a quantum computer gets deployed. ECDSA doesn't prove anything anymore. Can we prune the witness area to save space and turn old transactions into a proper anyone can spend?

**Tags:** quantum-computing, witness-data

> **Comments:**
> **username_1**: If ECDSA is broken, aren't pre-segwit transactions also vulnerable? What would this gain?  
> **username_0**: it would prune storage (save unnecessarily occupied disk space) after the point when segwit gained traction. It will also prune the ordinal spam  
> **username_1**: Why not prune everything  vulnerable to a break of ECDSA?  
> **username_0**: Good idea. And soft fork in a new postsegwit area for postquantum sigs.  

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## 1 answers

### Answer by username_2 on 2023-07-09. Score: 4

> Can we prune the witness area to save space

You can so do today already, with a pruned node. It precludes the ability to let other post-segwit nodes synchronize from you, and loses the ability to audit which participant(s) spent coins in case of a multisig. Other than that, it's perfectly feasible today; it's not done because it's much easier to prune everything past a certain point (rather than just witness data).

> and turn old transactions into a proper anyone can spend?

That is unrelated, and would require a hard fork. Without witness data, no pre-hardfork post-segwit node will be able to synchronize.

From comments:

> Good idea. And soft fork in a new postsegwit area for postquantum sigs.

You don't need a post-segwit area for that. Segwit v0 and v1 use ECDSA and Schnorr/BIP340 signatures respectively, but v2 or other future versions could be introduced that use post-quantum signatures.

> **Comments:**
> **username_0**: > Without witness data, no pre-hardfork post-segwit node will be able to synchronize. ... I doubt this is the case. As the quantum computer can feed garbage signatures to pre-hardfork post-segwit node and cause bugs anyway.  
> **username_2**: That would require the quantum computer to forge PoW (as the witness data is committed to by PoW), which very likely remains nontrivial even with powerful quantum computers (you get the sqrt() Grover's quantum speedup, but not the polynomial Shor speedup).  

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