Subject: Re: [bitcoindev] Signing a Bitcoin Transaction with Lamport Signatures (no changes needed)

From: Andrew Poelstra <[email-masked]>
Date: Thu, 9 May 2024 12:46:46 +0000

On Wed, May 08, 2024 at 05:31:18PM -0700, Ben Carman wrote:
> I think it is possible to get past the 201 op code limit doing it in 
> tapscript. I don't think it would have the same quantum security but could 
> maybe be a path to covenants. My understanding is that you're using the 
> OP_SIZE of the sig to basically decide to verify if the bit is a 0 or a 1, 
> then do that verification. You could do the same trick with schnorr sigs, 
> just for 0 bits don't include the sighash_all flag, and for 1 bits include 
> it. This would allow you to get around all the resource limits that taproot 
> lifted. This still should be safe since the the signature commits to if it 
> is SIGHASH_DEFAULT vs SIGHASH_ALL. I am not sure if this will enable very 
> complex things or just let you do it on 1 bit of information in tapscript.
>

If I'm understanding you right, then what you're signing is your choice
of sighash flags, rather than anything inherent to the transaction. So I
don't think this works.

-- 
Andrew Poelstra
Director, Blockstream Research
Email: apoelstra at wpsoftware.net
Web:   https://www.wpsoftware.net/andrew

The sun is always shining in space
    -Justin Lewis-Webster

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