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List:       bitcoin-dev
Subject:    Re: [bitcoin-dev] CheckSigFromStack for Arithmetic Values
From:       ZmnSCPxj via bitcoin-dev <bitcoin-dev () lists ! linuxfoundation ! org>
Date:       2021-07-04 13:10:36
Message-ID: gke1-m0LNsMpPk9TB2ZeeUGgBza7guUJWFWjEhGRMt3MhkYZ7FDOhytx8gY7lv5P2lojyO943NL3T7Jkgwardq2UfLktKcU0TZeQCD70hr4= () protonmail ! com
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Good morning Erik and Jeremy,

> The "for" arithmetic here is largely to mean that this cleverness allows an \
> implementation of `OP_CHECKSIGFROMSTACK`, using arithmetic operation `OP_ADD`. 
> To my mind this cleverness is more of an argument against ever enabling `OP_ADD` \
> and friends, LOL. This is more of a "bad but ridiculously clever thing" post than a \
> "Bitcoin should totally use this thing" post.

Turns out `OP_ADD` is actually still enabled in Bitcoin, LOL, I thought it was hit in \
the same banhammer that hit `OP_CAT` and `OP_MUL`. Limited to 32 bits, but that \
simply means that you just validate longer bitvectors (e.g. the `s` in the \
"lamport-sign the EC signature") in sections of 32 bits.

In any case, the point still mostly stands, I think this is more of a "overall bad \
but still ridiculously clever" idea; the script and witness sizes are fairly awful. \
Mostly just worth discussing just in case it triggers somebody else to think of a \
related idea that takes some of the cleverness but is overall better.

On the other hand if we can actually implement the "Lamport-sign the EC sig" idea (I \
imagine the 32-bit limit requires some kind of `OP_CAT` or similar, or other bit or \
vector slicing operetion), that does mean Bitcoin is already quantum-safe (but has a \
fairly lousy quantum-safe signing scheme, I really do not know the characteristics of \
better ones though).

Regards,
ZmnSCPxj
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