Date: Mon, 18 Jan 2021 04:15:49 +0000
To: nakagat <nakagat@gmail.com>
From: Pieter Wuille <bitcoin-dev@wuille.net>
Reply-To: Pieter Wuille <bitcoin-dev@wuille.net>
Message-ID: <N9ny4XfpI4SATvCXSKO_ns03ONm4p17tAGXxInoXIe16S7zfH6b8Uj2SkS-pL5sEEp7Wpyi0RZ8J92WZPDeHYKBBuq1xnV6eEUbKouej-TU=@wuille.net>
In-Reply-To: <CAHk9a9d_xm2nO1t5GsLJiny1V3H=uv8jGuUTywQetZQOXxyG9w@mail.gmail.com>
References: <jfRUzc8uB5fpIQy-a_TfTwjAD4FMtf2eInfHdgZRoLwc0NdTv7srnRLtmwFHPLInJfglSzOXXe0SVR3cgHejGPi0Kwl81UV_wkwVJcQi1rA=@wuille.net>
 <CAHk9a9d_xm2nO1t5GsLJiny1V3H=uv8jGuUTywQetZQOXxyG9w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Bech32m BIP: new checksum,
	and usage for segwit address
Precedence: list

Hi all,

A few updates, in response to comments here and in a few other places:

- Updated several reference implementations (C, C++, Python, Javascript) to=
 support Bech32m: https://github.com/sipa/bech32/tree/bech32m (but contribu=
tions to update other languages are welcome!)

- Updated website, including error-locating JS decoder, and demo: http://bi=
tcoin.sipa.be/bech32/demo/demo.html

- Opened a Bitcoin Core PR: https://github.com/bitcoin/bitcoin/pull/20861

- Updates to the BIP draft (https://github.com/sipa/bips/blob/bip-bech32m/b=
ip-bech32m.mediawiki):
  * Made the title clearer (so it doesn't imply Bech32m is used for v0)
  * Added rationale for not permitting both Bech32 and Bech32m for v0
  * Added a section on error location
  * Added links for more reference implementations

On Friday, January 15, 2021 12:01 AM, nakagat <nakagat@gmail.com> wrote:

> I read the BIP draft of Bech32m and implemented it in Go.

Cool! Do feel like contributing it to https://github.com/sipa/bech32/tree/b=
ech32m?

> Let me ask you one question.
> Does Checksum have to be fixed?
> The 'bech32_verify_checksum' function has hrp and data as parameters,
> so how about committing Checksum with these two values?
>
> For example, calculate Checksum from hrp and data using hash, chacha20, e=
tc.

I'm not entirely sure what you mean. Do you mean:

1) Can we use a hash function to compute the checksum instead of Bech32's a=
lgorithm?

If you compute the checksum using the HRP and the data using a hash functio=
n, you just 2^-30 failure probability for any error. The idea behind Bech32=
 was doing better than that for common errors: any error that consists of u=
p to 4 substitutions are a failure probability of 0 - far better than a has=
h can do.

2) Can we keep using Bech32's algorithm, but compute the final xorred-in co=
nstant from the HRP and the data using a hash function?

That would be functionally equivalent to (1).

3) Can we keep using Bech32's algorithm, but compute the final xorred-in co=
nstant from the HRP (but not the data) using a hash function?

It would mean that some (very) small set of potential HRPs would exhibit mu=
ch worse behavior than others - including the 'q'-before-'p' that the origi=
nal Bech32 has.

Does that clarify things?

Cheers,

--
Pieter