Date: Sat, 3 Jul 2021 00:05:40 -1000
From: "David A. Harding" <dave@dtrt.org>
To: Craig Raw <craigraw@gmail.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP Proposals for Output Script Descriptors
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On Sat, Jul 03, 2021 at 10:35:48AM +0200, Craig Raw wrote:
> There is a downside to using "h"/"H" from a UX perspective - taking up mo=
re
> space=20

Is this a serious concern of yours?  An apostrophe is 1/2 en; an "h" is
1 en; the following descriptor contains three hardened derivations in 149
characters; assuming the average non-'/h character width is 1.5 en, the
difference between 207 en and 208.5 en is barely more than half a
percent.

    pkh([d34db33f/44h/0h/0h]xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQV=
HQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/*)#ml40v=
0wf

Here's a direct visual comparison: https://gist.github.com/harding/2fbbf2bf=
dce04c3e4110082f03ae3c80

> appearing as alphanumeric characters similar to the path numbers

First, I think you'd have to be using an awful font to confuse "h" with
any arabic numeral.  Second, avoiding transcription errors is exactly
why descriptors now have checksums.

> they make derivation paths and descriptors more difficult to read.

The example descriptor pasted above looks equally (un)readable to me
whether it uses ' or h.

> Also, although not as important, less efficient when making metal
> backups.

I think many metal backup schemes are using stamps or punch grids that
are fixed-width in nature, so there's no difference either way.  (And
you can argue that h is better since it's part of both the base58check
and bech32 character sets, so you already need a stamp or a grid row for
it---but ' is otherwise unused, so a stamp or grid row for it would be
special).

But even if people are manually etching descriptors into metal, we're
back to the original point where we're looking at something like a 0.7%
difference in "efficiency".

By comparison, the Bitcoin Core issue I cited in my earlier post
contains several examples of actual users needing technical support
because they tried to use '-containing descriptors in a bourne-style
shell.  (And I've personally lost time to that class of problems.)  In
the worst case, a shell-quoting accident can cause loss of money by
sending bitcoins to the descriptor for a key your hardware signing
device won't sign for.  I think these problems are much more serious
than using a tiny bit of extra space in a GUI or on a physical backup
medium.

-Dave

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