To: bitcoin-dev@lists.linuxfoundation.org
From: Andreas Schildbach <andreas@schildbach.de>
Date: Wed, 29 Mar 2017 12:07:40 +0200
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	<20170321191454.GA17834@savin.petertodd.org>
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In-Reply-To: <20170321191454.GA17834@savin.petertodd.org>
Subject: Re: [bitcoin-dev] A BIP proposal for segwit addresses
Precedence: list

On 03/21/2017 08:14 PM, Peter Todd via bitcoin-dev wrote:
> On Tue, Mar 21, 2017 at 05:16:30PM +0100, Andreas Schildbach via bitcoin-dev wrote:
>> Why use Base 32 when the QR code alphanumeric mode allows 44 characters?
>> In Bitcoin Wallet, I use Base 43 (alphabet:
>> "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ$*+-./:") for most efficient QR
>> code encoding. I only leave out the space character because it gets
>> replaced by "+" in URLs.
> 
> Doing that only makes addresses a few % shorter, at the cost of significant
> downsides.  For example, not everyone knows what those additional characters
> are called, particularly for non-English-speaking users. Non-alphanumeric
> characters also complicate using the addresses in a variety of contexts ('/'
> in particularly isn't valid in filenames).

I'm not convinced that transmitting addresses via voice should be a
usecase to target at. I don't understand your comment about non-english
speaking users. Obviously they cannot voice-communicate at all with
only-english-speaking users, so there is no need to communicate
voice-communicate addresses between them.

Addresses in QR codes, addresses in URLs and addresses in NFC NDEF
messages are the three most used forms.

Speaking of URLs, actually Base 32 (as well as Base 43) makes QR codes
*bigger* because due to the characters used for URL parameters (?&=)
those QR codes are locked to binary mode. To make them shorter, we'd
need to use something like "Base 64url" (or ideally Base 94 -- all
printable ASCII characters).