Re: Musings about Usernames in adduser and Debian

[Gioele Barabucci <gioele@svario.it>]

On 03/12/24 22:02, Marc Haber wrote:
> On Tue, Dec 03, 2024 at 09:39:03PM +0100, Gioele Barabucci wrote:
> > On 03/12/24 17:59, Marc Haber wrote:
> > > > in preparation for a PRECIS future, couldn't adduser pass the usernames
> > > > through NFC instead of doing no normalization?
> > > >
> > > > RFC 8264 5.2.4 Normalization Rule states:
> > > >
> > > >      In accordance with [RFC5198], Normalization Form C (NFC) is
> > > >      RECOMMENDED.
> > >
> > > that would solve the étienne and étienne issue (where the two characters
> > > are just different renderings of the same character), but not the
> > > Ohm-against-Omega issue, right?
> >
> > NFC would solve both of these "problems":
> >
> > * Both U+00E9 (é) and U+0065, U+0301 are NFC-normalized to U+00E9,
> > * Both U+2126 (Ohm sign) and U+0349 (omega) are NFC-normalized to U+0349
> > (omega).
>
> Converting Ohm into an Omega is losing intended information, isnt it?

Normalization is always lossy, at least in principle.

Applications that employ normalization accept that tradeoff in order to 
gain something valuable: in this case the ability to have a Ohm sign 
codepoint as part of your username is traded for the ability to compare 
usernames across different OSes and applications.

Regards,

--
Gioele Barabucci