[UA-discuss] Fw: Re: IDN Implementation Guidelines [RE: Re : And now about phishing...]

Asmus Freytag asmusf at ix.netcom.com
Sat Apr 22 18:55:54 UTC 2017

On 4/22/2017 9:16 AM, Andrew Sullivan wrote:
> On Sat, Apr 22, 2017 at 01:32:08PM +0000, nalini.elkins at insidethestack.com wrote>
>> For example, you may wish to see the following permutations which have already been obtained.  (And, it appears not by Apple)
>> www.applé.com   www.xn--appl-epa.com   www.xn--appl-epa.com	
>> www.applê.com   www.xn--appl-jpa.com    www.xn--appl-jpa.com	
>> www.applė.com   www.xn--appl-yva.com   www.xn--appl-yva.com	
>> www.applę.com   www.xn--appl-8va.com   www.xn--appl-8va.com
> Do you think that those qualify as "homographs"?  I suppose they
> might, as might àpple.com and so on, but these at least don't seem to
> me to be any different than app1e.com, which we decided long ago was
> Apple's problem and nobody else's.

The claim that letters with diacritics are homoglyphs of the undecorated 
letters is
rather tenuous. There are some words where diacritics are optional in 
some languages,
and for those words, even a native reader may not notice the difference 
in spelling,
but that is not all that different from "color" vs. "colour".

A slightly stronger case might be made that some diacritics are not reliably
distinguished from each other. Cedilla and comma below come to mind. 
There are
plenty of examples, mostly in print, that show the use of one in place 
of the other,
even if the language ostensibly calls for a specific one and not the 
other. Their shapes
are not so different that the substitution would always be jarring.

Extending that, it's generally the diacritics below that are less 
readily distinguished
from each other; partially that's because there's less real estate in 
the glyph (and the
bottom of the line may be clipped by the following line of text if the 
spacing is too

The real issue with diacritics is when multiple ones are applied to a 
base letter.
While they are supposed to stack neatly outward in the order that they 
are entered,
there isn't room enough at the bottom of the glyph to show that 
reliably. Also,
sometimes diacritics "overprint" instead of stacking.

 From a perspective of making IDNs universally acceptable, registries 
should be
encouraged to restrict the use of dual diacritics unless central to the 
writing system,
as it is for Vietnamese. The Unicode principle of allowing all 
combinations is fine
for general texts (or more likely, academic texts), but misplaced for 

> This is quite different to the case of true homoglyphs of the sort
> that Asmus is talking about, where the very same glyph is normally
> used in two different scripts such that nobody would be able to tell
> the difference.  One maybe could argue that "аррӏе" is pure homoglyphs
> (0430,0440,0440,04CF, 0435), but I think it's tough to argue for it.

"арр" / "app" or "аре" / "ape" would be true homographs (always identical),
but the palochka (04CF - "ӏ") is at best a near homoglyph. It renders
identical in many fonts, even though it can be rather distinct in
others (especially certain console fonts).

Since those console fonts are a minority, the Palochka should probably 
be treated
conservatively as a homoglyph.

> Remember, the IDNA rules are really _quite_ restrictive, and if
> registries also require "same script per label" those restrictions
> catch an _awful_ lot of corner cases (that was the outcome of the
> "paypal" controversy some time ago).
> If you want to argue that policy should be different, that's fine, but
> it seems to me to require some PDP within ICANN.  Note that ICANN is
> probably going to propose some rules for variant handling, and
> combined with the LGR stuff that is working its way through the system
> we may find an awful lot of stuff is blocked.

Actually, you can block "an awful lot" and yet not affect the universe 
of valid
labels very much.

A case in point is Ethiopic, which for linguistic reasons I won't go 
into, is best
handled by treating a number of code points internal to the script as 
variants of
each other (making them mutually exclusive if they occur as alternates 
in otherwise
identical labels).

The linguistic reasons apply, strictly speaking, only to one of the 
languages (albeit
the most prominent one). The concern was raised how that would interfere 
the ability to register labels in other languages.

For the TLD IDN project we ran an analysis over a corpus of unique 
words, separated
by language. We found that the reduction in available labels was much 
less than
one might have guessed from the considerable number of variants. The 
came to a few percent, much less than the effect of the languages 
sharing words
that happened to be spelled the same (e.g. like English/French "but" or 

The main reason for this is that legitimate labels would tend to contain 
at least one
distinct code point, enough to prevent the label from being blocked. 
(Just as
"dapple" is no longer a homograph of any Cyrillic string even if "apple" 

The other reason is many strings that would otherwise be homographs do not
make sense in the other context, and therefore are much less likely to 
be used for
legitimate labels (and only used for phishing).

Just like the string "аррӏе" (using Cyrillic code points) makes no sense 
to anyone
using a language written in Cyrillic.

For short labels, acronyms etc. might increase the set of legitimate 
labels beyond
the word analysis we were doing, but it would be instructive to run such 
on Latin/Cyrillic corpora assuming the widest definition of homoglyph 
if those corpora are not limited to dictionary words, but include names, 
and acronyms, that would yield a pretty reliable estimate.

I predict that the overlap will prove smaller than feared, for the same 
that we found for Ethiopic, some high visibility exceptions notwithstanding.

> In any case, I think our purpose is very badly served by conflating
> these two different kinds of issues.

Agreed. Our purpose is best served by making careful distinctions among 

- identical              renders same in all fonts and sizes

- near identical         may not be perfectly identical but almost

- not reliably distinct  may be distinct if shown side by side or in some contexts

- confusingly similar    close enough that it can get misidentified

- similar		 everything else that is not clearly distinct

My take is that there is a call for addressing the first two at the 
level of an LGR
(registry policy) and that the third requires some judgement call on 
whether it's
more like the first two, or more like the latter two.


> Best regards,
> A

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