Not sure why so many things use the compatibility form of normalisation.
Some older RFCs even recommended using it for passwords, which needlessly reduces entropy (yes we need to normalise passwords because of combining characters, but we don’t need to collapse symbols that a user can choose from, like ſ and s).
In my opinion, the compatibility form makes mostly sense for searching text, and even then it’s sometimes annoying (I want to search exactly for ss and not ß, browser). If you know of other good use cases let me know.
It also OK to disallow registering two identifiers with the same compatibility normalisation form (edit: this does not prevent all homoglyph attacks BTW, that is another can of worms), but I don’t see the need to normalise the identifier when it’s used.
Tangentially related - 20+ years ago I managed to register a π domain under one of the primary TLDs.
As in, the registration form was accepted and the fee was charged.
Then, few days after they emailed to say that "due to technical difficulties" the registration can be registered and they have no choice but to unregister it.
My brother had a friend who tried to register fuck.com in the early days of the Internet, around 1994, and the registrar was confused and wanted to know why he wanted to register it. This was when the Internet was mostly universities and a .com cost $100 to register.
I managed to register a one letter domain below a CC-tld, despite that country having a rule against it. Their signup form had two stages and the check was only on the first page... so all it took was changing a hidden form field.
I had it for a while until they started charging a lot for it (it was Turkmenistan).
> My favorite unicode character is zero width space. One of its funniest properties is that it's not a whitespace.
My editor is configured to never show any character (except the one and proper newline) at less than the full-width of a regular character (in the monospace font I'm using ofc).
And if it's not a visible ASCII char, not only it's always shown at least at full-width, it's also shown as bold magenta on a black background. As the non visibe zero-width is empty, it shows as full-width on a black background.
Oh, it can. In fact there's an entire official tome of documentation describing how to carefully do Unicode-in-URLs to reduce the risk[0]. Browsers also have some mitigations to avoid the most common issues like homoglyph attacks where they show the domain in punycode if it doesn't match some local heuristic (like if you're in en-US, it's unlikely you're actually trying to visit a site with Cyrillic letter "a" instead of ASCII "a").
It's implemented because we have thousands of writing systems and we decided, for better or worse, we want to reflect those in URLs. Solving the subsequent security issues is likely easier than getting everyone to agree to read and write the same language.
As to me I'm running my own DNS resolver (I use unbound) and everything goes through port 53 UDP (and AIUI technically 53 TCP should be allowed, but nothing will happen if you just block it), unencrypted. What then unbound does on the Internet, that's up to you: you can encrypt those requests...
The nice thing with everything being in the clear, is that you can null route / NX DOMAIN every single domain that uses Unicode (punnycode) characters and you can even do that at the firewall level, by inspecting UDP packets.
Of course you gotta be sure to really block DoH / DoT internally but it's all doable.
I set that up years ago and I've been running like that since then without any issue.
Just as entire countries's IP blocks do not exist in my world, domains using Unicode characters do not exist. And I really don't care about your feelings about it: I'm just explaining that technically it can be done to block them all and that the Internet keeps working just fine.
Unicode really is just too complex to ever be secure. And those who don't understand that are part of the problem.
Some older RFCs even recommended using it for passwords, which needlessly reduces entropy (yes we need to normalise passwords because of combining characters, but we don’t need to collapse symbols that a user can choose from, like ſ and s).
In my opinion, the compatibility form makes mostly sense for searching text, and even then it’s sometimes annoying (I want to search exactly for ss and not ß, browser). If you know of other good use cases let me know.
It also OK to disallow registering two identifiers with the same compatibility normalisation form (edit: this does not prevent all homoglyph attacks BTW, that is another can of worms), but I don’t see the need to normalise the identifier when it’s used.
https://shkspr.mobi/blog/2018/11/domain-hacks-with-unusual-u...
HN seems to encode it as punycode when it shouldn’t; it skipped normalization.
As in, the registration form was accepted and the fee was charged.
Then, few days after they emailed to say that "due to technical difficulties" the registration can be registered and they have no choice but to unregister it.
I was so close, damn amateurs.
There was a story about Jon Postel (pre-ICANN) and fuck.com, this might be it:
https://www.links.net/webpub/fuck.com.html
I had it for a while until they started charging a lot for it (it was Turkmenistan).
Also, some programming languages treat it as a valid identifier.
My editor is configured to never show any character (except the one and proper newline) at less than the full-width of a regular character (in the monospace font I'm using ofc).
And if it's not a visible ASCII char, not only it's always shown at least at full-width, it's also shown as bold magenta on a black background. As the non visibe zero-width is empty, it shows as full-width on a black background.
Sticks out like a sore thumb.
It's implemented because we have thousands of writing systems and we decided, for better or worse, we want to reflect those in URLs. Solving the subsequent security issues is likely easier than getting everyone to agree to read and write the same language.
[0]: https://www.unicode.org/reports/tr36/tr36-10.html
I have a domain that contains Nordic characters and it is a crapshoot if the email client will accept and send.
Meanwhile I have not encountered problems with http access.
aHR0cHM6Ly/wn4WC8J2WjfCdkKTigpvhtZbwnZKTLuKTnPCdlaDwnZKD8J2Tsi/wn4aG8J+Gg/CfhbU=
https://www.schneier.com/crypto-gram/archives/2000/0715.html...
"Unicode is just too complex to eve be secure"
As to me I'm running my own DNS resolver (I use unbound) and everything goes through port 53 UDP (and AIUI technically 53 TCP should be allowed, but nothing will happen if you just block it), unencrypted. What then unbound does on the Internet, that's up to you: you can encrypt those requests...
The nice thing with everything being in the clear, is that you can null route / NX DOMAIN every single domain that uses Unicode (punnycode) characters and you can even do that at the firewall level, by inspecting UDP packets.
Of course you gotta be sure to really block DoH / DoT internally but it's all doable.
I set that up years ago and I've been running like that since then without any issue.
Just as entire countries's IP blocks do not exist in my world, domains using Unicode characters do not exist. And I really don't care about your feelings about it: I'm just explaining that technically it can be done to block them all and that the Internet keeps working just fine.
Unicode really is just too complex to ever be secure. And those who don't understand that are part of the problem.
Now, present the same list to an I.T. professional with the same questions. Perhaps make sure they are not carrying any weapons before you try.
This is just one reason why visual inspection of URLs and "hover over this link" haven't been useful defenses for a long time.