A wrong address warning you

People expect a mistake to announce itself. Somewhere in the back of the mind is a browser warning, a red page, something. There is nothing.

Why nobody can raise the alarm

A warning requires somebody who knows both where you went and where you meant to go. On the ordinary web the browser knows the second, roughly, because a certificate names a host and can be compared. Here there is nothing to compare against. Tor reaches the key you gave it and that operation succeeded.

The same property that removes the third parties removes the ones who could warn you. This is the cost side of the address being the key and it is rarely stated next to the benefit.

The two failure modes

A wrong address either fails to resolve or resolves somewhere. Failing to resolve is the lucky case, because a typo usually produces a string nobody has a key for, and you get a plain error that looks like every other outage.

Resolving somewhere is the case that costs. It means somebody generated an address near enough to the one you wanted that your mistake landed on their key. That is not luck, it is planning, and the page you land on will be a copy of the one you expected.

What people get wrong

They expect the copy to be shoddy. Broken images, spelling errors, an out of date layout. Copying a website is mechanical and takes minutes. Assume the copy is perfect, because assuming otherwise means your check is looking for craftsmanship rather than correctness.

They also expect a login failure to reveal it. It will not. A copy accepts whatever you type and shows you whatever comes next. Your credentials being wrong for the real site is not a fact the copy needs to respect.

The one moment it can be caught

Before pressing enter. That is the entire window. After the page loads, everything you see is being drawn by whoever answered, and none of it is evidence about who that was. The check has to happen while the string is still in the bar and unsent.

Once the page has loaded, nothing on it can tell you which service you reached.

Where the wrong string comes from

Rarely from a keyboard. Most wrong addresses arrive already wrong, copied from a message, a comment, a list, or an image somebody transcribed. The typo was made once by somebody else and then passed on faithfully by everyone after.

That changes where the check has to sit. Checking your own typing is nearly pointless if you pasted. The comparison has to be against a copy from a different source and a different moment.

What would move this

Browser support for pinning an onion address to a name you chose, so that a mismatch produced a warning. Bookmarks are the weak version of this, since a bookmark you follow goes where it goes, but a bookmark cannot help when the string was typed. A proper feature would need to compare intent against destination, and intent is not currently written down anywhere the software can see.

• Checking the first characters
• Every character weighs the same
• The addresses