A trailing dot after a nexus market onion

This is the dossier for the nexus market onion trap where a trailing dot lands at the end of a paste after .onion, and the paste behaves differently from the source the reader thought they copied.

What it is

A nexus market onion in a paste has fifty six characters before the .onion label and four characters in the label. Any extra character past the last n is a character the source did not intend the address to carry. A trailing dot is the most common of these because a dot is what tor browser prints between the label and the path, and because a dot is what ends a sentence when the address is quoted in prose.

The trailing dot changes the address as a token. On some paths through the browser and the tor client the dot is stripped and the address resolves. On other paths the dot is kept and the address is treated as a subdomain of the .onion. label, which is not what the reader wanted. Either way the paste is not the source, and the paste is where the reader will look when the result is not what they expected.

Where the dot comes from

A copy from the middle of a sentence in an article is the first origin. The sentence ends with a full stop the moment after the address is quoted. A reader who double clicks on the address in the sentence may catch the full stop by accident. The paste carries the extra character to the address bar.

A copy from a chat message is the second, when the message ended with a full stop or an ellipsis directly after the address. A copy from a status line, a caption or a footnote is the third. All three are surfaces where a nexus market onion sits inside prose rather than on its own line.

Lifeline

How to catch it

The catch is a look at the very end of the paste before the paste is opened. The last character of a nexus market onion is the letter n. Anything after that letter is extra. A reader who has trained the habit of looking at the last character of every paste of an onion address catches this trap without a tool. On this site the copy buttons on the addresses panel copy only the address itself, so the paste that comes out of the panel has no trailing character to strip.

On the paste

Move the cursor to the end of the string. If the last character is not the letter n, the paste has a stray character.

On the source

If the source is a sentence, expect a full stop after the address. Copy the address twice from the source, once from a triple click and once from a hand selection, and compare.

On the address bar

The tor browser address bar is monospace. A stray character at the tail is visible as an extra column.

What this card does not claim

• It does not print a nexus market onion with a trailing dot on a live line. The trap is a shape at the tail, and the card describes the shape.
• It does not say tor browser resolves the trailing dot in every case. Behaviour varies with the version and the platform.
• It does not say the trailing dot is always a dot. A trailing space or a trailing comma is the same trap in a slightly different shape.

A paste that ends where it should end

A paste that ends with the letter n and nothing after it is a paste that has kept the shape of the source. Every copy button on the addresses panel on this site produces a paste of that shape. A reader who has read this dossier can copy any nexus market onion from the panel above and check the last character before opening.

The trailing space and the trailing comma

A trailing space is the same trap in a quieter shape. The space is invisible on the page, invisible on the paste target, and behaves differently again on different browsers. A trailing comma appears when the address was quoted in a list, and the comma between two items of the list survived the copy. Both are handled by the same catch as the trailing dot. Read the last character of the paste, and remove anything after the letter n.

A trailing bracket appears when the address was quoted inside parentheses in a footnote. A trailing quote appears when the address was quoted between quotation marks in a chat message. The family of trailing characters is longer than the trailing dot alone, and the check for the whole family is a single check at the tail.

A double click that ends where the word ends

A double click on an address inside prose selects the word the address forms. On many browsers the selection stops at the last letter of the word and does not include the punctuation after it. On other browsers the selection includes the trailing punctuation. The behaviour is not the same across every layout, so the same double click on the same source can produce two different pastes on two different machines. A quick look at the tail of the paste is the only way to know which one happened.

Engagement

Discover more