The address itself
Terms
- Onion address
- The 56 character string plus the .onion suffix. It is an encoding of a public key rather than a name registered with anybody.
- Version 3 address
- The current generation, 56 characters before the suffix. The older 16 character generation was retired and no longer resolves.
- Base32
- The encoding used, drawing on 26 lowercase letters and the digits 2 through 7. Thirty-two symbols in total.
- Alphabet check
- A test that a string contains only those 32 symbols. All 12 addresses here pass it.
- Length check
- A test that the part before .onion is exactly 56 characters. All 12 here pass it.
- Checksum
- Bits inside the address derived from the key, which let software reject a mistyped address instead of trying to reach it.
- Version byte
- A constant carried at the end of every address of this generation, which is why all 12 strings here end with the same character.
Things people say about addresses
Usage
- Vanity address
- One whose opening characters were chosen by generating keys repeatedly until the encoding started the wanted way. One of the 12 here is a vanity address.
- Vanity prefix
- The chosen part. Cost rises by a factor of 32 for each character added, so short prefixes are cheap and long ones are impossible.
- Mirror
- In ordinary web usage, a copy of a site on another server. Applied to onion addresses it means a second published address, which is a different claim entirely.
- Shared prefix
- How many opening characters two addresses agree on. The longest in this set across all 66 pairs is 1 character.
- Head, middle, tail
- This site names the first eight, characters 21 to 40, and the last eight. They are printed separately because readers treat them very differently.
- Published set
- A list of addresses somebody has put in public. Publication is a claim about who published it, not a claim about the addresses.
Words that carry more weight than they deserve
Verified is the worst offender. It appears constantly next to onion addresses and almost never comes with the three things that would make it mean something, which are what was checked, what it was checked against, and when. An address can be verified in the sense that its checksum is consistent, which any software does automatically, and that is a completely different statement from somebody vouching for where it leads.
Official is the second. Nothing about a string can establish that an operator published it. That is a fact about publication history, not about characters. This site can tell you that one address opens with the market name, and that is a fact about the characters, and it is not the same thing at all.
Working is the third, and it is the one this site refuses outright. Working is a claim about a moment in time and about a network path from one particular machine. It cannot be printed on a page and remain true, and it cannot be checked by a reader without doing the thing the page claimed to have done for them.
The useful test on any page offering you an address is to ask which of its statements would still be true tomorrow. A character count would. A claim about reachability would not, and a page that mixes the two without marking the difference is asking you to extend the credibility of the first to the second.
Questions
What is the difference between an onion address and a domain name?
A domain name is a label assigned to you by a registry that can reassign it. An onion address is a public key rendered as text, so it is not assigned by anyone and cannot be transferred without the private key.
Is a mirror the same site as the main address?
Not necessarily, and nothing in the string can tell you. A second address is a second key. Whether it leads to the same place depends on who controls that key.