Knowing what the string actually is explains, in advance, every attack described anywhere on this site.
- What it literally says
- The current generation of onion address format.
- What it actually means
- Fifty six characters computed from a public key, with a checksum and a version byte folded in. Nobody assigns them and nobody can revoke one, because holding the address means holding the matching private key.
- What it does not mean
- That the string tells you anything about who runs it. Identifiers carry no reputation, and two addresses that look equally random may be a market and a copy of it.
- What to do
- Copy rather than retype. When comparing, look at the middle rather than the ends.
- If it looks different
- A sixteen character address is from a retired version that stopped resolving years ago, which tells you everything about whatever published it.
CommonEvery address
Needs actionCompare the middle
Warning signShort addresses
Why forgery takes the shape it does
You cannot choose an address, but you can generate keypairs until one begins with characters you want. That is ordinary, and it is why real addresses here open recognisably.
| Matching | Cost |
|---|---|
| Four or five characters | Seconds to minutes on an ordinary machine |
| Seven or eight | Hours to days, still entirely practical |
| Twelve or more | Not feasible |
| The whole address | Impossible, and everything rests on this |
The five second changeSo every forgery has a familiar opening and a different middle. If you are going to spot check rather than paste and compare, check characters twenty through forty. It takes exactly as long as checking the ends.
Things that are not the problem
- Confusable characters. The alphabet used here excludes visually ambiguous pairs by design, so an address that looks slightly off genuinely is off. Never a font issue.
- Case. These are case insensitive, so mixed case is formatting rather than a different address.
- Length. Always fifty six characters before the suffix.
The one claim it makes
That whoever answers holds the key. That is genuinely strong and it is narrow, because it says nothing about whether the key holder is the party you wanted. Turning it into evidence about identity requires a signature checked against a fingerprint you established independently, which is the next entry.