[tor-bugs] #18191 [Tor]: .onion name collision

[Tor Bug Tracker & Wiki]

#18191: .onion name collision
-----------------------------+-----------------
     Reporter:  cypherpunks  |      Owner:
         Type:  defect       |     Status:  new
     Priority:  Medium       |  Milestone:
    Component:  Tor          |    Version:
     Severity:  Normal       |   Keywords:
Actual Points:               |  Parent ID:
       Points:               |    Sponsor:
-----------------------------+-----------------
 >The output of SHA1 has a length of 160 bit. To make handling the URLs
 more convenient we only use the first half of the hash, so 80 bit remain.
 Taking advantage of the ​Birthday Attack, entropy can be reduced to 40
 bit. That's why collisions could be found with moderate means. This is not
 a problem for Tor since all an attacker might be able to do is create two
 different public keys that match the same .onion name. He would not be
 able to impersonate already existing hidden services.

 Why he would not be able? As I know, there is no built-in way to
 authenticate a HS if there is a collision: the legit and fake HSes will be
 indistinguishable from each other.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18191>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online