[tor-bugs] #8106 [Tor]: Make .onion addresses harder to harvest by directory servers

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#8106: Make .onion addresses harder to harvest by directory servers
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 Reporter:  asn              |          Owner:                    
     Type:  defect           |         Status:  new               
 Priority:  major            |      Milestone:  Tor: 0.2.5.x-final
Component:  Tor              |        Version:                    
 Keywords:  SponsorZ tor-hs  |         Parent:                    
   Points:                   |   Actualpoints:                    
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Comment(by hyperelliptic):

 Replying to [comment:19 rransom]:
 > Replying to [comment:18 asn]:
 > > Hey Robert,
 > >
 > > I talked with hyperelliptic today and she explained me her concerns of
 comment:17.
 >
 > None of those concerns are legitimate.
 >
 Huh? Let me try this again.

 There are two security requirements:
 * Nobody can produce a signature that passes verification by a user
 knowing A's long-term key.
 AND
 * Nobody can produce a signature that passes verification for the short-
 term public key.

 The second proposal of rransom flunks the second requirement.

 Here is why this requirement matters:
 The HS address is the x-cooordinate of the short-term public key. This can
 be computed by anybody knowing the long-term public key. An attacker could
 overwrite the correct information on the directory service with bogus
 information if he could produce a signature under the short-term public
 key.

 What makes the attack work on the second scheme is that the basepoint is
 provided as part of the signature and is therefore under the control of
 the attacker.

 To avoid this problem, use a fixed basepoint or use x(short-term
 key),x(basepoint) as HS address.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/8106#comment:20>
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