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Re: [tor-bugs] #17694 [Tor]: Hash PRNG output before use, so that it's not revealed to the network

#17694: Hash PRNG output before use, so that it's not revealed to the network
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 Reporter:  teor         |          Owner:
     Type:  enhancement  |         Status:  needs_information
 Priority:  Medium       |      Milestone:  Tor: 0.2.8.x-final
Component:  Tor          |        Version:  Tor: unspecified
 Severity:  Normal       |     Resolution:
 Keywords:               |  Actual Points:
Parent ID:               |         Points:
  Sponsor:               |
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Comment (by ioerror):

 I asked a cryptographer sitting next to me and they suggested that my
 suggested approach is reasonable. Hash the PRNG output. Or more directly:
 "Never reveal pure randomness outputs."

 For example, what happens when someone uses RDRAND internally? In theory,
 nothing in our stack does that; in practice, I guess that is incorrect.
 Something in the kernel, for example? Some weird OpenSSL builds or
 something?

 Not to say that RDRAND is backdoored but that if it was, I think a hash
 would prevent what we currently understand to be a way to exploit a Dual-
 EC like backdoor.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17694#comment:5>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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