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

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#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_review
 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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Changes (by teor):

 * status:  new => needs_review


Comment:

 Since I'd written the code already, I updated my rand-hash-v2 branch based
 on bug17686_v2_027 in #17686. See https://github.com/teir2345/tor.git

 It contains the modifications to crypto_rand, and new benchmarks comparing
 crypto_rand (hashed PRNG output) with crypto_rand_raw (PRNG output).

 While I don't think PRNG performance is critical-path, on typical random
 data requests, random performance increases up to 48% at smaller sizes (4
 bytes) due to the hash output buffer, and performance decreases up to 27%
 at larger sizes (32 bytes).

 If we do choose to go ahead with this, we should run the unit tests on
 both crypto_rand_raw and crypto_rand. I can update the existing unit tests
 to do that, and I'd like to include the unit tests in #17697 as well. But
 I'll wait until we decide we want this change.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17694#comment:3>
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