[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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Comment (by dgoulet):

 Replying to [comment:9 nickm]:
 > feature17694_strongest_027 starts this, based on the code for #17686.  I
 suggest it for inclusion in 0.2.8 only.  I'm going to extend it to know
 about other prngs.

 I would really like to see comments added to `crypto_strongest_rand()`
 since this is not that obvious to get at first glance. For instance:

 * Why is `inp` twice the size and the second half is randomized
 differently? (I assume to mix different entropy source but would be nice
 that it's explain why we do that).

 * Why do we `tor_assert(0)` instead of clean exit?

 The rest lgtm! I'm those in favor of this as well which will simplifies
 things for prop#250 that right now explicitely hash the return value of
 `crypto_rand()` as a precaution of not leaking any raw bytes to the wire.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17694#comment:11>
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