[tor-bugs] #18221 [Tor]: Validate our DH parameters to prevent socat-type fails.

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#18221: Validate our DH parameters to prevent socat-type fails.
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 Reporter:  yawning          |          Owner:
     Type:  enhancement      |         Status:  needs_review
 Priority:  Medium           |      Milestone:  Tor: 0.2.8.x-final
Component:  Tor              |        Version:  Tor: unspecified
 Severity:  Normal           |     Resolution:
 Keywords:  tor-core crypto  |  Actual Points:
Parent ID:                   |         Points:
  Sponsor:                   |
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Comment (by yawning):

 Replying to [comment:2 nickm]:
 > Looks correctly written.  I'm not clear what exactly the threat model is
 here, though.  "We replace the primes with something we think is prime,
 but we forget to check"?  "An attacker backdoors our software but doesn't
 figure out how to remove this check, or can't for some reason"?

 More the former than the latter.  We no longer have `DynamicDHGroups` so
 this isn't as big of a deal as it used to be (and our current p/g sets
 pass the checks).  My rationale is a combination of:

  * ~10 ms is a trivial amount of startup time to add to prevent foot + gun
 type issues
  *  If we have lots of sanity checks, we can view commits that mess with
 certain areas of the code with Extreme Suspicion.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18221#comment:3>
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