[tor-bugs] #13280 [Tor]: Stop signed left shift overflows in ed25519

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#13280: Stop signed left shift overflows in ed25519
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     Reporter:  teor    |      Owner:
         Type:  defect  |     Status:  needs_review
     Priority:  major   |  Milestone:  Tor: 0.2.6.x-final
    Component:  Tor     |    Version:  Tor: unspecified
   Resolution:          |   Keywords:  tor-router ed25519
Actual Points:          |  Parent ID:
       Points:          |
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Comment (by teor):

 Nick, your script looks like it does the opposite of cpp -E
 -DUNSAFE_SIGNED_LSHIFT (which is handy).

 The only existing (relevant) left shifts that it misses are two performed
 on signed char types in ge_scalarmult_base.c. I had also missed one of
 these. (I've attached a patch which standardises both of these shifts
 using new SHL8().)

 All other left shifts are performed on (signed) constants or unsigned
 types.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13280#comment:9>
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