Document that infinity must not be passed to ecmult_const #789

1. 
   real-or-random commented at 4:10 pm on August 7, 2020: contributor
2. Document that infinity must not be passed to ecmult_const 2a45b80afe
3. real-or-random force-pushed on Aug 7, 2020
4. 
   real-or-random commented at 4:12 pm on August 7, 2020: contributor

   Related to #788.
5. 
   gmaxwell commented at 9:52 pm on August 7, 2020: contributor

   What happens if you pass in a point at infinity? :)
6. 
   gmaxwell commented at 10:53 pm on August 7, 2020: contributor

   Ah. Storage type doesn’t currently encode infinities so the to precomputed tables have issues. Other than that it looks like it takes a smaller change to fix infinity support, most of which is obviously more correct than not doing it.
7. 
   gmaxwell commented at 3:13 am on August 8, 2020: contributor

   Unless I’m mistaken, ecmult isn’t constant time with respect to the point input. If so, it could just return infinity in this case. It would be a smaller diff and less weird-surface to handle for future users of the function.
8. gmaxwell cross-referenced this on Aug 8, 2020 from issue Cleaner infinity handling in group law and ecmult_const. by gmaxwell
9. 
   real-or-random commented at 6:18 pm on August 8, 2020: contributor

   Unless I’m mistaken, ecmult isn’t constant time with respect to the point input.

   Oh that’s a good point. I took the easy way with constant-timeness in mind but yes, it’s constant-time in the scalar only.

10. real-or-random closed this on Aug 8, 2020

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