Questions about some clear functions usage #659

1. 
   spartucus commented at 3:07 am on August 28, 2019: none

   I saw a lot of clear functions used to clear local scalar, ge or gej variable in the last step of function, does this necessary? I thought the local variables should be no longer exists(or used) after function quit. Is this a manual destruct for local variable? Because it takes longer time(maybe just a small longer time) than just leave them alone.

   Here are example codes.

   0static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context *ctx, secp256k1_gej *r, const secp256k1_scalar *gn) {
   1    secp256k1_ge add;
   2    secp256k1_scalar gnb;
   3    int bits;
   4    // ........
   5    secp256k1_ge_clear(&add);
   6    secp256k1_scalar_clear(&gnb);
   7}
   

2. 
   sipa commented at 4:10 am on August 28, 2019: contributor

   They (optimistically) try to wipe potentially secret data.
3. 
   elichai commented at 4:11 am on August 28, 2019: contributor

   See #636
4. 
   spartucus commented at 5:09 am on August 28, 2019: none

   Thanks for reply. Solve the questions lasted for days.
5. spartucus closed this on Aug 28, 2019

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