Make extra sure final byte of s and r is 0

src/groth16.cpp

@@ -291,11 +291,15 @@ Prover<Engine>::prove(typename Engine::FrElement* wtns)
  E.fr.copy(r, E.fr.zero());
  E.fr.copy(s, E.fr.zero());
 
- // FIlling in the last byte here with a non-zero value causes a small amount of proofs to fail,
+ // Filling in the last byte here with a non-zero value causes a small amount of proofs to fail,
  // possibly due to overflowing the field modulus
  randombytes_buf((void*)&(r.v[0]), sizeof(r) - 1);
  randombytes_buf((void*)&(s.v[0]), sizeof(s) - 1);
 
+ // Make extra sure the final byte is 0
+ reinterpret_cast<char*>(&r)[sizeof(r) - 1] = 0;
+ reinterpret_cast<char*>(&s)[sizeof(s) - 1] = 0;
+
 # ifndef DONT_USE_FUTURES
  pA_future.get();
  pB1_future.get();