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Merge #699: Initialize field elements when resulting in infinity

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47a7b8382f Clear field elements when writing infinity (Elichai Turkel)
61d1ecb028 Added test with additions resulting in infinity (Elichai Turkel)

Pull request description:

  Currently if `secp256k1_gej_add_var` / `secp256k1_gej_add_ge_var` /` secp256k1_gej_add_zinv_var` receive `P + (-P)` it will set `gej->infinity = 1` but doesn't call initialize the field elements.
  Notice that this is the only branch in the function that results in an uninitialized output.

  By using `secp256k1_gej_set_infinity()` it will set the field elements to zero while also setting the infinity flag.

  I also added a test that fails with valgrind on current master but passes with the fix.

  EDIT: This isn't a bug or something necessary, I just personally found this helpful.

ACKs for top commit:
  real-or-random:
    ACK 47a7b8382f

Tree-SHA512: cdc2efc242a1b04b4f081183c07d4b2602cdba705e6b30b548df4e115e54fb97691f4b1a28f142f02d5e523c020721337a297b17d732acde147b910f5c53bd0a
This commit is contained in:
Tim Ruffing
2020-09-09 16:00:12 +02:00
parent 54caf2e74f 47a7b8382f
commit 875d68b95f
2 changed files with 37 additions and 3 deletions
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6
src/group_impl.h
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@@ -399,7 +399,7 @@ static void secp256k1_gej_add_var(secp256k1_gej *r, const secp256k1_gej *a, cons
if (rzr != NULL) {
secp256k1_fe_set_int(rzr, 0);
}
r->infinity = 1;
secp256k1_gej_set_infinity(r);
}
return;
}
@@ -449,7 +449,7 @@ static void secp256k1_gej_add_ge_var(secp256k1_gej *r, const secp256k1_gej *a, c
if (rzr != NULL) {
secp256k1_fe_set_int(rzr, 0);
}
r->infinity = 1;
secp256k1_gej_set_infinity(r);
}
return;
}
@@ -508,7 +508,7 @@ static void secp256k1_gej_add_zinv_var(secp256k1_gej *r, const secp256k1_gej *a,
if (secp256k1_fe_normalizes_to_zero_var(&i)) {
secp256k1_gej_double_var(r, a, NULL);
} else {
r->infinity = 1;
secp256k1_gej_set_infinity(r);
}
return;
}