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Merge #699: Initialize field elements when resulting in infinity

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47a7b8382fd6f1458d859b315cf3bcd3b9790b68 Clear field elements when writing infinity (Elichai Turkel)
61d1ecb02847be9d65ffe9df2d2408d85f3a0711 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 47a7b8382fd6f1458d859b315cf3bcd3b9790b68

Tree-SHA512: cdc2efc242a1b04b4f081183c07d4b2602cdba705e6b30b548df4e115e54fb97691f4b1a28f142f02d5e523c020721337a297b17d732acde147b910f5c53bd0a
This commit is contained in:
Tim Ruffing 2020-09-09 16:00:12 +02:00
commit 875d68b95f
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GPG Key ID: 8C461CCD293F6011
2 changed files with 37 additions and 3 deletions
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6
src/group_impl.h
View File

@ -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;
}

34
src/tests.c
View File

@ -2318,6 +2318,39 @@ void test_ge(void) {
free(zinv);
}
void test_intialized_inf(void) {
secp256k1_ge p;
secp256k1_gej pj, npj, infj1, infj2, infj3;
secp256k1_fe zinv;
/* Test that adding P+(-P) results in a fully initalized infinity*/
random_group_element_test(&p);
secp256k1_gej_set_ge(&pj, &p);
secp256k1_gej_neg(&npj, &pj);
secp256k1_gej_add_var(&infj1, &pj, &npj, NULL);
CHECK(secp256k1_gej_is_infinity(&infj1));
CHECK(secp256k1_fe_is_zero(&infj1.x));
CHECK(secp256k1_fe_is_zero(&infj1.y));
CHECK(secp256k1_fe_is_zero(&infj1.z));
secp256k1_gej_add_ge_var(&infj2, &npj, &p, NULL);
CHECK(secp256k1_gej_is_infinity(&infj2));
CHECK(secp256k1_fe_is_zero(&infj2.x));
CHECK(secp256k1_fe_is_zero(&infj2.y));
CHECK(secp256k1_fe_is_zero(&infj2.z));
secp256k1_fe_set_int(&zinv, 1);
secp256k1_gej_add_zinv_var(&infj3, &npj, &p, &zinv);
CHECK(secp256k1_gej_is_infinity(&infj3));
CHECK(secp256k1_fe_is_zero(&infj3.x));
CHECK(secp256k1_fe_is_zero(&infj3.y));
CHECK(secp256k1_fe_is_zero(&infj3.z));
}
void test_add_neg_y_diff_x(void) {
/* The point of this test is to check that we can add two points
* whose y-coordinates are negatives of each other but whose x
@ -2391,6 +2424,7 @@ void run_ge(void) {
test_ge();
}
test_add_neg_y_diff_x();
test_intialized_inf();
}
void test_ec_combine(void) {