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field: add magnitude check and _fe_verify check for internal field APIs
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1. _fe_verify on inputs of the functions:
	1. _fe_normalizes_to_zero, _fe_normalizes_to_zero_var
	2. _fe_to_storage
	3. _fe_inv,_fe_inv_var
	4. _fe_equal, _fe_equal_var
	5. _fe_sqrt
2. _fe_verify on the result calculated in the functions:
	1.  _fe_inv,_fe_inv_var
	2. _fe_sqrt
3. magnitude checks for inputs of the functions:
	1. _fe_inv,_fe_inv_var
	2. _fe_equal, _fe_equal_var
	3. _fe_sqrt
4. moved a VERIFY_CHECK call (in _fe_inv, _fe_inv_var) out of #ifdef VERIFY in `field_5x52_impl.h`
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@siv2r
siv2r committed Jan 14, 2022
1 parent c6c44f4 commit 08186e8
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Showing 3 changed files with 57 additions and 17 deletions.
27 changes: 21 additions & 6 deletions src/field_10x26_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -200,7 +200,9 @@ static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {

/* Reduce t9 at the start so there will be at most a single carry from the first pass */
uint32_t x = t9 >> 22; t9 &= 0x03FFFFFUL;

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
/* The first pass ensures the magnitude is 1, ... */
t0 += x * 0x3D1UL; t1 += (x << 6);
t1 += (t0 >> 26); t0 &= 0x3FFFFFFUL; z0 = t0; z1 = t0 ^ 0x3D0UL;
Expand All @@ -224,7 +226,9 @@ static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
uint32_t t0, t1, t2, t3, t4, t5, t6, t7, t8, t9;
uint32_t z0, z1;
uint32_t x;

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
t0 = r->n[0];
t9 = r->n[9];

Expand Down Expand Up @@ -1151,6 +1155,7 @@ static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r,
static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
#ifdef VERIFY
VERIFY_CHECK(a->normalized);
secp256k1_fe_verify(a);
#endif
r->n[0] = a->n[0] | a->n[1] << 26;
r->n[1] = a->n[1] >> 6 | a->n[2] << 20;
Expand Down Expand Up @@ -1245,26 +1250,36 @@ static const secp256k1_modinv32_modinfo secp256k1_const_modinfo_fe = {
static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *x) {
secp256k1_fe tmp;
secp256k1_modinv32_signed30 s;

#ifdef VERIFY
VERIFY_CHECK(x->magnitude <= 8);
secp256k1_fe_verify(x);
#endif
tmp = *x;
secp256k1_fe_normalize(&tmp);
secp256k1_fe_to_signed30(&s, &tmp);
secp256k1_modinv32(&s, &secp256k1_const_modinfo_fe);
secp256k1_fe_from_signed30(r, &s);

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
VERIFY_CHECK(secp256k1_fe_normalizes_to_zero(r) == secp256k1_fe_normalizes_to_zero(&tmp));
}

static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *x) {
secp256k1_fe tmp;
secp256k1_modinv32_signed30 s;

#ifdef VERIFY
VERIFY_CHECK(x->magnitude <= 8);
secp256k1_fe_verify(x);
#endif
tmp = *x;
secp256k1_fe_normalize_var(&tmp);
secp256k1_fe_to_signed30(&s, &tmp);
secp256k1_modinv32_var(&s, &secp256k1_const_modinfo_fe);
secp256k1_fe_from_signed30(r, &s);

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
VERIFY_CHECK(secp256k1_fe_normalizes_to_zero(r) == secp256k1_fe_normalizes_to_zero(&tmp));
}

Expand Down
27 changes: 19 additions & 8 deletions src/field_5x52_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,9 @@ static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {

/* Reduce t4 at the start so there will be at most a single carry from the first pass */
uint64_t x = t4 >> 48; t4 &= 0x0FFFFFFFFFFFFULL;

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
/* The first pass ensures the magnitude is 1, ... */
t0 += x * 0x1000003D1ULL;
t1 += (t0 >> 52); t0 &= 0xFFFFFFFFFFFFFULL; z0 = t0; z1 = t0 ^ 0x1000003D0ULL;
Expand All @@ -196,7 +198,9 @@ static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
uint64_t t0, t1, t2, t3, t4;
uint64_t z0, z1;
uint64_t x;

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
t0 = r->n[0];
t4 = r->n[4];

Expand Down Expand Up @@ -491,6 +495,7 @@ static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r,
static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
#ifdef VERIFY
VERIFY_CHECK(a->normalized);
secp256k1_fe_verify(a);
#endif
r->n[0] = a->n[0] | a->n[1] << 52;
r->n[1] = a->n[1] >> 12 | a->n[2] << 40;
Expand Down Expand Up @@ -560,31 +565,37 @@ static const secp256k1_modinv64_modinfo secp256k1_const_modinfo_fe = {
static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *x) {
secp256k1_fe tmp;
secp256k1_modinv64_signed62 s;

#ifdef VERIFY
VERIFY_CHECK(x->magnitude <= 8);
secp256k1_fe_verify(x);
#endif
tmp = *x;
secp256k1_fe_normalize(&tmp);
secp256k1_fe_to_signed62(&s, &tmp);
secp256k1_modinv64(&s, &secp256k1_const_modinfo_fe);
secp256k1_fe_from_signed62(r, &s);

#ifdef VERIFY
VERIFY_CHECK(secp256k1_fe_normalizes_to_zero(r) == secp256k1_fe_normalizes_to_zero(&tmp));
secp256k1_fe_verify(r);
#endif
VERIFY_CHECK(secp256k1_fe_normalizes_to_zero(r) == secp256k1_fe_normalizes_to_zero(&tmp));
}

static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *x) {
secp256k1_fe tmp;
secp256k1_modinv64_signed62 s;

#ifdef VERIFY
VERIFY_CHECK(x->magnitude <= 8);
secp256k1_fe_verify(x);
#endif
tmp = *x;
secp256k1_fe_normalize_var(&tmp);
secp256k1_fe_to_signed62(&s, &tmp);
secp256k1_modinv64_var(&s, &secp256k1_const_modinfo_fe);
secp256k1_fe_from_signed62(r, &s);

#ifdef VERIFY
VERIFY_CHECK(secp256k1_fe_normalizes_to_zero(r) == secp256k1_fe_normalizes_to_zero(&tmp));
secp256k1_fe_verify(r);
#endif
VERIFY_CHECK(secp256k1_fe_normalizes_to_zero(r) == secp256k1_fe_normalizes_to_zero(&tmp));
}

#endif /* SECP256K1_FIELD_REPR_IMPL_H */
20 changes: 17 additions & 3 deletions src/field_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -23,13 +23,23 @@

SECP256K1_INLINE static int secp256k1_fe_equal(const secp256k1_fe *a, const secp256k1_fe *b) {
secp256k1_fe na;
#ifdef VERIFY
VERIFY_CHECK(a->magnitude == 1);
secp256k1_fe_verify(a);
secp256k1_fe_verify(b);
#endif
secp256k1_fe_negate(&na, a, 1);
secp256k1_fe_add(&na, b);
return secp256k1_fe_normalizes_to_zero(&na);
}

SECP256K1_INLINE static int secp256k1_fe_equal_var(const secp256k1_fe *a, const secp256k1_fe *b) {
secp256k1_fe na;
#ifdef VERIFY
VERIFY_CHECK(a->magnitude == 1);
secp256k1_fe_verify(a);
secp256k1_fe_verify(b);
#endif
secp256k1_fe_negate(&na, a, 1);
secp256k1_fe_add(&na, b);
return secp256k1_fe_normalizes_to_zero_var(&na);
Expand All @@ -47,7 +57,10 @@ static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe * SECP256K1_RES
*/
secp256k1_fe x2, x3, x6, x9, x11, x22, x44, x88, x176, x220, x223, t1;
int j;

#ifdef VERIFY
VERIFY_CHECK(a->magnitude <= 8);
secp256k1_fe_verify(a);
#endif
VERIFY_CHECK(r != a);

/** The binary representation of (p + 1)/4 has 3 blocks of 1s, with lengths in
Expand Down Expand Up @@ -128,9 +141,10 @@ static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe * SECP256K1_RES
secp256k1_fe_mul(&t1, &t1, &x2);
secp256k1_fe_sqr(&t1, &t1);
secp256k1_fe_sqr(r, &t1);

#ifdef VERIFY
secp256k1_fe_verify(r);
#endif
/* Check that a square root was actually calculated */

secp256k1_fe_sqr(&t1, r);
return secp256k1_fe_equal(&t1, a);
}
Expand Down

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