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Abstract out verify logic for fe_cmov

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This commit is contained in:
Pieter Wuille 2022-01-28 18:45:42 -05:00
parent be82bd8e03
commit 1e6894bdd7
4 changed files with 22 additions and 15 deletions
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8
src/field.h
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@ -92,6 +92,7 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
# define secp256k1_fe_add secp256k1_fe_impl_add
# define secp256k1_fe_mul secp256k1_fe_impl_mul
# define secp256k1_fe_sqr secp256k1_fe_impl_sqr
# define secp256k1_fe_cmov secp256k1_fe_impl_cmov
#endif /* !defined(VERIFY) */
/** Normalize a field element.
@ -271,7 +272,12 @@ static void secp256k1_fe_from_storage(secp256k1_fe *r, const secp256k1_fe_storag
/** If flag is true, set *r equal to *a; otherwise leave it. Constant-time. Both *r and *a must be initialized.*/
static void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r, const secp256k1_fe_storage *a, int flag);
/** If flag is true, set *r equal to *a; otherwise leave it. Constant-time. Both *r and *a must be initialized.*/
/** Conditionally move a field element in constant time.
*
* On input, both r and a must be valid field elements. Flag must be 0 or 1.
* Performs {r = flag ? a : r}.
* On output, r's magnitude and normalized will equal a's in case of flag=1, unchanged otherwise.
*/
static void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag);
/** Halves the value of a field element modulo the field prime. Constant-time.

8
src/field_10x26_impl.h
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@ -1035,7 +1035,7 @@ SECP256K1_INLINE static void secp256k1_fe_impl_sqr(secp256k1_fe *r, const secp25
secp256k1_fe_sqr_inner(r->n, a->n);
}
static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
SECP256K1_INLINE static void secp256k1_fe_impl_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
uint32_t mask0, mask1;
volatile int vflag = flag;
SECP256K1_CHECKMEM_CHECK_VERIFY(r->n, sizeof(r->n));
@ -1051,12 +1051,6 @@ static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_
r->n[7] = (r->n[7] & mask0) | (a->n[7] & mask1);
r->n[8] = (r->n[8] & mask0) | (a->n[8] & mask1);
r->n[9] = (r->n[9] & mask0) | (a->n[9] & mask1);
#ifdef VERIFY
if (flag) {
r->magnitude = a->magnitude;
r->normalized = a->normalized;
}
#endif
}
static SECP256K1_INLINE void secp256k1_fe_half(secp256k1_fe *r) {

8
src/field_5x52_impl.h
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@ -369,7 +369,7 @@ SECP256K1_INLINE static void secp256k1_fe_impl_sqr(secp256k1_fe *r, const secp25
secp256k1_fe_sqr_inner(r->n, a->n);
}
static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
SECP256K1_INLINE static void secp256k1_fe_impl_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
uint64_t mask0, mask1;
volatile int vflag = flag;
SECP256K1_CHECKMEM_CHECK_VERIFY(r->n, sizeof(r->n));
@ -380,12 +380,6 @@ static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_
r->n[2] = (r->n[2] & mask0) | (a->n[2] & mask1);
r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
r->n[4] = (r->n[4] & mask0) | (a->n[4] & mask1);
#ifdef VERIFY
if (flag) {
r->magnitude = a->magnitude;
r->normalized = a->normalized;
}
#endif
}
static SECP256K1_INLINE void secp256k1_fe_half(secp256k1_fe *r) {

13
src/field_impl.h
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@ -323,6 +323,19 @@ SECP256K1_INLINE static void secp256k1_fe_sqr(secp256k1_fe *r, const secp256k1_f
r->normalized = 0;
secp256k1_fe_verify(r);
}
static void secp256k1_fe_impl_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag);
SECP256K1_INLINE static void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
VERIFY_CHECK(flag == 0 || flag == 1);
secp256k1_fe_verify(a);
secp256k1_fe_verify(r);
secp256k1_fe_impl_cmov(r, a, flag);
if (flag) {
r->magnitude = a->magnitude;
r->normalized = a->normalized;
}
secp256k1_fe_verify(r);
}
#endif /* defined(VERIFY) */
#endif /* SECP256K1_FIELD_IMPL_H */