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Abstract out verify logic for fe_inv{,_var}

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Pieter Wuille
2022-01-28 19:20:51 -05:00
parent 3167646072
commit d5aa2f0358
4 changed files with 43 additions and 51 deletions
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16
src/field.h
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@@ -95,6 +95,8 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
# define secp256k1_fe_cmov secp256k1_fe_impl_cmov
# define secp256k1_fe_to_storage secp256k1_fe_impl_to_storage
# define secp256k1_fe_from_storage secp256k1_fe_impl_from_storage
# define secp256k1_fe_inv secp256k1_fe_impl_inv
# define secp256k1_fe_inv_var secp256k1_fe_impl_inv_var
#endif /* !defined(VERIFY) */
/** Normalize a field element.
@@ -258,11 +260,19 @@ static void secp256k1_fe_sqr(secp256k1_fe *r, const secp256k1_fe *a);
*/
static int secp256k1_fe_sqrt(secp256k1_fe * SECP256K1_RESTRICT r, const secp256k1_fe * SECP256K1_RESTRICT a);
/** Sets a field element to be the (modular) inverse of another. Requires the input's magnitude to be
* at most 8. The output magnitude is 1 (but not guaranteed to be normalized). */
/** Compute the modular inverse of a field element.
*
* On input, a must be a valid field element; r need not be initialized.
* Performs {r = a**(p-2)} (which maps 0 to 0, and every other element to its
* inverse).
* On output, r will have magnitude (a.magnitude != 0) and be normalized.
*/
static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *a);
/** Potentially faster version of secp256k1_fe_inv, without constant-time guarantee. */
/** Compute the modular inverse of a field element, without constant-time guarantee.
*
* Behaves identically to secp256k1_fe_inv, but is not constant-time in a.
*/
static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *a);
/** Convert a field element to secp256k1_fe_storage.