Provide method specific functions for EC POINT infinity.

Provide method specific functions for EC_POINT_set_to_infinity() and
EC_POINT_is_at_infinity(). These are not always the same thing and
will depend on the coordinate system in use.

ok beck@ tb@

3 files changed, 27 insertions, 10 deletions

diff --git a/src/lib/libcrypto/ec/ec_lib.c b/src/lib/libcrypto/ec/ec_lib.c
index d760ecfb95..7cc7efe73f 100644
--- a/src/lib/libcrypto/ec/ec_lib.c
+++ b/src/lib/libcrypto/ec/ec_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ec_lib.c,v 1.124 2025/05/10 05:54:38 tb Exp $ */
+/* $OpenBSD: ec_lib.c,v 1.125 2025/05/24 08:25:58 jsing Exp $ */
 /*
  * Originally written by Bodo Moeller for the OpenSSL project.
  */
@@ -894,11 +894,7 @@ EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point)
                 ECerror(EC_R_INCOMPATIBLE_OBJECTS);
                 return 0;
         }
-
-        BN_zero(point->Z);
-        point->Z_is_one = 0;
-
-        return 1;
+        return point->meth->point_set_to_infinity(group, point);
 }
 LCRYPTO_ALIAS(EC_POINT_set_to_infinity);
 
@@ -1200,8 +1196,7 @@ EC_POINT_is_at_infinity(const EC_GROUP *group, const EC_POINT *point)
                 ECerror(EC_R_INCOMPATIBLE_OBJECTS);
                 return 0;
         }
-
-        return BN_is_zero(point->Z);
+        return point->meth->point_is_at_infinity(group, point);
 }
 LCRYPTO_ALIAS(EC_POINT_is_at_infinity);
 
diff --git a/src/lib/libcrypto/ec/ec_local.h b/src/lib/libcrypto/ec/ec_local.h
index c7a54d3a2b..c0ff026fb2 100644
--- a/src/lib/libcrypto/ec/ec_local.h
+++ b/src/lib/libcrypto/ec/ec_local.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: ec_local.h,v 1.67 2025/03/24 13:07:04 jsing Exp $ */
+/* $OpenBSD: ec_local.h,v 1.68 2025/05/24 08:25:58 jsing Exp $ */
 /*
  * Originally written by Bodo Moeller for the OpenSSL project.
  */
@@ -85,6 +85,9 @@ typedef struct ec_method_st {
         int (*group_get_curve)(const EC_GROUP *, BIGNUM *p, BIGNUM *a,
             BIGNUM *b, BN_CTX *);
 
+        int (*point_set_to_infinity)(const EC_GROUP *, EC_POINT *);
+        int (*point_is_at_infinity)(const EC_GROUP *, const EC_POINT *);
+
         int (*point_is_on_curve)(const EC_GROUP *, const EC_POINT *, BN_CTX *);
         int (*point_cmp)(const EC_GROUP *, const EC_POINT *a, const EC_POINT *b,
             BN_CTX *);
diff --git a/src/lib/libcrypto/ec/ecp_methods.c b/src/lib/libcrypto/ec/ecp_methods.c
index 5adc049ab7..fcb48d9e33 100644
--- a/src/lib/libcrypto/ec/ecp_methods.c
+++ b/src/lib/libcrypto/ec/ecp_methods.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecp_methods.c,v 1.46 2025/05/10 05:54:38 tb Exp $ */
+/* $OpenBSD: ecp_methods.c,v 1.47 2025/05/24 08:25:58 jsing Exp $ */
 /* Includes code written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>
  * for the OpenSSL project.
  * Includes code written by Bodo Moeller for the OpenSSL project.
@@ -180,6 +180,21 @@ ec_group_get_curve(const EC_GROUP *group, BIGNUM *p, BIGNUM *a, BIGNUM *b,
 }
 
 static int
+ec_point_set_to_infinity(const EC_GROUP *group, EC_POINT *point)
+{
+        BN_zero(point->Z);
+        point->Z_is_one = 0;
+
+        return 1;
+}
+
+static int
+ec_point_is_at_infinity(const EC_GROUP *group, const EC_POINT *point)
+{
+        return BN_is_zero(point->Z);
+}
+
+static int
 ec_point_is_on_curve(const EC_GROUP *group, const EC_POINT *point, BN_CTX *ctx)
 {
         BIGNUM *rh, *tmp, *Z4, *Z6;
@@ -1281,6 +1296,8 @@ ec_mont_field_decode(const EC_GROUP *group, BIGNUM *r, const BIGNUM *a,
 static const EC_METHOD ec_GFp_simple_method = {
         .group_set_curve = ec_group_set_curve,
         .group_get_curve = ec_group_get_curve,
+        .point_set_to_infinity = ec_point_set_to_infinity,
+        .point_is_at_infinity = ec_point_is_at_infinity,
         .point_is_on_curve = ec_point_is_on_curve,
         .point_cmp = ec_point_cmp,
         .point_set_affine_coordinates = ec_point_set_affine_coordinates,
@@ -1304,6 +1321,8 @@ EC_GFp_simple_method(void)
 static const EC_METHOD ec_GFp_mont_method = {
         .group_set_curve = ec_mont_group_set_curve,
         .group_get_curve = ec_group_get_curve,
+        .point_set_to_infinity = ec_point_set_to_infinity,
+        .point_is_at_infinity = ec_point_is_at_infinity,
         .point_is_on_curve = ec_point_is_on_curve,
         .point_cmp = ec_point_cmp,
         .point_set_affine_coordinates = ec_point_set_affine_coordinates,