Provide ec_point_from_octets()

This is a wrapper that is the reverse of ec_point_to_octets(). It is a
bit simpler since EC_POINT_oct2point() expects the point to be allocated
already. It also hands back the correctly parsed point conversion form
so that we don't have to do this by hand in a few places.

ok jsing

2 files changed, 35 insertions, 3 deletions

diff --git a/src/lib/libcrypto/ec/ec_local.h b/src/lib/libcrypto/ec/ec_local.h
index 7aa1c3f64e..148e94b766 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 1.33 2024/10/30 06:10:35 tb Exp $ */
+/* $OpenBSD: ec_local.h,v 1.34 2024/10/30 17:52:34 tb Exp $ */
 /*
  * Originally written by Bodo Moeller for the OpenSSL project.
  */
@@ -360,8 +360,10 @@ int ec_group_is_builtin_curve(const EC_GROUP *group);
 int ec_group_get_field_type(const EC_GROUP *group);
 
 /*
- * Wrapper around the unergonomic EC_POINT_point2oct().
+ * Wrappers around the unergonomic EC_POINT_{oct2point,point2oct}().
  */
+int ec_point_from_octets(const EC_GROUP *group, const unsigned char *buf,
+    size_t buf_len, EC_POINT **out_point, uint8_t *out_form, BN_CTX *ctx_in);
 int ec_point_to_octets(const EC_GROUP *group, const EC_POINT *point, int form,
     unsigned char **out_buf, size_t *len, BN_CTX *ctx_in);
 
diff --git a/src/lib/libcrypto/ec/ec_oct.c b/src/lib/libcrypto/ec/ec_oct.c
index 6fcda17403..3277bf4dd5 100644
--- a/src/lib/libcrypto/ec/ec_oct.c
+++ b/src/lib/libcrypto/ec/ec_oct.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ec_oct.c,v 1.18 2024/10/30 06:10:35 tb Exp $ */
+/* $OpenBSD: ec_oct.c,v 1.19 2024/10/30 17:52:34 tb Exp $ */
 /*
  * Originally written by Bodo Moeller for the OpenSSL project.
  */
@@ -149,6 +149,36 @@ ec_point_to_octets(const EC_GROUP *group, const EC_POINT *point, int form,
         return ret;
 }
 
+int
+ec_point_from_octets(const EC_GROUP *group, const unsigned char *buf, size_t buf_len,
+    EC_POINT **out_point, uint8_t *out_form, BN_CTX *ctx)
+{
+        EC_POINT *point;
+        int ret = 0;
+
+        if ((point = *out_point) == NULL)
+                point = EC_POINT_new(group);
+        if (point == NULL)
+                goto err;
+
+        if (!EC_POINT_oct2point(group, point, buf, buf_len, ctx))
+                goto err;
+
+        if (out_form != NULL)
+                *out_form = buf[0] & ~1U;       /* XXX - EC_OCT_YBIT */
+
+        *out_point = point;
+        point = NULL;
+
+        ret = 1;
+
+ err:
+        if (*out_point != point)
+                EC_POINT_free(point);
+
+        return ret;
+}
+
 size_t
 EC_POINT_point2oct(const EC_GROUP *group, const EC_POINT *point,
     point_conversion_form_t form, unsigned char *buf, size_t len,