EC_POINT_point2oct() need to special case the point at infinity

This is annoying since it undoes some polishing done before commit and
reintroduces an unpleasant asymmetry.

found by anton via openssl-ruby tests
ok jsing

1 files changed, 10 insertions, 4 deletions

diff --git a/src/lib/libcrypto/ec/ecp_oct.c b/src/lib/libcrypto/ec/ecp_oct.c
index d4ef0406f5..5444b5ec34 100644
--- a/src/lib/libcrypto/ec/ecp_oct.c
+++ b/src/lib/libcrypto/ec/ecp_oct.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecp_oct.c,v 1.26 2024/10/22 21:28:53 tb Exp $ */
+/* $OpenBSD: ecp_oct.c,v 1.27 2024/10/23 13:42:50 tb 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.
@@ -377,6 +377,13 @@ ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
         CBB_init_fixed(&cbb, buf, len);
         BN_CTX_start(ctx);
 
+        if (form == EC_OCT_POINT_AT_INFINITY) {
+                if (!ec_oct_add_leading_octet_cbb(&cbb, form, 0))
+                        goto err;
+
+                goto done;
+        }
+
         if ((x = BN_CTX_get(ctx)) == NULL)
                 goto err;
         if ((y = BN_CTX_get(ctx)) == NULL)
@@ -387,9 +394,7 @@ ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
         if (!ec_oct_add_leading_octet_cbb(&cbb, form, BN_is_odd(y)))
                 goto err;
 
-        if (form == EC_OCT_POINT_AT_INFINITY) {
-                /* Encoded in leading octet. */;
-        } else if (form == EC_OCT_POINT_COMPRESSED) {
+        if (form == EC_OCT_POINT_COMPRESSED) {
                 if (!ec_oct_add_field_element_cbb(&cbb, group, x))
                         goto err;
         } else {
@@ -399,6 +404,7 @@ ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
                         goto err;
         }
 
+ done:
         if (!CBB_finish(&cbb, NULL, &ret))
                 goto err;