Add ec_point_from_asn1_bit_string()

This is inverse to ec_point_to_asn1_bit_string(). Use it to simplify the
ec_key_set_public_key() helper.

ok jsing

1 files changed, 20 insertions, 16 deletions

diff --git a/src/lib/libcrypto/ec/ec_asn1.c b/src/lib/libcrypto/ec/ec_asn1.c
index ec322a8559..7cc9a75c55 100644
--- a/src/lib/libcrypto/ec/ec_asn1.c
+++ b/src/lib/libcrypto/ec/ec_asn1.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ec_asn1.c,v 1.100 2024/10/30 17:53:28 tb Exp $ */
+/* $OpenBSD: ec_asn1.c,v 1.101 2024/10/30 17:54:54 tb Exp $ */
 /*
  * Written by Nils Larsch for the OpenSSL project.
  */
@@ -569,6 +569,22 @@ ec_point_from_asn1_string(const EC_GROUP *group, const ASN1_STRING *astr,
 }
 
 static int
+ec_point_from_asn1_bit_string(const EC_GROUP *group, const ASN1_BIT_STRING *abs,
+    EC_POINT **out_point, uint8_t *out_form)
+{
+        /*
+         * Per SEC 1, C.3, the bit string representing the public key comes from
+         * an octet string, therefore the unused bits octet must be 0x00.
+         * XXX - move this check to a helper in a_bitstr.c?
+         */
+        if ((abs->flags & ASN1_STRING_FLAG_BITS_LEFT) != 0 &&
+            (abs->flags & 0x07) != 0)
+                return 0;
+
+        return ec_point_from_asn1_string(group, abs, out_point, out_form);
+}
+
+static int
 ec_point_from_asn1_octet_string(const EC_GROUP *group, const ASN1_OCTET_STRING *aos,
     EC_POINT **out_point, uint8_t *out_form)
 {
@@ -1207,8 +1223,8 @@ ec_key_set_private_key(EC_KEY *ec_key, const ASN1_OCTET_STRING *aos)
 static int
 ec_key_set_public_key(EC_KEY *ec_key, const ASN1_BIT_STRING *abs)
 {
-        const EC_GROUP *group = ec_key->group;
         EC_POINT *pub_key = NULL;
+        uint8_t form;
         int ret = 0;
 
         if (abs == NULL) {
@@ -1216,24 +1232,12 @@ ec_key_set_public_key(EC_KEY *ec_key, const ASN1_BIT_STRING *abs)
                 return eckey_compute_pubkey(ec_key);
         }
 
-        /*
-         * Per SEC 1, C.3, the bit string representing the public key comes from
-         * an octet string, therefore the unused bits octet must be 0x00.
-         * XXX - move this check to a helper in a_bitstr.c?
-         */
-        if ((abs->flags & ASN1_STRING_FLAG_BITS_LEFT) != 0 &&
-            (abs->flags & 0x07) != 0)
-                goto err;
-
         /* XXX - SEC 1, 2.3.4 does not allow hybrid encoding. */
-        if ((pub_key = EC_POINT_new(group)) == NULL)
-                goto err;
-        if (!EC_POINT_oct2point(group, pub_key, abs->data, abs->length, NULL))
+        if (!ec_point_from_asn1_bit_string(ec_key->group, abs, &pub_key, &form))
                 goto err;
         if (!EC_KEY_set_public_key(ec_key, pub_key))
                 goto err;
-        /* oct2point has ensured that to be compressed, uncompressed, or hybrid. */
-        ec_key->conv_form = abs->data[0] & ~1U;
+        EC_KEY_set_conv_form(ec_key, form);
 
         ret = 1;