Simplify tls1_set_ec_id.

Reviewed-by: NMatt Caswell <matt@openssl.org>

ssl/t1_lib.c

@@ -221,6 +221,7 @@ typedef struct {
     unsigned int flags;         /* Flags: currently just field type */
 } tls_curve_info;
 
+# define TLS_CURVE_TYPE          0x1
 # define TLS_CURVE_CHAR2         0x1
 # define TLS_CURVE_PRIME         0x0
 
@@ -617,46 +618,33 @@ int tls1_set_curves_list(unsigned char **pext, size_t *pextlen,
 static int tls1_set_ec_id(unsigned char *curve_id, unsigned char *comp_id,
                           EC_KEY *ec)
 {
-    int is_prime, id;
+    int id;
     const EC_GROUP *grp;
-    const EC_METHOD *meth;
     if (!ec)
         return 0;
     /* Determine if it is a prime field */
     grp = EC_KEY_get0_group(ec);
     if (!grp)
         return 0;
-    meth = EC_GROUP_method_of(grp);
-    if (!meth)
-        return 0;
-    if (EC_METHOD_get_field_type(meth) == NID_X9_62_prime_field)
-        is_prime = 1;
-    else
-        is_prime = 0;
     /* Determine curve ID */
     id = EC_GROUP_get_curve_name(grp);
     id = tls1_ec_nid2curve_id(id);
-    /* If we have an ID set it, otherwise set arbitrary explicit curve */
-    if (id) {
-        curve_id[0] = 0;
-        curve_id[1] = (unsigned char)id;
-    } else {
-        curve_id[0] = 0xff;
-        if (is_prime)
-            curve_id[1] = 0x01;
-        else
-            curve_id[1] = 0x02;
-    }
+    /* If no id return error: we don't support arbitrary explicit curves */
+    if (id == 0)
+        return 0;
+    curve_id[0] = 0;
+    curve_id[1] = (unsigned char)id;
     if (comp_id) {
         if (EC_KEY_get0_public_key(ec) == NULL)
             return 0;
-        if (EC_KEY_get_conv_form(ec) == POINT_CONVERSION_COMPRESSED) {
-            if (is_prime)
+        if (EC_KEY_get_conv_form(ec) == POINT_CONVERSION_UNCOMPRESSED) {
+            *comp_id = TLSEXT_ECPOINTFORMAT_uncompressed;
+        } else {
+            if ((nid_list[id - 1].flags & TLS_CURVE_TYPE) == TLS_CURVE_PRIME)
                 *comp_id = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_prime;
             else
                 *comp_id = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_char2;
-        } else
-            *comp_id = TLSEXT_ECPOINTFORMAT_uncompressed;
+        }
     }
     return 1;
 }