EC: Refactor ec_curve_name2nid() to accept NIST curve names

We can find no reason why everyone should have to call both
EC_curve_nist2nid() and ec_curve_name2nid() to find the NID for a
name, and it's too easy to forget EC_curve_nist2nid(), so we make life
simpler.

One could argue that FIPS only allows a limited set of names, but that
now gets handled internally, and those who really want to be really
sure to only get the NIST names can still do so with EC_curve_nist2nid()
Reviewed-by: NShane Lontis <shane.lontis@oracle.com>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11391)

crypto/ec/ec_curve.c

@@ -3117,25 +3117,65 @@ static const ec_list_element curve_list[] = {
 
 #define curve_list_length OSSL_NELEM(curve_list)
 
-const char *ec_curve_nid2name(int nid)
+static const ec_list_element *ec_curve_nid2curve(int nid)
 {
-    int i;
+    size_t i;
+
+    if (nid <= 0)
+        return NULL;
 
-    for (i = 0; i < (int)curve_list_length; i++) {
+    for (i = 0; i < curve_list_length; i++) {
         if (curve_list[i].nid == nid)
-            return curve_list[i].name;
+            return &curve_list[i];
     }
     return NULL;
 }
 
-int ec_curve_name2nid(const char *name)
+static const ec_list_element *ec_curve_name2curve(const char *name)
 {
-    int i;
+    size_t i;
 
-    for (i = 0; i < (int)curve_list_length; i++) {
+    for (i = 0; i < curve_list_length; i++) {
         if (strcasecmp(curve_list[i].name, name) == 0)
-            return curve_list[i].nid;
+            return &curve_list[i];
     }
+    return NULL;
+}
+
+const char *ec_curve_nid2name(int nid)
+{
+    /*
+     * TODO(3.0) Figure out if we should try to find the nid with
+     * EC_curve_nid2nist() first, i.e. make it a priority to return
+     * NIST names if there is one for the NID.  This is related to
+     * the TODO comment in ec_curve_name2nid().
+     */
+    const ec_list_element *curve = ec_curve_nid2curve(nid);
+
+    if (curve != NULL)
+        return curve->name;
+    return NULL;
+}
+
+int ec_curve_name2nid(const char *name)
+{
+    const ec_list_element *curve = NULL;
+    int nid;
+
+    if ((nid = EC_curve_nist2nid(name)) != NID_undef)
+        return nid;
+
+#ifndef FIPS_MODE
+    /*
+     * TODO(3.0) Figure out if we can use other names than the NIST names
+     * ("B-163", "K-163" & "P-192") in the FIPS module, or if other names
+     * are allowed as well as long as they lead to the same curve data.
+     * If only the NIST names are allowed in the FIPS module, we should
+     * move '#endif' to just before 'return NID_undef'.
+     */
+#endif
+    if ((curve = ec_curve_name2curve(name)) != NULL)
+        return curve->nid;
     return NID_undef;
 }
 
@@ -3250,28 +3290,11 @@ static EC_GROUP *ec_group_new_from_data(OPENSSL_CTX *libctx,
 
 EC_GROUP *EC_GROUP_new_by_curve_name_ex(OPENSSL_CTX *libctx, int nid)
 {
-    size_t i;
     EC_GROUP *ret = NULL;
+    const ec_list_element *curve;
 
-    if (nid <= 0)
-        return NULL;
-
-#ifdef FIPS_MODE
-    /*
-     * Only use approved NIST curves in FIPS.
-     * NOTE: "B-163", "K-163" & "P-192" can only be used for legacy use
-     * (i.e- ECDSA signature verification).
-     */
-    if (EC_curve_nid2nist(nid) == NULL)
-        return NULL;
-#endif /* FIPS_MODE */
-    for (i = 0; i < curve_list_length; i++)
-        if (curve_list[i].nid == nid) {
-            ret = ec_group_new_from_data(libctx, curve_list[i]);
-            break;
-        }
-
-    if (ret == NULL) {
+    if ((curve = ec_curve_nid2curve(nid)) == NULL
+        || (ret = ec_group_new_from_data(libctx, *curve)) == NULL) {
         ECerr(EC_F_EC_GROUP_NEW_BY_CURVE_NAME_EX, EC_R_UNKNOWN_GROUP);
         return NULL;
     }