openssl: use OpenSSL's default ciphers by default

Up2date versions of OpenSSL maintain the default reasonably secure
without breaking compatibility, so it is better not to override the
default by curl.  Suggested at https://bugzilla.redhat.com/1483972

Closes #1846

lib/vtls/openssl.c

@@ -154,8 +154,16 @@ static unsigned long OpenSSL_version_num(void)
 #define OSSL_PACKAGE "OpenSSL"
 #endif
 
+#if (OPENSSL_VERSION_NUMBER >= 0x10100000L)
+/* up2date versions of OpenSSL maintain the default reasonably secure without
+ * breaking compatibility, so it is better not to override the default by curl
+ */
+#define DEFAULT_CIPHER_SELECTION NULL
+#else
+/* ... but it is not the case with old versions of OpenSSL */
 #define DEFAULT_CIPHER_SELECTION \
   "ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH"
+#endif
 
 struct ssl_backend_data {
   /* these ones requires specific SSL-types */
@@ -2116,11 +2124,13 @@ static CURLcode ossl_connect_step1(struct connectdata *conn, int sockindex)
   ciphers = SSL_CONN_CONFIG(cipher_list);
   if(!ciphers)
     ciphers = (char *)DEFAULT_CIPHER_SELECTION;
-  if(!SSL_CTX_set_cipher_list(BACKEND->ctx, ciphers)) {
-    failf(data, "failed setting cipher list: %s", ciphers);
-    return CURLE_SSL_CIPHER;
+  if(ciphers) {
+    if(!SSL_CTX_set_cipher_list(BACKEND->ctx, ciphers)) {
+      failf(data, "failed setting cipher list: %s", ciphers);
+      return CURLE_SSL_CIPHER;
+    }
+    infof(data, "Cipher selection: %s\n", ciphers);
   }
-  infof(data, "Cipher selection: %s\n", ciphers);
 
 #ifdef USE_TLS_SRP
   if(ssl_authtype == CURL_TLSAUTH_SRP) {