- * For SSL Clients, SSL Challenge controlled OPER feature, and encrypted server links,
- a working OpenSSL library or GnuTLS library. CHALLENGE is not supported on GnuTLS
- yet.
+ * For SSL/TLS client and server connections, one of:
+
+ * OpenSSL 1.0 or newer
+ * LibreSSL
+ * mbedTLS
+ * GnuTLS
+
+ * For certificate-based oper CHALLENGE, OpenSSL 1.0 or newer.
+ (Using CHALLENGE is not recommended for new deployments, so if you want to use a different TLS library,
+ feel free.)