Routing Information Protocol version 2 includes authentication types simple, none, and MD5 (MD5 message-digest algorithm.)

Both simple and none authentication types are vulnerable to passive attacks currently widespread in the Internet. Clear text passwords, currently specified for use with Routing Internet Protocol version 2 (RIPv2), are no longer considered sufficient to provide security. Keyed MD5 is the standard authentication algorithm for RIPv2. It provides a greatly enhanced probability that a system being attacked will detect and ignore hostile messages.

MD5 use case diagram