Security Prior to RPCSEC_GSS

One of the first security flavors supported by RPC was AUTH_SYS (also known as AUTH_UNIX). AUTH_SYS provided a UNIX-style credential, using user and group IDs, to identify the sender and recipient of a message. AUTH_SYS is easy to implement; however, it is also easy to circumvent, since it does not provide true authentication -- that is, there is no way for a server to verify that a client is in fact whom it claims to be. Therefore, it is relatively simple to forge a network request under AUTH_SYS.

A later security flavor, AUTH_DES, appeared not long after AUTH_SYS. AUTH_DES is based on a public key authentication -- it uses a Diffie-Hellman key exchange to produce a common key between a client's private key and a server's public key. The common key is then used to encrypt a DES session key, which a server decrypts to establish a session.

Although AUTH_DES represented a significant advance over AUTH_SYS, it has some limitations to widespread usage. The main objection for many people is that the key size is, by today's encryption standards, somewhat undersized.

Eventually, another RPC security flavor was introduced. AUTH_KERB, based on Kerberos V4, provides yet better security than either AUTH_DES or AUTH_SYS. However, it too can be exploited.

For more information on these security flavors, see the ONC+ Developer's Guide.