The Kerberos V4 components have been replaced by their equivalents from Kerberos V5 (RFC 1510 and 1964). Some of the Kerberos components effected by this replacement include: kinit(1), kdestroy(1), klist(1), ksrvtgt(1), libkrb.so(4), kerbd(1M), mount_nfs(1M), share_nfs(1M) and parts of the ONC RPC programming API (kerberos_rpc(3N)).
The Kerberos V5 functionality provides equivalent authentication, integrity and secrecy functionality, but using a modern, standards-based mechanism. The Kerberos V5 implementation does not provide a backward compatibility mode with V4.
The new Kerberos V5 framework (based on the SEAM implementation) provides developers with a secure platform for secure distributed authentication that is interoperable with other Kerberos implementations, such as MIT's. Kerberos can be used as the basis for secure single network sign-on, but does require the application to be "Kerberos aware." Being "Kerberos aware" means that the application must be written to call the Kerberos APIs or an equivalent higher level security API like GSS-API (RFC 2744) or RPCSEC_GSS (RFC 2203). Sun recommends using GSS-API or RPCSEC_GSS instead of direct Kerberos calls so the application can be more portable to use other future, GSS-based mechanisms (for example, a public-key-based protocol). Thus, it is recommended that developers wishing to use libkrb functionality refer to the GSS API Programming Guide and IETF RFCs. GSS-API provides an abstracted interface for Sun's SEAM (Kerberos V5) and Diffie-Hellman-based security mechanisms.