The Telnet client and server applications uses RFC 1416 for authentication. The 95.05.31 version has Kerberos version 4 [4] authentication. In addition it has experimental implementations of Kerberos version 5 and SPX.
The US version uses DES in CFB mode for encryption. This encryption implementation is on the experimental stage. Details are not known, since the encryption code is removed in exported releases.
BSD Telnet is written in the ``C'' programming language. It implements the RFC 1416 authentication framework, which are described in section 2.10. The framework handles the initial AUTHENTICATION negotiation and the selection of the authentication type. Functions for handling the SEND, IS and REPLY commands must be added for each new authentication type. The framework automatically call the handlers for the selected authentication type. The framework also provide functions which simplifies the transmission and retrieval of sub-negotiation commands.