http://www.rfc-editor.org/rfc/rfc2949.txt
RFC 2949: Telnet Encryption: CAST-128 64 bit Output Feedback, J. Altman2000-09-01T23:00:00-00:00This document specifies how to use the CAST-128 encryption algorithm in output feedback mode with the telnet encryption option. Two key sizes are defined: 40 bit and 128 bit. [STANDARDS-TRACK]