You may want to refer to the following sources for background information on network security, cryptography, and SKIP.
Applied CryptographyBruce Schneier John Wiley & Sons, 1996, 2nd edition, ISBN 0-471-12845-7
Building Internet FirewallsD. Brent Chapman and Elizabeth D. Zwicky O'Reilly & Associates, 1995, ISBN 1-56592-124-0
Computer Security Policies and SunScreen FirewallsKathryn M. Walker and Linda Croswhite Cavanaugh Sun Microsystems Press, 1998, ISBN 0-13-096015-0
Firewalls and Internet SecurityBill Cheswick and Steve Bellovin Addison-Wesley, 1994, ISBN 0-201-63357-4
Handbook of Computer-Communications Standards Volume 3: The TCP/IP Protocol SuiteWilliam Stallings, Macmillan, 1990
Internetworking with TCP/IP, Volume 1Douglas E. Comer Prentice Hall, 1995, ISBN 0-13-216987-8
Network and Internetwork Security Principles and PracticeWilliam Stallings Prentice Hall, 1995, ISBN 0-02-415483-0
Practical UNIX and Internet SecuritySimson Garfinkel and Gene Spafford O'Reilly & Associates, 1996, 2nd edition, ISBN 1-56592-148-8
TCP/IP Illustrated, Volume 1 The ProtocolsW. Richard Stevens Addison-Wesley, 1994, ISBN 0-201-63346-9
TCP/IP Network AdministrationCraig Hunt O'Reilly & Associates, 1992
Network Security: Private Communication in a Public WorldCharlie Kaufman, Radia Perlman, and Mike Speciner Prentice Hall, 1995
SKIP IP-Level Cryptography [http://skip.incog.com/]
Sun Software and Networking Security [http://www.sun.com/security/]