You may want to refer to the following sources for background information on network security, cryptography, and SKIP.
Schneier, Bruce, Applied Cryptography, John Wiley & Sons, 1996, 2nd edition, ISBN 0471128457
Chapman, D. Brent, and Zwicky, Elizabeth D., Building Internet Firewalls, O'Reilly & Associates, 1995, ISBN 1565921240
Walker, Kathryn M., and Cavanaugh, Linda Croswhite, Computer Security Policies and SunScreen Firewalls, Sun Microsystems Press, Prentice Hall, 1998, ISBN 0130960150
Cheswick, Bill, and Bellovin, Steve, Firewalls and Internet Security, Addison-Wesley, 1994, ISBN 201633574
Comer, Douglas E., Internetworking with TCP/IP, Volume 1, Prentice Hall, 1995, ISBN 0132169878
Stallings, William, Network and Internetwork Security Principles and Practice, Institute of Electrical and Electronics, 1994, ISBN 078031108
Garfinkel, Simson, and Spafford, Gene, Practical UNIX and Internet Security, O'Reilly & Associates, 1996, 2nd edition, ISBN 1565921488
Stevens, W. Richard, TCP/IP Illustrated, Volume 1: The Protocols, Addison-Wesley, 1994, ISBN 0201633469
Hunt, Craig, TCP/IP Network Administration, Addison Wesley, 1994, ISBN 020163469
Kaufman, Charlie, Perlman, Radia, et al., Network Security: Private Communication in a Public World, Prentice Hall, 1995, ISBN 078816522.
SKIP IP-Level Cryptography http://skip.incog.com/
Sun Software and Networking Security http://www.sun.com/security/