maybe this is not what u request..

other than online reference, i suggest to use these 2 books for ur tutoring;
1. William Stallings, Cryptography and Network Security: Principles and Practices, 3rd Edition, Prentice Hall, 2003.
2.Charles P. Pfleeger and Shari Lawrence Pfleeger, "Security in Computing, Third Edition", Prentice Hall PTR, 02 December, 2002.

easy to understand books for beginner..