Summary: When students learn mathematics, they tend to understand and remember the mathematical processes that they find practical and relevant. It is not surprising then that "Principles and Standards for School Mathematics" (NCTM 2000) encourages teachers to help students discover the relevance of mathematics in their daily lives. To help young people realize that mathematics is alive and constantly evolving, it is important for teachers to share information with students about new developments in mathematics. However, it is often difficult to find source material that illustrates appropriate applications of mathematical concepts. In addition, finding items that are interesting and comprehensible to students is even harder. The topic of functions is a case in point. Therefore, this article describes some teaching ideas based on cryptography, a practical application of functions and their inverses that students should be able to comprehend. (Contains 3 tables and 1 figure.) (ERIC)