Implementing Public - Key Cryptography in Haskell ∗

In this paper we describe how the RSA public-key cipher can be implemented in the functional programming language Haskell and we present a complete working implementation. This implementation serves two useful pedagogical purposes: (1) it is a very clear, high-level implementation of RSA that can easily be understood and manipulated by students of cryptography , and (2) it is an excellent example of how a functional programming language such as Haskell can be used to implement real applications. While the main goal of our implementation is clarity rather than efficiency , no treatment of public-key cryptography can ignore efficiency and we show how well-known techniques for improving the efficiency of RSA can be implemented. We also compare the performance of our implementation with an equivalent implementation in Java, and show that it is also practical to implement public-key cryptography in Haskell.