2 - Public key cryptosystems

Summary

Public key cryptosystems represent a basic tool for the implementation of useful security services that are able to protect the resources of an organization and provide an efficient security for the services and Web sites that an enterprise may offer on the Internet. This chapter describes the main components, functions, and usage of a public key cryptosystem. It also discusses some major attacks that have been developed to reduce cryptosystem efficiency.

Introduction

A text containing data that can be read and understood without any special measure is called plaintext. The method of transforming a plaintext in a way to hide its content to unauthorized parties is called encryption. Encrypting a plaintext results in unreadable text called ciphertext. Therefore, encryption is used to ensure that information is hidden from anyone for whom it is not intended, including those who can capture a copy of the encrypted data (while it is flowing through the network). The process of inversing the ciphertext to its original form is called decryption. Cryptography can be defined as the science of using mathematics to encrypt and decrypt data. Cryptography securely provides for the storage of sensitive information and its transmission across insecure networks, like the Internet, so that it cannot be read (under its original form) by any unauthorized individual (Menezes et al., 1996).

A cryptographic algorithm, also called cipher, is a mathematical function used in the encryption and decryption processes.