Communications security is increasing in importance as a result of the use of electronic communications in more and more business activities. Cryptography is the only practical means to provide security services in many applications. Research into cryptography has exploded in the last 18 years and a variety of cryptographic algorithms and techniques have emerged.Cryptographic algorithms may be classified as either symmetric, if the same key is shared by the sender and receiver, or asymmetric, if they use different keys. Symmetric algorithms have been dominated by the Data Encryption Standard since 1976, but a number of replacements are now being proposed. Asymmetric, or public key, algorithms allow provision of new security services such as digital signatures. The RSA algorithm is the most widely known of these, but a recently proposed standard for digital signatures is also of intense current interest.