By Luba Vangelova

May 1, 1997

Cryptography-the science of encoding messages so their content can only be understood by the intended recipient-dates back to ancient times. Today, encryption is used to transmit sensitive digital data across computer networks or, increasingly, to keep sensitive computer files private while they remain stored on a desktop or laptop computer. The messages are changed from readable to unreadable and back again using complex mathematical algorithms known as keys. Security experts expect to see more use of encryption for unclassified computer information.

There are two encryption strategies: symmetric and asymmetric. Symmetric encryption uses the same key for both the encryption and the decryption; that key must be securely relayed from the sender to the recipient.

Asymmetric encryption requires each person to have one publicly known key and one private key, both of them unique to that individual. To send an encrypted message, the sender must look up the recipient's publicly known key and use it to encrypt the message, which can then be read only if it is decrypted with the recipient's private key. No keys need change hands using this technique, although it is more time-consuming than symmetric encryption. Many solutions combine the two strategies, using the public key to encrypt a secret key, which is used to encrypt the actual message.

The most popular asymmetric algorithms are from RSA Data Security Inc., although agencies, unless they apply for a waiver, are required to use the symmetric Digital Encryption Standard.

Encryption has applications in many areas, including electronic commerce and message authentication. A "digital signature" is a message attachment containing the mathematical output of applying the sender's private key to the message contents. This ensures that the purported message sender is the person who really sent the message and also that the message contents have not been altered.

Encryption products can be hardware- or software-based. Hardware-based solutions-on PC cards, credit-card size "smart cards," or on separate boxes attached to a network-offer security advantages but are generally harder to implement than software solutions.

Companies that provide hardware-based encryption include GTE and Paralon Technologies Inc. Encryption software packages such as Pretty Good Privacy are available free on the Internet. Commercial software packages-some of them specializing in encrypting e-mail, although interoperability remains a problem in that area-cost between $45 and $180. They are available from companies such as RSA Data Security Inc., OpenSoft Corp. and ConnectSoft Inc.

The controversial Escrowed Encryption Standard (EES), designed to ensure that law enforcement officials have access to encrypted documents, remains in effect for now. The voluntary program divides encryption keys into two components, one safeguarded by NIST, the other by the Treasury Department. But critics are wary of concentrating too much power in the government's hands. A Commerce Department advisory committee is looking into other ways to address the administration's concerns about encryption.

By Luba Vangelova

May 1, 1997