December 1994 Network Security

businesses wishing to take advan tage of online commerce. Bank of America, using client/server security software from Netscape Communications Corporation, will be offering the new service by the end of January. The online card authorization and payment service, which is free to consumers, will let businesses accep t Visa, MasterCard, Discover Card, Diners Club, Carte Blanche, JCB Card or American Express credit cards as payment for purchases made over the Internet.

"'This partnership with Bank of America represents a significant step in providing consumers and businesses with a secure means for payment and credit card authorization online,'" said Jim Clark, chairman and CEO of Netscape Communications. "Bank of America reaches a significant percentage of merchants who today use traditional bankcard payment processing services. With this announcement, Bank of America takes a leadership role in confirming for companies and consumers that the Internet is a safe and efficient channel for conduct ing business on the Internet."

The payment service will be centred around Netscape Communications' Netsite Commerce Server software, which offers the security of both encryption and authentication. The Commerce Server features Netscape Communications' Secure Sockets Layer, security based on public and private key encryption technology from RSA Data Security. Netscape has added applications which plug into the Commerce Server to enable completely automat ic credit card c learance for merchants, as well as security which is implemented at a level just above the network layer. Merchants design their

own Internet retail sites, then access a secure connect ion with the Commerce Server and transmit the credit card information, which is then processed by Bank of America. "Once you come to a secure server, everything is encrypted," said Rosanne Siino, director of communications at Netscape. "Everything is transparent to the user."

Laser beams as a LAN connectivity alternative

P h i l H a l l

Laser beams, once the exclusive domain of Flash Gordon and James Bond fantasies, have become integral parts of daily life - - often to the point where we don' t even realise the lasers are at work. Whether providing the gift of renewed life in the hospital operating room or blasting the latest pop tune in a compac t disc player, laser beams have travelled a great distance from the days when they were imagined as futuristic weaponry cutting something or someone in half.

Wireless telecommunications have also benefitted from advances in infrared laser technology. The notion of using laser beams as a short-haul interbuilding local area network (LAN) connectivity vehicle was once greeted with the same incredulity that accompan ied the old Flash Gordon adventures. Yet this technology - - developed by the American firm Laser Communications Inc. of Lancaster, Pennsylvania, and currently in use on all continents except Antarctica - - has gained increasingly wider popularity and can now be found in diverse locations ranging from the financial power centres in New York City to the Treasury Ministry of the Kingdom of Lesotho in southern Africa.

The interest in laser-based LAN connectivity has its obvious drawing power. Its ability to transmit through the air at up to 20 Mbps in applications up to 1 km proves the versatility of this form of connectivity, especially for high demand, high-speed transmission such as CAD/CAM and image processing. Unlike microwave broadcasting, it does not require governmental approval. Unlike telephone lines, the laser network is private and thus free of the monthly lease fees demanded by telecom carriers. And unlike cabling, no overhead or underground wiring needs to be installed, which spares the time and expense inevitably involved in laying new cables between buildings.

Yet frequently, the question arises concerning both security and atmospheric effects on laser transmissions. Is it safe from hackers and other technological villains? Can it work during rain, fog or snow? Is it harmful to the environment? And if a bird glides through the laser beam, will the poor creature get fried in flight? The answers are, in order, yes, yes, no and definitely not. To understand why, we need to address how the technology itself works and then consider in-field applications.

The laser transmission system itself is generally employed in point-to-point, line-of-sight applications, though multipoint or repeated configurations are possible. The beams cannot pass through solid obstacles such as a tree or smokestack, so the line-of-sight must be clear. The laser units themselves must be mounted on secure structures; any swaying or mechanical vibration will throw off the transmission. This is, after all, a short-haul telecommunications system - - the technology is not at a point where lasers can shoot between cities or

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Network Security December 1994

bounce off mirrors. The technology's transmitter receives input data (this could include audio or video), which is modulated onto the laser beam. The beam itself is not the fluorescent strip of light associated with Flash Gordon; rather, it is a narrow, col l imated beam of monochromat ic light with precious little natural d ivergence that is generally unseen by the naked eye. The laser beams do not disrupt the environment, and birds which fly through the beams are in no immediate or far-reaching physical danger.

The beam passes through a lens system which produces a slightly divergent beam. The laser receiver itself has a field of view which is narrower than the divergence of the incident laser beam, The receiver is quite selective since little of the incoming laser beam is lost in dispersion, unlike the transmission of infrared LED light. The receiver also requires a certain minimum level of incident light (sensitivity) to demodulate the light to form its output signal.

Security

The beauty of the technology is that it offers a perfect vehicle for the interbuilding transmission of data, voice and video without fear of interception by outside parties. Since the transmissions travel on laser beams, any unauthorized foray into the path of transmission is immediately realised. The information in the transmission is stored until the disruption is clear and normal transmission can resume. Since the transmissions can only be sent and received via the units created by Laser Communicat ions Inc, it is impossible (and, quite frankly, cartoonish) to imagine any mad hacker trying to divert the beams into a source beyond its set target. Not surprisingly,

many financial institutions of both international esteem (the World Bank, Deutsche Bank) and local reputation (Citadel Federal Credit Union in Thorndale, Pennsylvania) found this aspect of the technology appeal ing and use it for the confidential transmission of their data between sites. Other institutions which rely on confidential data

schools, medical research facilities, government agencies, military installations - - are also using the technology for this purpose.

Weather

No wireless technology is wholly immune to the whims and furies of nature. Laser telecommunications, not unlike radio and microwave transmissions, are effected to varying degrees due to differences in wavelengths. Four conditions should be considered: absorption, scattering, shimmering and land disruptions.

Absorption is caused mainly by the water vapour and carbon dioxide content of the air along the transmission path which depends upon the humidity and altitude. Gases that form in the atmosphere have many resonant bands which allow specific frequencies of light to pass through. These resonant bands occur at various wavelengths, with the most obvious at visible range. The near infrared wavelength of light 820 nm used in laser transmission was selected because it occurs at one of these windows, so absorption is not as great a concern with this technology.

Scattering, however, has a greater effect than absorption. The atmospheric scattering of light is a function of its wavelength and the number and size of scattering particles in the air. The optical visibility along the path is directly

related to the number and size of these particles, Weather conditions such as rain, fog and snow can be considered sources of scattering.

However, these weather conditions have a limited adverse affect on the technology. Laser-based communications operate in rain up to about four inches per hour before the I0e-9 Bit Error Rate (BER) is affected. In dry snow, the technology operates up to about one inch per hour before the BER is affected while wet snow requires two inches per hour. Attenuation by fog is created largely by waterdrops less than a few microns in radius, so a scattering effect would involve the wavelength of the laser beam and the size of the water droplets. Thus, a smaller percentage of the transmit beam would reach the receiver than normal, though it would not shut down the system completely.

Shimmer, the visual distortion of images seen looking down a long, hot asphalt road, has its effect depending on time of day, terrain, cloud cover, wind and height of the optical path above the source of the shimmer. Heat from chimneys or smokestacks can also create shimmer. Variations of atmospheric temperature and density along the path create localized differences in the air's index of refraction, causing fluctuation in the received signal level by directing some of the light out of its intended path. Avoiding shimmer is a simple matter of proper path selection. The laser-based telecommunications systems, as they exist today, can reach distances up to 1 km. With new advances, the distance of transmission will increase, thus requiring modifications to deal with any unfriendly atmospheric conditions.

6 ©1994 Elsevier Science Ltd