Unformatted text preview: o compromising information. General-purpose computers can be shielded as well, but it is a far more complex problem. The U.S. military calls this TEMPEST; it’s a subject well beyond the scope of this book. The final reason for the prevalence of hardware is the ease of installation. Most encryption applications don’t involve general-purpose computers. People may wish to encrypt their telephone conversations, facsimile transmissions, or data links. It is cheaper to put special-purpose encryption hardware in the telephones, facsimile machines, and modems than it is to put in a microprocessor and software. Even when the encrypted data comes from a computer, it is easier to install a dedicated hardware encryption device than it is to modify the computer’s system software. Encryption should be invisible; it should not hamper the user. The only way to do this in software is to write encryption deep into the operating system. This isn’t easy. On the other hand, even a computer neophyte can plug an encryption box between his computer and his external modem. The three basic kinds of encryption hardware on the market today are: self-contained encryption modules (that perform functions such as password verification and key management for banks), dedicated encryption boxes for communications links, and boards that plug into personal computers. Some encryption boxes are designed for certain types of communications links, such as T-1 encryption boxes that are designed not to encrypt synchronization bits. There are different boxes for synchronous and asynchronous communications lines. Newer boxes tend to accept higher bit rates and are more versatile. Even so, many of these devices have some incompatibilities. Buyers should be aware of this and be well-versed in their particular needs, lest they find themselves the owners of encryption equipment unable to perform the task at hand. Pay attention to restrictions in hardware type, operating system, applications software, network, and so forth. PC-boa...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips