博文
[时文]数字证书 (2005-06-23 17:39:00)
摘要：Digital Certificates Digital certificates are data files used to establish the identity of people and electronic assets on the Internet. They allow for secure, encrypted online communication and are often used to protect online transactions. Digital certificates are issued by a trusted third party known as a certification authority (CA). The CA validates the identity of a certificate holder and “signs” the certificate to attest that it hasn’t been forged or altered in any way. New Uses For Digital Certificates Digital certificates are now being used to provide security and validation for wireless connections, and hardware manufacturers are one of the latest groups to use them. Not long ago, VeriSign Inc. announced its Cable Modem Authentication Services, which allow hardware manufacturers to embed digital certificates into cable modems to help prevent the pirating of broadband services through device cloning. Using VeriSign software, hardware makers can generate cryptographic keys and ......
[时文]缓冲溢出(2005-06-23 17:36:00)
摘要：Buffer Overflow Do an Internet search on the term buffer overflow, and you’ll come up with hundreds of thousands of links, most related to security. In the National Institute of Standards and Technology’s ICAT index of computer vulnerabilities, six of the top 10 involve buffer overflows. In 1999, buffer overflow was named the No. 1 computer vulnerability. Five years later, it’s still a major problem. If you’ve ever poured a gallon of water into a pint-size pot, you know what overflow means ——water spills all around. Inside a computer, something similar happens if you try to store too much data in a space designed for less. Input normally goes into a temporary storage area, called a buffer, whose length is defined in the program or the operating system. Ideally, programs check data length and won't let you input an overlong data string. But most programs assume that data will always fit into the space assigned to it. Operating systems use buffers called stacks, where data is stored temp......
[时文]家庭自动化技术(2005-06-23 17:22:00)
摘要：Home automation technologies X10 Automation: Lighting, Climate, Security, Home Cinema and Beyond When it first appeared in 1978, X10 became the standard in home automation technology. Using conventional home electrical wiring, X10 transmits digital packets through up to 256 compatible devices on a single power circuit. A control centre for an X10 system may be a standalone hardware unit or a PC running Linux or Windows. Remote controls and keypads can also be used to control light dimmers, TVs, VCRs, security alarms, door locks and surveillance equipment. With no specialised wiring required, X10 is an affordable and reliable beginning to any digital home project. For around $250, an X10 starter kit usually contains PC and hand-held remote controls as well as modules for two appliances, two lamps and a ceiling-mounted light. To use a module, you simply plug it into a power socket and then plug the appliance into the module. The appliance is then controlled via an infrared remote control......
[时文]数字光处理(2005-06-23 17:16:00)
摘要： Digital Light Processing When one first hears about digital light processing (DLP), it seems almost impossibly complex, even magical —— millions of tiny mirrors on a chip the size of your thumbnail, each of them capable of moving thousands of times per second to create a digital image. In fact, DLP gives new meaning to the phrase “smoke and mirrors” as it applies to computer-related technology. How DLP Works In essence, DLP is a nanotechnology implementation of the old survival technique of using a mirror to signal for help ——its purpose is to shine a controlled series of light flashes on a target to send a message. The mirror in this case is part of an optical semiconductor called a digital micromirror device, or DMD. The DMD chip contains not one but an array of up to 2.1 million microscopic mirrors, each just 16 micrometers square (less than one-fifth the size of a human hair) and 1 micrometer apart. The DMD chip is driven by a digital video or graphic signal in which each dig......