Biometrics

What is “biometrics”? Biometrics is a field of security and identification technology based on the measurement of unique physical characteristics such as fingerprints, retinal patterns, and facial structure. To verify an individual's identity, biometric devices scan certain characteristics and compare them with a stored entry in a computer database. While the technology goes back years and has been used in highly sensitive institutions such as defense and nuclear facilities, the proliferation of electronic data exchange generated new demand for biometric applications that can secure electronically stored data and online transactions. Biometrics is the practice of automatically identifying people by one or more physical characteristics. TYPES OF BIOMETRIC SYSTEMS FINGERPRINTS. Fingerprint-based biometric systems scan the dimensions, patterns, and topography of fingers, thumbs, and palms. The most common biometric in forensic and governmental databases, fingerprints contain up to 60 possibilities for minute variation, and extremely large and increasingly integrated networks of these stored databases already exist. The largest of these is the Federal Bureau of Investigation's (FBI) Automated Fingerprint Identification System, with more than 630 million fingerprint images. FACIAL RECOGNITION. Facial recognition systems vary according to the features they measure. Some look at the shadow patterns under a set lighting pattern, while others scan heat patterns or thermal images using an infrared camera that illuminates the eyes and cheekbones. These systems are powerful enough to scope out the minutest differences in facial patterns, even between identical twins. The hardware for facial recognition systems is relatively inexpensive, and is increasingly installed in computer monitors. EYE SCANS. There are two main features of the eye that are targeted by biometric systems: the retina and the iris. Each contains more points of identification than a fingerprint. Retina scanners trace the pattern of blood cells behind the retina by quickly flashing an infrared light into the eye. Iris scanners create a unique biological bar code by scanning the eye's distinctive color patterns. Eye scans tend to occupy less space in a computer and thus operate relatively quickly, although some users are squeamish about having beams of light shot into their eyes. VOICE VERIFICATION. Although voices can sound similar and can be consciously altered, the topography of the mouth, teeth, and vocal cords produces distinct pitch, cadence, tone, and dynamics that give away would-be impersonators. Widely used in phone-based identification systems, voice-verification biometrics also is used with personal computers. HAND GEOMETRY. Hand-geometry biometric systems take two infrared photographs—one from the side and one from above—of an individual's hand. These images measure up to 90 different characteristics, such as height, width, thickness, finger shape, and joint positions and compare them with stored data. KEYSTROKE DYNAMICS. A biometric system that is tailor-made for personal computers, keystroke-dynamic biometrics measures unique patterns in the way an individual uses a keyboard—such as speed, force, the variation of force on different parts of the keyboard, and multiple-key functions—and exploits them as a means of identification. These things are indeed very interesting, and it would be better if I would explain each and every types in details to all of you...

Tuesday, 13 May 2008

BitTorrent (Protocol)

BitTorrent is a protocol designed for transferring files. It is peer-to-peer in nature, as users connect to each other directly to send and receive portions of the file.

BitTorrent is a method of distributing large amounts of data widely without the original distributor incurring the entire costs of hardware, hosting, and bandwidth resources.

However, there is a central server (called a tracker) which coordinates the action of all such peers. The tracker only manages connections, it does not have any knowledge of the contents of the files being distributed, and therefore a large number of users can be supported with relatively limited tracker bandwidth. The key philosophy of BitTorrent is that users should upload (transmit outbound) at the same time they are downloading (receiving inbound.) In this manner, network bandwidth is utilized as efficiently as possible. BitTorrent is designed to work better as the number of people interested in a certain file increases, in contrast to other file transfer protocols.

Instead, when data is distributed using the BitTorrent protocol, each recipient supplies pieces of the data to newer recipients, reducing the cost and burden on any given individual source, providing redundancy against system problems, and reducing dependence on the original distributor.

The most common method by which files are transferred on the Internet is the client-server model. A central server sends the entire file to each client that requests it -- this is how both http and ftp work. The clients only speak to the server, and never to each other. The main advantages of this method are that it's simple to set up, and the files are usually always available since the servers tend to be dedicated to the task of serving, and are always on and connected to the Internet. However, this model has a significant problem with files that are large or very popular, or both.

Namely, it takes a great deal of bandwidth and server resources to distribute such a file, since the server must transmit the entire file to each client. Perhaps you may have tried to download a demo of a new game just released, or CD images of a new Linux distribution, and found that all the servers report "too many users," or there is a long queue that you have to wait through. The concept of mirrors partially addresses this shortcoming by distributing the load across multiple servers. But it requires a lot of coordination and effort to set up an efficient network of mirrors, and it's usually only feasible for the busiest of sites.

Another method of transferring files has become popular recently: the peer-to-peer network, systems such as Kazaa, eDonkey, Gnutella, Direct Connect, etc. In most of these networks, ordinary Internet users trade files by directly connecting one-to-one. The advantage here is that files can be shared without having access to a proper server, and because of this there is little accountability for the contents of the files. Hence, these networks tend to be very popular for illicit files such as music, movies, pirated software, etc. Typically, a downloader receives a file from a single source, however the newest version of some clients allow downloading a single file from multiple sources for higher speeds.

A BitTorrent client is any program that implements the BitTorrent protocol. Each client is capable of preparing, requesting, and transmitting any type of computer file over a network, using the protocol. A peer is any computer running an instance of a client. To share a file or group of files, a peer first creates a small file called a "torrent" (e.g. MyFile.torrent). This file contains metadata about the files to be shared and about the tracker, the computer that coordinates the file distribution. Peers that want to download the file first obtain a torrent file for it, and connect to the specified tracker, which tells them from which other peers to download the pieces of the file.

Though both ultimately transfer files over a network, a BitTorrent download differs from a classic full-file HTTP request in several fundamental ways:

BitTorrent makes many small data requests over different TCP sockets, while web-browsers typically make a single HTTP GET request over a single TCP socket. BitTorrent downloads in a random or in a "rarest-first"[2] approach that ensures high availability, while HTTP downloads in a sequential manner. Taken together, these differences allow BitTorrent to achieve much lower cost, much higher redundancy, and much greater resistance to abuse or to "flash crowds" than a regular HTTP server. However, this protection comes at a cost: downloads can take time to rise to full speed because it may take time for enough peer connections to be established, and it takes time for a node to receive sufficient data to become an effective uploader. As such, a typical BitTorrent download will gradually rise to very high speeds, and then slowly fall back down toward the end of the download. This contrasts with an HTTP server that, while more vulnerable to overload and abuse, rises to full speed very quickly and maintains this speed throughout.