Cipher
In cryptography, a cipher replaces a piece of information (a syntactic element of the plaintext that may consist of a letter or grouping of letters without inherent meaning) with another letter or letter group.
The transposition or substitution is controlled by a cryptographic algorithm (or procedure). In most cases, that procedure is varied depending on a key which changes the detailed operation of the algorithm. If the algorithm is symmetric, the key must be known to the receipient and to no one else. If the algorithm is an asymmetric one, the encyphering key is different from, but closely related to, the decyphering key. If one key cannot be deduced from the other, the asymmetric key algorithm has the public/private key property and one of the keys may be made public without loss of confidentiality.
In the past, the blurring of the distinction between codes and ciphers was relatively unimportant for anyone except cryptographers. In contemporary communications, however, information is frequently both encoded and encrypted, so that it is important to understand the difference. A satellite communications link, for example, may 'encode' information in ASCII characters if it is textual, or into some other representation of the data such as a JPEG file if it is an image. In neither case is confidentiality a desiratum. Optionally, the transmission may then be encyphered using (for instance) the Data Encryption Standard (DES). Finally, the cipher stream itself is 'encoded' again, using
error-correcting codes
for transmission from the ground station to the orbiting satellite. These operations are undone, in reverse order, after reception to recover the original information.
Note the multiple meanings of the word code in this example. Thinking clearly with words having such flexibility is not easy.
Most modern ciphers can be categorized in several ways:
- By whether they work on blocks of symbols of a fixed size (Block ciphers), or on a continuous stream of symbols (Stream ciphers).
- By whether the same key is used for both encryption and decryption (Symmetric key algorithms), or if a different key is used for each (Asymmetric key algorithms).
Note that, in English, the spelling 'cypher' is the original for this word. It is still favoured by many.
See also: Code, Cryptography, Cryptology
In the News
What's Inside: Nondairy Creamer
This coffee-bar staple is off-limits to vegans and could potentially explode. By Patrick Di Justo from Wired magazine. Children's Memory Of Long-ago Events May Be More Accurate Than Previou
Research with 5- and 6-year olds indicates that children's memories can be accurate even when interviewed well after an event. A long delay (three versus twenty one days), had no effect on the accuracy of children's memory of certain activities. The researchers observed differences in memory depending on how much the details varied each time the activity took place. These findings have implications for interviewing child witnesses who are interviewed a while after an incident. Government Defends Anti-Porn Law
Salon, Nerve and the ACLU, along with other web publishers, team up in a suit over the 1988 Child Online Protection Act. They argue it could restrict publishing legitimate material online and expose them to fines or jail time. Chemical Imaging: Potential New Crime Busting Tool
A new fingerprinting technique could potentially detect the diet, race and sex of a suspected criminal, according to new research. A strong trace of urea, a chemical found in urine, could indicate a male. Weak traces of urea in a chemical sample could indicate a female. Specific amino acids could potentially indicate whether the suspect was a vegetarian or meat-eater. [Ironic] LONDON: A jailed cocaine dealer is working as Santa Claus on
John Tams, who dons beard, boots and red suit to work in a cafe's Christmas grotto, said he wanted to give something back to the community... IRS to Launch New National Research Program Study in October [2007]
This release describes the Internal Revenue Service's "new National Research Program (NRP) reporting compliance study for individual taxpayers. ... The study will examine about 13,000 randomly selected tax year 2006 individual returns."Includes links to a more extensive fact sheet on the program, and to documents about the tax gap, "the difference between the amount of tax that taxpayers should pay and the amount that is paid voluntarily and on time."From the IRS. Rehab For Fried Food Loving Couch Dwellers
Northwestern University is using an economics theory to rehab people with lousy health habits. Researchers want participants to just change two unhealthy behaviors to see if the others will tag along. Sort of a buy two, get two free sale based on the Behavioral Economics Theory used by Nobel Prize winner Daniel Kahneman. Couch potatoes also get an arsenal of high-tech tools to help them make the changes. Spotlight on the physical sciences
Spotlight the PSIgate portal science news webzine goes monthly. In Issue 22, David Bradley asks, "Why ice, man?", reports on lighting up time for nanotechnology, and reveals the science behind moving oil droplets. Cancer Related Gene P53 Not Regulated As Indicated By Previous Tissue
The cellular cascade of molecular signals that instructs cells with fatally damaged DNA to self-destruct pivots on the p53 tumor suppressor gene. If p53 is inactivated, as it is in over half of all human cancers, checks and balances on cell growth fail to operate, and body cells start to accumulate mutations, which ultimately may lead to cancer. Not surprisingly, the regulation of this vital safeguard has been studied in great detail for many years but mainly in tissue culture, or in vitro, models. Caffeine Cream Tones Thighs
Caffeine appears to have the novel benefit of slenderizing thighs. Researchers studied 99 women treated with a cream consisting mostly of a 7 percent caffeine solution. More than 80 percent of the women had a reduction in the circumference of their upper and lower thighs. Nearly 68 percent also reduced their hip measurements.
MP3 Music Downloads
Preview songs, Download Free Music,Burn CDs at ITunes.com
 
|
