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== '''[[Block cipher]]''' ==
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In [[cryptography]], '''block ciphers''' are one of the two main types of [[symmetric cipher]]; they operate on fixed-size blocks of [[plaintext]], giving a block of [[ciphertext]] for each. The other main type are [[stream cipher]]s, which generate a continuous stream of keying material to be mixed with messages.
==Footnotes==
 
The basic function of block ciphers is to keep messages or stored data [[Information_security#Content_confidentiality | secret]]; the intent is that an unauthorised person be completely unable to read the enciphered material. Block ciphers therefore use a [[Key (cryptography)|key]] and are designed to be hard to read without that key. Of course an attacker's intent is exactly the opposite; he wants to read the material without authorisation, and often without the key. See [[cryptanalysis]] for his methods.
 
Among the best-known and most widely used block ciphers are two US government standards. The [[Data Encryption Standard]] (DES) from the 1970s is now considered obsolete; the [[Advanced Encryption Standard]] (AES) replaced it in 2002. To choose the new standard, the [[National Institute of Standards and Technology]] ran an AES competition. Fifteen ciphers were entered, five finalists selected, and eventually AES chosen. Text below gives an overview; for details of the process and the criteria, and descriptions of all fifteen candidates, see the [[AES competition]] article.
 
These standards greatly influenced the design of other block ciphers, and the latter part of this article is divided into sections based on that. [[#DES and alternatives | DES and alternatives]] describes 20th century block ciphers, all with the 64-bit block size of DES. [[#The AES generation | The AES generation]] describes the next generation, the first 21st century ciphers, all with the 128-bit block size of AES. [[#Large-block ciphers | Large-block ciphers]] covers a few special cases that do not fit in the other sections.
 
 
''[[Block cipher|.... (read more)]]''
 
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Latest revision as of 10:19, 11 September 2020

1901 photograph of a stentor (announcer) at the Budapest Telefon Hirmondó.

Telephone newspaper is a general term for the telephone-based news and entertainment services which were introduced beginning in the 1890s, and primarily located in large European cities. These systems were the first example of electronic broadcasting, and offered a wide variety of programming, however, only a relative few were ever established. Although these systems predated the invention of radio, they were supplanted by radio broadcasting stations beginning in the 1920s, primarily because radio signals were able to cover much wider areas with higher quality audio.

History

After the electric telephone was introduced in the mid-1870s, it was mainly used for personal communication. But the idea of distributing entertainment and news appeared soon thereafter, and many early demonstrations included the transmission of musical concerts. In one particularly advanced example, Clément Ader, at the 1881 Paris Electrical Exhibition, prepared a listening room where participants could hear, in stereo, performances from the Paris Grand Opera. Also, in 1888, Edward Bellamy's influential novel Looking Backward: 2000-1887 foresaw the establishment of entertainment transmitted by telephone lines to individual homes.

The scattered demonstrations were eventually followed by the establishment of more organized services, which were generally called Telephone Newspapers, although all of these systems also included entertainment programming. However, the technical capabilities of the time meant that there were limited means for amplifying and transmitting telephone signals over long distances, so listeners had to wear headphones to receive the programs, and service areas were generally limited to a single city. While some of the systems, including the Telefon Hirmondó, built their own one-way transmission lines, others, including the Electrophone, used standard commercial telephone lines, which allowed subscribers to talk to operators in order to select programming. The Telephone Newspapers drew upon a mixture of outside sources for their programs, including local live theaters and church services, whose programs were picked up by special telephone lines, and then retransmitted to the subscribers. Other programs were transmitted directly from the system's own studios. In later years, retransmitted radio programs were added.

During this era telephones were expensive luxury items, so the subscribers tended to be the wealthy elite of society. Financing was normally done by charging fees, including monthly subscriptions for home users, and, in locations such as hotel lobbies, through the use of coin-operated receivers, which provided short periods of listening for a set payment. Some systems also accepted paid advertising.

Footnotes