Here the keys for encryption and decryption differ. There needs to exist a private key, which is only known to the individual, and a public key, which is published. Every person has her or his own private key that is never published. It is used for decrypting only. Mathematically the different keys are linked to each other, still it is nearly impossible to derive the private key from the public one.
For sending a message to someone, one has to look up the other's public key and encrypt the message with it. The keyholder will use his/her private key to decrypt it. While everybody can send a message with the public key, the private key absolutely has to stay secret - and probably will.
"The best system is to use a simple, well understood algorithm which relies on the security of a key rather than the algorithm itself. This means if anybody steals a key, you could just roll another and they have to start all over." (Andrew Carol)
very famous examples for public-key systems are:
· RSA:
The RSA is probably one of the most popular public-key cryptosystems. With the help of RSA, messages can be encrypted, but also digital signatures are provided.
The mathematics behind are supposedly quite easy to understand (see:
· PGP:
PGP is a public key encryption program. Most of all it is used for e-mail encryption.
It is supposed to be quite safe - until now.
· PGPi is simply the international variation of PGP.
for further information about the RSA and other key-systems visit the RSA homepage:
or:
All of those tools, like hash functions, too, can help to enhance security and prevent crime.
They can theoretically, but sometimes they do not, as the example of the published credit card key of France in March 2000 showed.
For more information see:
Still, cryptography can help privacy.
On the other hand cryptography is only one element to assure safe transport of data. It is especially the persons using it who have to pay attention. A key that is told to others or a lost cryptographic key are the end of secrecy.
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Founded in 1929 Disney primarily engages in child and adult entertainment. Starting with the production of animated motion-picture cartoons in the late 1940s Disney began to make also nature documentaries and live-action motion pictures, as well as short cartoons and live-action programs for television. In 1955 the company opened Disneyland, which was their first amusement park. Further openings of amusement parks in the U.S. and Europe followed. In 1996 Disney acquired Capital Cities/ABC Inc., which owned the ABC television network.
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150
A
The Roman smoke signals network consisted of towers within a visible range of each other and had a total length of about 4500 kilometers. It was used for military signaling.
For a similar telegraph network in ancient Greece see
About 750
In Japan block printing is used for the first time.
868
In China the world's first dated book, the Diamond Sutra, is printed.
1041-1048
In China moveable types made from clay are invented.
1088
The first of the great medieval universities was established in Bologna. At the beginning universities predominantly offered a kind of do-it-yourself publishing service.
Books still had to be copied by hand and were so rare that a copy of a widely desired book qualified for being invited to a university. Holding a lecture equaled to reading a book aloud, like a priest read from the Bible during services. Attending a lecture equaled to copy a lecture word by word, so that you had your own copy of a book, thus enabling you to hold a lecture, too.
For further details see History of the Idea of a University,
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A
Aeneas Tacitus, a Greek military scientist and cryptographer, invented an optical communication system that combines water and beacon telegraphy. Torches indicated the beginnings and the ends of message transmissions while water jars were used to transmit the messages. These jars had a plugged standard-size hole drilled on the bottom side and were filled with water. As those who sent and those who received the message unplugged the jars simultaneously, the water drained out. Because the transmitted messages corresponded to water levels, the sender indicated by torch signal that the appropriate water level has been reached. It is a disadvantage that the possible messages are restricted to a given code, but as this system was mainly used for military purposes, this was offset by the advantage that it was almost impossible for outsiders to understand these messages unless they possessed the codebook.
With communication separated from transportation, the distant became near.
Tacitus' telegraph system was very fast and not excelled until
For further information see Joanne Chang & Anna Soellner, Decoding Device,
The News Corporation Ltd., a global media holding company, which governed News Limited (Australia), News International (U.K.), and News America Holdings Inc. (U.S.) was founded by the Australian-born newspaper publisher and media entrepreneur, Rupert Murdoch. Murdoch's corporate interests center on newspaper, magazine, book, and electronic publishing; television broadcasting; and film and video production, principally in the United States, the United Kingdom, and Australia.
Gutenberg's printing press, an innovative aggregation of inventions known for centuries before Gutenberg: the olive oil press, oil-based ink, block-print technology, and movable types, allowed the mass production of the movable type used to reproduce a page of text and increased the production rate enormously. During the Middle Ages monks took at least a year over making a handwriting copy of a book. Gutenberg printed about 300 sheets per day. Because parchment was too costly for mass production - often for the production of one copy of a medieval book a whole flock of sheep was used - it was substituted by cheap paper made from recycled clothing left over from the massive number of dead caused by the Great Plague.
Within forty-five years, in 1500, already ten million copies were available for a few hundred thousand literate. Because individuals could examine a range of opinions now, the printed Bible, especially after having been translated into German by Martin Luther, and increasing literacy added to the subversion of clerical authorities. The interest in books increased with the rise of vernacular, non-Latin literary texts, beginning with Dante's Divine Comedy, the first literary text written in Italian.
Among others, the improvement of the distribution and the production of books and increased literacy made the development of print mass media possible.
Michael Giesecke (Sinnenwandel Sprachwandel Kulturwandel. Studien zur Vorgeschichte der Informationsgesellschaft, Frankfurt am Main: Suhrkamp, 1992) has shown that due to a division of labor among authors, printers and typesetters Gutenberg's invention increasingly led to a standardization of - written and unwritten - language in form of orthography, grammar and signs. To communicate one's ideas became linked to the use of a kind of code, and reading became a kind of rite of passage, in every human's life an important step towards independency.
With the increasing linkage of knowledge to wide reading and learnedness, the history of knowledge becomes the history of readings, of readings dependent on chance and on circumstance.
For further details see:
Martin Warnke, Text und Technik,
Bruce Jones, Manuscripts, Books, and Maps: The Printing Press and a Changing World,