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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-1994
Viacom multimedia and industrial corporation takes control of Paramount Communications for US$ 9.6 billion, as well as Blockbuster Entertainment, a huge video store chain, for US$ 8.4. billion.
1995
Entertainment giant Disney buys Capital Cities-ABC for US$ 19 billion.
The industrial and broadcasting company Westinghouse Corp. buys out CBS for US$ 5.4 billion.
In a US$ 7.2 billion deal, Time Warner acquires Turner Communications, owner of prime cable TV channels CNN, TBS and TNT and a major classic American film library.
1996
Westinghouse/CBS buys Infinity Broadcasting's large group of radio stations.
Murdoch and News Corp. acquire ten more TV stations and TV production studios with the US$ 2.5 billion purchase of New World Communications Group.
Viacom buys half of UPN-TV network, adding that to its other holdings, which include eleven TV stations, along with MTV, VH-1, and other cable TV channels and Paramount movie studios.
1997
Radio Groups Chancellor Media and Evergreen merge and are linked by ownership with Capstar Broadcasting; they also buy ten radio stations from Viacom. By mid-1997 Chancellor/Capstar controls no fewer than 325 radio stations around the United States.
Chancellor/Capstar's controlling ownership group, Hicks Muse Tate & Furst, buys the seventh largest radio group, SFX, adding another seventy-two radio stations, making a total of nearly four hundred stations controlled by this one source.
Westinghouse-CBS buys out American Radio Systems, the fourth largest radio chain in total audience, which gives Westinghouse-CBS over 170 radio stations with a total audience nearly equal to that of the Chancellor/Capstar group.
Giant European-based print and electronic publishing and data base corporations Reed Elsevier and Wolters Kluwer merge.
1998
Bertelsmann buys the Random House-Alfred A. Knopf-Crown Publishing group of book publishers from Newhouse/Advance Publications, adding to its Bantam-Doubleday-Dell publishing group and giving Bertelsmann by far the largest English-language publishing operations.
1999
AOL, the worlds leading Internet service provider and Time Warner, the worlds leading classical media company merge in a US$ 243.3 billion deal.
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A mark (trademark or service mark) is "... a sign, or a combination of signs, capable of distinguishing the goods or services of one undertaking from those of other undertakings. The sign may particularly consist of one or more distinctive words, letters, numbers, drawings or pictures, emblems, colors or combinations of colors, or may be three-dimensional..." (
Bruce Schneier is president of Counterpane Systems in Minneapolis. This consulting enterprise specialized in cryptography and computer security. He is the author of the book Applied Cryptography and inventor of the Blowfish and Twofish encryption algorithms.