Symmetric-Key Algorithm

In , or secret key cryptography, both the sender and the receiver of the message share the same key, which must be kept secret by both. The same key is used to encode and decode the message.


Secret key cryptography
adapted from http://informatica.hsw.uol.com.br/criptografia4.htm


If a person wants to communicate with another with security he must give him the key used. This process is called key distribution. As the key is the primary element of security for the algorithm, it should be transmitted by a secure means. The secure means of communication are generally expensive and more difficult to be obtained. Its use is only acceptable once, but not continuously.

Imagine the case of three people - A, B and C - who want to communicate using secret keys. You will need three keys, as described in the figure below:


Sharing secret keys
adapted from http://informatica.hsw.uol.com.br/criptografia4.htm

One of the attempts to solve the problem of the distribution of secret keys was the creation of a Key Distribution Center (KDC), which would be responsible for the communication established between pairs of people. Therefore, the KDC must own all the secret keys of the users of its services.

Main algorithms using secret key:

  • DES
  • Triple-DES
  • AES
  • RC2
  • RC4
  • IDEA
  • Skipjack

AES Algorithm


copied from http://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndael_ingles2004.swf


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References:
http://www.di.ufpe.br/~flash/ais98/cripto/criptografia.htm
http://informatica.hsw.uol.com.br/criptografia4.htm


 
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