For this, a series of techniques is used and many others appear with passing of the time. In the computation the method most common involves the concept of keys; which is called keys of criptogrficas. Which if deals with a set of bits that has as base an algorithm that has the capacity to codify and to descodificar information. If somebody receives a message and to use of a different key of that it emitted the message, then will be impossible this receiver to have access to the content of the message that was sent to it. Thus, in case that somebody that possesss a computer, which, some people if they possess constantly as, for example, relative and friends, this user will be able to save its archives, to criptografar adding it a password and it will only be able to have access to the information of this archive, therefore he is sufficiently useful and pleasant the criptografia also in simple things that are part of our daily one. In the principle, when the criptogrficos methods had started to appear, they were used the criptografia with only one algorithm, what it would not be useful to keep sigilosas the information which these people were criptografando. We go to imagine that certain Joozinho had that to send a message to the Maria, and let us say that Joozinho criptografou this message, however Joozinho already had at another ordered moment some message for the Luluzinha, and also had criptografado this message for the Luluzinha with the same algorithm, imagines now that Luluzinha also wants the message that Joozinho sent to the Maria, and says that it obtains the message, then, it will use, of the password that Joozinho sent for it, and also would be easy to unmask this criptografia. Therefore, the new cryptographers needed to extend the number of algorithms to get success in this new discovery.