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Criptografia

To establish a data communication between two entities (people, equipment, etc.) requires at least three basic elements: the sender of the message (the source), the recipient of it (the destination ) and physical media by which data is transferred (the middle).

In a normal communication data is sent through the media as they are, without undergoing any changes, so that the message they represent can be intercepted and read by any other entity that accesses to it during your trip the middle.

But there are times when we are concerned that the message can only be interpreted correctly by the issuer thereof and the receptor to which it is addressed. On these occasions it is necessary to implement some mechanism to protect sensitive information such that the message safe journey from source to destination, making it impossible for third interception of the message, or if it occurs, the message captured is incomprehensible to anyone with access.

One way to accomplish this is to send the message clear, as drafted by the issuer, and to protect it on the road using power systems defend him along the way, such as message protection by security personnel.

Another method is to send the message along a road with much traffic of information that is very difficult to identify third parties that is confidential information (the best way to hide a tree is within a forest), as If the message is sent a letter by standard mail system. Unfortunately these methods

Protective messages, as well as other similar, have proven ineffective over time, so there was to find other mechanisms to protect sensitive information on their way between sender and receiver.

Cryptology has proven over time to be one of the best techniques to solve this issue. So much so that today, in the era of computers and information, is the mechanism used in the data protection processes, such as Internet banking, e-mail encryption,.

Definition We define

Cryptography Cryptography (Kripto = hide, Graphos = writing) the technique of transforming a intelligible message, called plaintext , another that only authorized persons can understand this, we will call cryptogram or ciphertext. The method or system used to encrypt the plaintext is called encryption algorithm .

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classical cryptography encryption texts is an activity that has been widely used throughout human history, especially in the military and in those where it is necessary to send confidential information and sensitive data through unsafe means. Although

in some ways the Egyptian hieroglyphs sitema can be considered as a form of cryptography (could only be understood by persons with sufficient knowledge), the first cryptographic system known as such due to Julius Caesar. His system was replaced in the message to be sent each letter by three positions ahead situated in the Latin alphabet. In our current alphabet would have the following table:

Q

A B C

D E F

G H I

J

K

L

M

N

Ñ

O

P

Q

R

S

T

U

V

W

X

Y

Z

D

E

F

G

H

I

J

K

L

M

N

Ñ

O

P

R S T

U V W

X Y Z

A B C

So the message " HELLO WORLD "would become" KRÑD OXPGR. " To return to the original message from the ciphertext only have to take a script and start replacing each letter that is three positions before the MSIM.

substitution is to change the character components original message in others by a particular rule natural position in the alphabet . For example, setting an equivalence between the original alphabet and a variation of it, similar to what happens in the method of Julius Caesar. If we set the equivalence of alphabets:

C D E

A

B C D

E F G

H I J

K L M

N Ñ

O

P

Q

R

S

T

U

V

W

X

Y

Z

J

K

L

M

N

Ñ

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

F G H

I

The message "Hello World" would like "PXTJ UDVMX."

The transposition instead is to change the character of the original message components according to a rule other certain position in the order of the message. For example, if we set the following rule change in the order of the letters in the text:

	1 point		2 3 4			5 6 7		8 9
becomes the		1 5 4			7 8	2		9 3 6

the phrase "Hello World" we would "OUDL HOAMN." Both

substitution as the transposition are basic techniques to hide the text level redundancy, redundancy is sent to the ciphertext, and can be the starting point for an attack cryptanalysis. Redundancy is the fact that almost all the symbols of a message in natural language contain information that can be drawn from the symbols around him.