Information Security Cryptography ( L03- Old Cryptography Algorithms )

Cryptography L03- Old Encryption algorithms

outline

Old Encryption algorithms OR Classical Method

● Replacement Algorithms

● Caesar Cipher

● Full vigenere cipher

● Atbash Cipher

● Affine Cipher

● THE JEFFERSON CYLINDER

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Classical Method Cryptography

Replacement Algorithms

This algorithm is deployed in the Middle Ages and this algorithm based

on replacing each character of the alphabet with another character

in a particular order.

The number of attempts needed to break this algorithm is 26! ,and it is

equal to almost 10264.

To be breached depending on the frequency of the original language characters ,Where are calculated by testing a large number of texts.

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Classical Method Cryptography

Replacement Algorithms

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Classical Method Cryptography

Caesar Cipher

Julius Caesar has to find a way that they named after him in 58 BC.

This method is based on a comparison between each letter of the alphabet with a letter last, depending on the value of rotation.

We do not need a lot of effort to prove the weakness of this simple algorithm where they depend on the rotation and therefore the value of knowing the value of the rotation loosen the entire encrypted message.

And calculates the number of possibilities for the value of rotation in the English language, we find that it is a small value of 26 field easily break through the algorithm and the discovery of the original message.

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Classical Method Cryptography

Caesar Cipher

Example : Word “SECRET” the encryption of this "VHFUHW“

where the rotation key is 3

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Classical Method Cryptography

Full vigenere cipher

The Leon Battista Albert develop this algorithm in 1467 AD.

The code is used to switch between the appropriate disk letters.

The working principle of this algorithm depends on the encryption table.

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Classical Method Cryptography

Table of Full vigenere cipher

Example : the text “helloGreenDay” and key is “ForumForumFor”

The text after encryotion

became “Mscfalvyzlop”

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Classical Method Cryptography

Atbash Cipher

This Cipher of the simplest types of Cipher which was originally the

Hebrew language.

But it can be used in other languages.

Mode of operation as follows :

To make the first letter in the language is the last letter and the second

character is the last before etc...

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Classical Method Cryptography

Atbash Cipher

AZ

B Y

Etc >>>

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Classical Method Cryptography

Affine Cipher

Encryption is a way Affine Cipher confusion between the two types of

encryption ,the first type, a Caesar Cipher and the second is the

product Cipher.

Caesar be in encryption mathematical relation :

C = p + key MOD n

Product Cipher be in encryption relation :

C = p * key MOD n

Affine code brought together the two previous two relationships :

C = m*p + key MOD n

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Classical Method Cryptography

THE JEFFERSON CYLINDER

is one of the strongest encryption used in devices where the Cipher

generated strong can be broken easily never except in the case of the

theft of the entire device.

Name Jefferson back to its inventor THOMAS JEFFERSON Name.

This disc consists of some 36 wheel beside a row and 26, meaning that each row by 36 character.

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Classical Method Cryptography

THE JEFFERSON CYLINDER

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