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Cryptology
101 - Part 5
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to the Ancient Substitution Cipher: The Caesarian Shift -->
What Julius Caesar did with the invention of the Caesarian
Shift established the foundations of cryptology. From that point
onward all cryptology has evolved from the basic principle of
substituting one letter for another. This is called creating
a Substitution Cipher.
The next step in the evolution of Caeser's substitution cipher
was the use of a keyword. Caeser created a cipher alphabet by
shifting the alphabet by a previously agreed upon number.
For example an alphabet shifted by one letter would start with
B and end with A. Shifting by two would result
in the alphabet beginning with C and ending with B.
Shifting three would cause the cipher alphabet to start with
D and end with C, etc.
The weakness of the Caesarian Shift is that there are only 26
possible cipher alphabets. Given enough time anyone can decipher
a ciphertext that is encrypted using a Caesarian Shift.
To create more secure and unique cipher alphabets a keyword
is used when implementing the shift. The result is an easy to
use secure cipher that can only be deciphered if you know the
keyword. This type of substitution shift is called a monoalphabetic
cipher because it makes use of a single fixed substitution
alphabet. Later on we will look at polyalphabetic ciphers which
use multiple alphabets.
So lets get started on using a simple monoalphabetic cipher.
Learn to Write a Monoalphabetic Cipher -->
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