What is a Cipher?

Ciphers are the specific algorithms which are used to encrypt and decrypt data.  
A cipher is series of well-defined steps that can be followed as a procedure to encrypt and decrypt messages.


Cipher Methods



                  Transposition Cipher
·         No letters are replaced. They are simply rearranged.
·         E.g.:  Backward cipher
                Rail fence cipher
                Scytale
                DES/3DES

                  One Time Pad
·         Key is consisting of arbitrarily long, non-repeated sequence of numbers.
·         Key length = message length in number of characters
·         Key is combined character by character with plain text by using XOR to produce cipher text.
·         Many Time Pods – if the key is used for more than once.

                 Substitution Cipher
·         Substitute/replace one letter for another.
·         Key is used.
·         Two types
1.      Monoalphabetic – Cipher text retain the letter frequency of the original message.
Key => 3
E.g.: Caesar cipher
2.      Polyalphabetic – key => CAT
E.g.: Vigenere cipher




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