Substitution cipher

The convenience of indexers is not a primary consideration for nomenclature development. Here is a conflict requiring resolution. The obvious step is to define the limits within which the additive and the substitutive principle are severally preferable, unless all indexers adopt a ciphering system where such problems do not arise and the field is left clear for cursive text. 

The Atbash Cipher is an old cipher used in the book of the Prophet Jeremiah based on the twenty-two letters of the Hebrew Alphabet.The cipher is applied by substituting the first letter of the Hebrew Alphabet aleph with the last letter tav, the second letter beth by the penultimate letter shin, and so on. 

The Atbash cipher converts Babel (BBL), meaning Babylon, to Shishak (ShShK). " This is achieved by substituting Beth, Beth and Lamed with Shin, Shin and Kaph respectively. 

Substitution or Monoalphabetic Ciphers. A variation of the plaintext shift is the substitution or monoalphabetic cipher. This method involves permuting the letters of the alphabet. In other words, the letters are more than simply shifted they are jumbled up into an arbitrary order. For example, suppose that Alice wants to send Bob the message T/ie Berlin wall will fall tonight/ First, Alice and Bob must agree on the monoalphabetic cipher they will use. They agree to use the one presented in Figure 2.5. 

Sample Ciphertext Message Using a Substitution Cipher... 

Used together, repeated combinations of substitution and transpositions can make the job of an attacker who is trying to break the system without knowing the key harder by more thoroughly obscuring the relationship between the plaintext and the ciphertext, requiring an attacker to explore many more possibilities. Many of the mechanical and electrical ciphers used in World Wars I and II, such as the Enigma rotor machine, relied on various combinations of substitutions and permutations. 

For example, substitution creates confusion, while transpositions create diffusion. While confusion alone can be enough for a strong cipher, diffusion and confusion are most effective and efficient when used in conjiuiction. 

Traditionally, all cryptography was symmetric key cryptography. In a symmetric key cryptosystem, the encryption key Ke and the decryption key Kd are the same, denoted simply by K. The key K must be kept secret, and it is also important that an eavesdropper who sees repeated encryptions using the same key can not learn the key. The simple substitution cipher described earlier is an example of a symmetric key cryptosystem. 

The most common type of cipher in ancient times was the substitution cipher. This was the type of cipher employed by Julius Caesar during the Gallic Wars, by the Italian Leon Battista Alberti in a device called the Alberti Cipher Disk described in a treatise in 1467, and by Sir Francis Bacon of Great Britain. In the 1400 s, the Egyptians discovered a way to decrypt substitution ciphers by analyzing the frequency of the letters of the alphabet. Knowing the frequency of a letter made it easy to decipher a message. 

Codes and ciphers have been used since the beginning of recorded time, when humans drew figures on a cave wall to communicate ideas. During the Gallic Wars, Julius Caesar devised one of the first substitution ciphers by printing the ciphertext alphabet with the letters moved four places to the left under the plaintext alphabet. 

There are few different types of encryption methods substitution, transposition, and one-time pad cipher. One of the oldest ciphers is substitution cipher, known as Caesar cipher, which substitutes every symbol with another from its group. For example A with D, B with G, and so on. This is very easy to analyze and break with common letter statistics. Transposition cipher preserves... 

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