Permutation/Transposition Cryptography

Permutation/Transposition Cryptography is a #Cryptographic method that encrypt a message by rearranging the plaintexts. This includes changing Encoding# system of the plaintexts. Since it doesn’t alter the frequency of letters from the original plaintext, it is vulnerable to Frequency Analysis#. It is even more dangerous to group the ciphertext in group that match the key size used by the cipher.

A Cryptanalytic Attack done on Permutation/Transposition Cryptographic algorithm is by first guessing period, try all possible permutation on the period (Brute Force Attack), search for common patterns and then use lists of common diagrams and trigrams (Frequency Analysis#).

The examples are:

Using geometric figure to write and read out following the pattern
Rail Fencer Cipher#
Row Transposition Cipher#
Block/Columnar Transposition Cipher#

Links to this page

TAC3121 Chapter 3: Classic Ciphers

Permutation/Transposition Cryptography
Row Transposition Cipher

Row Transposition Cipher is a #Permutation/Transposition Cryptographic #algorithm that arrange the plaintext in an order specified by a key (a sequence of numbers or a word) accordingly in a row to produce a ciphertext. Initially, the plaintext should be written out in rows according to the key size (determine how many columns should the plaintext be written).
Rail Fencer Cipher

Rail Fencer Cipher is a #Permutation/Transposition Cryptographic #algorithm by writing message letters out diagonally over a number of rows (arbitrary) then read off the cipher row by row.
Product Cipher

Product Cipher is a cipher that composed of both #substitution (S-box) and #permutation (P-box). Introduced by Claude Shannon, it is the backbone for the modern Block Cipher. It provides diffusion and confusion of message and key.
Output Feedback (OFB)

Output Feedback is a stream mode of operation# of #Data Encryption Standard (DES) and #Advanced Encryption Standard (AES) where the preceding encryption output of the permuted encrypted initialisation value (feedback) is used as the input to the encryption #algorithm. The feedback is indenpendent of message thus can be computed in advance. Full blocks are used. It is pretty similar to Cipher Feedback (CFB) otherwise.
Feistel Cipher Structure

First, it starts its cipher process halving input blocks, which then perform substitution# on left data half based on round function with right halve and subkey as parameters. After that, it performs a permutation# by swapping the halves. The process is then repeated for multiple rounds. The process is shown as formula below:
Data Encryption Standard (DES)

DES is an encryption standard that adheres to #Symmetric Cryptography. It utilises Feistel Cipher Structure#, by doing 16 rounds of encrypting, where the underlying encryption method also exhibits Avalanche Effect# (34 bits and 35 bits difference for the plaintext and the key). Both 64-bit plaintext and the 64-bit key will undergo permutation before going through the Feistel cipher structure where only 56 bits of the key selected. The key will be left circular shifted in order to produce subkeys (in 48 bits), which will be done 16 rounds like the main encryption process. After 16 rounds, a 32-bit swap follows by an inverse initial permutation will produce a 64-bit ciphertext.
Cryptography

Permutation/Transposition Cryptography#
Block/Columnar Transposition Cipher

Columnar Transposition Cipher is a #Permutation/Transposition Cryptography #algorithm that arrange plaintext in an order specified by a key (a sequence of numbers or a word) accordingly in a column to produce ciphertext. The key size determines how long should the plaintext be written in a row before proceed to a new line.
Advanced Encryption Standard (AES)

AES processes data as block of 4 columns of 4 bytes. It will then operate on the entire data block in every round (up to 9, 11, 13 rounds) with byte substitution#, shift rows#, mix columns (substitution using matrix multiply of group), and add round key (XOR the data block with key) which view the data block as alternate XOR key and scramble data bytes. Decryption is done in reverse to encryption process.

#cryptography #)