Julius Caesar: Substitution Technique

Substitution Techniques

Caesar Cipher

Caesar cipher was earlier known as substitution cipher. Julius Caesar made its attested use in military affairs. Its core idea is to replace one basic unit (letter/byte) with another. It replaces each letter by third letter. For example:

PLAIN: meet me after the toga party

CIPHER: PHHW PH DIWHU WKH WRJD SDUWB

Monoalphabetic Cipher In this technique instead of simply moving the 26 alphabets, the letters could be rearranged discretionally. Each plaintext letter shows a different arbitrary ciphertext letter.

Play Fair Cipher

This technique does not provide enough security though large numbers of keys are used in monoalphabetic cipher. Numerous letters can be encrypted to deal with

It is unbreakable since ciphertext has no information of the plaintext. Practically, it was not easy to implement, as it needs large quantities of random keys. For every message to be sent, a key of equal length is needed by both, the sender and the receiver. It is of limited utility and is used for low-bandwidth channels with high security.

Transposition Techniques

Transposition Cipher

As the word ‘Transposition’ itself explains that the idea is to rearrange the order of basic units (letters/bytes/bits) without changing the actual letters used in the plaintext. The above-mentioned techniques gone through so far involve the substitution of a ciphertext symbol for a plaintext symbol. But with this technique, a very different type of mapping is attained by doing permutation on the plaintext letters.

Steganography

“Steganography is the art and science of writing hidden messages in such a way that no one apart from the sender and intended recipient, suspects the existence of the message.” It uses various methods to hide a secret message in any other data; it may be a picture, a mp3, a video

It is most widely used in the world. There is enough controversy over its security.

Triple-DES (3DES) and DESX are the two important variants that strengthen DES.

Advanced Encryption Standard (AES)

The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of 128, 192, or 256 bits and blocks of length 128, 192, or 256 bits.

AES is a symmetric block cipher which replaces DES as the approved standard for a range of applications.

Triple DES is regarded as secure and well understood, but it is slow.

In June 1998 in the first round of evaluation, 15 proposed algorithms were accepted. Only 5 algorithms were short-listed in the second round in August 1999.

In 2000, Rijndael was selected as the AES algorithm by NIST. : Dr. Joan Daemen and Dr.Vincent Rijmen, both cryptographers from Belgium, developed and submitted Rijndael for the AES.

AES was published by NIST in 2001.

International Data Encryption Algorithm