Showing Page:
1/19
What Is Encryption?
In cryptography, encryption is the process of encoding a message or information in a way that
only authorized parties can access it and those who are not authorized cannot.
Asymmetric Encryption
In public-key encryption schemes, the encryption key is published for anyone to use and
for encrypting messages. Only the receiving party has access to the decryption key that
enables messages to be read. Public-key encryption was first described in a secret
document in 1973. Before that, all encryption schemes were symmetric-key (also called
private-key).
Symmetric Encryption
In symmetric-key schemes, the encryption and decryption keys are the same.
Communicating parties must have the same key in order to achieve secure
communication.
1 Caesar Cipher
The Caesar cipher, also known as a shift cipher is one of the oldest and most famous
ciphers in history. While being deceptively simple, it has been used historically for
important secrets and is still popular among puzzlers. In a Caesar cipher, each letter is
shifted a fixed number of steps in the alphabet.
This cryptosystem is generally referred to as the Shift Cipher. The concept is to replace each
alphabet by another alphabet which is ‘shifted’ by some fixed number between 0 and 25.
It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed
number of positions down the alphabet. For example, with a left shift of 3, D would be replaced
by A, E would become B, and so on.
2 Monoalphabetic Substitution Cipher
The monoalphabetic substitution cipher is one of the most popular ciphers among
puzzle makers. Each letter is substituted by another letter in the alphabet. If it contains
word boundaries (spaces and punctuation), it is called an Aristocrat. The more difficult
variant, without word boundaries, is called a Patristocrat.
Showing Page:
2/19
Monoalphabetic cipher is a substitution cipher in which for a given key, the cipher alphabet for
each plain alphabet is fixed throughout the encryption process. For example, if ‘A’ is encrypted
as ‘D’, for any number of occurrence in that plaintext, ‘A’ will always get encrypted to ‘D’.
3 Atbash Cipher
The Atbash Cipher is a really simple substitution cipher that is sometimes called mirror
code. It is believed to be the first cipher ever used. To use Atbash, you simply reverse
the alphabet, so A becomes Z, B becomes Y and so on.
4 Vigere Cipher
The Vigenère cipher was invented in the mid-16th century and has ever since been
popular in the cryptography and code-breaking community. Despite being called the
Vigenère cipher in honor of Blaise de Vigenère, it was actually developed by Giovan
Battista Bellaso. The Vigenère cipher is an improvement of the Caesar cipher, by using
a sequence of shifts instead of applying the same shift to every letter.
A variant of the Vigenère cipher, which uses numbers instead of letters to describe the
sequence of shifts, is called a Gronsfeld cipher. Gronsfeld ciphers can be solved as well
through the Vigenère tool.
This scheme of cipher uses a text string (say, a word) as a key, which is then used for
doing a number of shifts on the plaintext.
For example, let’s assume the key is ‘point’. Each alphabet of the key is converted to
its respective numeric value: In this case,
p → 16, o → 15, i → 9, n → 14, and t → 20.
Thus, the key is: 16 15 9 14 20.
Process of Vigenere Cipher
The sender and the receiver decide on a key. Say ‘point’ is the key. Numeric
representation of this key is ‘16 15 9 14 20’.
The sender wants to encrypt the message, say ‘attack from south east’. He will
arrange plaintext and numeric key as follows −
Showing Page:
3/19