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NIS Practical 5

The document describes the Caesar Cipher, a simple encryption technique where each letter in the plaintext is replaced by a letter a fixed number of positions down the alphabet. It includes an algorithm for encryption and a Python program implementation that demonstrates how to encrypt text using a specified shift value. The method is named after Julius Caesar and is one of the earliest forms of substitution cipher.

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15 views3 pages

NIS Practical 5

The document describes the Caesar Cipher, a simple encryption technique where each letter in the plaintext is replaced by a letter a fixed number of positions down the alphabet. It includes an algorithm for encryption and a Python program implementation that demonstrates how to encrypt text using a specified shift value. The method is named after Julius Caesar and is one of the earliest forms of substitution cipher.

Uploaded by

labonimsonawane05
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Practical No.

5
Aim: Write a program to implement Caesar Cipher
Introduction:

Algorithm of Caesar Cipher

The algorithm of Caesar cipher holds the following features −

• Caesar Cipher Technique is the simple and easy method of encryption


technique.

• It is simple type of substitution cipher.

• Each letter of plain text is replaced by a letter with some fixed number of positions
down with alphabet.

The following diagram depicts the working of Caesar cipher algorithm


implementation −

Explanation

The plain text character is traversed one at a time.


• For each character in the given plain text, transform the given character as per the
rule depending on the procedure of encryption and decryption of text.

• After the steps is followed, a new string is generated which is referred as cipher
text.
Feature of Caesar Cipher Algorithm

This algorithm consists of a few features that are given below. o This technique is quite
simple to apply encryption. o Each text is replaced by the fixed number of position
down or up with the alphabet. o It is a simple type of substitute cipher.

There is an integer value required to define each latter of the text that has been move
down. This integer value is also known as the shift.

We can represent this concept using modular arithmetic by first transmuting the letter
into numbers, according to the schema, A = 0, B = 1, C = 2, D = 3 Z = 25.

The following mathematical formula can be used to shift n letter.

The program implementation of Caesar cipher algorithm is as follows –

Program:
#A python program to illustrate
Caesar Cipher Technique
def encrypt(text,s):
result = ""

# traverse text
for i in range(len(text)):
char = text[i]

# Encrypt uppercase characters


if (char.isupper()):
result += chr((ord(char)
+ s-65) % 26 + 65)

# Encrypt lowercase characters


else:
result += chr((ord(char)
+ s - 97) % 26 + 97)

return result

#check the above function


text = "ATTACKATONCE"
s=4
print ("Text : " + text)
print ("Shift : " + str(s))
print ("Cipher: " + encrypt(text,s))
Output
:

Conclusion :
The Caesar Cipher technique is one of the earliest and simplest method of
encryption technique. It’s simply a type of substitution cipher, i.e., each letter of a
given text is replaced by a letter some fixed number of positions down the alphabet.
For example with a shift of 1, A would be replaced by B, B would become C, and
so on. The method is apparently named after Julius Caesar, who apparently used it
to communicate with his officials.

Thus to cipher a given text we need an integer value, known as shift which
indicates the number of position each letter of the text has been moved down

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