How To Encode And Decode A Message using Python?

Last Updated : 11 May, 2023

Encryption is the process of converting a normal message (plain text) into a meaningless message (Ciphertext). Whereas, Decryption is the process of converting a meaningless message (Cipher text) into its original form (Plain text). In this article, we will take forward the idea of encryption and decryption and draft a python program.

In this article, we will be given a single-line message as input it is either encoded or decoded as per requirement and the resultant message is printed as output. Here, the conversion has been done by replacing A to Z, B to Y, ... Z to A. The case of the characters, numbers, spaces, and special characters present in the message is being kept unchanged.

Sample Example 1:

Encryption

Input : Hello World
Output : Svool Dliow

Explanation: (Reference- conversion table)

H is replaced with S
e is replaced with v
l is replaced with o
W is replaced with D
r is replaced with i

Decryption

Input : Svool Dliow 
Output : Hello World

Explanation: (Reference- conversion table)

S is replaced with H
v is replaced with e
o is replaced with l
D is replaced with W
i is replaced with r

Sample Example 2:

Encryption

Input : GeeksForGeeks
Output : TvvphUliTvvph

Explanation: (Reference- conversion table)

G is replaced with T
e is replaced with v
k is replaced with p
s is replaced with h
F is replaced with U
o is replaced with l
r is replaced with i

Decryption

Input : TvvphUliTvvph 
Output : GeeksForGeeks

Explanation: (Reference- conversion table)

T is replaced with G
v is replaced with e
p is replaced with k
h is replaced with s
U is replaced with F
l is replaced with o
i is replaced with r

Below is the implementation.

Python3

# Taking input from user
data = 'Welcome to GeeksForGeeks...'


# conversion Chart
conversion_code = {

    # Uppercase Alphabets
    'A': 'Z', 'B': 'Y', 'C': 'X', 'D': 'W', 'E': 'V', 'F': 'U',
    'G': 'T', 'H': 'S', 'I': 'R', 'J': 'Q', 'K': 'P', 'L': 'O',
    'M': 'N', 'N': 'M', 'O': 'L', 'P': 'K', 'Q': 'J', 'R': 'I',
    'S': 'H', 'T': 'G', 'U': 'F', 'V': 'E', 'W': 'D', 'X': 'C',
    'Y': 'B', 'Z': 'A',

    # Lowercase Alphabets
    'a': 'z', 'b': 'y', 'c': 'x', 'd': 'w', 'e': 'v', 'f': 'u',
    'g': 't', 'h': 's', 'i': 'r', 'j': 'q', 'k': 'p', 'l': 'o',
    'm': 'n', 'n': 'm', 'o': 'l', 'p': 'k', 'q': 'j', 'r': 'i',
    's': 'h', 't': 'g', 'u': 'F', 'v': 'e', 'w': 'd', 'x': 'c',
    'y': 'b', 'z': 'a'
}

# Creating converted output
converted_data = ""


for i in range(0, len(data)):
    if data[i] in conversion_code.keys():
        converted_data += conversion_code[data[i]]
    else:
        converted_data += data[i]

# Printing converted output
print(converted_data)

Output

Dvoxlnv gl TvvphUliTvvph...

Approach: Using strings and index() method

Python3

# Taking input from user
data = 'Welcome to GeeksForGeeks...'
# conversion Chart
la="abcdefghijklmnopqrstuvwxyz"
ua="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
lra=la[::-1]
ura=ua[::-1]
# Creating converted output
converted_data = ""


for i in range(0, len(data)):
    if data[i] in la:
        converted_data+=lra[la.index(data[i])]
    elif data[i] in ua:
        converted_data+=ura[ua.index(data[i])]
    else:
        converted_data+=" "
# Printing converted output
print(converted_data)

Output

Dvoxlnv gl TvvphUliTvvph

Method #3: Using maketrans(), translate()

Python3

# Fn to encrypt the message
def encrypt(message):
    conversion_table = str.maketrans("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", "zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA")
    return message.translate(conversion_table)
 
# Initializing the innput
message = "Hello World"

# Calling Function
encrypted_message = encrypt(message)

# print the encrypted messages
print(encrypted_message)