vigenere_cipher.py

#Python program to implement Vigener Cipher
#For explaination refer to GeeksforGeeks


# Dictionary to lookup the index of alphabets
dict1 = {'A': 0, 'B': 1, 'C': 2, 'D': 3, 'E': 4,
         'F': 5, 'G': 6, 'H': 7, 'I': 8, 'J': 9,
         'K': 10, 'L': 11, 'M': 12, 'N': 13, 'O': 14,
         'P': 15, 'Q': 16, 'R': 17, 'S': 18, 'T': 19,
         'U': 20, 'V': 21, 'W': 22, 'X': 23, 'Y': 24, 'Z': 25}

dict2={0:'A',1:'B',2:'C',3:'D',4:'E',
       5:'F',6:'G',7:'H',8:'I',9:'J',
       10:'K',11:'L',12:'M',13:'N',14:'O',
       15:'P',16:'Q',17:'R',18:'S',19:'T',
       20:'U',21:'V',22:'W',23:'X',24:'Y',25:'Z'}


#This function generates the key in
#a cyclic manner until it's length isi'nt
#equal to the length of original text
def generate_key(message,key):
	x=len(message)
	i=0
	while True:
		if x==i:
			i=0
		if len(key)==len(message):
			break
		key+=key[i]
		i+=1
	return key

#This function returns the encrypted text
#generated with the help of the key
def cipherText(message,key_new):
	cipher_text=''
	i=0
	for letter in message:
		if letter==' ':
			cipher_text+=' '
		else:
			x=(dict1[letter]+dict1[key_new[i]])%26
			i+=1
			cipher_text+=dict2[x]
	return cipher_text

#This function decrypts the encrypted text
#and returns the original text
def originalText(cipher_text,key_new):
	or_txt=''
	i=0
	for letter in cipher_text:
		if letter==' ':
			or_txt+=' '
		else:
			x=(dict1[letter]-dict1[key_new[i]]+26)%26
			i+=1
			or_txt+=dict2[x]
	return or_txt

def main():
	message='THE GERMAN ATTACK'
	key='SECRET'
	key_new=generate_key(message,key)
	cipher_text=cipherText(message,key_new)
	original_text=originalText(cipher_text,key_new)
	print("Encrypted Text = "+cipher_text)
	print("Original Text = "+original_text)

#Executes the main function
if __name__ == '__main__':
	main()