#this program will encrypt and decrypt
#the message using Caesar cipher

#encryptedLetter=(originalLetter+3)%26
#originalLetter=(encryptedLetter-3)%26

#we will assume that ORIGINAL message (PLAINTEXT) 
#consits of upper case letters only
#we will assume that CIPHERTEXT
#consits of lower case letter only

#your program must have a choice
#1 - encryption
#2 - decryption

A_ASCII=65
a_ASCII=97
SHIFT = 3
ALPHABET = 26
def encrypt(plaintext):
	ciphertext=""
	for i in range(len(plaintext)):
		numeric=ord(plaintext[i])-A_ASCII
		encrNum=(numeric + SHIFT)% ALPHABET + a_ASCII
		ciphertext=ciphertext+chr(encrNum)
	
	return ciphertext

def decrypt(ciphertext):
	plaintext=""
	for i in range(len(ciphertext)):
		numeric=ord(ciphertext[i])-a_ASCII
		decrNum=(numeric-SHIFT)%ALPHABET + A_ASCII
		plaintext += chr(decrNum)
	return plaintext
def menu(choice):
	if (choice==1):
		plain=input("enter plaintext ")
		if(plain.isupper()):
			print("ciphertext is ")
			print(encrypt(plain))
		else:
			print("error ")
	elif(choice == 2):
		cipher=input("enter ciphertext ")
		if(cipher.islower()):
			print("plaintext is ")
			print(decrypt(cipher))
		else:
                        print("error ")

	else:
		print("invalid choice ")
def main():
	my_list=['ALICE', 'BOB', 'YANA', 'BONY']
	encr_list=[]
	for i in my_list:
		encr_list.append(encrypt(i))
	print(encr_list)
	
	#choice=int(input("enter 1 to encrypt 2 to decrypt "))
	#menu(choice)

main()