caesarCipher.py

# Python program to implement Caesar cipher

'''This script uses dictionaries instead of 'chr()' & 'ord()' function'''

# Dictionary to lookup the index of alphabets
dict1 = {'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': 26}

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

# Function to encrypt the string according to the shift provided


def encrypt(message, shift):
    cipher = ''
    for letter in message:
        # checks for space
        if(letter != ' '):
            # looks up the dictionary and adds the shift to the index
            num = (dict1[letter] + shift) % 26
            # looks up the second dictionary for the
            # shifted alphabets and adds them
            cipher += dict2[num]
        else:
            # adds space
            cipher += ' '

    return cipher

# Function to decrypt the string according to the shift provided


def decrypt(message, shift):
    decipher = ''
    for letter in message:
        # checks for space
        if(letter != ' '):
            # looks up the dictionary and subtracts the shift to the index
            num = (dict1[letter] - shift + 26) % 26
            # looks up the second dictionary for the
            # shifted alphabets and adds them
            decipher += dict2[num]
        else:
            # adds space
            decipher += ' '

    return decipher


def main():
    message = 'ALICE KILLED BOB'
    shift = 13
    result = encrypt(message.upper(), shift)
    print(result)

    message = 'NYVPR XVYYRQ OBO'
    shift = 13
    result = decrypt(message, upper(), shift)
    print(result)


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