CODEWITHSUNDEEP
pythonpython-3.xencryptioncaesar-cipher
Tom E.
Tom E.

Reputation: 25

Checking for symbols and upper/lower-case for encrypting with ceasar cipher?

I tried for several hours to make a simple ceasar cipher encryption programm. It finally works. But it is only able to encrypt text without spaces and symbols. I have no idea how to implement a checking part for these things into the code. Critics for making the code cleaner and DRY are appreciated. Thx.

The Code where i tried to implement the functionality:

#Taking Input String + converting to list
message = input("Enter the message for encrypting: ")
message_list = list(message)

#Taking Input Cipher
cipher = int(input("Enter shifting value (1-26): "))

#Alphabet
alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]

#Defining variable
encrypted_message = []

#Shifting
for letter in message_list:
    if letter not in alphabet:
        encrypted_message.append(letter)
    else:
        #Getting Index of the letter in alphabet
        letter_position = alphabet.index(letter)
        #Getting the shifting value for the letter
        shifting_value = letter_position + cipher
        #Getting the shifted letter
        shifted_letter = alphabet[shifting_value]
        #Adding the corresponding letter to the encrypted message
        encrypted_message.append(shifted_letter)

#Output
print("Original Message: " + message)
print("Encrypted Message: " + str(encrypted_message))
print("Cipher: " + str(cipher))

What it should do: Encrypt the Message with spaces and symbols(ceasar cipher),

What it is doing: Exception has occurred: IndexError list index out of range

Upvotes: 2

Views: 237

Answers (2)

Chrismon Chin
Chrismon Chin

Reputation: 429

Here is a arguably cleaner method taking into account the comments given.

#Taking Input String + converting to list
message = input("Enter the message for encrypting: ")
message_list = list(message)

#Taking Input Cipher
cipher = int(input("Enter shifting value (1-26): "))

#Defining variable
encrypted_message = ''

#Shifting
for letter in message_list:
    code_point = ord(letter)
    if code_point > ord('z') or code_point < ord('a') :
        encrypted_message += letter
    else:
        #Getting Index of the letter in alphabet
        letter_position = code_point - ord('a')
        #Getting the shifting value for the letter
        shifting_value = (letter_position + cipher) % 26
        #Getting the shifted letter
        shifted_letter = chr(ord('a') + shifting_value)
        #Adding the corresponding letter to the encrypted message
        encrypted_message += shifted_letter

#Output
print("Original Message: " + message)
print("Encrypted Message: " + str(encrypted_message))
print("Cipher: " + str(cipher))

Of course can replace ord('a') and ord('z') with their respective values so that it does not have to calculate it, but it is good for understanding.

Python 2.7 replace input with raw_input

Working version of the original:

#Taking Input String + converting to list
message = input("Enter the message for encrypting: ")
message_list = list(message)

#Taking Input Cipher
cipher = int(input("Enter shifting value (1-26): "))

#Alphabet
alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]

#Defining variable
encrypted_message = ''

#Shifting
for letter in message_list:
    if letter not in alphabet:
        encrypted_message += letter
    else:
        #Getting Index of the letter in alphabet
        letter_position = alphabet.index(letter)
        #Getting the shifting value for the letter
        shifting_value = (letter_position + cipher) % 26
        #Getting the shifted letter
        shifted_letter = alphabet[shifting_value]
        #Adding the corresponding letter to the encrypted message
        encrypted_message += shifted_letter

#Output
print("Original Message: " + message)
print("Encrypted Message: " + str(encrypted_message))
print("Cipher: " + str(cipher))

Upvotes: 1

kelalaka
kelalaka

Reputation: 5636

IndexError list index out of range error occurs since you forgot the modulus. Without the modulus, 

shifting_value = letter_position + cipher

this line will have higher values then the array you are indexing. Remember, Ceasar cipher is

c = p + 3 mod 26

so the line must be

shifting_value = (letter_position + cipher) % 26

  • Note 1 : cipher is not a good variable name here. It should be shiftAmount.

  • Note 2: If you want to combine the list into string, use

    str1 = ''.join(encrypted_message)

Upvotes: 2

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