Question

Using Python;

Caesar part of the homework: Write c_encrypt() and c_decrypt(), both of which take two arguments, the first one a string and the second one an integer key.

Both should return a string.

Vigenère part of the homework: Write vig_encrypt() and vig_decrypt() functions. Each takes two strings as inputs, with the first being the plaintext/ciphertext, and the second being the key. Both should be calling functions you wrote earlier to help make the work easier.

The key will be a string consisting only of letters, but the letters might be in upper, lower, or mixed case. I

mportant: If the plaintext to be encrypted has non-alphabetic characters (e.g., spaces or punctuation):

• Leave the non-alphabetic character unchanged just as you did for Caesar Cipher.
• Do not advance in use of the key for non-alphabetic characters in the plaintext. So for vig_encrypt('Hi Mom!', 'LEMON'), the H is encrypted according to the L from the key, the i (after conversion to I) is encrypted according to the E in the key, and the M in the plaintext is encrypted according to the M in the key (rather than according to the O in the key).

You may not use the Python ord() or chr() functions

One check on your work: vig_encrypt('ATTACKATDAWN', 'LEMON') should return the string LXFOPVEFRNHR; another is that vig_encrypt('Hi Mom!', 'LEMON') should return the string SM YCZ!

Answer 1

Using these two lists we can encrypt without having to use ascii values of the characters:

lower_letters = ['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']
upper_letters = ['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']

Now, for ceaser encryption:

def c_encrypt(text,s):
lower_letters = ['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']
upper_letters = ['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']
  
result = ""
  
# Going through text one character at a time
for i in range(len(text)):
char = text[i]
  
# Encrypt uppercase characters
if (char.isupper()):
result += upper_letters[(s + upper_letters.index(char)) % 26]
  
# Encrypt lowercase characters
elif(char.islower()):
result += upper_letters[(s + lower_letters.index(char)) % 26]
  
# Does not encrypt if number or special character
else:
result += char
  
return result

Now, for ceaser decryption:

def c_decrypt(text,s):
lower_letters = ['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']
upper_letters = ['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']
  
result = ""
  
# Going through text one character at a time
for i in range(len(text)):
char = text[i]
  
# Decrypt uppercase characters
if (char.isupper()):
result += upper_letters[(upper_letters.index(char) - s) % 26]
  
# Decrypt lowercase characters
elif(char.islower()):
result += upper_letters[(lower_letters.index(char) - s) % 26]
  
# Does not decrypt if number or special character
else:
result += char
  
return result

For Vigenère encryption:

def vig_encrypt(text,key):
lower_letters = ['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']
upper_letters = ['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']
  
result = ""

#Making key as long as plaintext
key = list(key)
if len(text) == len(key):
return(key)
else:
for i in range(len(text) - len(key)):
key.append(key[i % len(key)])

#Key is assumed to be all upper case letters
#Keeping a seperate counter for key so that it only moves for alphabets
key_counter =0;

# Going through text one character at a time
for i in range(len(text)):
char = text[i]
  
# Encrypt uppercase characters
if (char.isupper()):
  
result += upper_letters[(upper_letters.index(char) + upper_letters.index(key[key_counter])) % 26]
key_counter+=1
  
# Encrypt lowercase characters
elif(char.islower()):
  
result += upper_letters[(lower_letters.index(char) + upper_letters.index(key[key_counter])) % 26]
key_counter+=1
  
# Does not encrypt if number or special character
else:
result += char
  
return result

Plain text Input: Hi Mom!

Key Input: LEMON

Output: SM YCZ!

For Vigenère Decryption:

def vig_decrypt(text,key):
lower_letters = ['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']
upper_letters = ['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']
  
result = ""

#Making key as long as text
key = list(key)
if len(text) == len(key):
return(key)
else:
for i in range(len(text) - len(key)):
key.append(key[i % len(key)])

#Key is assumed to be all upper case letters
#Keeping a seperate counter for key so that it only moves for alphabets
key_counter =0;

# Going through text one character at a time
for i in range(len(text)):
char = text[i]
  
# Decrypt uppercase characters
if (char.isupper()):
  
result += upper_letters[(upper_letters.index(char) - upper_letters.index(key[key_counter])) % 26]
key_counter+=1
  
# Decrypt lowercase characters
elif(char.islower()):
  
result += upper_letters[(lower_letters.index(char) - upper_letters.index(key[key_counter])) % 26]
key_counter+=1
  
# Does not decrypt if number or special character
else:
result += char
  
return result

ciphered text Input: SM YCZ!

Key Input: LEMON

Output: HI MOM!