Question

Write two methods: encrypt and decrypt. encrypt should #take as input a string, and return an encrypted version #of it according to the rules above. # #To encrypt the string, you would: # # - Convert the string to uppercase. # - Replace all Js with Is. # - Remove all non-letter characters. # - Add an X to the end if the length if odd. # - Break the string into character pairs. # - Replace the second letter of any same-character # pair with X (e.g. LL -> LX). # - Encrypt it. # #decrypt should, in turn, take as input a string and #return the unencrypted version, just undoing the last #step. You don't need to worry about Js and Is, duplicate #letters, or odd numbers of characters in decrypt. # #For example: # # encrypt("PS. Hello, world") -> "QLGRQTVZIBTYQZ" # decrypt("QLGRQTVZIBTYQZ") -> "PSHELXOWORLDSX" # #HINT: You might find it easier if you implement some #helper functions, like a find_letter function that #returns the row and column of a letter in the cipher.

Answer 1

The code is given below with appropriate comments

Step-by-step explanation:

CIPHER = (("D", "A", "V", "I", "O"),

("Y", "N", "E", "R", "B"),

("C", "F", "G", "H", "K"),

("L", "M", "P", "Q", "S"),

("T", "U", "W", "X", "Z"))

# Add your code here!

def encrypt(plaintext):

theList = []

for char in plaintext:

if char.isalpha():

char = char.upper()

if char == "J":

char = "I"

theList.append(char)

if len(theList) % 2 == 1:

theList.append("X")

for i in range(0, len(theList), 2):

if theList[i] == theList[i + 1]:

theList[i + 1] = "X"

findex = [-1, -1]

sindex = [-1, -1]

for j in range(len(CIPHER)):

for k in range(len(CIPHER)):

if theList[i] == CIPHER[j][k]:

findex = [j, k]

if theList[i + 1] == CIPHER[j][k]:

sindex = [j, k]

# same row

if (findex[0] == sindex[0]):

findex[1] += 1

sindex[1] += 1

if findex[1] == 5:

findex[1] = 0

if sindex[1] == 5:

sindex[1] = 0

theList[i] = CIPHER[findex[0]][findex[1]]

theList[i + 1] = CIPHER[sindex[0]][sindex[1]]

# same column

elif (findex[1] == sindex[1]):

findex[0] += 1

sindex[0] += 1

if findex[0] == 5:

findex[0] = 0

if sindex[0] == 5:

sindex[0] = 0

theList[i] = CIPHER[findex[0]][findex[1]]

theList[i + 1] = CIPHER[sindex[0]][sindex[1]]

else:

theList[i] = CIPHER[findex[0]][sindex[1]]

theList[i + 1] = CIPHER[sindex[0]][findex[1]]

return "".join(theList)

def decrypt(ciphertext):

theString = ""

findex = [-1, -1]

sindex = [-1, -1]

for i in range(0, len(ciphertext), 2):

for j in range(len(CIPHER)):

for k in range(len(CIPHER)):

if ciphertext[i] == CIPHER[j][k]:

findex = [j, k]

if ciphertext[i + 1] == CIPHER[j][k]:

sindex = [j, k]

if (findex[0] == sindex[0]):

findex[1] -= 1

sindex[1] -= 1

if findex[1] == -1:

findex[1] = 4

if sindex[1] == -1:

sindex[1] = 4

theString += CIPHER[findex[0]][findex[1]]

theString += CIPHER[sindex[0]][sindex[1]]

# same column

elif (findex[1] == sindex[1]):

findex[0] -= 1

sindex[0] -= 1

if findex[0] == -1:

findex[0] = 4

if sindex[0] == -1:

sindex[0] = 4

theString += CIPHER[findex[0]][findex[1]]

theString += CIPHER[sindex[0]][sindex[1]]

else:

theString += CIPHER[findex[0]][sindex[1]]

theString += CIPHER[sindex[0]][findex[1]]

return theString

# Below are some lines of code that will test your function.

# You can change the value of the variable(s) to test your

# function with different inputs.

#

# If your function works correctly, this will originally

# print: QLGRQTVZIBTYQZ, then PSHELXOWORLDSX

print(encrypt("PS. Hello, worlds"))

print(decrypt("QLGRQTVZIBTYQZ"))