Question

WE ARE USING PYTHON TO COMPLETE THIS ASSIGNMENT :) THANK YOU!

In this programming assignment, you will write functions to encrypt and decrypt messages using simple substitution ciphers. Your solution MUST include:

• a function called encode that takes two parameters:
  • key, a 26-character long string that identifies the ciphertext mapping for each letter of the alphabet, in order;
  • plaintext, a string of unspecified length that represents the message to be encoded.

  encode will return a string representing the ciphertext.

• a function called decode that takes two parameters:
  • key, a 26-character long string that identifies the ciphertext mapping for each letter of the alphabet, in order;
  • ciphertext, a string of unspecified length that represents the message to be decoded.

  decode will return a string representing the plaintext.

Copy and paste the following statements into your file as the first two statements of your main program. These lines represent Python lists of messages for you to encode and decode to test the functions you write.

    plaintextMessages = [
        ["This is the plaintext message.",
         "bcdefghijklmnopqrstuvwxyza"],
        ["Let the Wookiee win!",
         "epqomxuagrdwkhnftjizlcbvys"],
        ["Baseball is 90% mental. The other half is physical.\n\t\t- Yogi Berra",
         "hnftjizlcbvysepqomxuagrdwk"],
        ["I used to think I was indecisive, but now I'm not too sure.",
         "mqncdaigyhkxflujzervptobws"],
        ["Einstein's equation 'e = mc squared' shows that mass and\n\t\tenergy are interchangeable.",
         "bludcmhojaifxrkzenpsgqtywv"] ]

    codedMessages = [
        ["Uijt jt uif dpefe nfttbhf.",
         "bcdefghijklmnopqrstuvwxyza"],
        ["Qnhxgomhqm gi 10% bnjd eho 90% omwlignh. - Zghe Xmy",
         "epqomxuagrdwkhnftjizlcbvys"],
        ["Ulj njxu htgcfj C'gj jgjm mjfjcgjt cx, 'Ep pej jyxj veprx rlhu\n\t\t uljw'mj tpcez jculjm'. - Mcfvw Zjmghcx",
         "hnftjizlcbvysepqomxuagrdwk"],
        ["M 2-wdme uxc yr kylc ua xykd m qxdlcde, qpv wup cul'v gmtd mlw\n\t\t vuj aue yv. - Hdeew Rdyladxc",
         "mqncdaigyhkxflujzervptobws"] ]

You may alter the spacing or indentation of the two lines to conform to the rest of your code, but you are not allowed to change the strings or structure of the lists.

plaintextMessages is a list consisting of five items. Each item is a list of two strings corresponding to a plaintext message and a key. For each of these five items, you should:

• print the plaintext message.
• encode the message and print the ciphertext.
• decode the ciphertext message you just calculated and print the plaintext message again. The purpose of this is to demonstrate that your encode and decode functions work properly as inverses of each other.

If you have done this correctly, the output from your program for the first data item should look like the following:

plaintext:   This is the plaintext message.
encoded:     Uijt jt uif qmbjoufyu nfttbhf.
re-decoded:  This is the plaintext message.

Then print a blank line to separate this block of three lines from the next block.

codedMessages is a list consisting of four items. Each item is a list of two strings corresponding to a ciphertext message and a key. For each of these four items, you should:

• print the ciphertext message.
• decode the message and print the ciphertext.

If you have done this correctly, the output from your program for the first data item should look like the following:

encoded:  Uijt jt uif dpefe nfttbhf.
decoded:  

Then print a blank line to separate this block of two lines from the next block.

Special notes:

• Encrypted and decrypted lower-case letters should map to lower-case letters, as defined by the key.
• Encrypted and decrypted upper-case letters should map to upper-case letters. Note that upper-case letters do not appear in the key! (Look at the first character in the expected output shown above: the upper-case "T" maps to an upper-case "U" in the encoded message.) Your program must detect when an upper-case letter appears in the data, and figure out how to convert it to the correct upper-case letter based on the corresponding lower-case letters in the key.
• Non-alphabetic characters, such as numbers, spaces, tabs, punctuation, etc. should not be changed by either encode() or decode().

Answer 1

def encode( key, message):
# Create the running alphabet string
alphabetlist = "abcdefghijklmnopqrstuvwxyz"

# Create an empty string where the encoded message is to be stored.
encmessage = ""
# We walk through each character of the message and find its index in the alphabetlist string.
# If it is not present in that, it will return -1 and we copy the character as it is to the
# encoded message. While finding the index we convert it to lower case because the key and alphabetlist
# are lower case. We use python string find method to find the index.
for ch in message:
idx = alphabetlist.find(ch.lower())
# Once index is found, we will fetch the character at the same index from the key string. This is
# the encoded character and check if it was uppercase or lowercase before and convert the case correctly
# and add it to the encoded message.
if idx != -1:
if ch.isupper():
encmessage = encmessage + key[idx].upper()
else:
encmessage = encmessage + key[idx]
# This is the case where the character is a non alphabet and we add it as it is
else:
encmessage = encmessage + ch

return encmessage

def decode( key, message):
# Create the running alphabet string
alphabetlist = "abcdefghijklmnopqrstuvwxyz"

# Create an empty string where the decoded message is to be stored.
decmessage = ""
# We walk through each character of the message and find its index in the key string since it is already encoded.
# If it is not present in that, it will return -1 and we copy the character as it is to the
# encoded message. While finding the index we convert it to lower case because the key and alphabetlist
# are lower case. We use python string find method to find the index.
for ch in message:
idx = key.find(ch.lower())
# Once index is found, we will fetch the character at the same index from the alphabet string to find the decoded character. This is
# the decoded character and check if it was uppercase or lowercase before and convert the case correctly
# and add it to the decoded message.
if idx != -1:
if ch.isupper():
decmessage = decmessage + alphabetlist[idx].upper()
else:
decmessage = decmessage + alphabetlist[idx]
# This is the case where the character is a non alphabet and we add it as it is
else:
decmessage = decmessage + ch

return decmessage

plaintextMessages = [
["This is the plaintext message.",
"bcdefghijklmnopqrstuvwxyza"],
["Let the Wookiee win!",
"epqomxuagrdwkhnftjizlcbvys"],
["Baseball is 90% mental. The other half is physical.\n\t\t- Yogi Berra",
"hnftjizlcbvysepqomxuagrdwk"],
["I used to think I was indecisive, but now I'm not too sure.",
"mqncdaigyhkxflujzervptobws"],
["Einstein's equation 'e = mc squared' shows that mass and\n\t\tenergy are interchangeable.",
"bludcmhojaifxrkzenpsgqtywv"] ]

codedMessages = [
["Uijt jt uif dpefe nfttbhf.",
"bcdefghijklmnopqrstuvwxyza"],
["Qnhxgomhqm gi 10% bnjd eho 90% omwlignh. - Zghe Xmy",
"epqomxuagrdwkhnftjizlcbvys"],
["Ulj njxu htgcfj C'gj jgjm mjfjcgjt cx, 'Ep pej jyxj veprx rlhu\n\t\t uljw'mj tpcez jculjm'. - Mcfvw Zjmghcx",
"hnftjizlcbvysepqomxuagrdwk"],
["M 2-wdme uxc yr kylc ua xykd m qxdlcde, qpv wup cul'v gmtd mlw\n\t\t vuj aue yv. - Hdeew Rdyladxc",
"mqncdaigyhkxflujzervptobws"] ]

# We loop through the plaintext message call the encode and decode functions and print message accordingly
# We use python string formatting to achieve the desired output.
for msg in plaintextMessages:
print("plaintext: {}".format(msg[0]))
encmessage = encode(msg[1],msg[0])
print("encoded: {}".format(encmessage))
decmessage = decode(msg[1],encmessage)
print("re-decoded: {}".format(decmessage))
print("")

for msg in codedMessages:
print("encoded: {}".format(msg[0]))
decmessage = decode(msg[1],msg[0])
print("decoded: {}".format(decmessage))
print("")

Since the program was long attached the split screenshots and output.