Python programming please help!!!! (Python 3.5) Introduction to Problem Solving

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Python programming please help!!!! (Python 3.5)

Introduction to Problem Solving and Programming: Cipher Program

A cipher works by replacing the characters in some input. For example, we might swap each “a” with a “b”, each “b” with a “c”, and each “c” with a “d”. That means the word “cab” would be encrypted as “dbc”:

c => d

a => b

b => c

If we know the rules of a cipher, we can also go backwards to decrypt: d => c b => a c => b So, “dbc” becomes “cab”. In this assignment, you will write a program that uses a cipher to encode and decode secret messages. Cipher Rules Use the following cipher to encode and decode your messages:

Requirements

The program should start with a menu. It should ask the user whether they’d like to encode a message, decode a message, or exit. The next section contains sample output.

Limitations

Note that the cipher rules described above do not account for uppercase characters, numbers, or symbols in the user’s input.

In other words, if you were to encode the word “HELLO”, you’d get “HELLO” right back:

Welcome to the Secret Message Encoder/Decoder

1. Encode a message

2. Decode a message

3. Exit What would you like to do? 1

Enter a message to encode: HELLO Encoded message: HELLO

This is a limitation of the cipher we’re using. It’s not a problem that you need to account for in this assignment.

This is a sample output:

Cipher Rules Use the following cipher to encode and decode your messages: Input Replace with Input Replace with 0 % 4 5 m Hf

Explanation / Answer

Encryption formula:

E(x)=(x+n)mod26

Decryption:

D(x)=(x-n)mod26.

Sample code logic-

key = 'abcdefghijklmnopqrstuvwxyz'

def encrypt(n, plaintext):

    """Encrypt the string and return the ciphertext"""

    result = ''

    for l in plaintext.lower():

        try:

            i = (key.index(l) + n) % 26

            result += key[i]

        except ValueError:

            result += l

    return result.lower()

def decrypt(n, ciphertext):

    """Decrypt the string and return the plaintext"""

    result = ''

    for l in ciphertext:

        try:

            i = (key.index(l) - n) % 26

            result += key[i]

        except ValueError:

            result += l

    return result

def show_result(plaintext, n):

    """Generate a resulting cipher with elements shown"""

    encrypted = encrypt(n, plaintext)

    decrypted = decrypt(n, encrypted)

    print 'Rotation: %s' % n

    print 'Plaintext: %s' % plaintext

    print 'Encrytped: %s' % encrypted

    print 'Decrytped: %s' % decrypted

Sample logic for cipher-

import sys

def encrypt(k):

plaintext = raw_input('Enter plain text message: ')

cipher = ''

for each in plaintext:

c = (ord(each)+k) % 126

if c < 32:

c+=31

cipher += chr(c)

print 'Your encrypted message is: ' + cipher

def decrypt(k):

cipher = raw_input('Enter encrypted message: ')

plaintext = ''   

for each in cipher:

p = (ord(each)-k) % 126

if p < 32:

p+=95

plaintext += chr(p)

print 'Your plain text message is: ' + plaintext

def main(argv):

if (len(sys.argv) != 3):

sys.exit('Usage: ceaser.py <k> <mode>')

if sys.argv[2] == 'e':

encrypt(int(sys.argv[1]))

elif sys.argv[2] == 'd':

decrypt(int(sys.argv[1]))

else:

sys.exit('Error in mode type')

if __name__ == "__main__":

main(sys.argv[1:])

note-by using the above code logics with requied modifications the given question can be answered.

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