Goal : Write a P ython program plaifair .py as follows: def playfair(key, plaint

ID: 3600751 • Letter: G

Question

Goal

Write

a P

ython program

plaifair

.py

as follows:

def

playfair(key, plaintext):

your code here

if __name__ == "__main__":

# your code here

The

conditional statement above

allows

the program

to be

ran

directly.

STEP

ompute

and print the encryption tab

Create

a 5x5 table as a list of lists

–

efine a function called

init

_table()

which

initializes the table

with stars

. This function does not return anything

–

Print out the table. The output should look like this:

* * * * *

–

Define a function called

table_has

(

letter

)

which checks if a

letter already exists in the table

. This function should return true

or false depending on

whether

the letter exists.

–

Define a function

clean_key(key)

which changes

the secret key

uppercase and replace I by J, then returns the clean key

–

Define a function

set_cell(letter)

whic

h sets a table cell to a

specific letter.

–

Define a function

create

_table(key)

populate

the encryp

tion

table given the secret key.

This function should:

nitialize the table

lean the secret key

Build

the table using the set_cell

()

and table_has

()

function

–

out the encryption table.

STEP

–

Encrypt

your

secret message

–

efine

a functio

find_letter(letter)

which

returns

the row and

column of the letter in the table.

efine a

function

encode_pair(a,

which takes

a pair of letters

a and b,

runs t

he encoding rules

and returns the encoded pair as

follows:

“AB

”

> “LF” (sample)

unction should print an error message if a equals b

and stop

program execution.

Suggested approach

ompute

a_row, a_col, b_row, b_col

using the find_letter

function

se an if

elif

else statement to compute a_new_row, a_new_col,

b_new_row

, b_new_col

based on the encryption rules

Optional: To make your code cleaner, y

ou may want to create

separate

encoding

functions for the 3 different

cases:

same

row

(

with

wrapping

)

, same column

(

with

wrapping

)

, and rectangle

–

efine a function

cleanup(plaintext)

which

return

the cleaned up

message as follows

Change

it to uppercase

Remove

spaces

Replaces J by I

Places a letter “X” between 2

consecutive repeating letters

follows:

> EXE

f the repeated

letter

happen to be an

“X”, insert the letter Q

in between as follows:

> XQX

If the length of the resulting text is an

add

number, add the

letter “Z”

at the end as follows:

..G

> ..GZ

If the last letter happens to be a “Z”

, add

the letter “Q” at the

end as follows:

..Z

> ..ZQ

ggested appro

ach

Note that fixing a problem may lead to an new

one

. E.g. insert

ing

“X” may lead to

plaintext with an odd

length. Therefore, you should

eate a while loop which will

repeatedly

call a function to

fix

issue

and return a

new

plaintext until no more issues are found.

STEP C

–

Encrypt your secret message

–

Define

a function

encrypt

(

plaintext

)

which encode

the message

plaintext

and

returns the cipher

text.

Make

sure

to insert a space

every 5 letters

in the resulting ciphertext

(e.g. KLDGD NXSLO CWGQH

KUINF ACWER)

–

Execute and print the ciphertext. The execution phase should:

Prompt for the secret key

Prints the secret key as

entered.

Prompt for the secret message (plaintext)

Prints the secret message as

entered.

Computes and p

rints the encrypted message (ciphertext)

Asks if

user

want

to encrypt another message

If “yes”, program goes back to step a

If “no”, program stops

ecution.

STEP D

–

Extra

Credit

Create a

function

decrypt

(key, ciphertext)

which takes two parameters,

the secret and the ciphertext and returns the plaintext.

THE SUBMISSION

Submit a playfair.txt

or py

file as follows:

Program should be structure as

described in this project.

ll functions

should have the same names as indicated above. T

hey

may be tested separately for partial credit in case your program

fails.

All functions have a comment above them explaining their purpose.

Submission should be free

from debugging code or test code.

TESTIN

G YOUR CODE

–

Not to include with you

submission

Create a Python program called test_playfair.py in and place it in the

same directory as your main program. The code should import your

encryption code and then

run some tests as follows:

import playfair

def

test(key, plain, expected):

cipher = playfair.playfair(key, plain)

cipher != expected:

print("%s : %s != %s" % (plain, cipher, expected))

# execute test:

test(“mysecretkey”, “this is my secret message”,

“WQIUW QOKSG ADAJH

AOIQU WIQUW”

)

Explanation / Answer

import re class PlayfairError(Exception): def __init__(self, message): print message class Playfair: # omissionRule determines which omission rule you want to use (go figure). See the list at the beginning of the constructor # doublePadding determines what letter you would like to use to pad a digraph that is double letters # endPadding determines what letter you would like to use to pad the end of an input containing an odd number of letters def __init__(self, omissionRule = 0, doublePadding = 'X', endPadding = 'X'): omissionRules = [ 'Merge J into I', 'Omit Q', 'Merge I into J', ] if omissionRule >= 0 and omissionRule

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Goal : Write a P ython program plaifair .py as follows: def playfair(key, plaint

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