Lab 2 Custom Encryption function

Lab2
Objectives
• Write Python functions for implementing and testing a particular feature, such as
encrypting userid and passwords, in this particular case
• Write Python code for a custom encryption technique
• Learn how to use this feature in a (close-to) real-world application
Outcomes
• You will be incrementally better at using functions in Python
• You will develop a module that can be leveraged for your final project
In this lab, we will develop a customized encryption technique to encrypt any given text, userIDs
and passwords, in this particular case.
Note: Please setup some way of running iPython notebooks (.ipynb) on your computer (this can
be done using an ipynb IDE like Jupyter/Anaconda, Google Colab, or a Jupyter/ipynb plugin for
VSCode, Intellij, PyCharm, etc.)
Task 1: Custom Encryption function
In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext
using an algorithm, called a cipher. In an iPython notebook cell, write a function
customEncrypt to convert plain text string into a ciphertext, encoded using your
customized encryption technique, as described below (helper functions are allowed):
Inputs (please read Task 2 for information regarding valid and invalid inputs):
o string inputText: text to be encrypted
o NOTE: inputText can contain any ASCII printable characters, with the exception of
“space” (ASCII code 32) and “!” (ASCII code 33)
o Int N: number of positions to shift characters in the inputText by
o NOTE: N has to be >= 1
o Int D = direction of shift
o NOTE: +1 shift right, -1 shift left, any other values are invalid
Outputs:
o String encryptedText: encrypted version of inputText
The algorithm for this technique will follow these steps:
1. Reverse the input text
2. Shift all the ASCII characters in reversed input text by “N” positions.
• In other words, each letter in the reversed text string is replaced by a letter N
positions down the ASCII printable characters list cyclically.
• The direction of shift is also taken into consideration here
• For example, if the inputs are N=3 and D=1(shift right), then then 'A' is replaced
by 'D', 'B' by 'E', 'C' by 'F', ..., 'X' by '[', ..., 'Z' by ']'
• On the other hand, if the inputs are N=3 and D=-1(shift left), then then 'D' is
replaced by 'A', 'E' by 'B', 'F' by 'C', ..., '[' by 'X', ..., ']' by 'Z'
Other rules:
1. “space” and “!” are not encrypted. This means that when encrypting, your modulo should
start at 34, that way the cipher text does not contain “!” or “space”. Please see the table
of ASCII printable characters below:
 Example:
If reversed text string is TEST, N=2, and D=1, the encrypted text is VGUV
Task 2: Test Customer Encryption Code function
In a new iPython notebook cell, write a function called testCustomEncrypt to test the func
tion written in Task 1. The program shall:
• Prompt user for an input text string, which can contain any ASCII printable characters,
with the exception of “space” (ASCII code 32) and “!” (ASCII code 33)
• NOTE: You will prompt the user twice, once for a userID, and once for a password
• Prompt user for a value for N (N must be >=1)
• Prompt user for a value of D (D must be +1 or –1)
• NOTE: You must gracefully handle checking for valid inputs for the input text, N, and D.
o This can be done using try-catch statements, error codes, and re-prompting
users if there is an invalid input
• Call the customEncrypt function to convert the text to ciphertext using custom encryptio
n algorithm, and pass in the user inputs as parameters
• Print the returned ciphertext.
• In order to test if the customEncrypt function is written correctly, you now have to rever
se the process. Pass the ciphertext into the customEncrypt function (this time with a sa
me value of N, but with a different value of D), and see if you can get the function to ret
urn the original user input strings.
Example:
Testing Custom Encryption Algorithm
Enter UserID as text : asamant
Enter password as text : Temp123
Enter value of n: 3
Enter value of d: 1
encrypted userid: wqdpdvd
encrypted password: 654sphW
Original userid: asamant
Original passwd: Temp123
Task 3:
You have been provided a text file (database.txt) which contains encrypted versions of the useri
ds and passwords in the table below. Userid and password have been encrypted using the algor
ithm described above, with the values of N=3 and D=1. Think of the text file as a simple represe
ntation of the information stored in a database. Use the function that you have developed to an
swer the following questions.
Userid Password
asamant Temp123
aissa TheKing%^&
bjha $72messenger
skharel Life15$
Ally! God$12
Write your answers for the following into the Python notebook in a new Markdown (md) cell:
1. Which of the userid and password combination(s) in the table above are present in the d
atabase?
2. Which userid(s) is/are present in the database, but the password does not match the pa
ssword(s) in the table above?
3. Which userid(s) do/does not meet the requirements of a userid?
What to Submit
Upload these deliverables to Canvas.
Deliverables:
1. iPython Notebook file <Lab2-utid.ipynb> with two functions customEncrypt and
testCustomEncrypt and answers to Task 3 questions in a Markdown (md) cell.
Rubric
Task Points
Task 1 3
Task 2 2
Task 3 3