Daniel Hillier Text Encryption Wildern School
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Unit 1
Practical Programming
Python
Text Encryption
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Daniel Hillier Text Encryption Wildern School
Design Solution
The Problem
The problem is a program for text encryption, we are to create a program that will
allow the user to ‘encrypt a message’, ‘decrypt a message’ or ‘exit the program’. If
the user decides to encrypt a message then it will display a message asking the
user to input the file name containing the message to be encrypted, this file will then
be encrypted but in a sperate file that contains the encrypted message. If the user
decides to decrypt the file then a message will be displayed asking the user to input
the name of the file containing the message that the user wants to decrypt.
User Needs
User Menu



Encrypt
Decrypt
Exit
-To be able to encrypt a message.
-To be able to decrypt a message.
-To be able to exit the program.
-To be able to enter a file name that will load the contents of a specified file to be
encrypted or decrypted (sample.txt).
-To be able to enter the new text file name so the user will be able to see the
finished encryption or decryption in an empty file.
-To be able to enter an 8 character key, previously generated by the program.
-To be able to see the encrypted or decrypted message.
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Daniel Hillier Text Encryption Wildern School
Plan Overview
I will produce/develop a piece of code that will encrypt/decrypt messages. To start of
I will create a menu to allows the user to navigate around the program to encrypt or
decrypt messages using if, elif and else. If and when the user selects to encrypt a
message they will be asked to enter a new file name (sample.txt) the program will
then read the contents of the file ‘sample.txt’ to be encrypted. Next I will create the
part of the program that will generate an eight character key that the program will
use to encrypt the message this will generate several different random keys (A, B,
C, -,}, *, etc.) That will then encrypt the message e.g. “Hello” to “A6B89K,]”. Also I
will create the part of the program that will covert each character (A, a, B, b, etc.)
into its ASCII code. The user will be asked to enter the name of the text file that they
want to be decrypted (sample.txt). The solution will then reads the contents of the
specified file that will be decrypted. The programme will then use the eight character
key that was entered by the user and use it to decrypt the encrypted message
located in the sample.txt file. It will then display the decrypted message to the user
on screen.
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Flowchart
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Daniel Hillier Text Encryption Wildern School
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Solution Development
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Programming Techniques
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Daniel Hillier Text Encryption Wildern School
Code
Evidence
Explanation
Print
The ‘print’ function will allow the
programme to display text to the user.
Int
The ‘int’ statement is a data type,
usually associated with whole
numbers.
If
The ‘if’ statement is a follow up from
the input function and is a traditional
control flow construct. Also known as
‘clean-up code’ it controls what will
happen when the user inputs there
answer.
Import
The ‘import’ statement combines two
operations; it searches for the named
module, then it binds the results of
that search to a name in the local
scope.
Range
The ‘range’ function is a versatile
function it sets a range for the amount
of random generations there will be.
Input
The ‘input’ function allows the user to
input text/numbers to answer a
question or navigate around the
program if the input is not valid, a
‘Syntax Error’ will appear (It does not
catch user errors!).
The ‘chr’ function converts a whole
number to its ASCII equivalent.
Chr()
Ord()
The ‘ord’ function converts a letter to
its decimal equivalent.
In
The ‘in’ statement is combined with the
range function and sets a particular
target for the random generation.
For
The ‘for’ statement which repeats a
group of statements a specified
number of times. You can use any
object (such as strings, arrays, lists,
tuples, dict and so on) in a for loop
in Python.
The ‘from’ function calls a function
form a particular module.
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From
Daniel Hillier Text Encryption Wildern School
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Code
From/Import
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Partnership
Daniel Hillier Text Encryption Wildern School
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Design of Solution (9 marks)
The problem - 2
User Needs / Success Criteria - 2
Overview Plan - 3
Psuedo Code / Flowchart - 4
Solution Development (Python Program) (9 marks)
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Daniel Hillier Text Encryption Wildern School
Comparison of Solution Against User Needs/ Success Criteria
Solution screenshots with text explaining which Task it addresses
(ensure code is #commented fully to achieve higher marks)
Programming Techniques (36 marks)
Check Mr Knight's blog for the list of headings
Testing & Evaluation (9 marks)
Test Table to test the success criteria
Show at least one re-test
How well does it meet user need?
What else could you have done to improve the program?
Could you have worked harder on this task?
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