Olivia Dolan
4512 Text Encryption
Wildern School
AQA COMPUTER SCIENCE
4512/1 Practical Programing
Scenario 4
Olivia Dolan
3457
58243
Design of Solution- 2
Solution Development- 4
Programming Techniques- 7
Testing Techniques- 8
Evaluation- 9
1
Olivia Dolan
4512 Text Encryption
Wildern School
Design of Solution
I will create a program that includes a randomly generated key to encrypt the contents of a file. My
program will allow the person using it to decrypt the cipher text of the encrypted file if the right key
is correct. Encryption is a way to talk secretly without anyone knowing what you’re saying without
the key.
User Needs- Task 1




Develop a main menu
Encrypt message
Decrypt message
Exit the program
Task 2



Develop a program that reads the contents of a text file to be encrypted
Ask the user to enter the name of the file containing the message to be encrypted
Load the contents of the specified file
Task 3
Develop the part of the program that generates an eight character key the program will use to
encrypt the message
To generate an eight character key the program should:
a. Generate a random integer between 33 and 126
b. Convert the random number into its equivalent ASCII character ( for example the number 65
would be converted into the character ‘A’)
c. Repeat steps a and b eight times to generate an eight character key
d. Display the eight character key to the user
Task 4






Convert each of the eight characters into its ASCII code
Add numbers together
Divide results by 8
Round down to whole number
Subtract 32
Offset factor calculated
Task 5
Develop the part of the program that converts each character in the message in to its ASCII code and
encrypts it using the following rules:
a. If the character is a space then do not encrypt the character
b. Otherwise:
i.
ii.
2
Convert the character into its ASCII code (eg B=66)
Add the ASCII code to the offset factor calculated in Task 4. If the result is greater than 126
then subtract 94 so that the result is a valid ASCII code
Olivia Dolan
4512 Text Encryption
Wildern School
iii.
Convert the result into its equivalent ASCII character.
Flowchart for task 2
Flowchart for task 1
This is my
flow chart
showing
the process
for the
start of my
program.
Flowchart for task 3
This is my
flowchart
for the 2nd
part of my
program
that I will
write.
This is my
flowchart
for the 3rd
part of my
program.
Flowchart for task 5
Start
Convert the character
into its ASCII code
Flowchart for task 4
This is my
flowchart
for the 4th
part of my
program.
3
Add the ASCII code to the offset
factor calculated in Task 4. If the
result is greater than 126 then
subtract 94 so that the result is a
valid ASCII code
Convert the
result into its
equivalent ASCII
character.
This is my
flowchart
for the 5th
part of my
program.
Olivia Dolan
4512 Text Encryption
Wildern School
Solution Development
This is my main program and my outcomes
This is a screen shot of my python program
for 1&2.
4
Olivia Dolan
4512 Text Encryption
Wildern School
Programing Techniques
Technique used Explanation
Print() The print function in python is a
function that outputs to your
console window whatever you say
you want to print out.
If The ‘If’ function is a function that
processes the option you have
chosen on the main menu.
Choice The choice statement is the
function that gives the program
user several options to pick from.
Int/input The Input function saves what the
program user inputs and uses it.
Else This else option is if you pick
anything else like the ‘if’
statement.
While While repeats a section of the
program and allows 2 things to
happen at the same time.
Or The ‘or’ function allows there to
be more than one of the options.
Elif The elif function is a comination of
the the ‘If’ and else statement and
used in between the 2.
Import The import function is where
something that can be added onto
a program something that is
already in the program this means
you don’t have to rewrite it.
Exit The exit function allows you to
leave that section of the code.
5
Justification of
technique used
Robustness &
efficiency
Olivia Dolan
4512 Text Encryption
Wildern School
False False part of the program
Import os.path This function will use this to check
if file path is present.
Import random Will use this to help generate
random numbers.
def readafile(filename): Reads a file.
If If file is a certain filename.
os.path.isfile(filename):
File=open(filename, Open and then read the chosen
“r”) file.
Task 4
For Specifying part of program and
looping the program
Ord()
Int() Changing it into a whole number
Print()
6
Olivia Dolan
4512 Text Encryption
Wildern School
Programing Techniques
Task 1 and 2 run
7
Olivia Dolan
4512 Text Encryption
Wildern School
Testing Techniques
8
Test No
Description
Test data
1
Press option 1
on the main
menu
If choice ==1:
print (“you
have chosen
option1”)
2
Press option 2
on the main
menu
If choice ==2:
Print(“you
have chosen
option2”)
3
Press option 3
on the main
menu
If choice ==3:
print (“you
have chosen
option3”)
Expected
outcome
This should be
printed on
screen if you
select ‘option
1’ (“You have
chosen
option1”)
This should be
printed on the
screen if you
select ‘option
2’ (“ you have
chosen
option2”)
This should be
printed on the
screen if you
select ‘option
3’ (“ you have
chosen
option3”)
Actual
outcome
(“you have
chosen
option1”) was
printed on
screen
Further
action?
No, works
correctly
(“you have
No, works
chosen
correctly
option2”) was
printed on the
screen
(“you have
No, works
chosen
correctly
option3”) was
printed on the
screen
Olivia Dolan
4512 Text Encryption
Wildern School
Evaluation
Task number
User needs
Did I meet this
need
How was this
need met?
1
Develop a main menu
Encrypt message
Decrypt message
Exit the program
yes
I have an option
for each of the
user needs on
the menu
How could this
need be better
met?
Could have been
more colourful
and more
decretive
2
Develop a program that reads the contents
of a text file to be encrypted
Ask the user to enter the name of the file
containing the message to be encrypted
Load the contents of the specified file
yes
I have made a
code that allows
users to type in
their name
Could have
included
background
music
3
Generate a random integer between 33 and
126
Convert the random number into its
equivalent ASCII character ( for example the
number 65 would be converted into the
character ‘A’)
Repeat steps a and b eight times to
generate an eight character key
Display the eight character key to the user
yes
I have included
code that
generates a
random numbers
for encryption
N/A
4
Convert each of the eight characters into its
ASCII code
Add numbers together
Divide results by 8
Round down to whole number
Subtract 32
Offset factor calculated
yes
I have programed
a part that
generates a code
for encryption
N/A
9
5
Olivia Dolan
4512 Text Encryption
Wildern School
If the character is a space then do not
encrypt the character
Otherwise:
Convert the character into its ASCII code (eg
B=66)
Add the ASCII code to the offset factor
calculated in Task 4. If the result is greater
than 126 then subtract 94 so that the result
is a valid ASCII code
Convert the result into its equivalent ASCII
character.
10
yes
These user needs
make sure if
there are any
problems then
they are solved
by the program
N/A