HW # 7: Theme: Conditionals, Booleans, Loops Solution

    1. Draft a program that scans an array to determine the first even integer in an array.  If a value is found, the program should print “even integer found” its value and index.  If no even integer is found, the program should print “no even integer found.” Submit the asm/list file and screenshots that shows the output of your code for the following example arrays:    
        a. Array has all odd integers

        b. Array has all even integers 

        c. Several arrays with a mix of odd and even integers positioned at different indices



    2. Write a program which encodes any string using the XOR instruction.  Test it using your <first name last name> in the data segment to produce cipher text and then decode using the program to get plain text.  Use the last two digits of your student id as the key.  Print plane text from the data segment, print the cipher text, and then print the plain text upon execution.  Submit the asm/list file and screenshots that shows the output of your code.


What are the strengths and weaknesses of this encryption method (25% of points, Typewritten answer required)?  
Some strengths of this encryption method is that it is easy to implement. Another strength is that it is difficult to break without the key. Some weakness of this encryption method are that you must have the key to decrypt the message. If you try and send the key then it can be intercepted, so you must determine the key beforehand and it is hard to change the key once chosen. Another weakness is that you can use character occurrence to guess which characters represent which decrypted characters, which would not take long with the right computer. Once you can decrypt one character then you can decrypt them all.

    3. Write a program that gets its input from two sensors.  If the values of the sensors differ by no more than +/- 5, print “Agree”, otherwise, print “Disagree.”  You can assume that the values are integers.  Additionally, if the values Agree and they are each more than 45, print “Take Action”. Submit asm/list file and show screenshots of robust testing for various inputs, including boundary conditions, in the closed interval (-90 … 90).  






    4. Draw the stack (word/pdf) before every instruction that is marked red is executed to show your understanding of the call and return functions.   Use N/A to represent unpredictable values.
     
    Main Proc
    4040018    mov ecx, 0000000Ch
    404001C    mov ebx, 0000000Bh
4040020     call FMul
4040026    mov eax, ebx
    …
    …        
Main EndP 

FMul  PROC
4041040    Push ecx
4041044    Push ebx
4041048    mov eax, edx
    …
    …
        404A060    Pop ebx
        404A062    Pop ecx
404A064    ret
FMul EndP



Before call FMul:
Offset:
0000 1000       N/A (ESP)
0000 0FFC      N/A
0000 0FF8       N/A
0000 0FF4       N/A
EIP: 0404 0020

Before push ecx:
Offset:
0000 1000       4040026 (ESP)
0000 0FFC      N/A
0000 0FF8       N/A
0000 0FF4       N/A 
EIP: 0404 1040

Before push ebx:
Offset:
0000 1000       04040026
0000 0FFC      0000000C (ESP)
0000 0FF8       N/A
0000 0FF4       N/A 
EIP: 0404 1044

Before mov eax, edx:
Offset:
0000 1000       04040026
0000 0FFC      0000000C
0000 0FF8       0000000B (ESP)
0000 0FF4       N/A 
EIP: 0404 1048

Before pop ebx:
Offset:
0000 1000       04040026
0000 0FFC      0000000C
0000 0FF8       0000000B (ESP)
0000 0FF4       N/A 
EIP: 0404 A060







Before pop ecx:
Offset:
0000 1000       04040026
0000 0FFC      0000000C (ESP)
0000 0FF8       0000000B 
0000 0FF4       N/A 
EIP: 0404 A062

Before ret:
Offset:
0000 1000       04040026 (ESP)
0000 0FFC      0000000C 
0000 0FF8       0000000B 
0000 0FF4       N/A 
EIP: 0404 A064

Before mov eax, ebx:
Offset:
0000 1000       04040026 (ESP)
0000 0FFC      0000000C 
0000 0FF8       0000000B 
0000 0FF4       N/A 
EIP: 0404 0026