Description
- Draft a program that scans an array to determine the first positive EVEN number in the array. If a positive value is found, the program should print “positive even number found” and the value. If no positive EVEN value is found in the array, the program should print “no positive even number found.” Submit list file and show the runs for the following data items:
- all negative even values
- all positive odd values
- mixed negative and positive values which are odd and even (two different examples with odd and even numbers at different indices)
a.
b.
c.Mix1
c.Mix2
- 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 three 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. What are the strengths and weaknesses of this encryption method? Can you think of another way doing such encryption? What are the strengths and weaknesses of your method?
Strengths: Hard to find out original text at one glance
Weaknesses: The length of cipher text is the same with original text, the original text can be guessed in long run. Using only one key will also increase the risk.
Other method: One time pad encryption
Strengths: Every key is one-time used, more secure.
Weakness: Cannot be decode if losing the key pad.
- Implement the following two pseudo-codes in assembly language (assume signed numbers). Declare Apple and Pear as word sized variables. Test the program for input data sets listed below and print values assigned to Apple and Pear. Submit list file and show output for all input data sets.
- if ( (cx = bx) AND (cx >= val1) )
Apple = 1;
Else
Apple = 0;
- if ( (bx = cx) OR (cx >= val1) )
Pear = 1;
Else
Pear = 0;
Input test data
| CX | BX | Val1 |
| 0 | 0 | 0 |
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
| 1 | 1 | 1 |
000
001
010
011
100
101
110
111
- Draw the stack (pencil-paper or wordàpdf) at different points of the main and subroutine to show your understanding of the call and return functions.
Main PROC
4040040 call FloatAdd 4040046 mov eax, ebx
…
…
FloatAdd PROC
4041020 Push ecx
4041024 Push ebx
4041028 mov eax, edx
…
…
404A030 Pop ebx
404A032 Pop ecx
404A034 ret
FloatAdd ENDP
| Before call to FloatAdd | ||
| OFFSET | ||
| ESP | ||
| 00000FF0 00000000 |
|
|||
| EIP = 04040040 | ||||
| After call to FloatAdd | ||||
| OFFSET | ||||
| ESP | ||||
| 00000FF0 00000000 | |
| EIP = 04041020 | |
After Push ecx
OFFSET
00001000
00000FFC 04040046
00000FF8 (ecx) ESP
00000FF4 00000000
00000FF0 00000000
After Push ebx
OFFSET
00001000
00000FFC 04040046
00000FF8 (ecx)
00000FF4 (ebx) ESP
00000FF0 00000000
After Pop ebx
OFFSET
00001000
00000FFC 04040046
00000FF8 (ecx) ESP
00000FF4 00000000
00000FF0 00000000
After Pop ecx
OFFSET
00001000 ESP
00000FFC 04040046
00000FF8 00000000
| 00000FF4 | 00000000 |
| 00000FF0 | 00000000 |
| After Re | turn | |
| OFFSET | ||
| ESP | ||
| 00000FF0 00000000 | |
| EIP = 04040046 | |
