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EC312 Six Week Exam Spring 2018 February 15th, 2018
United States Na val Academy Electrical and Computer Engineering Department
EC312 - 6 Week Midterm - Spring 2018
1. Do a page check: you should have 6 pages including this cover sheet. 2. You have 50 minutes to complete this exam. 3. An FE-approved calculator may be used for this exam. Calculators may not be shared. 4. This is a closed book and closed notes exam. You may use one single-sided hand-written page of notes. 5. Turn in your single-sided hand-written page of notes with your exam. 6. This exam may be given as a makeup exam to several midshipmen at a later time. No communication is
permitted concerning this exam with anyone who has not yet taken the exam.
Name:
Instructor:
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EC312 Six Week Exam Spring 2018 February 15th, 2018
Question 1. a) (4 pts) For the given circuit fill in the truth table where 0 is OV and 1 is 5V.
A B Out -sv
0 0 I
0 \ ()
I 0 0
I ( 0
A
b) (2 pts) Determine the logic function the circuit performs. Logic function: ~0(2.-
-~~-----
Question 2. For the logic circuit shown below: a) (6 pts) Complete the truth table.
A w
B
c
A 0 0 0 0 1 1 1
y I
B c 0 0 o. 1 1 0 1 1 0 0 0 1 1 0 I I
b) (4 pts) Determine the Boolean expression for the output Zin terms of A, B & C.
w x y z I l 0 1 I I 0 \
' \ b \
' l \ 0 ~ 0 n I
t> 0 0 I
0 \ 0 \ 0 I I ()
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EC312 Six Week Exam Spring 2018 February 15th, 2018
Question 3. a) (3 pts) What is the danger with the following code snippet? int x=5 ; int array[ SJ={ 1,2,3,4,5}; array[7]=1 O;
o. \lo ~h.J .S fX'UL h_,. 5 e~b c...V\J
\(ov l,vr •~ h,
b) (3 pts) What feature of C allows this to happen?
t.~r--0\-1- f!, .:i? y(.)u.. l.oJJ ()..J<..>V-v.>r ."-k :g;,,,. ... ~Jt11!.i.J c..Lc_,
(_ ~u no.\- vu)-.,_{ ~.., ...... Jc.,..;~s, Question 4. (10 pts) What will be the output of this program when it is compiled and run?
#include <stdio .. h> int main ()
0 I Z 5 '-/ S int counter [ 10 ] = { 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 } ; int i;
for ( i = 5 ; i >= O; i =i- 2) {
if (i >l) printf( " %d\n", counter[i]) ;
else printf( " Go Navy\n " ) ;
. }
Question 5. (a) (8 pts) Fill in the blanks
The setuid flag allows other users to execute a program with the same permissions as
Sudo allows a user to act as 1 o ~ r for one command. ------
Write out the exact gdb command you would use to look at four bytes of memory iq hexadecimal starting at the address which esp points to: 2< / L-4 '/. b 4 ~f or x/xL.J f e...y
The Cq, ~ command displays the contents of a file but does not enable editing the file .
(b) (6 pts) If midshipman is part of group mids and class, what permissions does midshipman have
on the follkwinj file? - rwxr - x -- 1 coordinator instructo r 542 2018 - 01-24 02 :4 3 grader .. exe
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EC312 Six Week Exam Spring 2018 February 15th, 2018
Question 6. Consider the C program below. The program is run up to a breakpoint on line 9. 1 #include<stdio.h> 2 #include<string.h> 3 int getinfo() 4 5 6 7 8 9
int number=O; printf("\nEnter your company number " ) ; scanf ( " %d", number) ; return number;
10 int main () 11 12 13 14 15 16 17 18 19 20 21
int x =27 ; char name[20]="USNA"; int company=30 ; int i ;
printf ("%s ", name); printf (" \nEnter your name : "); scanf ("%s" , name) ; getinfo();
(a) (3 pts) How much memory in bytes, must the compiler set aside for the main function assuming no
padding? Lf + -z_o 4- y + lf, -=- 3 1 b1.;w I
7' n4~ (¥1'\f<~ .1
(b) (8 pts) Fill out this sketch of the stack at this point in program execution, including each item's name and size.
t--~~~~~~~~~....,..,..,r+-~~~~---;
esp_ main points here
~~~~~~~~~~~~~~~~~
ebp _main points here
( c) (3 pts) When the user enters their name what is the maximum number of characters they can enter in the variable name without overwriting any other variable? Explain.
' 1
(d) (5 pts) Which variable(s) are not vulnerable to being overwritten by buffer overflow? Explain . •
0.\,\_v"'\.W 1 1 /
(_oM p~" ! Page 4 of 6
EC312 Six Week Exam Spring 2018 February XX, 2018
Continued from the code on the previous page, you compile the program and running gdb you get the following
screen:
(e) (6 pts) How big is the stack the compiler created? 17 3
b ~+ ~ ~ ,2 t g- l b
- b ~~~-\:(c.O ' 5 ~ 0
+ q-
jYfblfu j (f) (6 pts) Which memory location stores company? (This should be a hexadecimal number)
7 /(. Z"j
30 ~7 I e e_ b F - roo b Pt f= ~ g,n; 10 f(o
~01/ J C11.,
(g) (4 pts) What is the next assembly instructi o e executed?
L \f'-? O <{ ()LI '6 5 b 2 - ) \Y\cV U~RD
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EC312 Six Week Exam Spring 2018 February XX, 2018
Qu~<,tion 7. ( un..,tlkr the C program bclo\\ .
line 15.
\ s..,umc no padding. The progrnm j.., run up lo a hn:al,point 1111
\cl d IT..,S \ a luc l)eq: npt11111
-'11.P<'s:..u1c . h>
r. ... -~·-'- :r~r...:i . . 1 lJ\BI I I I 8%
nr r 1-:11 ... 1 J ( :!.r. .... :--:=2S l ; ChBI I I 1· 898 -t &'
char nam '. '~; " [J~Nl\ " ; I"
'Odr 'f"' I ;d:.• ; lhBI I 11 89<>
ll\131 I I HilJ \ ") ..
I I.
f ' ' ... .... f' J • II f (l\BI I I I l\ll( l I! < ( ,. ..J
4 ,.. II .· fl\ 131 I I I 8 <l I) ;xr ') ~
tl\lll I I I 81!1
tal r8 pl J \\ hm 1.., th\.' output nfthc print!'. tatL'l11C111 \)Jl
line I Y.' Shu\\ :111\ ''nrh. in the Value column . lh.ll l I I I ~NI
)Y ,,..
/rJ
u lh.HI 11 I 8 \fl / /1
()\ B I I r· r 8 \ I 01 )) I' ---
( b) t 6 ph l \\ hat i · the output o !'the pri ntf. talcment on 0' line J.r.1
, .. ,plain tl\1311 I I 8 \3
L VJ 11,ll l I I I 8 \ ·
+ l l l\ r l r t 1> I O\.l~I I I I 8 \ "
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Qul'~tion 8. (::' pb I I ist and describe a technical uluti11n ag.1111'-l ii hunl.·r ti\ L'rllP\\ ~1ttack
I
t
Tu1·11 in) our l'lJLlalio11 -,hcl'I "ith .'o ur C\alll!
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