Desklib Study Material Library: Solved Assignments, Essays, Dissertations

This document contains solutions to various problems from different chapters of a book. It also includes calculations for password generation and expected time to guess a password. The document also discusses finer grained access control for large number of roles.

Contents
Chapter 2, Problem 2.7.c.......................................................................................................................3
1 - Chapter 3, Problem 3.2.....................................................................................................................3
2 - Chapter 3, Problem 3.3.....................................................................................................................4
2. A)......................................................................................................................................................4
2 B)........................................................................................................................................................5
3 - Chapter 3, Problem 3.5.....................................................................................................................5
3a).........................................................................................................................................................5
3b).........................................................................................................................................................6
Chapter 4, Problem 4.12........................................................................................................................6

Chapter 2, Problem 2.7.c
The given letter message = I leave thirty million dollars to my friendly cousin John
The letter message contains 48 letter and we have divide that letter for 4 X 4 matrix. So that
40 letter divide by 3 block and each block have 16 letters (4 x 4 matrix)
First 16 letter = I leave thirty mill
Round 1
The text arranged by row wise (4 x 4 matrix) and that text convert into number (a=0, b=1,
c=2, d=3 etc.)
I l e a
v e t h
i r t y
m i l l
8 11 4 0
21 4 19 7
8 17 19 24
12 8 11 11
Add the each column value and mod 26.
8 11 4 0
21 4 19 7
8 17 19 24
12 8 11 11
49 40 53 42
To calculate the module value

= 49 mod 26 = 23
= 40 mod 26 = 14
= 53 mod 26 = 1
= 42 mod 26 = 16
The running total is (23,14,1,16)
Round 2
Using round 1 matrix table and rotate the every column value. The first row value start from
second row value, the second row value start from third row value, the third row value start
from fourth row value and reverse the order for final row.
l e a I
t h v e
y i r t
l l i m
11 4 0 8
19 7 21 4
24 8 17 19
11 11 8 12
Again add the each column value.
11 4 0 8
19 7 21 4
24 8 17 19
11 11 8 12

65 30 46 43
Calculate the module value.
= 65 mod 26= 13
= 30 mod 26 =4
= 46 mod 26 =20
= 43 mod 26 =17
The running total is (4,13,17,20)
The message is “I leave thirty mill” and hash is “enru”
Second 16 letter = ion dollars to my fr
Round 1
The text arranged by row wise(4 x 4 matrix) and that text convert into
number(a=0,b=1,c=2,d=3 etc.,)
i o n d
o l l a
r s t o
m y f r
8 14 13 3
14 11 11 0
17 18 19 14
12 24 5 17
Add the each column value and mod 26.

8 14 13 3
14 11 11 0
17 18 19 14
12 24 5 17
51 67 48 34
To calculate the module value
= 51 mod 26 = 25
= 67 mod 26 = 15
= 48mod 26 = 22
= 34 mod 26 = 8
The running total is (25,15,22,8)
Round 2
Using round 1 matrix table and rotate the every column value. The first row value start from
second row value, The second row value start from third row value, the third row value start
from fourth row value and reverse the order for final row.
o n d i
l a o l
o r s t

r f y m
14 13 3 8
11 0 14 11
14 17 18 19
17 5 24 12
Again add the each column value.
14 13 3 8
11 0 14 11
14 17 18 19
17 5 24 12
56 35 59 50
Calculate the module value.
= 56 mod 26 =4
= 354 mod 26 =9
= 59 mod 26 =7
= 50 mod 26 =24
The running total is (4,7,9,24)
The message is “ion dollars to my fr” and hash is “ehjy”
Third 16 letter =iendly cousin John
Round 1

The text arranged by row wise(4 x 4 matrix) and that text convert into
number(a=0,b=1,c=2,d=3 etc.,)
i e n d
l y c o
u s i n
j o h n
8 4 13 3
11 24 2 14
20 18 8 13
9 14 7 13
Add the each column value and mod 26.
8 4 13 3
11 24 2 14
20 18 8 13
9 14 7 13
48 60 30 43
To calculate the module value
= 48 mod 26 = 22
= 60 mod 26 = 8
= 30mod 26 = 4
= 43 mod 26 = 17

The running total is (22,8,4,17)
Round 2
Using round 1 matrix table and rotate the every column value. The first row value start from
second row value, The second row value start from third row value, the third row value start
from fourth row value and reverse the order for final row.
e n d i
c o l y
n u s i
n h o j
4 13 3 8
2 14 11 24
13 20 18 8
13 7 14 9
Again add the each column value.
4 13 3 8
2 14 11 24
13 20 18 8
13 7 14 9
32 54 46 9
Calculate the module value.
= 32 mod 26 =6

= 54 mod 26 =2
= 46 mod 26 =20
= 49 mod 26 =23
The running total is (2,6,20,23)
The message is “iendly cousin John” and hash is “cgux”
The total letter message “I leave thirty million dollars to my friendly cousin John” and hash is
“enruehjycgux”
1 - Chapter 3, Problem 3.2
The password contains uppercase, lowercase or digits.
Total possible passwords = 628 (lowercase, uppercase and digit)
Uppercase letters passwords = 268 (Uppercase = A-Z)
Lowercase letters password = 268 (Lowercase = a-z)
Total alphabet letters password = 528 (Lowercase and uppercase = 26+26 =52)
Digit passwords = 108 (Numbers = 0-9)
= 268+268+108
Uppercase letters passwords
with special characters = 368
Lowercase letters password
with special characters = 368
Total alphabet letters password
with special characters = 528

= 368+368+528
We are using inclusion – exclusion principle
= 628 - [368+368+528] + [268+268+108]
= 159655911367680
2 - Chapter 3, Problem 3.3
The alphanumeric password means combination of letters and numerical. The alphabetical
like upper and lower case and digit are zero to more digits. So we have create the so many
passwords like
3463677
A578GVHJGH
Ad567Gjjkg
DGHAJ
Consider the 5 to 10 characters.52 possible letters (upper and lower case 26+26=52)
552+652+752+852+952+1052
Possible alphanumeric passwords
=10,041,837,000,000,000,000,088,928,256,128,832,568,808,656,600,600,440
2. A)
Consider the adversary that incorrect character does not get feedback.
The possibilities = 264

= 456976
Half possibilities for correct password = 456976/2
= 228488 attempts
Consider the one day hours = 60 x60 x24
= 86400 seconds
The attempts are equal to seconds.
228488 attempts = 228488 seconds
Calculate the number of days = 228488/86400
= 2.644 days
That days calculte to hours
2.644 days = 24 X 2.644
= 63.456 hrs
63.456 hrs = 63.5 hrs(approximately)
63.5 hrs is the expexted time to discover the correct password.
2 B)
Alphebetic character = 26
Expected tries for each digit = 26/2
= 13
Combination character = 4
Time = 13 X 4
= 52 seconds
52 seconds is the expected time to discover the coorrect password.

3 - Chapter 3, Problem 3.5
3a)
The password generated 3 segments randomly for each 9 letters.
The segment is CVN that means consonant, vowel and number
The vowels are a,e,i,o,u
Consonant = 21 (b,c,d,f,g,h,j,k,l,m,n,p,q,r,s,t,v,w,x,y,z)
N = single digit number (0-9)
C = 21
V = 5
N = 10
Three segments = CVNCVNCVN
The total password
Population = 21 x 5 x 10 x 21 x 5 x 10 x 21 x 5 x 10
= 1157625000
3b)
The probability of guessing password = 1/1157625000
=0.0000000008638376
Very low probability of an adversary guessing a password correctly.

Chapter 4, Problem 4.12
Role Permission
Adult (view,rating(m) =R))
Teenager (view,rating(m) =G))
Role Permissions Conditions
Adult (view,(Rating(m)=R ^
release(m)=new))
(view,(Rating(m)=R ^
release(m)=old))
(userType(u)=premium V
today € PromoDates)
Nil
Teenager (view,(Rating(m)=G ^
release(m)=new))
(view,(Rating(m)=G ^
release(m)=new))
(userType(u)=premium V
today € PromoDates)
nil
Finer grained access control
It is applicable for large number of roles. To check attributes associated with user and
environment by using conditions at permission level and that permission based on member of
a role.