Login

Create Account
Customer Service Chat
+14156709189
info@expertsmind.com
Submit Homework/Assignment
Get quote & make Payment
Get Solution
Cryptography, computer science, Basic Computer Science
Question 1
Consider the onetime pad encryption scheme to encrypt a 1bit message m,
and assume m is chosen with uniform distribution from message space M={0,1}.
Let E1 be the event "message m is = 1" and let E2 be the event
"ciphertext c is = 0". What is the probability that both event E1 and
event E2 happen?
Answer
a.0
b.0.5
c.0.25
d.1
Question 2
Consider the onetime pad encryption scheme to encrypt a 1bit message m,
and assume m is chosen with uniform distribution from message space M={0,1}.
For b=0,1, let E[b] be the event "message m is = b" and let F be the event
"ciphertext c is = 1". What is the probability that event F happens?
Answer
a.0
b.0.5
c.0.25
d.1
Question 3
Consider the onetime pad encryption scheme to encrypt a 1bit message m.
For b=0,1, let E[b] be the event "message m is = b", assume
prob(E[0])=p and prob(E[1])=1p, for some p in [0,1],
and let F be the event "ciphertext C is = 1".
What is the probability of event E[0] given that event F happens?
Use the Bayes theorem to find your answer.
Answer
a.1
b.0.5
c.1p
d.p
Question 4
Assume a meaningful plaintext is encrypted using the shift cipher.
How many encryption attempts are sufficient for an exhaustive (or bruteforce)
search attack to find the plaintext with probability at least 1/2?
Answer
a.1
b.2
c.13
d.26
Question 5
Assume a meaningful plaintext is encrypted using the monoalphabetic substitution cipher. How many encryption attempts are sufficient for an exhaustive (or bruteforce)
search attack to find the plaintext (with probability 1)?
Answer
a.1
b.2
c.26
d.26!
Question 6
Assume a meaningful plaintext is encrypted using the polyalphabetic substitution
cipher (with t random numbers in [0,26], for a known t).
How many encryption attempts are sufficient for an exhaustive (or bruteforce)
search attack to find the plaintext (with probability 1)?
Answer
a.1
b.t
c.26
d.26 to the tth power
Question 7
Which of these statements summarizes an equivalent form of the perfect secrecy notion?
Answer
a.The probability of the ciphertext conditioned by one plaintext is the same as the probability of the ciphertext conditioned by another plaintext
b. Knowledge of the plaintext does not affect the probability of the ciphertext
c.The probability that an adversary, after returning two plaintexts, guesses from a ciphertext c which of these two plaintexts was encrypted as c is 1/2
d.All of the above
Question 8
Which of these are valid properties of the one time pad?
Answer
a. satisfies perfect secrecy
b. the length of the key is equal to the length of the message
c.encryption and decryption are very efficient
d.all of the above
Question 9
Let L1, L2 be languages and let X,Y be either P or NP.
Consider the statement: if L1 is polynomialtime reducible to L2,
and L2 is in X, then L1 is in Y. Which of the following holds:
Answer
a.When X=P and Y=P, then the statement is true
b.When X=P and Y=NP, then the statement is true
c.When X=NP and Y=NP, then the statement is true
d. all of the above
Question 10
In an encryption scheme, let Enc denote the encryption algorithm,
Dec denote the decryption algorithm, and A denote the adversary''s algorithm.
Furthermore, let e(n), d(n), denote the running times of algorithms
Enc, Dec, respectively, and let
a(n) denote the minimum running time that an attacker takes to break any such scheme,
where n is the security parameter.
When designing this scheme following the principles
of modern cryptography, which of these relationships would you use to choose
your algorithms?
Answer
a. e(n),d(n),a(n)=O(n^c) for some constant c
b. e(n)=O(n^c) and d(n),a(n)=Omega(2^{cn}) for some constant c
c. e(n),d(n)=O(n^c) and a(n)=Omega(2^{cn}) for some constant c
d. e(n),d(n),a(n)=Omega(2^{cn}) for some constant c
Question 11
For which X,Y in {o, O, Theta, Omega, omega}, do the relationships (log n)^2 = X(n^{1/2}) and n^2 = Y(2^n) hold?
Answer
a.X=o, Y=o
b.X=O, Y=Theta
c.X=o, Y=Theta
d.X=Theta, Y=O
Question 12
For which X,Y in {o, O, Theta, Omega, omega}, do the relationships t(n)+t''(n) = X(max(t(n),t''(n)))
and t(n)+t''(n) = Y(min(t(n),t''(n))) hold for all t,t'' such that t(n),t''(n)>0 ?
Answer
a.X=Theta, Y=Theta
b.X=Theta, Y=Omega
c.X=Omega, Y=Theta
d.X=omega, Y=Theta
Question 13
Informally, BPP is the class of languages that can be decided by a probabilistic algorithm in polynomial time with an error probability of at most 1=3 on any instance. More formally, a language L is in BPP if there exists a probabilistic algorithm A (i.e., an algorithm that is allowed to use a polynomiallength string of random bits) that runs in polynomial time and satisfies the following: if x is in L then A(x) returns 1 with probability at least 2/3; if x is not in L then A(x) returns 1 with probability at most 1/3. By performing independent repetitions of algorithm A and taking the majority output, one can amplify the (2/3; 1/3) gap to (1  2^k; 2^k), which is extremely close to (1,0). BPP seems to well capture the class of problems that can be efficiently computed
by a computer today. It is known that P is in BPP, and while it is conjectured that P = BPP, this is actually unknown. It is also unknown whether BPP is in NP. Consider the following statements:
1) if L1 is polynomialtime reducible to L2, and L2 is in P, then L1 is in BPP;
2) if L1 is polynomialtime reducible to L2, and L2 is in BPP, then L1 is in NP.
They are, respectively:
Answer
a.true, unknown
b.unknown, unknown
c.unknown, false
d.true, false
Question 14
Assume you want to construct a publickey cryptosystem using the principles of modern cryptography, and you are
allowed to choose a language L such that your cryptosystem can be proved secure assuming that deciding L is
hard; from which of the following complexity classes would you pick L?
Answer
a.P
b.BPP
c.NP minus P
d.NP minus BPP
Question 15
Consider the one time pad encryption scheme to encrypt a 1bit message.
Replace the XOR operation with another operation X. For which X does the
resulting scheme satisfy perfect secrecy? (Recall: OR(a,b)=1 if and only if
at least one of a,b=1; AND(a,b)=1 if and only if both a,b=1;
NOT(a)=1 if and only if a=0.)
Answer
a.X = AND
b.X = OR
c.X = NOT(XOR)
d.none of the above
Posted Date: 2/13/2012 1:10:42 AM  Location : United States
Ask an Expert
Related Discussions:
Cryptography, computer science, Assignment Help, Ask Question on Cryptography, computer science, Get Answer, Expert's Help, Cryptography, computer science Discussions
Write discussion on Cryptography, computer science
Your posts are moderated
Write your message here..
Related Questions
Functions, each of the following functions has the form f(x ) = (ax+b) mod ...
each of the following functions has the form f(x ) = (ax+b) mod n. assume that each function has type N base n arrow N base n, so that we can think of f as a cipher for an alphabet
Assembly language, An example code on LDS
An example code on LDS
How should an ideal hospital software be? , How Should an Ideal Software be...
How Should an Ideal Software be? It should be easy to operate, with minimal training of nursing personnel. Should be reliable, and thoroughly tested in various nur
Information Systems Engineering, Global treps weighted scoring model
Global treps weighted scoring model
Arinc 429 data bus specifications, ARINC 429 DATA Bus SPECIFICATIONS: A...
ARINC 429 DATA Bus SPECIFICATIONS: ARINC 429 sets specifications for the transfer of digital data between aircraft electronic system components and is a "Oneway" communication
C++, how to use expressions in c++ program with examble
how to use expressions in c++ program with examble
Explanation of characteristics of computers, Problem 1. Briefly explain...
Problem 1. Briefly explain on the characteristics of computers Explanation of characteristics of computers 2. Write a note on Cache Memory Note on Cache Memor
Research and development , Research and Development All intellectual ...
Research and Development All intellectual activities consciously pursued and systematically completed generate useful information. Research (also Research and Development) is
C++, Write a C++ program that declares three integers and three strings. Th...
Write a C++ program that declares three integers and three strings. The program prompts the user for three characters and three integers and prints them all on one line.
Open source software, Open Source Software: Open Source Software (OSS)...
Open Source Software: Open Source Software (OSS) is software that comes with source code, and importantly also provides rights (typically reserved for copyright holders) to st
Assignment Help
Accounting Assignment Help
Economics Assignment Help
Finance Assignment Help
Statistics Assignment Help
Physics Assignment Help
Chemistry Assignment Help
Math Assignment Help
Biology Assignment Help
English Assignment Help
Management Assignment Help
Engineering Assignment Help
Programming Assignment Help
Computer Science Assignment Help
IT Courses and Help
ExpertsMind Services
Online Tutoring
Projects Assistance
Exam Preparation
Coursework Help
Programming Courses
Engineering Courses
Why Us ?
~Experienced Tutors
~24x7 hrs Support
~Plagiarism Free
~Quality of Work
~Time on Delivery
~Privacy of Work