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
Advantages and disadvantages of elearning, Advantages and Disadvantages of...
Advantages and Disadvantages of ELearning: Before we discuss about advantages and disadvantages of elearning, you should know that elearning is just another model for learn
File organization, File Organization There are three types of fi...
File Organization There are three types of file organization used in practice. Let us consider the example of a dictionary. The dictionary contains listing of English wo
Explain data transfer and arithmetic operations, Question 1 Convert the fo...
Question 1 Convert the following binary numbers to decimal 101110 1110101 110110 101010 110010 Question 2 Explain CPU module and types of transfers betwe
Software engineering, how will a poorly conducted feasibility study affect ...
how will a poorly conducted feasibility study affect an implemented system
Optical fibres, Optical Fibres: Coaxial cables have limitations such a...
Optical Fibres: Coaxial cables have limitations such as broadband transmission medium which can be overcome by the use of optical fibres. Optical fibres carry light waves (rep
Embedded operating systems, Embedded Operating Systems, Devices have EOS bu...
Embedded Operating Systems, Devices have EOS builtin, OPERATING SYSTEM embed on the System itself, Cell phones, PDAs, medical equipment Fast, Application specific Stable a
Output devices, Output Devices: Each output unit of computer system tr...
Output Devices: Each output unit of computer system transmits information from the CPU and converts the electrical pulses to an appropriate output form. A printer, for example
E learning processes, E Learning Processes: Since, any elearning pr...
E Learning Processes: Since, any elearning project checks your achievements against a learning outcome, therefore, it starts with identification and verification process. Th
Logic instructions , They are used to act upon logic operations on the oper...
They are used to act upon logic operations on the operators. AND OR, NEG NOT TEST XOR AND INSTRUCTION Function: It acts upon the conjunction of the operators bit by bit. Syntax: A
Operating system (o.s), Operating System (O.S) An operating syst...
Operating System (O.S) An operating system is the complete set of programs written to utilize the computer resources in an optimal manner. The operating system supervise
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