Tel-Aviv University

School of Computer Science

Introduction to Modern Cryptography

0368.3049

Fall Semester 2009/2010

# News

### Exercise 4 is back

*Come to collect it from Rani (if you care).*

Feedback is always appreciated, right? so take back your HW#4 (and HW#3, if you hadn't already taken it).

Don't worry, we will maintain the conservative approximation of 100 to HW#4 grade when calculating the total HW grade (even though you may have a bit less…)

(02 Mar 2010 16:48)

### Moed A

*If you plan on Moed B, better solve Moed A first!*

Here is Moed A.

I also sent an email with sketch of solutions, but you'd better try to solve the exam on your own first.

(02 Feb 2010 12:40)

### Mistake in Q3, HW #4

*Forgot to divide by |X|.*

You'd better prove that $Pr\left(X_i^j \textrm{ is new}\right) > e^{-ijt/|X|$; this will make the next step more plausible.

Thanks to Yossi for pointing this out.

(17 Jan 2010 21:13)

### Sample exams

*Here are three past exams you could use while preparing for the exam.*

We don't have a whole lot of examples, but here are exams from the past years.

(15 Jan 2010 17:06)

### A clarification about Assignment 3

*Problem 1: more than one round is needed.*

It might not be clear from Problem 1 itself, but Prudence is not required to recover $p$ in a single shot;

if, for example, in a single attempt she can rule out 10% of the remaining passwords in the dictionary, then with $\log_{10/9}(2^{30}) \approx 200$ attempts she can single out the correct password.

(27 Dec 2009 10:24)

### Due date of assignment #3

*Postponed.*

We decided you could use another week, so you may submit assignment 3 until December 30th.

(20 Dec 2009 10:07)

### Assignment 2, problem 3

Please note that when you are asked to find collisions wrt a hash function H, namely

two mssgs m1,m2 s.t. H(m1)=H(m2), these messages can be of **different lengths**.

(28 Nov 2009 16:43)

### Change of Deadline, Assignment 1

All problems except problem 3 (the substitution cipher questions) are due on Wed., Nov. 11, 6:20 pm, Israel time.

Problem 3 is due on Sunday, Nov. 15, 5 pm, Israel time.

In both cases, the destination is Rani Hod’s mailbox (second floor, Schreiber building).

(08 Nov 2009 21:30)