HW3 - F such that for all a,b { , 1 } , for all public key...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Homework 3 Due in Class Thursday, March 27 1 Number of Quadratic Residues Consider N = Q n i =1 p i , where each p i is a prime and for i 6 = j , p i 6 = p j . How many qudratic residues are there in Z ? N ? Why? 2 Non-Blum Integer as Modulus Can we use a modulus that is not a Blum integer in the Rabin cryptosystem? Can we use a modulus that is not a Blum integer in the Goldwasser-Micali cryptosystem? Why or why not? 3 (Optional) Malleability of Goldwasser-Micali Cryptosystem Show that there exist a non-constant function f : { 0 , 1 } × { 0 , 1 } → { 0 , 1 } and an efficient (probabilistic polynomial-time) algorithm
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: F such that for all a,b { , 1 } , for all public key K , if A and B are ciphertexts of a and b under public key K , respectively, then F ( A,B ) is a ciphertext of f ( a,b ) under public key K . 4 MAC based on Encryption We construct a MAC scheme based on a good block cipher E(). Suppose the block size is . For an -bit message m and an -bit MAC key k , the MAC is dened as the rst /n bits of E k ( m ), where n is a constant. Is the above MAC scheme secure? Why or why not? 1...
View Full Document

Ask a homework question - tutors are online