# quiz9_sol - random numbers a b ∈ Z p-1 respectively and...

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

CIS 4360 Introduction to Computer Security QUIZ 9, Fall 2011 (5 minutes only) – with answers This quiz concerns cipher systems. 1. A cryptographic hash function h has the following properties: (a) h is a one way (or preimage resistant ) function. What does this mean? Given y it is hard to fnd x such that y = h ( x ) . Alternatively, Given y = h ( x ) it is hard to fnd x . (b) h is second preimage resistant . What does this mean? Given x it is hard to fnd x 0 6 = x such that h ( x ) = h ( x 0 ) . (c) h is collision resistant . What does this mean? It is hard to fnd x, x 0 , with x 6 = x 0 such that h ( x ) = h ( x 0 ) . Supppose that the lenght of the digest is 80 bits, and that it is hard to do 2 80 calculations. For such a hash function: (a) Is such a hash function second preimage resistant? TRUE or FALSE. TRUE (b) Is such a hash function collision resistant?. TRUE or FALSE. FALSE 2. The Di±e-Hellman key exchange is a Public Key Cryptosystem in which Alice and Bob each choose
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: random numbers a, b ∈ Z p-1 respectively, and then send each other g a mod p , g b mod p . (a) What is the secret key which is exchanged between Alice and Bob? g ab mod p . (b) What is the public key of the Di±e-Hellman cryptosystem? p, g, g a mod p, g b mod p . (c) What is the private key of the Di±e-Hellman cryptosystem? Either a (Alice uses this) or b (Bob uses this) . 3. The One-Time Pad. Encryption: • given a plaintext: 000000000 • and the key 011010101 • what is the ciphertext? 011010101 Decryption: • given a ciphertext: 011001101 • and the key 011010101 • recover the plaintext? 000011001 Mike Burmester...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online