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

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

View Full Document Right Arrow Icon
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
Background image of page 1
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 Die-Hellman cryptosystem? p, g, g a mod p, g b mod p . (c) What is the private key of the Die-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

Ask a homework question - tutors are online