CMPSCI 177  Computer Security
Fall 2011
Fourth Homework  DES and Public Key
Due: Tuesday, 25 OCT 11
2:00pm
Part I: DES
1. Consider the following 64 bit key:
1000110110001011101101001010100111101011001010011011001011001100
What is the value of the key used for the fourth round of the DES encryption algorithm?
2. Consider the following 48 bit string:
101101010110011010110000010101011001101111011011
If this string is input to the s boxes in the DES encryption algorithm, what string is output from the s boxes?
Part II: Public Key
1. What is the totient of 36? Defend your answer.
2. Use the superincreasing sequence S=[2,4,9,17,34,69,146], modulus n=311, and multiplier w=19 to gen
erate a public key sequence H for MerkleHellman.
3. Assume that you received the ciphertext C=101 from someone using the public key generated in exer
cise 2.
You are to decipher C and determine the message M that was used to generate C.
4. Alice has chosen primes p=2357 and q=2551 and exponent e=3674911 to use with the RSA algorithm.
What does Alice publish as her public key?
5. Suppose Alice receives the following message from Bob, who used the public key from exercise 4 to
encrypt it: 3650502.
Determine the plaintext that Alice obtains from this ciphertext.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '09
 Kemm
 Cryptography, key management

Click to edit the document details