CSE 539 - Applied Cryptography – HW 3 (2009)

Due – April 27^th, 2009, Start of class – 3:30 pm

Method - Print out (Hand written documents will not be accepted, do not e-mail the solutions to TA unless you have no other viable option)

Place your name and e-mail on the document.

1. This question is with reference to hierarchical digital certificates:

Consider Bob, a student at ASU. He works at two places on campus. He works 10 hours as a TA at College of Education, and the other 10 hours at WP Carey School of Business. Construct one digital certificate issued to him, where

1. ASU is the ROOT providing certificates to all Colleges.
2. Every College provides a certificate to its workers. This means:

i. College of Education provides a certificate to its workers.

ii. WP Carey School of business provides a certificate to its workers

Bob should be able to use the same certificate to log in at work at College of Education, and WP Carey School of business.

2. We need to split a document between Alice, Bob and Carol such that
1. Alice and Bob can recreate it
2. Bob and Carol can recreate it
3. Alice and Carol cannot recreate it
3. What is meant by Digital Cash, Explain the problems associated with it.
4. Compare Symmetric Key vs Asymmetric Key Cryptography. Why do we need to use a key of the order of 1000 bits or more in Asymmetric Key Schemes, when an order of 100 bits suffices in Symmetric Key Schemes.
5. Current credit cards use a magnetic layer that transmits all information stored on the card. Build an asymmetric key based response scheme for credit cards. Is the card feasible in the current state of the art? If so, show how it is feasible, and if not, what hardware changes would be required to achieve this? What possible flaws in the current scheme have you mitigated, and what flaws, if any, are still present?