Homework
#2

CMSC 414 Section 0201

Due before the beginning of class Feb. 17, 2003.

CMSC 414 Section 0201

Due before the beginning of class Feb. 17, 2003.

- (15 pts) (page 241, #4) Prove that the DES key consisting of all 0-bits and the DES key consisting of all 1-bits are both weak keys.
- (15 pts) (page 243, #19 and #20) Is the identity function a good
cryptographic checksum? Why or why not? Is the sum program a good
cryptographic checksum? Why or why not?

- (20 pts) (page 243, #17) The section on public key cryptosystems discussed nonrepudiation of origin in the context of public key cryptosystems. Consider a secret key system (in which a shared key is used). Bob has a message that he claims came from Alice, and to prove it he shows both the cleartext message and the ciphertext message. The ciphertext corresponds to the plaintext enciphered under the secret key that Alice and Bob share. Explain why this does NOT satisfy the requirements of nonrepudiation of origin. How might you modify a classical cryptosystem to provide nonrepudiation.
- (50 pts) Implement the Vigenere cipher using the J2ME
environment. Your program should accept a key, and then plaintext as
typed on the keypad. The program should then display the resultant
ciphertext. The TA will send an email to the class explaining
submission instructions.