Q1-2(Each 15 points) QII.1 Suppose we use key pair K1, K2 (public key and private key) for encryption and key pair K3, K4 (public key and private key) for the digital signature What are the advantages and disadvantages in the following cases A. K1 and K2 are the same as K3 and K4 B. K1 and K2 are different than K3 and K4 QII.2 Suppose your spy colleague wanted to send you messages that you could be sure came from him (and not an enemy trying to pretend to be him). Your colleague personally tells you: “Whenever I send you a message, the last thing in the message will be a number. That number will be a count of the number of letter E’s in the message. If you get a message, and the number at the end is NOT an accurate count of the number of letter E’s, then that message is from an imposter.” a. [2 pts] This number, put at the end of each message, is an example of what cryptographic item? b. [2 pts] Does it have the characteristic of being one-way i.e. can you deduce the original message? c. [4 pts] Is it collision resistant? Why? d. [7 pts] Can you suggest some other way to indicate that message is from the sender without resorting to encryption?

/in /by

Q1-2(Each 15 points)
QII.1 Suppose we use key pair K1, K2 (public key and private key) for encryption and key pair K3, K4 (public key and private key) for the digital signature
What are the advantages and disadvantages in the following cases
A. K1 and K2 are the same as K3 and K4
B. K1 and K2 are different than K3 and K4
QII.2 Suppose your spy colleague wanted to send you messages that you could be sure came from him (and not an enemy trying to pretend to be him). Your colleague personally tells you: “Whenever I send you a message, the last thing in the message will be a number. That number will be a count of the number of letter E’s in the message. If you get a message, and the number at the end is NOT an accurate count of the number of letter E’s, then that message is from an imposter.”
a. [2 pts] This number, put at the end of each message, is an example of what cryptographic item?
b. [2 pts] Does it have the characteristic of being one-way i.e. can you deduce the original message?
c. [4 pts] Is it collision resistant? Why?
d. [7 pts] Can you suggest some other way to indicate that message is from the sender without resorting to encryption?

Q1-2(Each 15 points) QII.1 Suppose we use key pair K1, K2 (public key and private key) for encryption and key pair K3, K4 (public key and private key) for the digital signature What are the advantages and disadvantages in the following cases A. K1 and K2 are the same as K3 and K4 B. K1 and K2 are different than K3 and K4 QII.2 Suppose your spy colleague wanted to send you messages that you could be sure came from him (and not an enemy trying to pretend to be him). Your colleague personally tells you: “Whenever I send you a message, the last thing in the message will be a number. That number will be a count of the number of letter E’s in the message. If you get a message, and the number at the end is NOT an accurate count of the number of letter E’s, then that message is from an imposter.” a. [2 pts] This number, put at the end of each message, is an example of what cryptographic item? b. [2 pts] Does it have the characteristic of being one-way i.e. can you deduce the original message? c. [4 pts] Is it collision resistant? Why? d. [7 pts] Can you suggest some other way to indicate that message is from the sender without resorting to encryption?

/in /by

Q1-2(Each 15 points)
QII.1 Suppose we use key pair K1, K2 (public key and private key) for encryption and key pair K3, K4 (public key and private key) for the digital signature
What are the advantages and disadvantages in the following cases
A. K1 and K2 are the same as K3 and K4
B. K1 and K2 are different than K3 and K4
QII.2 Suppose your spy colleague wanted to send you messages that you could be sure came from him (and not an enemy trying to pretend to be him). Your colleague personally tells you: “Whenever I send you a message, the last thing in the message will be a number. That number will be a count of the number of letter E’s in the message. If you get a message, and the number at the end is NOT an accurate count of the number of letter E’s, then that message is from an imposter.”
a. [2 pts] This number, put at the end of each message, is an example of what cryptographic item?
b. [2 pts] Does it have the characteristic of being one-way i.e. can you deduce the original message?
c. [4 pts] Is it collision resistant? Why?
d. [7 pts] Can you suggest some other way to indicate that message is from the sender without resorting to encryption?