1. A and B each has their own private keys and public keys B obtain a financial transaction request m generated by someone claims to be A. The encryption is unbreakable and the keys are not compromised.

2. A and B each has their own private keys and public keys B obtain a financial transaction request m generated by someone claims to be A. The encryption is unbreakable and the keys are not compromised.

If the request is encrypted with As public key

Can B be certain that the request is generated by A?

Later user A sues B and claims that he/she did not make the request. Can B prove to count that A is lying?

If the request is encrypted with Bs public key.

Can B be certain that the request is generated by A?

Later user A sues B and claims that he/she did not make the request. Can B prove to count that A is lying?

If the request is encrypted with As secret key.

Can B be certain that the request is generated by A?

Later user A sues B and claims that he/she did not make the request. Can B prove to count that A is lying?

3.

Alice owns public key and private key , Bob owns public key and private key . Alice needs to authenticate Bob.

What key(s) of Bobs should Alice know?

Alice picks a random challenge 78532 and sends it to Bob.

What does she expect Bob to send back? Show the detail formula

4. A message digest is defined for messages that are 50 bits or longer.

H(m) = (left shift m by 7 bits) % 548798433

Is this a strong message digest? If yes, explain. If not, give two values m that produce the same hash.