cryptography assignment

see attached

4
Section B
1. Assume that a client A and server B share a symmetric key K and have securely distributed
their public keys K+A and K+B. Suppose client A wants to send a message to server B
containing the name N, ID number, and a request R for Bob. Denote the message as C =
{N, ID, R}. Design the cryptographic messages that client must send to meet the security
requirements below:
(a) Using the symmetric key, design a message that enables server B to verify that the
message’s integrity has not been violated and that it is from client A. (2 Marks)
(b) Using the symmetric key, design a message that protects the confidentiality of the
request only and ensures that server B can verify the message’s integrity and source.
(2 Marks)
(c) Using public key cryptography, design a message that enables sever B to verify that
the message’s integrity has not been violated and that it is from client A.
(2 Marks)
(d) Using public key cryptography, design a message that protects the confidentiality of
the request only and ensures that server B can verify the message’s integrity and
source.
(2 Marks)
[Total: 8 Marks]
5
2. A painter comes up with a new business idea: He wants to offer custom painting from
photos. Both the photos and paintings will be transmitted in digital form via the Internet.
One concern that he has is discretion towards his customers, since potentially embarrassing
photos, e.g., nude photos, might be sent to him. Hence, the photo data should not be
accessible for third parties during transmission.
The painter needs multiple weeks for the creation of a painting, and hence he wants to
assure that he cannot be fooled by someone who sends in a photo assuming a false name.
He also wants to be assured that the painting will definitely be accepted by the customer
and that she cannot deny the order.
(a) Identify and explain THREE (3) necessary security services for the transmission of the
digitalized photos from the customers to the painter.
(3 Marks)
(b) Which cryptographic elements (e.g., symmetric/asymmetric encryption, digital
signature, and digital certificate) can be utilized to achieve the security services in part
(a)? Assume that several megabytes of data have to be transmitted for every photo.
(2 Marks)
(c) Data privacy is a main concern in this scenario. Does privacy always guarantee
integrity? How to uphold the integrity of data. Justify your answer.
(2 Marks)
[Total: 7 Marks]

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