Reliable Channels are important to the resilience and security of communications systems. They rely on means to detect naturally occurring errors and in many cases they are also required to detect intentional modification. 

a) Parity is a simple means to detect data errors.

Both streams below represent the transmission of the same 7-bit ASCII data. Explain what type of parity has been used for each stream. Assuming the red parity bits are correct, are any errors detected in the transmissions? Explain your answers. [5 marks]

Stream1: 01000111 00011011 00011000 01000010

Stream2: 01000110 00011010 00011001

b) An Integrity Check Value (ICV) is a simple means to detect errors in messages with multiple bytes. The computed ICV is sent with the message and recomputed by the receiver as verification.

2. ICV error detection can result in false positives and false negatives, as well as true positives and true negatives. Explain in a simple table how this occurs. [4 marks]
4. Give and justify your opinions on whether an ICV is suitable to detect deliberate modification of transmissions that are sent in the clear, and transmissions that are stream-ciphered. [4 marks]

c) A Cryptographic Checksum requires the sender to demonstrate knowledge of a secret when constructing the checksum. The computed checksum is sent with the message and verified by the receiver.

2. What are the common names of the two different classes of cryptographic checksum? [2 marks]
4. Give a practical example of each class of cryptographic algorithm used to compute the cryptographic checksum. [2 marks]
6. Explain what is meant by the term "data origin authentication" and give an opinion on whether cryptographic checksums provide this, and if there is any difference between the two classes. [3 marks]