Exam (elaborations)
TM256-23B Cyber Security TMA02
- Module
- TM256-23B (TM256)
- Institution
- The Open University (OU)
TM256-23B Cyber Security TMA02
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By: Rekah • 11 months ago
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TM256 TMA02TM256-23B
Cyber Security
TMA02
Page 1 of 10
, TM256 TMA02
Question 1 – 30 marks
Part 1 – 7 marks
The PGP Web of Trust - Activity 2.6
a. Ken has a score of 0 because he is not trusted by anyone in the web of trust. Nan has a score
of 2 because she is introduced by two trusted individuals (Liam and Sam). Each introduction adds
one point to the trust score.
b. If a new fully trusted individual, David, is introduced who introduces both Ken and Nan, their
scores would increase. Ken's score would become 1 (as he would be introduced by David), and
Nan's score would become 3 (as she would be introduced by David who has a score of 2). The
diagram would also change to reflect the new introductions and trust scores.
Part 2 – 13 marks
a.
i. A sends message R to B.
ii. B sends back an encrypted message {{M1}K, T1}K(B pr), where M1 is the plaintext message, T1
is a timestamp, K is a shared key, and B pr is B's private key.
iii. A sends an encrypted message {M2}K,{H(M2)}K(A pr), where M2 is the plaintext message, K is
the shared key, H is a cryptographic hash function, and A pr is A's private key.
b. The shared key may have been generated using a key exchange algorithm such as Diffie-
Hellman or RSA. These algorithms allow two parties to establish a shared secret key over an
insecure communication channel.
c. Alice realises the message is fraudulent because the timestamp T1 is three days old, indicating
that the message was intercepted and resent by Ian. This example demonstrates the concept of
message integrity, where the recipient can verify that the message has not been tampered with
by checking the integrity of its contents (using the hash function in this case) and any
accompanying metadata (such as the timestamp).
Part 3 – 10 marks
a. Insert Screenshot of completed Activity 2.15
b. There is no danger if the public key transfer is intercepted by an attacker because the public
key is only used for encryption and does not reveal any sensitive information. An attacker would
need access to the corresponding private key to decrypt any messages encrypted with the public
key.
c. It is no longer possible to log into the DVL machine from Kali using SSH and a password in
Step 23 because password authentication has been disabled in the SSH server configuration file.
d. It is still possible to log into the DVL machine from the Ubuntu machine in Step 24 because
public key authentication has been enabled and the Ubuntu machine has a copy of the
corresponding private key.
Page 2 of 10
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