Anna and Elsa Case Study - Engineering Assignment Help

Assignment Task:

By continuing beyond this point, you confirm that you have read the information and instructions  above, and understand the conditions of this examination. 

1.  

a) Anna and Elsa need to establish a shared secret key over an insecure  communication channel. Elsa tells Anna that she knows that a shared secret key  can be established using a key distribution centre (KDC), and she proposes the  following key management protocol, referred to as the Frozen Key Management  Protocol:  

i) Before initiating the protocol, Anna and Elsa are assumed to each share  a secret key with the KDC, respectively denoted KA and KE. Anna and Elsa  both have unique identifiers, IDA and IDE that are known to each other  and the KDC.  

ii) Anna contacts Elsa in plain and tells her that she would like them to  communicate confidentially. She send Elsa a message  rc||IDA||IDE||KA(rc, IDA , IDE) where rc denotes a random nonce and “||”  denotes the operation of concatenation.  

iii) Elsa sends two messages to the KDC, the first message is just forwarded  message from Anna, KA(rc, IDA, IDE), and the second is the confirmation  that Elsa also wants to communicate with Anna, KE(rE, rc, IDA, IDE), where  rE represents a fresh nonce generated by Elsa.  

iv) The KDC generates a fresh secret key for Anna and Elsa, KAE, and sends  the message rc||KA(KAE)||KE(rE,KAE) to Elsa.  

v) Elsa extracts the shared secret key, KAE, and forwards to Anna the part  intended for Anna, KA(KAE).  

vi) Upon extracting the key KAE, Anna starts sending confidential messages  to Elsa, KAE (”Hello”).  Draw a diagram of the Frozen Key Management Protocol. Critically analyse  some possible attacks against this protocol.  

b) In IEEE 802.11, open system authentication simply consists of two  communications. An authentication is requested by the client, which contains  the station ID (typically MAC address). This is followed by an authentication  response from the AP/router containing a success or failure message. Critically  discuss the benefits and security vulnerabilities of this authentication scheme. 

2.  

 a) What requirements should a digital signature scheme satisfy?  

 b) Anna and Elsa to use a hash function to guarantee data integrity in their  communications. The hash output is a 512-bits-long binary string. Given a  message m and its corresponding hash output h(m), what is the average  probability that an attacker Eve can find another message m’?m that has the  same hash output? In your computations, assume that the attacker makes 264 attempts.  

c) A generalization of Caesar cipher, known as the affine Caesar cipher has the  following form. For each plaintext p, substitute it with the ciphertext letter C:  

C=E([?,?],p)=(?p+?) mod 26;  

where ? and ? are two integers. A cipher text has been generated with this  affine cipher. It is known that the cipher letters “ed” correspond to plain letters  “if”. Decrypt the cipher letters “sgi”.  

3.  

a) With reference to the Access Control List, critically compare the first relevant entry rule  and the any permission rule.  

b) Explain the differences between an Access Control List and a Capability List.    

c) Re-write the list below to deny Eve access to File 2 without the need for a Group 2 to be  explicitly defined.  

Group1: Alice, Bob, Cynthia, David, Eve  

Group2: Alice, Bob, Cynthia, David  

File 1: Group1, RW  

File 2: Group2, RW  

4.  

a) Passwords are the most widely used means of authenticating human users to computer  networks. There are various rules on the use of passwords that can be applied to  mitigate the risk posed by dictionary attacks on passwords. Explain a dictionary attack  and describe two of the rules used to mitigate the risk from dictionary attacks applied in  the Brunel University London network.  

b) The National Cyber Security Centre (UK) recently advised against a regular change of  password. Discuss why a regular change of password may increase the risk posed by  dictionary attacks on passwords.  

5. The use of one-time passwords does not rule out the possibility that an attacker can  learn the password before the identification takes place. To get around this problem  challenge response identification systems are used.  

a) Briefly describe a Challenge Response Identification System.  

b) Design a Challenge Response Identification System for an online banking site and  comment on its limitations.  

c) The use of a random number generator is a design choice. Explain the limitations  of the use of random number generators.