SOLUTION: Computer Security | My Assignment Tutor

Computer Security Coursework, 2020/2021 Page 1School of Computing Module CoordinatorOther lecturersDr Benjamin Aziz Date Issued08 February 2021CodeM30606TitleComputer Security Schedule and Deliverables ItemValueFormatDeadlineLatedeadlineECFdeadlineItem 1 – courseworkreport, equivalent to3000 words, coveringall LOs50%A single .pdf file containing your answersto the coursework questions and yourexplanations of these answers (you mayuse the suggested answers template)2021-05-1423:00 [BST]YYYY-MMDD HH:MM Notes and Advice• The Extenuating Circumstances procedure is there to support you if you have had anycircumstances (problems) that have been serious or significant enough to prevent you fromattending, completing or submitting an assessment on time.• ASDAC are available to any students who disclose a disability or require additional supportfor their academic studies with a good set of resources on the ASDAC moodle site• The University takes plagiarism seriously. Please ensure you adhere to the plagiarismguidelines. and watch the video on Plagiarism• Any material included in your coursework should be fully cited and referenced in APA 7format. Detailed advice on referencing is available from the library .• Any material submitted that does not meet format or submission guidelines, or falls outside ofthe submission deadline could be subject to a cap on your overall result or disqualificationentirely.• If you need additional assistance, you can ask your personal tutor, student engagementofficer ana.baker@port.ac.uk , academic tutor xia.han@port.ac.uk or your lecturers.• If you are concerned about your mental well-being, please contact our Well-being service.Computer Security Coursework, 2020/2021 Page 2Coursework InstructionsPLEASE READ CAREFULLY THE FOLLOWING INSTRUCTIONSAnswer ALL of the following EIGHT questions. Each question carries its own mark and the totalcoursework mark is 100. The mark for each question and your coursework is calculated as follows:– If you choose the correct option among the multiple choices for a question, you will beawarded a mark “up to” the maximum of the mark allocated for that question. Yourawarded mark for the question will depend on the “explanation” you provide as to why youmade that (correct) choice. If you provide no explanation whatsoever, and you chose thecorrect answer, you will be awarded ONE mark only for that question– If you choose any of the wrong answers in a question, you may be awarded some marksdepending on how correct and relevant your explanation is– If you do not answer a question, you are awarded ZERO marks for that question– Always choose only one answer per question. If you choose more than one answer in asingle question, you will be awarded ZERO marks for that questionIn answering the eight questions, you may use up to 3000 words in total.Computer Security Coursework, 2020/2021 Page 3Question 1 (Marks: 15)Cryptographic Data ObjectsB has just received the following message, which represents a cryptographic data object: {({(KPbB)KPrS mod KPbS}K1,{|(NB, NA, {{({K2}KPbB, NS)}(G1)KPrA mod NA}K1, {|{({G3}(KPbA)KPrS mod KPbS, G2)}K1|}KPrB)|}KPrA)}KBS The following explains various terms in this object and some of the abbreviations used:• {M}K represents the encryption of some message/data M using the key K• {|M|}K represents the digital signing of some message/data M using the key K• NX represents a nonce (i.e. a fresh and possibly random number used once only) generatedby X• KpbX represents the public part of the key pair presumably owned by X• KprX represents the private part of the key pair presumably owned by X• KAB represents a symmetric key shared between A and B• K (or K1, K2, K3 etc.) represents some arbitrary key with no assumptions about its scope• M represents some alphanumeric/textual message with no assumptions• G1, G2, G3 etc. are prime numberswhich of the following sets of keys, nonces, numbers, and alphanumeric/textual messages “best”represents B’s knowledge, after B applies any number of possible cryptographic operations to theobject above, and assuming that B already has access to key K1 and the public key of any agent:a) KBS , G2 , KPrBb) {(KPbB)KPrS mod KPbS , G2 , KBS , KPrB , {(KPbB)KPrS mod KPbS}K1, NA , NBc) NA , NBd) NA , NB , KBS , KPrBe) {(KPbB)KPrS mod KPbS}K1 , {|(NB, NA, {{({K2}KPbB, NS)}(G1)KPrA mod NA}K1, {|{({G3}(KPbA)KPrS modKPbS, G2)}K1|}KPrB)|}KPrA , NA , NB , KBS , KPrB , {(KPbB)KPrS mod KPbSf) G2 , NA , NB , G1 , KBS , KPrBg) (KPbB)KPrS mod KPbS , NA , NB , G2 , KBS , KPrBh) (KPbB)KPrS mod KPbS , (G1)KPrA mod NA , NA, NB , G2 , KBS , KPrBi) (KPbB)KPrS mod KPbS , G3 , G2 , KBS , KPrBj) (KPbB)KPrS mod KPbS , NA , NB , G2 , KBS , KPrB , G3 , (KPbA)KPrS mod KPbSk) NBExplain your answer below:Computer Security Coursework, 2020/2021 Page 4Question 2 (Marks: 15)Authentication ProtocolsConsider the following 4-message protocol:1. A → S: (B, {(A, K1)}KpbS)2. S → B: A3. B → S: (A, {(B, K2)}KpbS)4. S → A: (B, {K2}K1)Which of the following statements is true, at the end of the protocol, and with regards to thepurpose of the protocol:a) Both A and B establish a session key K2, and B is sure of A’s identityb) Both A and B establish a session key K1, and B is sure of A’s identityc) Both A and B establish a session key K1, and A is sure of B’s identityd) Both A and B establish a session key K1, and both B and A are sure of each other’s identitye) Both A and B establish a session key K2, and A is sure of B’s identityf) Both A and B establish a session key K1g) Both A and B establish a session key K2h) Both A and B authenticate each other by knowing each other’s identitiesi) A ends up knowing B’s identityj) B ends up knowing A’s identityk) None of the abovel) All of the aboveExplain your answer below:Computer Security Coursework, 2020/2021 Page 5Question 3 (Marks: 10)Non-Repudiation and Anonymity ProtocolsFor the Zhou-Gollman non-repudiation protocol discussed in the lecture on “Non-Repudiation andAnonymity Protocols”, which one of the following statements is false:a) At time point 4, both A and B can produce evidence to prove that they received Kb) At time point 2, both A and B can produce evidence to prove that they received a signedmessage from the other partyc) At time point 0, S cannot prove anythingd) At time point 3, B cannot produce evidence to prove that A has access to key Ke) At time point 1, A can prove that B is alivef) At time point 4, S can prove that A is aliveg) At time point 3, S can produce evidence that that A has access to key Kh) At time point 0, A is not alivei) At time point 2, A can produce evidence to prove that B is alivej) At time point 4, the protocol terminatesExplain your answer below:Computer Security Coursework, 2020/2021 Page 6Question 4 (Marks: 10)Forward Secrecy ProtocolsConsider the following 4-message protocol:1. A → S: (B, {(A, K1)}KpbS)2. S → B: A3. B → S: (A, {(B, K2)}KpbS)4. S → A: (B, {K2}K1)Assume three runs of the above protocol, that we call P1, P2 and P3. If after completion of run P3,K1 is compromised, i.e. it is leaked to some external intruder, how would this impact the forwardsecrecy property of K2 for all the three runs of the protocol P1, P2 and P3? Choose the right answer:a) Compromising K1 in P3 compromises every other key in all of the three runs of the protocolb) The secrecy of P3.K2 is not compromised, and therefore P2.K2 and P1.K2 would remainsecretc) Compromising K1 in P3 compromises P3.K2, and therefore, every other previous version ofK1 and K2 are also compromisedd) The secrecy of P3.K2 is compromised, but P2.K2 and P1.K2 would remain secret since K1 isrefreshed after each run, therefore P3.K1 is different from P2.K1 and is different from P1.K1e) Even though K1 is compromised in P3, K2 is not compromised in any of the three runsExplain your answer below:Computer Security Coursework, 2020/2021 Page 7Question 5 (Marks: 10)Attacks on Security ProtocolsConsider the following 4-message protocol:1. A → S: (B, {(A, K1)}KpbS)2. S → B: A3. B → S: (A, {(B, K2)}KpbS)4. S → A: (B, {K2}K1)And the following attack trace:1. I(A) → S: (B, {(A, K)}KpbS)2. S → B: A3. B → S: (A, {(B, K2)}KpbS)4. S → I(A): (B, {K2}K)Which one of these changes to the protocol messages would fix the attack trace above, such as theattack then becomes impossible:a) 3. B → S: (A, {(B, {K2}KpbA)}KpbS)b) 4. S → A: (B, {K2, A}K1)c) 2. S → B: {A}KpbBd) 2. S → B: Be) 3. B → S: (A, {(B, {K2}KprS)}KpbS)f) 1. A → S: {(B, A, K1)}KpbSg) 1. A → S: (A, {(B, K1)}KpbS)h) 4. S → A: (B, {K1}K2)i) 4. S → A: (A, B, {K2}K1)j) 2. S → B: A, BExplain your answer below:Computer Security Coursework, 2020/2021 Page 8Question 6 (Marks: 10)Mutation and Type-Flaw AttacksConsider the following 4-message protocol between A and B, where (N+1) represents the incrementof N:1. A → B: (A, {NA}KAB)2. B → A: {(NA+1, NB)}KAB3. A → B: {NB+1}KAB4. B → A: {(K’AB, NA)}KABWhich of the following mutations to messages of the protocol above, would constitute a harmfulattack:a) 1. A → B: (C, {NA}KAB)b) 1. A → B: ({NA}KAB, A)c) 4. B → A: {(KAB, NA)}KABd) 4. B → A: {(K’AB, NB+1)}KABe) 3. A → B: {NB+1}KpbBf) 2. B → A: {(NA+1, NA)}KABExplain your answer below:Computer Security Coursework, 2020/2021 Page 9Question 7 (Marks: 15)Access Control ModelsAssume a network that consists of a set of nodes, {a, b, c, d, e, f, g, h, j, k, l, x, z}. These nodes havethe following partial order relation on them:{(b≤a), (f≤e), (z≤l), (z≤x), (l≤g), (c≤b), (g≤k), (e≤d), (g≤h), (k≤j), (g≤e), (e≤c), (d≤b), (x≤e)}Furthermore, assume that a BLP policy is being enforced in the above network. Now assume that atsome stage, node z becomes infected with a virus. Which one of the following sets of actions wouldalso lead to infecting node a, assuming that viruses propagate through a network using the read andwrite commands. A virus would propagate from one node to another either because the secondnode read from the first one, or because the first node wrote to the second one. All read and writecommands are subject to the policy being enforced and no read or write operation is possible in theabsence of an order (either direct or indirect) between two nodes:a) (l read from z), (l write to g), (g read from l), (g read from e), (e write to c), (c write to b), (aread from b)b) (z read from l), (a read from l)c) (z write to x), (x write to e), (a read from e)d) (z write to c), (b write to c), (a read from b)e) (z write to g), (g write to h), (b read from h), (b write to a)f) (x read from z), (x write to e), (e write to d), (a write to d)g) (z write to g), (j read from g), (j write to d), (d write to b), (a read from b)h) (z write to l), (l write to g), (g write to c), (c write to d), (d write to b), (b write to a)i) (a write to z)j) (f read from z), (a read from f)Explain your answer below:Computer Security Coursework, 2020/2021 Page 10Question 8 (Marks: 15)XACMLThe following represent two examples of XACML 2.0 policies.Which single one of these statements is false:a) An access request from Alice Samson at 14:00 on 01 January 2018 according to the firstpolicy, will failComputer Security Coursework, 2020/2021 Page 11b) Purpose of the last rule in each of the two policies is to deny any requests that are notcovered by the previous permitting rules in each of the two policiesc) If the two policies above were combined into one policy set in the order they appear with apolicy-combining algorithm “first-applicable”, then the outcome of the request by AliceSamson be at 14:00 on 01 January 2018 to access the “server.acme.co.uk/docsserver” wouldbe accepted when evaluated against the new policy setd) Adding to the AND of the condition a third part with a “anyURI-equal” function applied to anattribute “machine.alice.come” will strengthen the condition by also requiring that Alice’srequest arrives from a particular URI address equal to machine.alice.come) If the effects of rules “Example 2 Rule 1” and “Example 2 Rule 2” in the second policy werechanged to “Deny” and the effect of rule “Example 2 Rule 3” was changed to “Permit”, thenthe outcome of the request from Alice Samson at 14:00 on 01 December 2017 would bepermittedf) An access request from Alice Samson at 14:00 on 01 January 2018 according to the secondpolicy, will succeedExplain your answer below: