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ATTT

Total questions: 69

Worksheet time: 36mins

Name
Class
Date
1.
Which statement about "No read up" and "No write down" is true?
a)
While "No Read Up" restricts finding out information beyond the level, "No Write Down" requires all users to report/provide information only to their superiors.
b)
These are brief description of the two basic access rules in the mandatory access control model (MAC).
c)
These rules are operated by a centralized coordination mechanism, however there may be differences with trusted users.
d)
These are brief description of the two basic reporting axioms in the Bell Lapadulla model.
2.
Login procedures in modern information service systems are often stronger than traditional ones thanks to factors such as:
a)
Combining password authentication and OTP code authentication
b)
Using passwords with salts generated via timestamps
c)
Incorporating a challenge-response mechanism
d)
Mediating through popular social networking systems or search services
e)
Integrating password authentication with biometric factors
3.
In an authentication system, the system needs to store data supporting for verification in the user's account (or profile), and this verification data can be:
a)
a password and/or fingerprint image
b)
including the hash value of the password
c)
the hash value of the combining of password and fingerprint (concatenation)
d)
is the hashed value of a string concatenating password with the OTP authentication code
e)
including biometric factors such as fingerprints, voice, retinal images, etc. that have been processed
4.
Suppose the hierarchy of CAs in country X is organized as a tree graph (with a central CA at the root of this tree) having a maximum height of 5; this tree has 100 leaf nodes. When two parties A and B register in 2 different CAs in this tree, what is the maximum number of certificate validation checks that must be done for A to authenticate B’s public key?
a)
101
b)
100
c)
5
d)
Other
e)
9
5.
When relating the concept of login to authentication, is it possible to state as below?
a)
The Needham-Schroeder key protocol is for establishing a session key through a third party and has nothing to do with identity authentication
b)
Login procedures are usually performed through password checking, but can also be performed through other verification mechanisms, including biometrics
c)
The process of performing the login procedure always involves identity authentication, so it can be said that identity authentication is closely linked to the login procedure
d)
The login procedure is for connecting a user to a system (such as a server) but when two systems (such as 2 servers) need to establish a communication session with each other, the login procedure is not necessary, however, the authentication procedure is still necessary
6.
An Email authentication system is designed to allow users to log in remotely and can protect against replay attacks. Indicate which of the following four designs is best in security while allowing an user Alice to set up her account for exactly 1 year (no updates) assuming Alice will check her email about 3 times a normal day and about once a day on weekends.
a)
Applying S/Key Lamport using a hash chain of length 1000
b)
The user password is hashed along with a timestamp (rounded to the hour) and then the result is sent to the server for authentication
c)
Applying a challenge-response mechanism where the challenge is a random number in 10 bits.
d)
Applying a challenge-response mechanism where the challenge is the number of seconds that have passed since the last hour mark according to the server’s clock (e.g., if the current time is 10:05:07 then the challenge is 307-6057).
7.
Suppose H(m) is a collision-resistant hash function. Which of the following methods of generating a function H' is also collision-resistant?
a)
H'(X1 || X2) = H(X)
b)
H'(X1 || X2) = H(X1) ⊕ H(X2)
c)
H'(X) = H(X) || 00.0
d)
H'(X) = H(X) || r (where r is a random value)
8.
What type of malware is capable of interfering with a system to conceal its activity?
a)
Ransomware
b)
Rootkit
c)
Backdoor
d)
Metamorphic virus
9.
Determine which of the following statements about worms is NOT true.
a)
Both being malicious code, but worms are active while viruses are passive.
b)
A worm is a form of malicious code that any computer that actively downloads it as a file will be attacked immediately.
c)
A worm is a malicious program that, when activated, tries to probe for vulnerabilities in computers directly connected to the host computer, then tries to copy itself to these machines and execute right away.
d)
Relying on the worm, the enemy can develop a large army of minions that can perform a very effective password attack.
10.

How many hash operations Eve has to do in minimum in order to find the wanted session (that Eve has learned the corresponding session key of) within the log data per each day:

a)

60000

b)
100000
c)
50000
d)
2000
11.
In the "practical" algorithm to find the keylength of a given Vigenère cipher using IC, for each value p being tested as the keylength the ciphertext is divided into p letter groups (grouping letters at positions separating by multiples of p) and the IC of each group is computed and compared to IC of English. How do you think of the difference between these IC values and the IC of English?
a)
as small as 0.005
b)
no greater than 0.01
c)
roughly, 0.02
d)
at least 0.03
12.
Which of the following password storage methods is the most secure? Herein, the 'salt' is not necessarily secret, while the 'secret' is kept secret. All these values are randomly generated and have a size of 128 bits.
a)
SHA-1(password || salt || secret)
b)
SHA-256(password)
c)
SHA-1(password)
d)
SHA-256(SHA-256(password || salt || secret))
13.
Select the correct statement:
a)
The inverse of 37 by modulo 111 is 7 and by modulo 73 is 2.
b)
With p = 11, q = 13 and e = 37, we determine d = 10.
c)
The inverse of 37 by modulo 75 is 2 and by modulo 36 is 1.
d)
The inverse of 37 mod 111 is undefined because 111 is not a prime number.
e)
The inverse of 37 by modulo 110 is 3 and by modulo 73 is 2.
14.
In the RSA system with p = 11, q = 13 and e = 11, select the correct value for d.
a)
110
b)
101
c)
21
d)
111
e)
11
15.
From this below formal specification, what can we draw? roles(si) ⊆ { r | (user(si), r) ∈ UA }
a)
A session will be assigned the roles of the user who initiated it, but possibly not all.
b)
The roles assigned to a session must belong to the roles assigned to the user that initiated it, identified via the user() function, with the session ID as input.
c)
UA is the relationship that defines the pairing between roles and sessions.
d)
The role set of a session can be determined indirectly through the user's role set; these 2 sets can therefore be considered as one.
16.
When relating the concept of login to authentication, is it possible to state as below?
a)
The login procedure is always through the use of a password, but identity authentication may not be.
b)
Login is the procedure for a user to connect and create a session with a system based on a previously established account, which always includes an identity authentication phase.
c)
The process of performing the login procedure always includes identity authentication, so it can be said that identity authentication is closely linked to the login procedure.
d)
When two systems (possibly two servers) need to establish a communication session with each other, the login procedure is necessary.
e)
Identity authentication is typically invoked during system login procedures, but can also be used in other operations.
17.
Select the correct statement.
a)
Φ(p^2 × q^2) = (p−1) × 2 × (q−1)^2 if p, q are primes.
b)
Φ(21) = 12 and Φ(12) = 4
c)
Φ(105) = 48 and Φ(21) = 16
d)
Φ(12) = 6 and Φ(36) = 12
18.
Digital signature scheme can be seen as a combination of using:
a)
A public key encryption and a hash function
b)
A symmetric key encryption and a hash function
c)
A public key encryption and an authentication code
d)
An asymmetric key encryption and a hash function
19.
Which is the worst choice of selecting two primes p and q for constructing RSA?
a)
Both 70 digits
b)
One of 50 digits and the other 100 digits
c)
One of 60 digits and the other 80 digits
d)
Both 100 digits
e)
One of 55 digits and the other 200 digits
20.
Which mode is the most common way to operate a hash function?
a)
ECB
b)
CTR
c)
None of these mentioned
d)
OFB
21.

Given the concepts of Roles and Sessions in the RBAC access control model, which of the following statements is FALSE:

a)
The set of permissions for a given session code is determined through associated roles.
b)
A Session can have multiple roles.
c)
One role can be used in multiple Sessions.
d)
The two concepts are interchangeable.
22.
The security system of a bank building has been established with PAM (Pluggable Authentication Modules) that allows the coordination of multiple authentication methods and hence, is capable of changing authentication configuration daily. This multi-authentication system is designed to increase security against malicious attackers, while maintaining user convenience. Please point out which of the following authentication configurations is NOT really suitable for this purpose.
a)
Password and PIN authentication
b)
Fingerprint and Password authentication
c)
Face recognition and PIN authentication
d)
Location-based and password authentication
e)
Voice recognition and Location-based authentication
23.
In an authentication system, the system side needs to establish a set of complementation functions for computing a counterpart value based on information provided by the user side, and this set of functions is often:
a)
A relatively popular hash function
b)
A famous symmetric cryptographic algorithm
c)
A famous algorithm such as DES, AES or RSA
d)
A combination of an OTP authentication code and a random bit string (salt)
24.
Hãy cho biết đâu là chuỗi sắp xếp theo thứ tự về mức độ bảo mật:
a)
Unconditional security, Adhoc security, Provable Security, Computational Security
b)
Provable Security, Computational Security, Unconditional security
c)
Computational Security, Provable Security, Unconditional security
d)
Adhoc security, Computational Security, Unconditional security, Provable Security
25.
How many distinct keys are there in Affine cipher by using the Vietnamese alphabet?
a)
406
b)
812
c)
784
d)
392
26.
Select the correct statement on chosen-ciphertext attack (CCA) and chosen-plaintext attack (CPA) below
a)
CPA is considered a more difficult attack to execute than CCA because the attacker needs to train a "spy" on the team.
b)
Both are considered high security models.
c)
If the enemy can perform a CCA attack, it may not be able to perform CPA.
d)
If the enemy can perform a CPA attack, it may not be possible to perform CCA.
27.
In homophonic substitution cipher, each plaintext letter can be replaced with a variety of substitutes, i.e. each letter can be mapped into a randomly picked symbol from a predefined subset of ciphertext symbols. The set of ciphertext symbols is usually larger than the plaintext symbol set. Consider the following example & exercise. A language has an alphabet of only 4 letters {a, b, c, d} with frequencies as follows: Pa = 40%, Pb = 20%, Pc = 10% and Pd = 30%. Find an encryption function from this alphabet {a, b, c, d} into the set of numbers 0–9 so that the IC of the ciphertexts created by this encryption scheme will be minimum:
a)
a → {0,1,2,3}; b → {3,4}; c → {5,6}; d → {7,8,9}
b)
a → {0,1,2,3}; b → {3,4}; c → {5}; d → {7,8,9}
c)
a → {0,1,2,3}; b → {4,5}; c → {6,7}; d → {7,8,9}
d)
a → {0,1,8,9}; b → {2,3}; c → {4}; d → {7,6,5}
28.
When Alice needs to cryptanalyze a ciphertext Y generated from plaintext X using a mono-alphabetic cipher, she begins by discovering that the combination “INT” is the encoding of "the" in the plaintext. Which are the next few letters of the English alphabet that she should aim to try decipher that would bring the best chance?
a)
a, o, s, h, r
b)
t, a, o, i, n
c)
i, n, o, s, r
d)
a, o, n, l, s
29.
Which statement explains best about the man-in-the-middle (MITM) attack?
a)
Messages exchanged between Alice and Bob have been thwarted by Eve the attacker.
b)
Eve - the eavesdropper - makes independent connections with Alice and Bob - the victims - and relays messages between them to make them believe they are talking directly to each other over a private connection.
c)
In a typical MITM scenario, the attacker intercepts into a private communication and could twist messages in a smart way that the victims can make wrong decisions in the attacker's desire.
d)
In a typical MITM scenario, the attacker intercepts into a private communication and could twist messages for fun.
30.
Select the correct statement.
a)
The inverse of 7 according to mod 20 is 3 and according to mod 37 it is 16
b)
The inverse of 7 by mod 105 is undefined because 105 is not a prime
c)
With p = 11, q = 13, and e = 7, we determine d = 105
d)
The inverse of 7 according to mod 105 is 3 and according to mod 37 it is 16
e)
The inverse of 7 according to mod 50 is 7 and according to mod 37 it is 16
31.
Comparing MAC and CRC-32 codes, which of the following is true?
a)
MAC is more secure
b)
CRC-32 is more secure
c)
They are of different purposes
d)
Purpose has a lot in common
32.
Using the fast exponentiation algorithm, about how many congruent squares will be needed to calculate X^a mod n when a is about 10^9 (a billion)?
a)
about 30
b)
about 40
c)
about 20
d)
about 50
e)
about 10
33.

To practice constructing RSA cipher system, the students of a security class were asked to find 2 prime numbers p and q between 30 and 50 and had the following answers. Please show ALL the correct answers.

a)
13 and 17
b)
31 and 41
c)
33 and 37
d)
31 and 33
e)

37 and 31

34.

Select the correct statement.

a)

Φ(105) = 48 and Φ(21) = 16

b)
Φ(pqr) = (p−1)(q−1)(r−1) if p, q and r are primes
c)
Φ(21) = 12 and Φ(12) = 11
d)
Φ(15) = 8 and Φ(101) = 100
35.

Attackers can guess and test passwords by logging in (possibly remotely) to the server in multiple attempts. Choose the correct set of terms related to how to defend against this type of attack.

a)
Backoff, disconnection, proactive password checking
b)
Backoff, disabling, ageing
c)
Disabling, offline checking, backoff
d)
Jailing, disabling, disconnecting
36.

In designing DES cipher, the core function f has the following important characteristics:

a)
it provides a high level of confusion and diffusion
b)
it provides some confusion and diffusion but limited
c)
it is a complicated logarithmic function
d)
it is an involution function
37.
Not asking for any special properties, how many different S-boxes one can possibly come up with?
a)
(16!)^4
b)
(16!) Choose 4
c)
(16!)A4
d)
(16!)*4
38.

Select the statement that says most accurately about the core function f of DES design:

a)
it provides a high level of confusion and diffusion
b)
it provides some confusion and diffusion but limited
c)
it is an involution function that provides no diffusion
d)
it is an involution function that provides very high diffusion
39.

With respect to the cryptanalysis of DES-2, the meet-in-the-middle attack can most likely succeed:

a)
after just 2^57 DES operations
b)
usually requiring approximately 2(2^56 + 2^48) DES operations
c)
usually requiring 3 known plaintext-ciphertext pairs or more
d)
requiring just 2 known plaintext-ciphertext pairs
40.

In the RSA system with p = 11, q = 13, and e = 13, if we encrypt the 3-bit plaintext X = 110, then the result will be:

a)
Y = 1010100
b)
Y = 1010110
c)
Y = 1010101
d)
Y = 1011100
e)
Y = 1110100
41.
Block manipulation attacks:
a)
can be used successfully against the ECB and CTR encryption modes
b)
can be used successfully against the ECB encryption mode and the simple digital signature scheme without hash functions
c)
can be used successfully against the ECB encryption mode and the simple hash functions
d)
can not be used successfully against the CTR encryption mode and the digital signature scheme using a hash function
42.

Symmetric Key Encrypting with 32-bit plaintext blocks using CTR mode is OK for:

a)
a file of size 1Gb
b)
a file of size 32Gb
c)
a file of size 8Gb
d)
a file of size 2Gb
43.

Term "Encrypt-then-XOR" can be used to describe the two encryption modes:

a)
ECB and CTR
b)
CFB and OFB
c)
CBC and CFB
d)
CBF and CTR
44.

Which two are better amongst the following choices in picking the primes p and q?

a)
p has 80 digits while q has 500
b)
p has 50 digits while q has 200
c)
both 75 digits
d)
One has 70, the other has 80 digits
45.

Find the best statement below: Digitally signed documents are forged through a process ...

a)
starting from an original text, to find a way to add/remove spaces in many places to generate multiple documents, thereby finding 2 documents with the same hash value
b)
to build 2 sets of documents with content that are opposite in a certain sense and simultaneously hash and find 2 documents with the same hash value
c)
to find two texts with the same hash value and content on the same topic but different on a few important factors
d)
to find two texts with different content that have the same hash value
46.

Which two encryption modes are capable of parallel processing?

a)
ECB and OFB
b)
OFB and CTR
c)
CBC and CTR
d)
ECB and CTR
47.

To perform a successful 2-DES attack with O(2^57) number of DES encryption/decryption operations, the adversary needs to perform:

a)
Known-Plaintext Attack with one plaintext-ciphertext pair
b)
Known-Plaintext Attack with 2 plaintext-ciphertext pairs
c)
Known-Plaintext Attack with 3 plaintext-ciphertext pairs
d)
Chosen-Plaintext Attack with 3 plaintext-ciphertext pairs
48.

Select the correct statement.

a)
DES = (IP) ° F16 ° T ° F15 ° T ° ... ° F2 ° T ° F1 ° (IP)−1 and DES−1 = (IP)−1 ° F1 ° T ° F2 ° T ° ... ° F15 ° T ° F16 ° (IP)
b)
DES = (IP)−1 ° F16 ° T ° F15 ° T ° ... ° F2 ° T ° F1 ° (IP) and DES−1 = (IP)−1 ° F1 ° T ° F2 ° T ° ... ° F15 ° T ° F16 ° (IP)
c)
DES−1 = (IP)−1 ° F16 ° T ° F15 ° T ° ... ° F2 ° T ° F1 ° (IP) and DES = (IP)−1 ° F1 ° T ° F2 ° T ° ... ° F15 ° T ° F16 ° (IP)
d)
DES = (IP)−1 ° F1 ° T ° F2 ° T ° ... ° F15 ° T ° F16 ° (IP) and DES−1 = (IP)−1 ° F16 ° T ° F15 ° T ° ... ° F2 ° T ° F1 ° (IP)
49.

To find a very large prime, there are possibly a number of different approaches. Select the incorrect one amongst the followings:

a)
Using an existing deterministic algorithm with polynomial computation time
b)
It is possible to use an approximate prime generation algorithm, but there may be errors
c)
It is possible to use a probabilistic algorithm to check if a number is prime but then discard it if the resulting number is not prime
d)
A probabilistic algorithm can be used to check if a number is prime, but it must be controlled so that the probability of error is small enough
50.

Select the incorrect statement:

a)
If the balance of bits 0 and 1 in the output is always maintained, then when there is a balance deviation to either side, it will be difficult to infer anything about the input.
b)
When one input bit is kept fixed and the remaining 5 bits are changed, the S-box always ensures that the number of 0 and 1 bits in the output is always balanced.
c)
The "uniformly distributed" property makes it useless to apply statistical analysis to find a way to break the S-box.
d)
The S-box exhibits a property called "uniform distribution", where one input bit is kept fixed and the remaining 5 bits are variable.
51.

Select the correct statement:

a)
Compared to DES, 3-DES increases the key size by 3 times but also increases the computation time by 3 times
b)
Compared with DES, 3-DES increases the key size by twice but increases the computation time by 3 times
c)
Compared to DES, 3-DES increases the number of keys by 3 times but also increases the computation time by 3 times
d)
Compared to DES, 2-DES doubles the number of keys but also increases the computation time by 2 times
52.

Why is it said that a 64-bit hash function is not secure enough for digital signatures?

a)
Is not secure enough if used with DES but secure enough with AES
b)
To forge a signature using a 64-bit hash function, a hacker can reduce the computational load to around 2^35 trials or less, which is feasible in a few days per PC.
c)
To forge a signature using a 64-bit hash function, hackers can reduce the computational load to no more than 2^32 trials, feasible in a few days per PC.
d)
The ability to exhaust testing 2^64 space keys within 1 day is feasible for a powerful PC.
53.

Let the Affine cryptosystem be determined through the formula y = x*k + l (mod 26), where x and y are the character positions in the English alphabet (A positioned at 0, …, Z positioned at 25) and each possible key is a pair of numbers (k, l). The number of keys (k, l) actually distinguishing is:

a)
312
b)
338
c)
260
d)
300
e)
360
54.

In an authentication system, passwords are established with 8 characters chosen from a 128-letter alphabet; on the server, the password file contains 1000 password hash values and corresponding salt values. Suppose that an attacker has built a dictionary of 200,000 common passwords, where the probability that the password of any given user will be in the dictionary is 10%. How many hash operations would this attacker need to perform to successfully find a password of a certain user in the mentioned authentication system?

a)
About 1 million
b)
About 2 million
c)
About 4 million
d)
About 8 million
55.

Attackers can guess and test passwords by logging in (possibly remotely) to the server in multiple attempts. Choose the correct set of terms related to how to defend against this type of attack:

a)
Backoff, disconnection, proactive password checking
b)
Backoff, disabling, ticket granting
c)
Disabling, CAPTCHA test, backoff
d)
Password ageing, disabling, disconnecting
56.

Engineer Alice intends to create an Email authentication system that is secure enough for remote logins (where replay attacks are possible) while also allowing an average user to set up his or her account for up to 1 year without resetting. Choose the best design from the options below, assuming a typical user will check his email about 3 times a normal day and about twice a day on weekends.

a)
Apply S/Key Lamport using a hash string of size 1000
b)
The user password is hashed along with a timestamp (rounded to the hour) and then the result is sent to the server for authentication
c)
The server challenges the client with a 10-bit random number to which the client must respond by hashing the user password along with the number.
d)
Using a challenge-response mechanism where the challenge is the number of seconds that have passed since midnight according to the server's clock.
57.

The security system of a bank building has been established with PAM (Pluggable Authentication Modules) that allows the coordination of multiple authentication methods and hence, is capable of changing authentication configuration daily. This multi-authentication system is designed to increase security against malicious attackers, while maintaining user convenience. Please point out 2 authentication configurations of the below which are NOT really suitable for this purpose.

a)
Fingerprint and Password authentication
b)
Face recognition and Voice recognition
c)
Location-based and password authentication
d)
Voice recognition and Location-based authentication
58.

For fingerprint-based authentication, which fingerprint storage method is best?

a)
Stored in as bitmaps
b)
Stored as a list of hash values
c)
Stored in an encrypted file
d)
Stored as graph-based structures
59.

For a password-based authentication system, which password storage method is best?

a)
Stored in plaintext in the host computer
b)
Stored as a list of hash values
c)
Stored in an encrypted file
d)
Stored as a list of hash and salt value pairs
60.

In an authentication system, the passwords are set to consist of 8 characters chosen from a 128-letter alphabet. On the server, the password file contains 1000 password hashes and the corresponding salt values. Suppose an attacker has built a dictionary of 1 million common passwords, where the probability of any given user's password being in the dictionary is 25%. How many hash operations is this attacker expected to perform to successfully find the password of an arbitrary user in the authentication system in question?

a)
About 1 million or a bit less
b)
About 2 million or a bit less
c)

About 4 million or a bit less

d)
About 8 million or a bit less
61.

Select the set of different "realms" according to the view of Kerberos v5.

a)
Zalo Web, Zalo Pay, Zalo Video
b)
FB, Messenger, FB Marketplace, FB Gaming
c)
G-Mail, Youtube, Translate, Calendar
d)
Google, FB, Zalo, Viettel
62.

If A wants to send a message (X) to B in such a way that it is both secret and authentic, how should it be encrypted before sending? Note that (Z_A) and (z_A) are A's public and private keys, and (Z_B) and (z_B) are B's public and private keys.

a)
D_{Z_B}(E_{Z_A}(X))
b)
E_{Z_A}(D_{Z_B}(X))
c)
E_{Z_B}(D_{Z_A}(X))
d)
D_{Z_A}(E_{Z_B}(X))
63.

An and Binh decide to use the following protocol to establish a symmetric session key after exchanging their public keys:

  1. A --> B: eA || [(T || IDA) || dA]

  2. B --> A: eB || [(T || IDB) || dB]

  3. A --> B: [IDA || ks] dA

  4. B --> A: [IDB] ks

What is the weakness of this protocol?

a)

It is not necessary to use IDB and timestamp T

b)

It is not necessary to use ID values in the protocol

c)

An attacker Eve could instead substitute with the message eA || [(T || IDA) || dE} in step 1 and so on in step 2; and then make the necessary changes in steps 3 and 4

d)

Enemy Eve can perform the "man-in-the-middle" attack to make A and B unable to understand each other

64.

To compute the modulo inverse, a student drafted on paper a "dry run" of the extended GCD algorithm, but the second row was accidentally damaged by a few drops of water that smudged it. The table content was as below. What is the sum of n 1 and n 2 ?

a)

48

b)

15

c)

54

d)

28

65.

Which of the followings do you think matches Binh's idea?

a)

This is a login protocol, but the usage of timestamps can be easily forged by the enemy, so it is necessary to switch to a mechanism where the system challenges the user who can only meet if knows the real p A, thereby also incorporating session key generation as an utility.

b)

Binh considers that the protocol has a weakness in improper use of timestamps, so he proposes a change to use a response mechanism with a random value of R.

c)

Binh believes that using a random value R is preferable in this login protocol because it enables the protocol to both authenticate the user and integrate the generation of the session key necessary for secure communication immediately afterwards.

d)

Binh thinks that this protocol only accomplishes a simple identity check, so he extended it to be able to generate session keys for subsequent secure communication.

66.

Hacker Eve has secretly wiretapped the A-B communication and recorded all the data transfer between A and B for the whole year 2023. On Dec 30th, Eve then luckily captured an old session key ks that has been used by A and B during 2023, i.e. Eve has 24 hours to find a way to take advantage of this ks. Show the main idea that Eve can apply to get the most out of this situation.

a)

Eve compute the two values of CH and RS based on this old session key ks and then try to search for these from the log she has recorded

b)

Eve can compute M=H60(ks)⊕ H50(ks) and then try to search for M from the log she has recorded

c)

Eve can compute M=H50(ks)⊕ H60(ks) and compose the list of the counterpart values of all the sessions from the recorded log of 2023, and then find the former within the later

d)

Eve can compose the list of the value CH⊕RS per each session from the recorded log of 2023 and then use it to find the correct session of

the known old session key.

67.

An access control system according to the RBAC model has four system files A, B, C, and D, and four roles that are denoted P, Q, R, S. In the mathematical representation of this model, the Permission Assignment (PA) relation is defined as a set of triplet elements defining the permissions as follows:

  • (P, A, RW), (P, B, RX), (P, C, RWX), (Q, A, RX), (Q, B, O), (Q, C, RX), (Q, D, O), (R, A, RWX), (R, B, ORX), (R, C, RWX), (S, A, R), (S, B, RX), (S, C, RX), (R, D, O).
    In this initial phase of this system, there are only 4 users with the following roles: Alice has the role of R, Bob has the role of P, Cathy has the role of Q, and Dave has the role of S.

Find the statements that are likely to be true below:

a)

Alice is Bob's boss but not Cathy's

b)

Bob is no one's boss

c)

File D has only 1 owner

d)

Alice has Read, Write, and Execute permissions to file A

e)

Bob does not work under Cathy, but works under Alice

68.

BK student An is studying a course of Introduction to Information Security, and comes to visit Binh, a student studying two foreign languages, X and Y. An tells Binh that the two languages Binh is studying both have alphabets with sizes ranging from 25 to 30, and An takes the opportunity to “teach” Binh some simple knowledge about classical ciphers. After learning about multiplicative cipher, Binh immediately exclaimed, “If you apply multiplicative cipher to the two languages I am studying, you will have the same number of keys even though they have different alphabet sizes.”

Point out the following incorrect statements:

a)

Language X has an alphabet the same size as Vietnamese

b)

Languages X and Y cannot both be English

c)

The number of keys (multiplicative cipher) for X and Y is 12

d)

Languages X and Y both have even-sized alphabets

e)

The number of keys is 13

69.
a)

From QUIZ there are more than 7 thousand encoding variations

b)

The number of homophones of B, N, O and P combined is 220

c)

The number of homophones of Q and Z combined is 4

d)

J has 2 homonyms (after encoding)

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