Cryptography Concepts Quiz
Cryptography Concepts Quiz
Test your knowledge in the fascinating field of cryptography with our engaging quiz! Dive into questions covering groups, hash-fun
Key Highlights:
- 10 Challenging Questions
- Multiple Choice and Checkbox Formats
- Score your understanding of cryptographic principles
Choose the incorrect option(s) from the following:
(R, ×) is a group
(R − {0}, +) is a group.
C. (Z − {0}, +) is an abelian group.
(R − {0}, ×) is a group.
Which of the following is/are true for the hash-function based commitment scheme?
Collision-resistance property for the underlying hash function is not necessary for the binding property of the commitment scheme
Collision-resistance property for the underlying hash function is necessary for the binding property of the commitment scheme
The binding property can be proved only in the random-oracle model
Choose the correct option(s) from the following:
If an encryption scheme is CCA-secure, then it is also an authenticated encryption scheme
If an encryption scheme is an authenticated encryption scheme, then it is also CCA-secure
If an encryption scheme is an authenticated encryption scheme, then it is also CPA-secure
D) If an encryption scheme is CPA-secure, then it is also an authenticated encryption scheme
There exists a server A, who wants to broadcast messages to n recipients B1, . . . , Bn in an authentic manner. We are not interested in the privacy, but rather authenticity and integrity, where each user should be assured that the messages it receives are indeed sent by A. For this, the users decide to use a MAC, where server A shares a secret MAC key k with B1, . . . , Bn and each message from the server to the receivers is accompanied by a MAC tag, computed with key k.
A) Using a CMA-secure MAC solves the problem
B) Using an SCMA-secure MAC solves the problem
C) Neither a CMA-secure MAC, nor an SCMA-secure MAC can solve the problem
Using an information-theoretically secure MAC solves the problem
Let Π = (Gen, Enc, Dec) be a symmetric-key encryption scheme with message-space and ciphertext space M and C = {0, 1} ` respectively. Then consider a variant Π0 = (Gen, Enc’, Dec’) with message-space and ciphertext space M and C 0 = {0, 1} `+1 respectively, where Enc0 k (m) = Enck(m)||0 and Dec’k(c) = Deck(c[0, . . . , ` − 1]). Here c ∈ {0, 1} `+1 and c[0, . . . , ` − 1] denotes the first ` bits of c.
If Π is multi-message COA-secure then Π0 is also multi-message COA-secure
If Π is CPA-secure then Π0 is also CPA-secure
C) If Π is CCA-secure then Π0 is also CCA-secure
If Π is an authenticated encryption scheme then Π0 is also an authenticated encryption scheme
Choose the right option(s) for the authenticate-then-encrypt approach which is instantiated with a CPA-secure encryption scheme and an SCMA-secure MAC:
It is CCA-secure but not an authenticated encryption scheme
It does not provide ciphertext integrity
C) It provides ciphertext integrity
D) It is not CCA-secure
In the key-exchange problem, the goal of the sender and receiver is to:
Agree upon a common public key, over a private channel
Agree upon a fixed common key, over a public channel
Agree upon a fixed common key, over a private channel
Agree upon a random common key, over a public channel
Which of the following is/are sufficient to build an authenticated encryption scheme?
A block cipher
A PRG
A hash function
All of these
Let sender and receiver have a pre-shared, random and private AES key k. Then consider the following method of authen- ticating messages of size which is a multiple of 64 bits: to authenticate a message m ∈ {{0, 1} 64} ≤` containing ` blocks m1, . . . , m` each of size 64 bits, the tag-generation algorithm outputs t = (t1, . . . , t`) as the tag, where ti = AESk(mi || < ` >). Here < ` > denotes a 64-bit representation of the integer `, the number of blocks in m. Accordingly, the tag- verification algorithm performs the corresponding verification steps. Identify the false statement(s) from the following.
The above MAC is randomized and hence is SCMA-secure
The above MAC is deterministic and hence is CMA-secure
The above MAC when used in the encrypt-then-authenticate approach leads to an authenticated encryption scheme
The above MAC when used in the encrypt-and-authenticate approach leads to an authenticated encryption scheme
Consider a secure PRF Fk : {0, 1} n → {0, 1} n, using which we construct a keyed function F 0 k : {0, 1} 2n → {0, 1} 2n, where F 0 k (x1||x2) def = Fk(x1)||Fk(Fk(x2)) and x = x1||x2, where x1, x2 ∈ {0, 1} n.
Function F’ is not a secure PRF
Function F’ is a secure PRF
Function F’ when used directly leads to a CMA-secure MAC
Function F’ when used directly does not lead to a CMA-secure MAC
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