question
stringlengths 6
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| answer
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|---|---|---|
For an item that has not received any ratings, which method can make a prediction?
|
[
"User-based collaborative RS",
"Item-based collaborative RS",
"Content-based RS",
"None of the above"
] |
C
|
The SMART algorithm for query relevance feedback modifies? (Slide 11 Week 3)
|
[
"The original document weight vectors",
"The original query weight vectors",
"The result document weight vectors",
"The keywords of the original user query"
] |
B
|
In Ranked Retrieval, the result at position k is non-relevant and at k+1 is relevant. Which of the following is always true?Hint: P@k and R@k are the precision and recall of the result set consisting of the k top ranked documents.
|
[
"P@k-1>P@k+1",
"P@k-1=P@k+1",
"R@k-1<R@k+1",
"R@k-1=R@k+1"
] |
C
|
Suppose that for points p, q, and t in metric space, the following hold:p is density-reachable from q t is density-reachable from qp is density-reachable from tWhich of the following statements is false?
|
[
"t is a core point",
"p is a border point",
"p and q are density-connected",
"q is a core point "
] |
B
|
If for the χ2 statistics for a binary feature, we obtain P(χ2 |DF = 1) < 0.05, this means:
|
[
"That the class labels depends on the feature",
"That the class label is independent of the feature",
"That the class label correlates with the feature",
"No conclusion can be drawn"
] |
A
|
Which of the following is false regarding K-means and DBSCAN?
|
[
"K-means does not handle outliers, while DBSCAN does",
"K-means takes the number of clusters as parameter, while DBSCAN does not take any parameter",
"K-means does many iterations, while DBSCAN does not",
"Both are unsupervised"
] |
B
|
When constructing a word embedding, negative samples are:
|
[
"Word - context word combinations that are not occurring in the document collection",
"Context words that are not part of the vocabulary of the document collection",
"All less frequent words that do not occur in the context of a given word",
"Only words that never appear as context word"
] |
A
|
Which of the following statements about index merging (when constructing inverted files) is correct?
|
[
"While merging two partial indices on disk, the inverted lists of a term are concatenated without sorting",
"Index merging is used when the vocabulary does no longer fit into the main memory",
"The size of the final merged index file is O(nlog2(n)*M), where M is the size of the available memory",
"While merging two partial indices on disk, the vocabularies are concatenated without sorting"
] |
A
|
Let $f_{\mathrm{MLP}}: \mathbb{R}^{d} \rightarrow \mathbb{R}$ be an $L$-hidden layer multi-layer perceptron (MLP) such that $$ f_{\mathrm{MLP}}(\mathbf{x})=\mathbf{w}^{\top} \sigma\left(\mathbf{W}_{L} \sigma\left(\mathbf{W}_{L-1} \ldots \sigma\left(\mathbf{W}_{1} \mathbf{x}\right)\right)\right) $$ with $\mathbf{w} \in \mathbb{R}^{M}, \mathbf{W}_{1} \in \mathbb{R}^{M \times d}$ and $\mathbf{W}_{\ell} \in \mathbb{R}^{M \times M}$ for $\ell=2, \ldots, L$, and $\sigma$ is an entry-wise activation function. Also, let $f_{\mathrm{CNN}}: \mathbb{R}^{d} \rightarrow \mathbb{R}$ be an $L^{\prime}$-hidden layer convolutional neural network (CNN) such that $$ f_{\mathrm{CNN}}(\mathbf{x})=\mathbf{w}^{\top} \sigma\left(\mathbf{w}_{L^{\prime}} \star \sigma\left(\mathbf{w}_{L^{\prime}-1} \star \ldots \sigma\left(\mathbf{w}_{1} \star \mathbf{x}\right)\right)\right) $$ with $\mathbf{w} \in \mathbb{R}^{d}, \mathbf{w}_{\ell} \in \mathbb{R}^{K}$ for $\ell=1, \ldots, L^{\prime}$ and $\star$ denoting the one-dimensional convolution operator with zero-padding, i.e., output of the convolution has the same dimensionality as the input. Let's assume $\sigma$ is a tanh activation function. Thus, by flipping the signs of all of the weights leading in and out of a hidden neuron, the input-output mapping function represented by the network is unchanged. Besides, interchanging the values of all of the weights (i.e., by permuting the ordering of the hidden neurons within the layer) also leaves the network input-output mapping function unchanged. Suppose that, given the training data, SGD can find a solution with zero training loss, and the (absolute value) weights of such solution are non-zero and all unique. Choose the largest lower bound on the number of solutions (with zero training loss) achievable by $f_{\mathrm{MLP}}$ with $L=1$ and $M$ hidden units on this dataset.
|
[
"$M! 2^M$",
"$1$",
"$2^M$",
"$M !$"
] |
A
|
Consider a linear regression problem with $N$ samples $\left\{\left(\boldsymbol{x}_{n}, y_{n}\right)\right\}_{n=1}^{N}$, where each input $\boldsymbol{x}_{n}$ is a $D$-dimensional vector $\{-1,+1\}^{D}$, and all output values are $y_{i} \in \mathbb{R}$. Which of the following statements is correct?
|
[
"Linear regression always \"works\" very well for $N \\ll D$",
"A linear regressor works very well if the data is linearly separable.",
"Linear regression always \"works\" very well for $D \\ll N$",
"None of the above."
] |
D
|
Let $\mathcal{R}_{p}(f, \varepsilon)$ be the $\ell_{p}$ adversarial risk of a classifier $f: \mathbb{R}^{d} \rightarrow\{ \pm 1\}$, i.e., $$ \mathcal{R}_{p}(f, \varepsilon)=\mathbb{E}_{(\mathbf{x}, y) \sim \mathcal{D}}\left[\max _{\tilde{\mathbf{x}}:\|\mathbf{x}-\tilde{\mathbf{x}}\|_{p} \leq \varepsilon} \mathbb{1}_{\{f(\tilde{\mathbf{x}}) \neq y\}}\right], $$ for $p=1,2, \infty$. Which of the following relationships between the adversarial risks is true?
|
[
"$\\mathcal{R}_{2}(f, \\varepsilon) \\leq \\mathcal{R}_{1}(f, 2 \\varepsilon)$",
"$\\mathcal{R}_{\\infty}(f, \\varepsilon) \\leq \\mathcal{R}_{2}(f, \\sqrt{d} \\varepsilon)$",
"$\\mathcal{R}_{\\infty}(f, \\varepsilon) \\leq \\mathcal{R}_{1}(f, \\varepsilon)$",
"$\\mathcal{R}_{\\infty}(f, \\varepsilon) \\leq \\mathcal{R}_{2}(f, \\varepsilon / d)$"
] |
B
|
You are given two distributions over $\mathbb{R}$ : Uniform on the interval $[a, b]$ and Gaussian with mean $\mu$ and variance $\sigma^{2}$. Their respective probability density functions are $$ p_{\mathcal{U}}(y \mid a, b):=\left\{\begin{array}{ll} \frac{1}{b-a}, & \text { for } a \leq y \leq b, \\ 0 & \text { otherwise } \end{array} \quad p_{\mathcal{G}}\left(y \mid \mu, \sigma^{2}\right):=\frac{1}{\sqrt{2 \pi \sigma^{2}}} \exp \left(-\frac{(y-\mu)^{2}}{2 \sigma^{2}}\right)\right. $$ Which one(s) belong to the exponential family?
|
[
"Only Uniform.",
"Both of them.",
"Only Gaussian.",
"None of them."
] |
C
|
Church booleans are a representation of booleans in the lambda calculus. The Church encoding of true and false are functions of two parameters: Church encoding of tru: t => f => t Church encoding of fls: t => f => f What should replace ??? so that the following function computes not(b and c)? b => c => b ??? (not b)
|
[
"(not b)",
"(not c)",
"tru",
"fls"
] |
B
|
To which expression is the following for-loop translated? for x <- xs if x > 5; y <- ys yield x + y
|
[
"xs.flatMap(x => ys.map(y => x + y)).withFilter(x => x > 5)",
"xs.withFilter(x => x > 5).map(x => ys.flatMap(y => x + y))",
"xs.withFilter(x => x > 5).flatMap(x => ys.map(y => x + y))",
"xs.map(x => ys.flatMap(y => x + y)).withFilter(x => x > 5)"
] |
C
|
A query \(q\) has been submitted to two distinct Information Retrieval engines operating on the same document collection containing 1'000 documents, with 50 documents being truly relevant for \(q\).The following result lists have been produced by the two IR engines, \(S_1\) and \(S_2\) respectively:
\(S_1\text{:}\)
\(d_1\)
\(d_2\text{ (*)}\)
\(d_3\text{ (*)}\)
\(d_4\)
\(d_5\text{ (*)}\)
\(S_2\text{:}\)
\(d^\prime_1\text{ (*)}\)
\(d^\prime_2\text{ (*)}\)
\(d^\prime_3\)
\(d^\prime_4\)
\(d^\prime_5\)
In these result lists, the stars \(\text{(*)}\) identify the truly relevant documents.
By convention, we consider that any non retrieved document has been retrieved at rank 6.If Average Precision is used as evaluation metric, which of the two IR engines is performing better for the query \(q\)?
|
[
"\\(S_1\\)",
"\\(S_2\\)",
"Both engines perform equally.",
"This evaluation metric cannot be computed."
] |
B
|
A multiset is an unordered collection where elements can appear multiple times. We will represent a multiset of Char elements as a function from Char to Int: the function returns 0 for any Char argument that is not in the multiset, and the (positive) number of times it appears otherwise: type Multiset = Char => Int The filter operation on a multiset m returns the subset of m for which p holds. What should replace ??? so that the filter function is correct? def filter(m: Multiset, p: Char => Boolean): Multiset = ???
|
[
"x => if m(x) then p(x) else 0",
"x => m(x) && p(x)",
"x => if !m(x) then p(x) else 0",
"x => if p(x) then m(x) else 0"
] |
D
|
The little Fermat theorem states that for a prime $n$ and any $b\in \mathbb{Z}_n ^\star$ we have\dots
|
[
"$b^{n-1}\\mod n = 1$.",
"$b^{n-1}\\mod n = n$.",
"$b^{n}\\mod n = 1$.",
"$b^{n-1}\\mod n = b$."
] |
A
|
The number of permutations on a set of $n$ elements
|
[
"is always greater than $2^n$",
"is approximately $n(\\log n - 1)$",
"can be approximated using the Stirling formula",
"is independent of the size of the set"
] |
C
|
Select \emph{incorrect} statement. Complexity analysis of an attack consideres
|
[
"time complexity.",
"memory complexity.",
"probability of success.",
"difficulty to understand a corresponding journal paper."
] |
D
|
Which one of these is \emph{not} a stream cipher?
|
[
"IDEA",
"RC4",
"A5/1",
"E0"
] |
A
|
Tick the \emph{correct} assertion regarding GSM.
|
[
"In GSM, the communication is always encrypted.",
"The integrity of GSM messages is well protected.",
"GSM uses the GSME cipher to encrypt messages.",
"In GSM, the phone is authenticated to the network."
] |
D
|
Tick the \emph{wrong} assertion concerning 3G.
|
[
"In 3G, the network is authenticated to the phone.",
"The integrity of 3G messages is well protected.",
"In 3G, there is a counter to protect against replay attacks.",
"3G uses f8 for encryption."
] |
A
|
Tick the \textbf{false} statement.
|
[
"Cryptographic primitives used in Bluetooth are provably secure.",
"In WEP, authentication is done with the pre-shared keys.",
"The security of Bluetooth 2.0 pairing is based on PIN.",
"Due to memory limitations, dummy devices can share the same key with everyone."
] |
A
|
Why do block ciphers use modes of operation?
|
[
"it is necessary for the decryption to work.",
"to be provably secure.",
"to use keys of any size.",
"to encrypt messages of any size."
] |
D
|
If we pick independent random numbers in $\{1, 2, \dots, N\}$ with uniform distribution, $\theta \sqrt{N}$ times, we get at least one number twice with probability\dots
|
[
"$e^{\\theta ^2}$",
"$1-e^{\\theta ^2}$",
"$e^{-\\theta ^2 /2}$",
"$1-e^{-\\theta ^2 /2}$"
] |
D
|
In practice, what is the typical size of an RSA modulus?
|
[
"64 bits",
"256 bits",
"1024 bits",
"8192 bits"
] |
C
|
The one-time pad is\dots
|
[
"A perfectly binding commitment scheme.",
"A statistically (but not perfectly) binding commitment scheme.",
"A computationally (but not statistically) binding commitment scheme.",
"Not a commitment scheme."
] |
D
|
Tick the \textbf{false} statement.
|
[
"The identity element of $E_{a,b}$ is the point at infinity.",
"If a point is singular on an Elliptic curve, we can draw a tangent to this point.",
"$P=(x_p,y_p)$ and $Q=(x_p,-y_p)$ are the inverse of each other on an Elliptic curve of equation $y^2=x^3+ax+b$.",
"Elliptic curve cryptography is useful in public-key cryptography."
] |
B
|
Diffie-Hellman refers to \ldots
|
[
"a signature scheme.",
"a public-key cryptosystem.",
"a key-agreement protocol.",
"the inventors of the RSA cryptosystem."
] |
C
|
Consider the Rabin cryptosystem using a modulus $N=pq$ where $p$ and $q$ are both $\ell$-bit primes. What is the tightest complexity of the encryption algorithm?
|
[
"$O(\\ell)$",
"$O(\\ell^2)$",
"$O(\\ell^3)$",
"$O(\\ell^4)$"
] |
B
|
Select the \emph{incorrect} statement.
|
[
"The non-deterministic encryption can encrypt one plaintext into many ciphertexts.",
"The non-deterministic encryption always provides perfect secrecy.",
"Plain RSA encryption is deterministic.",
"ElGamal encryption is non-deterministic."
] |
B
|
Which mode of operation is similar to a stream cipher?
|
[
"ECB",
"OFB",
"CFB",
"CBC"
] |
B
|
Select the \emph{incorrect} statement.
|
[
"The Discrete Logarithm can be solved in polynomial time on a quantum computer.",
"The ElGamal cryptosystem is based on the Discrete Logarithm problem.",
"The Computational Diffie-Hellman problem reduces to the Discrete Logarithm problem.",
"The Discrete Logarithm is hard to compute for the additive group $\\mathbf{Z}_{n}$."
] |
D
|
In Bluetooth, the link key $K_{link}$ is ...
|
[
"used to generate an epheremal key $K_{init}$.",
"not used to generate the encryption key.",
"used to authenticate devices.",
"the input to the pairing protocol."
] |
C
|
Let $n=pq$ where $p$ and $q$ are prime numbers. We have:
|
[
"$\\varphi (n) = n-1$",
"$\\varphi (n) = pq$",
"$\\varphi (n) = p + q$",
"$\\varphi (n) = (p-1) (q-1)$"
] |
D
|
Which of the following elements belongs to $\mathbb{Z}_{78}^*$?
|
[
"46",
"35",
"21",
"65"
] |
B
|
Tick the \textbf{false} statement. Moore's Law ...
|
[
"is partly a reason why some existing cryptosystems are insecure.",
"was stated by the founder of Intel.",
"assumes the number of transistors per CPU increases exponentially fast with time.",
"implies that the heat generated by transistors of CPU doubles every 18 months."
] |
D
|
The elements of $\mathbf{Z}_{14}^*$ are
|
[
"$\\{ 0, 1, 3, 5, 9, 11, 13\\}$",
"$\\{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13\\}$",
"$\\{ 1, 3, 5, 9, 11, 13\\}$",
"$\\{ 1, 2, 3, 9, 11 \\}$"
] |
C
|
Tick the \textbf{false} statement.
|
[
"RSA can be accelerated by using CRT (Chinese Remainder Theorem).",
"An isomorphism is defined as a bijective homomorphism.",
"The CRT states $\\mathbb{Z}_{mn} \\equiv \\mathbb{Z}_{m} \\cup \\mathbb{Z}_{n}$.",
"The CRT implies $\\varphi(mn)=\\varphi(m)\\varphi(n)$ for $\\mathsf{gcd}(m,n)=1$."
] |
C
|
What is the advantage of using a salt in a password authentication protocol?
|
[
"It protects against online attacks.",
"It avoids multi-target bruteforce attacks from the database.",
"It avoids single-target exhaustive search attacks from the database.",
"It makes the protocol more spicy."
] |
B
|
Select \emph{incorrect} statement. The birthday paradox
|
[
"implies that in class of $23$ students we have two student with same birthday with approximately $50\\%$ probability.",
"can be used to find collisions in hash function.",
"implies that in a list of $\\Theta\\sqrt{N}$ random numbers from $\\mathbb{Z}_N$ we have at least one number twice with probability $1- e^{-{\\Theta^2\\over 2}}$.",
"implies that majority of people is born at full moon."
] |
D
|
Which scheme is the most secure?
|
[
"DES.",
"Two-key triple DES.",
"Three-key triple DES.",
"Double DES."
] |
C
|
Tick the \emph{false} assertion concerning WPA-TKIP.
|
[
"WPA-TKIP uses a fixed RC4 key.",
"WPA-TKIP avoids replay attacks using a counter.",
"WPA-TKIP provides much more confidentiality than WEP.",
"WPA-TKIP doesn't protect well the integrity of the messages."
] |
A
|
Tick the \emph{correct} assertion. In ElGamal $\ldots$
|
[
"the encryption algorithm is deterministic.",
"the key recovery problem is equivalent to the Computational Diffie Hellman problem.",
"the size of the ciphertext is always bigger than the size of the corresponding plaintext.",
"the decryption problem can be hard even if the discrete logarithm is easy to compute in the underlying group."
] |
C
|
One-time pad ...
|
[
"never uses a key $K$ which is picked from a uniform distribution.",
"pads the message at least once before encryption.",
"allows an efficient key management.",
"uses an invertible group operation such as ``$\\oplus$\" for encryption."
] |
D
|
The Merkle-D{\aa}mgard construction is
|
[
"a method which iterates a hash function to obtain a compression function.",
"a method which iterates a compression function to obtain a hash function.",
"a method which constructs a compression function from a block cipher.",
"a method which constructs a block cipher function from a hash function."
] |
B
|
The Fermat Test outputs `maybe prime' with probability which may be high given though $n$ is composite when ...
|
[
"$n$ is an even composite.",
"$n$ is a Fermat number.",
"$n$ is the multiplication of two primes.",
"$n$ is a Carmichael number."
] |
D
|
What should the minimal length of the output of a hash function be to provide security against \emph{collision attacks} of $2^{256}?$
|
[
"$2^{256}$ bits.",
"$2^{512}$ bits.",
"$256$ bits.",
"$512$ bits."
] |
D
|
Let $G$ be a group generated by $g$. What is the discrete logarithm problem?
|
[
"find $y$ such that $g^x=y$ for a given $x$.",
"find $x$ such that $g^x=y$ for a given $y$.",
"find $x,y$ such that $g^x=y$.",
"find $x,x'$ such that $g^x=g^{x'}$ and $x\\ne x'$."
] |
B
|
Bluetooth is \dots
|
[
"a long-range wireless technology.",
"first introduced by vikings.",
"\\emph{not} designed to transmit data.",
"a short-range wireless technology."
] |
D
|
Tick the \emph{false} answer. In a group, the operation\dots
|
[
"is commutative",
"is associative.",
"has a neutral element.",
"associates an inverse to each value."
] |
A
|
Consider a public-key cryptosystem. Let $K_p$, $K_s$, $X$, and $Y$ be respectively the public key, private key, plaintext and ciphertext. Which assertion is \emph{always true}?
|
[
"$Enc_{K_p}(Dec_{K_s}(X))=X$",
"$Enc_{K_s}(Dec_{K_p}(Y))=Y$",
"$Dec_{K_p}(Enc_{K_s}(Y))=Y$",
"$Dec_{K_s}(Enc_{K_p}(X))=X$"
] |
D
|
Select the \emph{incorrect} statement. Euler Theorem
|
[
"is a generalization of Little Fermat Theorem.",
"states that any $x \\in \\{0, \\dots, N-1 \\}$ and any $k$, we have $x^{k\\varphi(N)+1}=x \\pmod N$, where $N=pq$ for $p$,$q$ distinct primes.",
"gives the basis for polynomial time factoring.",
"allows us to prove that RSA decryption works."
] |
C
|
Tick the \textit{correct} assertion.
|
[
"In a finite field $K$, every element has exactly two square roots.",
"In a finite field $K$, 1 has exactly one square roots and it is 1.",
"The set of quadratic residues in $\\mathbb{Z}_n$ is a field.",
"An element can have more than two square roots in $\\mathbb{Z}_n$."
] |
D
|
Let $p$ be a prime number and $n$ be an integer. What is the order of $\mathrm{GF}(p^n)$?
|
[
"$p^n$",
"$p^n-1$",
"$p^{n-1}$",
"$1-p^n$"
] |
A
|
Under which condition is an element $x\in \mathbb{Z}_n$ invertible?
|
[
"$\\mathsf{gcd}(x,\\varphi (n)) = 1$.",
"$\\mathsf{gcd}(x,n-1) = 1$.",
"$\\mathsf{gcd}(x,n) = 1$.",
"$\\mathsf{gcd}(x,n) \\ne 1$."
] |
C
|
If Alice receives a message proven to be coming from Bob, we say that the message is\dots
|
[
"confidential",
"fresh",
"authenticated",
"correct"
] |
C
|
Which cryptographic primitive(s) is (are) used in S/Key - OTP ?
|
[
"Only encryption and a hash function",
"Only encryption and a MAC algorithm",
"Only a hash function",
"Only a MAC"
] |
C
|
Let $(e,N)$ be the public parameters of the RSA cryptosystem. What is the advantage of taking a \emph{small} value for $e$?
|
[
"The complexity of the parameters generation is smaller.",
"The complexity of the encryption step is smaller.",
"The complexity of the decryption step is smaller.",
"The whole system is stronger against several attacks."
] |
B
|
Let $p$ and $q$ be two distinct prime numbers and let $x \in \mathbf{Z}_{pq}^*$. Which of the following assertion is always true in $\mathbf{Z}_{pq}^*$?
|
[
"$x^{p} = 1$",
"$x^{q} = 1$",
"$x^{pq} = 1$",
"$x^{(p-1)(q-1)} = 1$"
] |
D
|
Let $h$ be a cryptographic hash function based on the Merkle-Damg{\aa}rd scheme. The Merkle-Damg{\aa}rd Theorem states that\dots
|
[
"\\dots $h$ is collision-resistant.",
"\\dots $h$ is resistant to a first preimage attack.",
"\\dots if the compression function is collision-resistant, then $h$ is collision-resistant.",
"\\dots if $h$ is collision-resistant, then the compression function is collision-resistant."
] |
C
|
$\mathbb{Z}_{37}^*$ denotes ...
|
[
"a field.",
"an additive group.",
"a multiplicative group.",
"a ring."
] |
C
|
Visual cryptography is a nice visual application of \ldots
|
[
"\\ldots the Vigen\\`ere cipher.",
"\\ldots the Vernam cipher.",
"\\ldots the Caesar cipher.",
"\\ldots ROT13."
] |
B
|
Select the \emph{incorrect} statement.
|
[
"The order of an element is always multiple of the order of its group.",
"An ideal $I$ of commutative ring $R$ is a subgroup closed under multiplication by all elements of $R$.",
"Given a prime $p$, we have $a^{p} = a$ for every $a \\in \\mathbb{Z}_p$.",
"Any element of order $\\varphi(n)$ is a generator of $\\mathbb{Z}_n^*$."
] |
A
|
Which one of these is a closed set?
|
[
"$\\mathbb{Z}$ with the addition.",
"$\\mathbb{Z}^\\star$ with the addition.",
"$\\mathbb{Z}^\\star$ with the substaction.",
"$\\mathbb{Z}-\\{0\\}$ with the division."
] |
A
|
Tick the \textbf{incorrect} assertion.
|
[
"ECDSA uses elliptic curves.",
"PKCS\\#1v1.5 uses plain RSA as an internal routine.",
"An ECDSA signature consists in the message and a pair of elements in $\\mathbb{Z}_n$.",
"Subtraction is hard to perform on an elliptic curve."
] |
D
|
Select the \emph{correct} statement. The Plain RSA Signature scheme
|
[
"has modulus $N=p^2$.",
"has public modulus $e$ to be selected so that $\\text{gcd} (e, \\varphi(N)) > 1$.",
"allows us to pick a fixed public key exponent like $e=3$ or $e=2^{16}+1$.",
"has a secret modulus $d$ to be selected so that $e+d = 0 \\pmod{\\varphi(N)}$."
] |
C
|
Which of the following is an element of $\mathbb{Z}_{60}^*$?
|
[
"49",
"30",
"26",
"21"
] |
A
|
Which of the following algorithms is \emph{not} a hash function?
|
[
"SHA-1",
"MD5",
"RC4",
"MD4"
] |
C
|
Select the \emph{correct} answer.
|
[
"The dictionary attack needs no precomputation.",
"The dictionary attack has a memory complexity of order 1.",
"The multi-target dictionary attack needs no precomputation.",
"The success probability of the dictionary attack depends on the size of the dictionary."
] |
D
|
Tick the \emph{false} assertion. Given a ring $R$, $R^\star$ is\ldots
|
[
"a group.",
"the set of invertible elements in $R$.",
"$R-\\{0\\}$.",
"the set of units."
] |
C
|
Select the \emph{incorrect} statement. Bluetooth is
|
[
"a short-range wireless technology.",
"designed both for data and voice transmission.",
"a standard for RFID tags.",
"able to transmit 1Mbit/sec in 10m distance."
] |
C
|
Which cipher is AES?
|
[
"SAFER",
"BLOWFISH",
"RIJNDAEL",
"RC5"
] |
C
|
Which of the following algorithms is a stream cipher?
|
[
"FOX",
"IDEA",
"RC4",
"AES"
] |
C
|
Consider a public key cryptosystem. The channel used to transmit the public key has to be\dots
|
[
"\\dots encrypted.",
"\\dots authenticated.",
"\\dots confidential.",
"\\dots authenticated and confidential."
] |
B
|
KEM/DEM refers to\dots
|
[
"an encryption scheme.",
"a digital signature scheme.",
"a commitment scheme.",
"a hash function."
] |
A
|
Tick the \textbf{false} statement.
|
[
"The cardinality of $E_{a,b}(\\mathsf{GF}(q))$ is bounded by $q+1+2\\sqrt{q}$.",
"$E_{a,b}$ is non-singular if $4a^3+27b^2 \\neq 0$ over a finite field of characteristic $p>3$.",
"In $(\\mathsf{GF}(2^k))$, we have $\\mathsf{Tr}(a+b)=\\mathsf{Tr}(a)+\\mathsf{Tr}(b)$.",
"Two Elliptic curves cannot have the same $j$-invariant."
] |
D
|
Select \emph{incorrect} statement. The brute force technique against a cipher with key $256$ bits is
|
[
"impossible even if we can compute without burning an energy.",
"impossible since the number of possible keys is too high $2^{256} \\approx 10^{77}$.",
"impossible in future even if we consider Moore's law.",
"feasible using all clusters at EPFL."
] |
D
|
Select the \emph{weakest} algorithm.
|
[
"A5/4",
"A5/2",
"A5/3",
"A5/1"
] |
B
|
Tick the \textit{incorrect} assertion.
|
[
"Plain CBCMAC resists forgery attacks.",
"GCM is a blockcipher mode of operation that provides both confidentiality and authenticity for messages.",
"A message authentication scheme that resists a chosen message forgery attack will also resist a known message forgery attack.",
"HMAC is a message authentication code based on a hash function."
] |
A
|
The Moore law
|
[
"implies the key size is doubled every every 18 months to preserve confidentiality",
"says that CPU speed doubles every 18 months",
"has no relevance for cryptography since it only considers speed of computation",
"states that anything that can go wrong will"
] |
B
|
Select the \emph{incorrect} statement. The Bluetooth project aims for
|
[
"low complexity.",
"low power.",
"low cost.",
"low security."
] |
D
|
Tick the \emph{false} assertion. The ambiguity issue in the decryption algorithm of the Rabin cryptosystem can be solved by\dots
|
[
"encrypting the message twice.",
"encrypting the message appended to itself.",
"appending some integrity checks to the message before encryption.",
"ensuring that the other possible plaintexts make no sense."
] |
A
|
What is the order of $2^{124}$ in $(\mathbb{Z}_{2^{128}},+)$?
|
[
"8.",
"$\\varphi(2^{128})$.",
"124.",
"16."
] |
D
|
Which problem in communication is \emph{not} treated by cryptography?
|
[
"confidentiality",
"integrity",
"authenthication",
"data transmission"
] |
D
|
What are the complexities for the single-target dictionary attacks, when there are $N$ keys?
|
[
"Preprocessing: $N$, Memory: $N$, Time: 1",
"Preprocessing: $N$, Memory: $1$, Time: $N$",
"Preprocessing: $1$, Memory: $N$, Time: $N$",
"Preprocessing: $0$, Memory: $1$, Time: $\\sqrt{N}$"
] |
A
|
Tick the \emph{incorrect} assertion. The Diffie-Hellman key agreement protocol \ldots
|
[
"allows two participants to set up a key so that they can communicate securely.",
"requires the hardness of the Discrete Logarithm problem.",
"uses ElGamal encryption in order to establish the key.",
"is easy to break when working on the group $\\mathbf{Z}_{n}$."
] |
C
|
Which of these components was not part of the Enigma machine?
|
[
"A reflector",
"A pseudo-random number generator",
"A Rotor",
"A plugboard with a wire connection"
] |
B
|
Consider password-based access control. Tick the \textit{incorrect} assertion.
|
[
"Double hashing the password can help avoid the problems related to low-entropy passwords.",
"Salt can be used to thwart multi-target attacks.",
"Increasing the delay between authentication attempts can protect from online attacks.",
"Blocking the access after 10 unsuccessful authentication attempts can protect from online attacks."
] |
A
|
Select the \emph{incorrect} statement. In ElGamal signature
|
[
"public parameters are a prime number $p$ and a generator $g$ of $\\mathbb{Z}_p^*$.",
"the public key is $K_p = y = g^x$, where $x$ is the secret key.",
"verification checks whether $y^rr^s=g^{H(M)}$ for signature $\\sigma=(r, s)$ of the message $M$ and the hash function $H$.",
"requires a secure channel to transfer the signature."
] |
D
|
You are given the task of choosing the parameters of a hash function. What value of the output will you recommend in order to be minimal and secure against second preimage attacks?
|
[
"40 bits",
"80 bits",
"160 bits",
"320 bits"
] |
C
|
$\mathrm{GF}(2^k)$ is represented by the set of\dots
|
[
"polynomials of degree at most $k-1$ with binary coefficients.",
"polynomials of degree at most $k-1$ with coefficients in $\\mathbb{Z}_k$.",
"polynomials of degree at most $2^k$ with coefficients in $\\mathbb{Z}$.",
"polynomials of degree at most $2$ with coefficients in $\\mathbb{Z}_k$."
] |
A
|
Thick the \emph{incorrect} assertion.
|
[
"The goal of SAS-based cryptography is to reduce the length of the string that has to be authenticated.",
"One way to authenticate a SAS is to use your phone.",
"One can obtain a secure channel from a narrowband authenticated channel using SAS-based cryptography.",
"SAS-based cryptography always requires the SAS to be collision-resistant."
] |
D
|
According to the Kerckhoffs Principle:
|
[
"The internal design of a cryptosystem should be public.",
"The internal design of a cryptosystem should \\emph{not} be public.",
"If there is a single security hole in a cryptosystem, somebody will discover it.",
"The security of the cryptosystem should \\emph{not} rely on the secrecy of the cryptosystem itself."
] |
D
|
KEM \dots
|
[
"stands for Keyless Encryption Mechanism.",
"is a Korean encryption mechanism.",
"is a symmetric-key algorithm.",
"is a public-key algorithm."
] |
D
|
Tick the \emph{false} assertion. Two-keys triple DES\dots
|
[
"is more secure than double encryption.",
"is less secure than AES.",
"is as secure as a block cipher using a key twice longer.",
"is vulnerable to a certain variant of a meet-in-the-middle attacks."
] |
C
|
Tick the \textbf{true} statement regarding $\mathbb{Z}_p^*$, where $p$ is an arbitrary prime number.
|
[
"It is a group of prime order when $p>3$.",
"It has $\\varphi(p-1)$ generators.",
"For any $x \\in \\mathbb{Z}_p^*$ we have $x^{p}=1 \\pmod p$",
"It is isomorphic to $\\mathbb{Z}_n^*$ for all $n >0$."
] |
B
|
Tick the \textbf{false} statement regarding the DES round function.
|
[
"There is an expansion operation $E$ from 32 to 48 bits.",
"A round key is XORed to an internal register.",
"There are $8$ identical S-boxes (substitution boxes) of size $6 \\times 4$.",
"There is a permutation $P$ on 32-bits."
] |
C
|
Which of the following ciphers is based on arithmetics over the finite field $\mathrm{GF}(2^8)$?
|
[
"AES",
"DES",
"A5/1",
"RC4"
] |
A
|
Ensuring the information integrity means that\dots
|
[
"\\dots the information should not leak to any unexpected party.",
"\\dots the information must be protected against any malicious modification.",
"\\dots the information should make clear who the author of it is.",
"\\dots DES is secure."
] |
B
|
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