question
stringlengths 6
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|---|---|---|
Given an odd prime $p$, for any $a \in \mathbb{Z}_p$ the equation
|
[
"$x^2 - a = 0$ always has a solution.",
"$x^2 - a = 0$ has exactly two solutions.",
"$x^2 - a = 0$ has at most two solutions.",
"$x^2 - a = 0$ may have four solutions."
] |
C
|
Which one of the following notions is not in the fundamental trilogy of cryptography?
|
[
"authentication",
"confidentiality",
"integrity",
"privacy"
] |
D
|
Consider a mobile station (MS) with a SIM card associated to a home network (HN). The MS tries to connect to a visited network (VN). In the GSM authentication, who knows the key $K_i$?
|
[
"SIM only.",
"SIM and HN.",
"SIM, MS and HN.",
"SIM, MS, VN and HN."
] |
B
|
Select \emph{incorrect} statement. Brithday paradox
|
[
"is a brute force technique.",
"can be implemented with constant memory using Rho ($\\rho$) method.",
"is used to recover the secret key of AES in $2^{64}$ computations.",
"can be implemented using a table of size $\\Theta\\sqrt{N}$"
] |
C
|
The Kerckhoffs principle says:
|
[
"security should not rely on the secrecy of the key.",
"the speed of CPUs doubles every 18 months",
"cryptosystems must be published.",
"security should not rely on the secrecy of the cryptosystem itself."
] |
D
|
Tick the \emph{correct} assertion. The Vernam cipher provides \dots
|
[
"authenticity.",
"integrity.",
"confidentiality.",
"none of the mentioned properties."
] |
C
|
What is the average complexity of exhaustive search when the key is distributed uniformly at random over $N$ keys?
|
[
"$\\log N$",
"$2^N$",
"$\\frac{N+1}{2}$",
"$\\sqrt{N}$"
] |
C
|
Select \emph{incorrect} statement. Generic attacks on DES include
|
[
"time memory tradeof against 2 key Triple DES.",
"collision attack against 3 key Triple DES.",
"meet in the middle attack against 3 key Triple DES.",
"known plaintext attack by Van Oorschot-Wiener agains 2 key Triple DES."
] |
B
|
AES\dots
|
[
"\\dots has a variable key length \\emph{and} a variable block length.",
"\\dots has a variable key length \\emph{and} a fixed block length.",
"\\dots has a fixed key length \\emph{and} a variable block length.",
"\\dots has a fixed key length \\emph{and} a fixed block length."
] |
B
|
Given that $100000000003$ is prime, what is the cardinality of $\mathbf{Z}_{200000000006}^*$?
|
[
"$2$",
"$100000000002$",
"$100000000003$",
"$200000000006$"
] |
B
|
Select the \emph{incorrect} statement. Elliptic Curve Diffie-Hellman is
|
[
"based on the difficulty of factoring the polynomial of EC.",
"based on the difficulty of computing the discrete logarithm in EC.",
"used in Bluetooth 2.1.",
"used for epassports."
] |
A
|
In which attack scenario does the adversary ask for the decryption of selected messages?
|
[
"Known plaintext attack",
"Chosen plaintext attack",
"Ciphertext only attack",
"Chosen ciphertext attack"
] |
D
|
An element of the finite field $\mathrm{GF}(2^8)$ is usually represented by\dots
|
[
"\\dots one hexadecimal digit.",
"\\dots eight bytes.",
"\\dots two hexadecimal digits.",
"\\dots an irreducible polynomial of degree 8."
] |
C
|
Consider $GF(8)$ defined as $\mathbb{Z}_2[X]/(P(X))$ with $P(x) = X^3 + X + 1$. Compute $X^2 \times (X + 1)$ in $\mathbb{Z}_2[X]/(P(X))$
|
[
"$X^2+X+1$.",
"$X^2 + 1$.",
"$X^2$.",
"$X+1$."
] |
A
|
Let $n$ be a positive integer. An element $x \in \mathbb{Z}_n$ is \emph{always} invertible when \dots
|
[
"$x$ and $n$ are coprime.",
"$x$ and $\\varphi(n)$ are coprime.",
"$x$ is even.",
"$n$ is prime."
] |
A
|
Which of these attacks applies to the Diffie-Hellman key exchange when the channel cannot be authenticated?
|
[
"Meet-in-the-middle attack",
"Birthday Paradox",
"Attack on low exponents",
"Man-in-the-middle attack"
] |
D
|
Which of the following is an acceptable commitment scheme, i.e., one that verifies the hiding and binding property (for a well chosen primitive and suitable $x$ and $r$):
|
[
"$Commit(x;r) = Enc_r(x)$, where $Enc_r$ is a symmetric encryption scheme with key $r$.",
"$Commit(x;r) = H(x)$, where $H$ is a hash function.",
"$Commit(x;r) = x \\oplus r$, where $\\oplus$ is the bitwise xor operation.",
"$Commit(x;r) = H(r\\|x)$, where $H$ is a hash function and $\\|$ denotes the concatenation."
] |
D
|
A 128-bit key ...
|
[
"has 128 decimal digits.",
"is too long for any practical application.",
"provides reasonable security for at least four decades.",
"adresses $n^2$ problem for $n=2^{64}$."
] |
C
|
Consider a hash function $H$ with $n$ output bits. Tick the \emph{incorrect} assertion.
|
[
"Due to birthday paradox, an output collision of $H$ can be found much faster than with running time $2^n$.",
"It is possible to find an output collision of $H$ with $O(2^{\\frac{n}{2}})$ memory and $O(2^{\\frac{n}{2}})$ running time.",
"It is possible to find an output collision of $H$ with $O(1)$ memory and $O(2^{\\frac{n}{2}})$ running time.",
"It is possible to find an output collision of $H$ with $O(2^{\\frac{n}{2}})$ memory and $O(1)$ running time."
] |
D
|
Enigma
|
[
"was a predecessor of a Turing machine model - a basis of Von Neumann architecture",
"achieves perfect security as was required due to military application",
"follows the Kerkhoffs principle",
"has approximately $2^{256}$ possible keys"
] |
C
|
Tick the \emph{incorrect} assertion. In RSA with public key $(e,N)$ and private key $(d,N)$ \ldots
|
[
"we can recover $d$ if we can compute square root modulo $N$ efficiently.",
"$e=3$ can be a valid choice of the public key-exponent.",
"to decrypt a ciphertext $c$, we compute $c^d \\bmod{N}$.",
"we must have that $\\gcd(e,d) = 1$ to be able to decrypt unambiguously."
] |
D
|
Tick the \emph{false} assertion concerning WEP
|
[
"In WEP, encryption is based on RC4.",
"In WEP, IVs repeat themselves too often.",
"In WEP, encryption is based on a block cipher.",
"WPA-TKIP was designed as a quick fix for WEP."
] |
C
|
Let $n$ be an integer. Which of the following is \emph{not} a group in the general case?
|
[
"$(\\mathbf{R},+)$",
"$(\\mathbf{Q}\\setminus \\{0\\},\\times)$",
"$(\\mathbf{Z}_n,+ \\pmod{n})$",
"$(\\mathbf{Z}_n,\\times \\pmod{n})$"
] |
D
|
Tick the \textbf{true} statement.
|
[
"If $x \\in \\mathbb{Z}_n^*$ has an order of $m$, then $x^i \\equiv x^{i \\pmod{m}} \\pmod{n} $ for all $i\\in \\mathbb{Z}$.",
"For all $x \\in \\mathbb{Z}_n$, we have $x^{\\varphi(n)}\\equiv 1 \\pmod{n}$.",
"For all $n \\geq 2$, $\\mathbb{Z}_n^*$ has order of $n-1$.",
"For all $n \\geq 2$ and all $x \\in \\mathbb{Z}_n$, $x$ is invertible if and only if $x$ divides $n$."
] |
A
|
What is $\varphi(48)$?
|
[
"$47$",
"$16$",
"$24$",
"$30$"
] |
B
|
Tick the true assertion.
|
[
"A dictionary attack requires less memory than a time-memory tradeoff.",
"Double-DES succumbs under a Meet-in-the-Middle attack.",
"AES is the ancestor of DES.",
"IDEA has the same round functions as DES."
] |
B
|
Tick the \emph{correct} assertion.
|
[
"MD5 is using a compression function based on the Davies-Meyer scheme.",
"The Keccak hash function is based on the Merkle-Damg{\\aa}rd construction.",
"Plain CBCMAC is resistant to forgery attacks.",
"GCM is an efficient MAC based on the CBC mode."
] |
A
|
The Time-Memory Tradeoff Attack ...
|
[
"is useful for finding a preimage within complexity $O\\big(\\big({\\frac{2}{3}}\\big)^N\\big).$",
"is useful for finding a preimage within complexity $O(N^{\\frac{2}{3}}).$",
"is a dedicated method which works only on SHA1.",
"can be combined with birthday paradox to find the order of the group in RSA efficiently."
] |
B
|
Let $f: \mathbb{Z}_{m n} \rightarrow \mathbb{Z}_m \times \mathbb{Z}_n$ be defined by $f (x) = (x \bmod m,x \bmod n)$. Then $f$ is a ring isomorphism between $\mathbb{Z}_{180}$ and:
|
[
"$\\mathbb{Z}_{2} \\times \\mathbb{Z}_{90}$.",
"$\\mathbb{Z}_{4} \\times \\mathbb{Z}_{45}$.",
"$\\mathbb{Z}_{10} \\times \\mathbb{Z}_{18}$.",
"$\\mathbb{Z}_{6} \\times \\mathbb{Z}_{30}$."
] |
B
|
A Carmichael number $n$ ...
|
[
"is a prime number.",
"will always pass Fermat's test for any $0 < b < n$.",
"verifies that $\\forall b$, $\\mathsf{gcd}(b,n)=1$ implies that $b^{n-1} \\equiv 1 \\ \\pmod n $.",
"will be considered as a prime by the Miller-Rabin algorithm."
] |
C
|
Which symmetric key primitive is used in WPA2 encryption?
|
[
"RC4 CBC Mode",
"KASUMI ECB Mode",
"MD5 OFB Mode",
"AES CCM Mode"
] |
D
|
Let $n$ be an integer. What is the cardinality of $\mathbf{Z}^*_n$?
|
[
"$n$",
"$n-1$",
"$\\varphi(n)$",
"$\\varphi(n-1)$"
] |
C
|
Let $n$ be any positive integer. Three of the following assertions are equivalent. Tick the remaining one.
|
[
"$\\mathbb{Z}_n$ is a field.",
"$\\varphi(n)=n-1 $, where $\\varphi$ denotes the Euler totient function.",
"$n$ is a prime power.",
"Any element $x \\in \\mathbb{Z}_n \\backslash \\{0\\}$ is invertible."
] |
C
|
Birthday attacks \dots
|
[
"are used to break Google Calendars.",
"can be used to find collisions in hash functions.",
"are equivalent to exhaustive search.",
"imply that a majority of people is born in Spring."
] |
B
|
What is the number of secret bits in a WEP key?
|
[
"64 or 128 bits.",
"40 or 104 bits.",
"64 or 128 bytes.",
"40 or 104 bytes."
] |
B
|
Tick the \emph{incorrect} assertion. In a multiplicative cyclic group $G$ of order $m > 1$ with neutral element $e_G$ \ldots
|
[
"$\\lambda = m$, where $\\lambda$ is the exponent of $G$.",
"the order of every element $x \\in G$ is $m$.",
"there exists $g \\in G$ that generates the whole group.",
"for any $x \\in G$, we have that $x^m = e_{G}$."
] |
B
|
Which one of the following notions means that ``the information must be protected against any malicious modification''?
|
[
"privacy.",
"integrity.",
"confidentiality.",
"reliability."
] |
B
|
Confidentiality means that:
|
[
"the message can be read by anyone.",
"information should not leak to any unexpected party.",
"the message should make clear who the author is.",
"the information must be protected against any malicious modification."
] |
B
|
Which of the following acronyms does not designate a mode of operation?
|
[
"CBC",
"CTR",
"CRC",
"ECB"
] |
C
|
Select the \emph{incorrect} statement. The brute force attack \dots
|
[
"can be applicable after decades according to Moore's law.",
"can break a cipher with a $128$-bit key on your PC today.",
"has higher worst case complexity than average case complexity.",
"refers to a way of getting the secret key, exhaustively."
] |
B
|
WEP \dots
|
[
"provides good confidentiality.",
"provides good message integrity.",
"provides good authentication.",
"is badly broken."
] |
D
|
The DES key schedule\dots
|
[
"\\dots is based on a Feistel scheme.",
"\\dots takes as an input a key of 128 bits.",
"\\dots generates 16 subkeys.",
"\\dots in only used during the encryption phase, not during the decryption phase."
] |
C
|
How many generators do we have in a group of order $13$?
|
[
"13.",
"12.",
"6.",
"2."
] |
B
|
Which of the following attacks needs no precomputation.
|
[
"Exhaustive search.",
"Dictionary attack.",
"Meet-in-the-middle attack.",
"A time memory tradeoff."
] |
A
|
Which one of these is \emph{not} a hard computational problem?
|
[
"Factoring.",
"Extracting square roots.",
"Computing the Jacobi symbol.",
"Computing the discrete log."
] |
C
|
Select the \textbf{most accurate} answer. For a hash function to be secure (\textbf{but still efficient}) against collision attacks in 2015, the output length should be\dots
|
[
"around 80 bits.",
"around 160 bits.",
"around 512 bits.",
"around 1024 bits."
] |
B
|
Tonelli Algorithm is for ...
|
[
"computing the discrete logarithm.",
"finding the inverse of an element in $\\mathbb{Z}$.",
"finding the square-root of an integer in $\\mathbb{Z}_p^*$.",
"solving the extended Euclidean algorithm $\\mathbb{Z}$."
] |
C
|
Select the \emph{incorrect} statement
|
[
"RC4, A5/1, E0 are stream ciphers",
"MD4, MD5, SHA0, SHA1 are hash functions",
"DES, AES are block ciphers",
"ECB, KDF, PRF are commitment schemes"
] |
D
|
Let $(G,+), (H,\times)$ be two groups and $f:G\to H$ be an homomorphism. For $x_1,x_2 \in G$, we have:
|
[
"$f(x_1) + f(x_2)=f(x_1)\\times f(x_2)$",
"$f(x_1 + x_2)=f(x_1)\\times f(x_2)$",
"$f(x_1 + f(x_2))=f(x_1\\times f(x_2))$",
"$f(x_1 \\times x_2)=f(x_1)+ f(x_2)$"
] |
B
|
Which of the following terms represents a mode of operation which transforms a block cipher into a stream cipher?
|
[
"3DES",
"CBC",
"ECB",
"CTR"
] |
D
|
The Shannon theorem states that perfect secrecy implies...
|
[
"$H(K)=H(X)$",
"$H(Y)\\geq H(X)$",
"$H(K)\\geq H(X)$",
"$H(Y)\\leq H(X)$"
] |
C
|
Tick the \textbf{false} statement. The Shannon Encryption Model ...
|
[
"requires a black-box encryption model.",
"assumes a known input distribution.",
"assumes the key is independent from the message.",
"requires the correctness property $\\Pr[C_K^{-1}(C_K(X))=X]=1$."
] |
A
|
Select the \emph{incorrect} statement. The UMTS improves the security of GSM using
|
[
"authentication of the challenge.",
"integrity protection.",
"A6/1 for encryption.",
"protection against replay attacks."
] |
C
|
Let $n$ be an integer. The extended Euclidean algorithm is typically used to\dots
|
[
"\\dots perform the addition of two integers in $\\mathbf{Z}_n^*$.",
"\\dots compute the inverse of an element in $\\mathbf{Z}_n^*$.",
"\\dots compute the square of an element of $\\mathbf{Z}_n^*$.",
"\\dots compute the order of $\\mathbf{Z}_n^*$."
] |
B
|
If we need to create a channel that protects confidentiality and we have at our disposal a channel that protects integrity and authenticity, we need to use
|
[
"symmetric key encryption.",
"message authentication codes.",
"public key encryption.",
"digital signatures."
] |
C
|
A \textit{Cryptographic Certificate} is the $\ldots$
|
[
"signature of the user who certifies that a public key belongs to the authority.",
"signature of the user who certifies that a public key belongs to the user.",
"signature of the authority who certifies that a public key belongs to a specific user.",
"diploma which certifies that one has taken the Cryptography and Security Course."
] |
C
|
The Advanced Encryption Standard (AES) is based on arithmetics on\dots
|
[
"$\\mathrm{GF}(256)$",
"$\\mathbf{Z}_{2^8}^*$",
"$\\mathbf{Q}\\setminus \\{0\\}$",
"$\\mathbf{Z}_{2^8}$"
] |
A
|
Tick the \emph{incorrect} assertion. In \emph{all} finite Abelian groups $(G,+)$ \ldots
|
[
"the order of any element divides the order of the group.",
"all the elements are generators.",
"the operation $+$ is commutative.",
"the neutral element has order $1$."
] |
B
|
The needed number of DES operations to attack DES is about ...
|
[
"$2^{54}.$",
"$2^{64}.$",
"$2^{128}.$",
"$2^{256}.$"
] |
A
|
Which algorithm can be typically used in order to generate a prime number?
|
[
"The Left to Right Algorithm",
"The Extended Euclidean Algorithm",
"The Miller-Rabin Test",
"The Tonelli Algorithm"
] |
C
|
Tick the \emph{correct} assertion. In RSA with public key $(e,N)$ and private key $(d,N)$ \ldots
|
[
"the key generation requires that $\\gcd(e,N) = 1$.",
"decryption does not work for some $y \\in \\mathbb{Z}_N$ for which $\\gcd(y,N) \\not= 1$.",
"if we know $\\phi(N)$, the ciphertext $y$ and the public key, we can decrypt $y$.",
"in order to decrypt we need to have $e^d \\equiv 1 \\pmod{N}$."
] |
C
|
Tick the \emph{correct} assertion concerning WPA2
|
[
"WPA2 uses RC4.",
"WPA2 uses AES.",
"WPA2 uses 64-bit keys.",
"WPA2 is badly broken."
] |
B
|
Tick the \textbf{false} statement regarding Kerckhoffs' principle.
|
[
"The system must be practically, if not mathematically, indecipherable.",
"Besides keeping the key secret, the cryptosystem must also be kept secret.",
"It must be applicable to telegraphic correspondence.",
"Its key must be communicable and retainable without the help of written notes, and changeable or modifiable at the will of the correspondents."
] |
B
|
Let $H$ be a hash function based on the Merkle-Damg{\aa}rd construction. The Merkle-Damg{\aa}rd theorem says that \dots
|
[
"\\dots $H$ is collision-resistant when the compression function is collision-resistant.",
"\\dots the compression function is collision-resistant when $H$ is collision-resistant.",
"\\dots $H$ is collision-resistant.",
"\\dots $H$ is not collision-resistant."
] |
A
|
Consider a blockcipher $\mathsf{B}:\mathcal{K}\times\{0,1\}^n \rightarrow \{0,1\}^n$ with $|\mathcal{K}|=N$ for which we choose a secret key $K\in\mathcal{K}$ uniformly at random. Tick the \textit{correct} assertion.
|
[
"If $\\mathsf{B}$ is secure against known-plaintext decryption attack, then it is surely secure against ciphertext-only key recovery attack.",
"If $\\mathsf{B}$ is secure against known-plaintext decryption attack, then it is surely secure against chosen-ciphertext decryption attack.",
"It is possible to recover $K$ with precomputation: $O(N^{2/3})$, memory: $O(N^{2/3})$, time: $O(1)$.",
"It is possible to recover $K$ key with precomputation: $O({1})$, memory: $O(N)$, time: $O(1)$."
] |
A
|
The $n^2$ problem ...
|
[
"is dealt with thanks to Moore's Law.",
"is a consequence of Murphy's Law.",
"is a direct consequence of the Kerchkoffs Principles.",
"appears when $n$ users need to communicate to each other using a symmetric cipher."
] |
D
|
A passive adversary\dots
|
[
"can only listen to the communications.",
"can play the man-in-the-middle.",
"can only alter messages.",
"can delete messages."
] |
A
|
Tick the \textbf{true} statement regarding RSA Cryptosystem.
|
[
"$(e,N,\\varphi(N))$ are the public parameters.",
"$e$ is a valid public key if $\\gcd(e,N)=1$.",
"Encryption and decryption are performed with the same key.",
"$ed \\equiv 1 \\pmod{\\varphi(N)}$."
] |
D
|
The Vernam cipher\dots
|
[
"\\dots is perfectly secure (if used in a proper way).",
"\\dots can be broken using an index of coincidence.",
"\\dots is always less secure than DES.",
"\\dots has a security which depends on the Moore law."
] |
A
|
Which protocol does \emph{not} use RC4.
|
[
"WEP",
"WPA",
"WPA2",
"TLS"
] |
C
|
Which of the following is a mode of operation for blockciphers that requires a non-repeating IV (a nonce) to be secure?
|
[
"ECB",
"CBC",
"TCS",
"CTR"
] |
D
|
How many generators are there in $\mathbb{Z}_n$?
|
[
"$1$",
"$n-1$",
"$n$",
"$\\varphi (n)$"
] |
D
|
Using salt for UNIX passwords \ldots
|
[
"allows to speed up the verification for the server.",
"makes the protocol secure against computationally unbounded adversary.",
"allows to transmit the password over a non confidential channel without compromising the security.",
"helps preventing dictionary attacks."
] |
D
|
One can find a collision in a hash function $h\colon \{0,1\}^* \rightarrow \{0,1\}^n$ with expected time complexity\dots
|
[
"$\\Theta(\\sqrt{n})$.",
"$\\Theta(n)$.",
"$\\Theta(2^n)$.",
"$\\Theta(2^{n/2})$."
] |
D
|
Tick the \textbf{false} statement regarding the Enigma machine.
|
[
"It is an electro-mechanical encryption device used by German armies in World War 2.",
"Its specifications are secret.",
"Its secret parameters are: ordered permutations, an involution, and a number.",
"It was patented in 1918."
] |
B
|
One of the following ciphers is a \emph{block} cipher. Which one?
|
[
"AES",
"RC4",
"A5/1",
"MD5"
] |
A
|
Compute $\phi(90)$.
|
[
"$36$.",
"$24$.",
"$16$.",
"$48$."
] |
B
|
Let $p$ and $q$ be two prime numbers and $n=pq$. Let $K_p=(e,n)$ and $K_s=(d,n)$ be the RSA public and private keys respectively. Recall that the encryption of a message $m$ is $c=m^e \bmod{n}$ and the decryption is $m=c^d \bmod{n}$. Which assertion is \emph{always true}?
|
[
"$ed=1 \\pmod{n}$",
"$ed=1 \\pmod{\\varphi(n)}$",
"$e=d \\pmod{n}$",
"$e=d \\pmod{\\varphi(n)}$"
] |
B
|
Select the non-associative operation.
|
[
"$+$ (addition)",
"$-$ (subtraction)",
"$\\times$ (multiplication)",
"$\\oplus$ (exclusive-or)"
] |
B
|
MD5 is
|
[
"a secure block cipher",
"a broken block cipher",
"a secure hash function",
"a broken hash function"
] |
D
|
Let $N=3\cdot5\cdot13$. Then a quadratic residue in $\mathbb{Z}_N^*$ has
|
[
"$2$ square roots.",
"$3$ square roots.",
"$6$ square roots.",
"$8$ square roots."
] |
D
|
Tick the \textbf{incorrect} assertion regarding WEP and WPA2.
|
[
"WPA2 seems to be more secure than WEP.",
"WPA2 seems to ensure confidentiality.",
"WPA2 uses AES.",
"WEP seems to ensure message integrity."
] |
D
|
Plain RSA (with an $\ell$-bit modulus) \dots
|
[
"is commonly used in practice.",
"decrypts in $O(\\ell^2)$ time.",
"encrypts in $O(\\ell)$ time.",
"has homomorphic properties."
] |
D
|
Pick the \emph{correct} statement.
|
[
"A homomorphism is defined as a bijective isomorphism.",
"An isomorphism is defined as a bijective homomorphism.",
"An isomorphism is any homomorphism $h: X\\rightarrow X$.",
"A homomorphism is any non-bijective isomorphism."
] |
B
|
Which of the following elements belong to $\mathbf{Z}_{35}^*$?
|
[
"$12$.",
"$20$.",
"$14$.",
"$15$."
] |
A
|
When using the plain ElGamal cryptosystem over the group $\mathbb{Z}_p^*$ with a fixed $\ell$-bit prime $p$ and a fixed generator $g\in\mathbb{Z}_p^*$, the \textit{tightest} complexity of generating a new key-pair is\ldots
|
[
"$\\mathcal{O}(4{\\ell})$.",
"$\\mathcal{O}(\\ell^3)$.",
"$\\mathcal{O}(\\ell^2)$.",
"$\\mathcal{O}(\\log{\\ell}^4)$."
] |
B
|
We represent $GF(2^8)$ as $\mathbb{Z}_2[X]/P(X)$ where $P(X) = X^8 + X^4+X^3+X+1$. Then, $(X^7+X^6)\times (X + 1)=$\dots
|
[
"$X^6+X^5+X^4+X^3+X$.",
"$X^6 + X^4 + X^3 + X + 1$.",
"$X^6$.",
"$X^7+X^6+X^4+X^3+X+1$."
] |
B
|
Tick the \textit{wrong} assertion.
|
[
"Factoring is believed to be a hard problem.",
"Factoring is easy if we know $\\varphi{(n)}$.",
"Computing square roots in $\\mathbb{Z}_n$ can be used to factor $n$.",
"Discrete logarithm problem is always hard on any group."
] |
D
|
Select the \emph{incorrect} statement: hash functions can be used to construct
|
[
"commitment schemes",
"key derivation functions",
"message authentication codes",
"public key cryptosystems"
] |
D
|
Tick the \emph{false} assertion about Diffie and Hellman.
|
[
"They wrote an article entitled ``\\emph{New directions in Cryptography}'' in 1976.",
"They introduced the notion of ``\\emph{trapdoor permutation}''.",
"They proposed a key agreement protocol.",
"They invented RSA."
] |
D
|
A hash function $h$ is collision-resistant if\dots
|
[
"\\dots given $y$, it is hard to find $x$ such that $h(x)=y$",
"\\dots given $x$, it is hard to find $y$ such that $h(x)=y$",
"\\dots given $x$, it is hard to find $x' \\ne x$ such that $h(x)=h(x')$",
"\\dots it is hard to find $x,x'$ such that $x \\ne x'$ and $h(x) = h(x')$"
] |
D
|
Tick the \textbf{false} statement. Bluetooth 2.0 Pairing is secure when ...
|
[
"the PIN has a large entropy.",
"it is done only once.",
"it runs in a Faraday cage.",
"it is not used."
] |
B
|
Bluetooth pairing v2.0 is based on\dots
|
[
"bilinar mappings over elliptic curves.",
"a short authenticated string.",
"an ephemeral secret PIN code.",
"a secure token."
] |
C
|
The Kerckhoffs principle says that
|
[
"the design of a cryptosystem has to be public to be secure.",
"the design of a cryptosystem has to be secure before being made public.",
"the security of a system should not rely on the secrecy of the cryptosystem.",
"a cryptosystem should have a public component (such as a key) to be secure."
] |
C
|
A MAC forgery is\dots
|
[
"a valid pair $(X,c)$ produced by the adversary.",
"a valid pair $(X,c)$ produced by the MAC issuer.",
"a valid pair $(X,c)$ produced by the MAC verifier.",
"a key recovery attack."
] |
A
|
Tick the \textbf{incorrect} assertion.
|
[
"Solving the discrete logarithm in the group $\\mathbb{Z}_N$ might help breaking the Rabin cryptosystem.",
"Solving the factoring problem might help breaking the Rabin cryptosystem.",
"Finding square roots in $\\mathbb{Z}_N$ might help breaking the Rabin cryptosystem.",
"To decrypt properly a Rabin ciphertext we usually assume that some redundancy was added to the plaintext."
] |
A
|
The encryption in GSM is done by ...
|
[
"A3.",
"A8.",
"E0.",
"A5."
] |
D
|
Tick the \textbf{false} statement. GSM anonymity is broken by ...
|
[
"replaying an A3 challenge.",
"desynchronizing the mobile station and the network.",
"using A5/1.",
"sniffing the very first connection protocol."
] |
C
|
Tick the \emph{true} assertion related to the ElGamal signature scheme.
|
[
"A signature of a given message is obtained in a deterministic way.",
"The generator $g$ generates a subgroup of prime order.",
"The signature verification procedure is probabilistic.",
"The main computational cost of the signature generation is due to one modular exponentiation."
] |
D
|
The Kerckhoff's principle is not followed when security requires that \dots
|
[
"the security of a cryptosystem relies on the secrecy of the encryption algorithm.",
"the name of the cryptosystem's designer is kept secret.",
"the key of the cryptosystem is kept secret.",
"the cryptosystem is kept secret."
] |
A
|
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