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WorksheetsCryptology Tools
Total questions: 73
Worksheet time: 18hrs 15mins
What is data confidentiality?
information is not disclosed to unauthorized parties
information cannot be modified by unauthorized parties
data and resources are available to authorized users
What is data integrity?
information is not disclosed to unauthorized parties
information cannot be modified by unauthorized parties
data and resources are available to authorized users
What is data availability?
information is not disclosed to unauthorized parties
information cannot be modified by unauthorized parties
data and resources are available to authorized users
What does a transposition cipher do?
rearranges plaintext characters to alter their position.
replaces plaintext characters by different ciphertext characters.
What does a substitution cipher do?
rearranges plaintext characters to alter their position.
replaces plaintext characters by different ciphertext characters.
A cryptosystem is a five-tuple (P, C,K, E, D). What is true about P?
P is a finite set of plaintexts (ranged over by m).
P is a finite set of ciphertexts (ranged over by c).
P, the keyspace, is a finite set of keys (ranged over by k).
P is a family of encryption rules ek : P → C.
P is a family of decryption rules dk : C → P.
A cryptosystem is a five-tuple (P, C,K, E, D). What is true about C?
C is a finite set of plaintexts (ranged over by m).
C is a finite set of ciphertexts (ranged over by c).
C, the keyspace, is a finite set of keys (ranged over by k).
C is a family of encryption rules ek : P → C.
C is a family of decryption rules dk : C → P.
A cryptosystem is a five-tuple (P, C,K, E, D). What is true about K?
K is a finite set of plaintexts (ranged over by m).
K is a finite set of ciphertexts (ranged over by c).
K, the keyspace, is a finite set of keys (ranged over by k).
K is a family of encryption rules ek : P → C.
K is a family of decryption rules dk : C → P.
A cryptosystem is a five-tuple (P, C,K, E, D). What is true about E?
E is a finite set of plaintexts (ranged over by m).
E is a finite set of ciphertexts (ranged over by c).
E, the keyspace, is a finite set of keys (ranged over by k).
E is a family of encryption rules ek : P → C.
E is a family of decryption rules dk : C → P.
A cryptosystem is a five-tuple (P, C,K, E, D). What is true about D?
D is a finite set of plaintexts (ranged over by m).
D is a finite set of ciphertexts (ranged over by c).
D, the keyspace, is a finite set of keys (ranged over by k).
D is a family of encryption rules ek : P → C.
D is a family of decryption rules dk : C → P.
What is Kerckhoffs’s principle?
a cryptosystem should be secure even if everything about the system, except the key, is public knowledge.
the number of transistors on a chip doubles approximately every two years.
a cryptosystem should be secure as long as the key is is not public knowledge.
A cryptosystem should be secure regardless of hardware
What is Moore's law?
a cryptosystem should be secure even if everything about the system, except the key, is public knowledge.
the number of transistors on a chip doubles approximately every two years.
a cryptosystem should be secure as long as the key is is not public knowledge.
A cryptosystem should be secure regardless of hardware
What would have taken the world’s fastest supercomputer a year back in 2000 can be computed in _____ today.
an hour
a day
a week
a month
half a year
Is 17 ≡ 7 (mod 5)?
Yes
No
Is 38 ≡ 14 (mod 12)?
Yes
No
Is 54 ≡ 21 (mod 7)?
Yes
No
What is 7 + 2 in Z9? (Zm is the set {0, . . . , m − 1})
0
1
2
3
4
What is 11*13 in Z16? (Zm is the set {0, . . . , m − 1})
13
14
15
16
17
Identify A with 0, B with 1, ..., Z with 25. For the plaintext: THISISASHIFTCIPHER, what would be the encrypted text given k = 11 for a shift cipher?
ESTDTDLDSTQENTASPC
ESTDTDLDSTRENTASPC
ESTDTDLESTQENTASPC
ESTDTDLDSTQENTBSPC
ESTDTDLDSTQFNTASPC
What is the multiplicative inverse of 3 modulo 5?
1
2
3
4
5
What is the multiplicative inverse of 1 modulo m?
1
2
3
4
0
Is there a multiplicative inverse of 2 modulo 6?
Yes
No
What is gcd(654, 444)?
4
5
6
7
8
What is true about a simple substitution cipher?
A simple substitution cipher operates on single letters.
A simple substitution cipher operates on larger groups of letters.
A simple cipher uses a fixed substitution over the entire message.
A simple cipher uses different substitutions at different places in the message.
What is true about a polygraphic substitution cipher?
A polygraphic substitution cipher operates on single letters.
A polygraphic substitution cipher operates on larger groups of letters.
A polygraphic cipher uses a fixed substitution over the entire message.
A polygraphic cipher uses different substitutions at different places in the message.
What is true about a monoalphabetic cipher?
A monoalphabetic cipher operates on single letters.
A monoalphabetic cipher operates on larger groups of letters.
A monoalphabetic cipher uses a fixed substitution over the entire message.
A monoalphabetic cipher uses different substitutions at different places in the message.
What is true about a polyalphabetic cipher?
A polyalphabetic cipher operates on single letters.
A polyalphabetic cipher operates on larger groups of letters.
A polyalphabetic cipher uses a fixed substitution over the entire message.
A polyalphabetic cipher uses different substitutions at different places in the message.
What type of cipher is the Vigenère Cipher?
A simple substitution cipher
A polygraphic substitution cipher
A monoalphabetic cipher
A polyalphabetic cipher
A synchronous stream cipher is a _____________
five-tuple
six-tuple
seven-tuple
eight-tuple
nine-tuple
What is P in a synchronous stream cipher?
a finite set of plaintext (ranged over b m)
a finite set of ciphertexts (ranged over by m)
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What is C in a synchronous stream cipher?
a finite set of plaintext (ranged over b m)
a finite set of ciphertexts (ranged over by m)
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What is K in a synchronous stream cipher?
a finite set of plaintext (ranged over b m)
a finite set of ciphertexts (ranged over by m)
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What is L in a synchronous stream cipher?
a finite set of plaintext (ranged over b m)
a finite set of ciphertexts (ranged over by m)
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What is E in a synchronous stream cipher?
a finite set of plaintext (ranged over b m)
a finite set of ciphertexts (ranged over by m)
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What is D in a synchronous stream cipher?
is a family of decryption rules dz : C → P.
a finite set of ciphertexts (ranged over by m)
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What is g in a synchronous stream cipher?
is a family of decryption rules dz : C → P.
K → L ω is the keystream generator.
the keyspace, is a finite set of keys (ranged over by k)
is a finite set, called the keystream alphabet (ranged over by z)
is a family of encryption rules ez : P → C.
What type of cipher is the Vernan Cipher?
A simple substitution cipher
A polygraphic substitution cipher
A monoalphabetic cipher
A polyalphabetic cipher
A polyalphabetic stream cipher
The following text is encrypted using a shift cipher: BEEAKFYDJXUQYHYJIQRYHTYJIQFBQDUYJIIKFUHCQD
What superhero does it mention?
Spiderman
Batman
Superman
Aquaman
The flash
What is true about a Ciphertext only attack?
The attacker possesses a string of ciphertext, y.
The attacker possesses a string of plaintext, x, and the corresponding ciphertext, y.
The attacker has obtained temporary access to the encryption machinery. He can choose plaintexts x, and construct the corresponding ciphertexts y
The attacker has obtained temporary access to the decryption machinery. He can choose ciphertexts y, and construct the corresponding plaintexts x.
What is true about a known plaintext attack?
The attacker possesses a string of ciphertext, y.
The attacker possesses a string of plaintext, x, and the corresponding ciphertext, y.
The attacker has obtained temporary access to the encryption machinery. He can choose plaintexts x, and construct the corresponding ciphertexts y
The attacker has obtained temporary access to the decryption machinery. He can choose ciphertexts y, and construct the corresponding plaintexts x.
What is true about a chosen plaintext attack?
The attacker possesses a string of ciphertext, y.
The attacker possesses a string of plaintext, x, and the corresponding ciphertext, y.
The attacker has obtained temporary access to the encryption machinery. He can choose plaintexts x, and construct the corresponding ciphertexts y
The attacker has obtained temporary access to the decryption machinery. He can choose ciphertexts y, and construct the corresponding plaintexts x.
What is true about a chosen ciphertext attack?
The attacker possesses a string of ciphertext, y.
The attacker possesses a string of plaintext, x, and the corresponding ciphertext, y.
The attacker has obtained temporary access to the encryption machinery. He can choose plaintexts x, and construct the corresponding ciphertexts y
The attacker has obtained temporary access to the decryption machinery. He can choose ciphertexts y, and construct the corresponding plaintexts x.
How many keys on average does a brute force attack have to check?
|K|
|K|/2
|K|/3
|K|/4
|K|/5
What block size does AES use?
128 bit
256 bit
64 bit
32 bit
512 bit
What key size does AES use?
128 bit
256 bit
64 bit
32 bit
192 bit
What are the the properties that help ensure security of a block cipher?
Confusion
Diffusion
Disguise
Divergence
Obscurity
What is true about confusion when it comes to security of a block cipher?
makes it hard to find the key even if one has a large number of plaintext-ciphertext pairs.
Each bit of the ciphertext block depends on the plaintext block bits and the key bits in a complex (highly nonlinear) way
Each plaintext block bit or key bit affects many bits of the ciphertext block.
Ideally, the strict avalanche criterion is satisfied: flipping a single input bit changes each output bit with probability 0.5.
dissipates statistical regularities of small plaintext structures into statistical regularities of much larger ciphertext structures.
What is true about diffusion when it comes to security of a block cipher?
makes it hard to find the key even if one has a large number of plaintext-ciphertext pairs.
Each bit of the ciphertext block depends on the plaintext block bits and the key bits in a complex (highly nonlinear) way
Each plaintext block bit or key bit affects many bits of the ciphertext block.
Ideally, the strict avalanche criterion is satisfied: flipping a single input bit changes each output bit with probability 0.5.
dissipates statistical regularities of small plaintext structures into statistical regularities of much larger ciphertext structures.
What is a one-way function?
a function that is easy to compute on every input, but hard to invert for the image of a random input.
a function that is easy to invert if one is given additional information
a function that is hard to compute on every input, but easy to invert for the image of a random input.
a function that is hard to invert despite given additional information
What is a trapdoor function?
a function that is easy to compute on every input, but hard to invert for the image of a random input.
a function that is easy to invert if one is given additional information
a function that is hard to compute on every input, but easy to invert for the image of a random input.
a function that is hard to invert despite given additional information
What year was the first key-recovery attacks on full AES published?
2009
2010
2011
2012
2013
How many keys does a public-key cryptosystem use?
1
2
3
4
5
What is the most widely-used public-key algorithm in the world?
AES
RSA
PGP
DNS
DKIM
Does a public-key encryption allow chosen plaintext attacks?
Yes
No
Does a public-key encryption rely on computational security or perfect secrecy?
Computational security
Perfect secrecy
A trapdoor function is a one-way function that is hard to invert regardless of any given additional information.
False
True
What does RSA rely on?
Integer factorization problem
Discrete logarithm
Simultaneous embedding
Matrix multiplication
Rotation distance
Compute 35 mod 7
3
4
5
6
7
What theorem does RSA rely on?
Fermat's little theorem
Prime number theorem
The infinitude of primes
Polyhedron formula
Fermat's last theorem
NIST key management guidelines suggest that 15360-bit RSA keys are equivalent in strength to _____-bit symmetric keys.
256
128
512
64
1024
NIST key management guidelines suggest that _____-bit RSA keys are equivalent in strength to 256-bit symmetric keys.
15360
7680
3840
1920
30720
What is the typical symmetric-key size?
50-250 bits
250-500 bits
500-4500 bits
25-50 bits
8 bits
What is the typical public-key size?
50-250 bits
250-500 bits
500-4500 bits
25-50 bits
8 bits
What is a key encapsulation scheme?
a public-key cryptosystem
a symmetric-key cryptosystem
What is a data encapsulation scheme?
a public-key cryptosystem
a symmetric-key cryptosystem
What is a hash family?
a three-tuple
a four-tuple
a five-tuple
a six-tuple
a seven-tuple
What is M in a hash family?
a (possibly infinite) set of messages
a finite set of message digests
the keyspace, a finite set of keys
For each k ∈ K, there is a hash function hk : H → D in M.
What is D in a hash family?
a (possibly infinite) set of messages
a finite set of message digests
the keyspace, a finite set of keys
For each k ∈ K, there is a hash function hk : H → D in M.
What is K in a hash family?
a (possibly infinite) set of messages
a finite set of message digests
the keyspace, a finite set of keys
For each k ∈ K, there is a hash function hk : H → D in M.
What is H in a hash family?
a (possibly infinite) set of messages
a finite set of message digests
the keyspace, a finite set of keys
For each k ∈ K, there is a hash function hk : M → D in H.
What is preimage resistance?
Given a digest y, it should be infeasible to find a message x such that h(x) = y. In other words, h is a one-way function.
Given a message x, it should be infeasible to find another message x' ≠ x such that h(x') = h(x).
It should be infeasible to find two messages x, x' (with x ≠ x' ) such that h(x) = h(x').
What is second preimage resistance?
Given a digest y, it should be infeasible to find a message x such that h(x) = y. In other words, h is a one-way function.
Given a message x, it should be infeasible to find another message x' ≠ x such that h(x') = h(x).
It should be infeasible to find two messages x, x' (with x ≠ x' ) such that h(x) = h(x').
What is collision resistance?
Given a digest y, it should be infeasible to find a message x such that h(x) = y. In other words, h is a one-way function.
Given a message x, it should be infeasible to find another message x' ≠ x such that h(x') = h(x).
It should be infeasible to find two messages x, x' (with x ≠ x' ) such that h(x) = h(x').
