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Questions and Answers
What is the main difference between perfect secrecy and computational secrecy?
What is the main difference between perfect secrecy and computational secrecy?
- Perfect secrecy is measured in terms of CPU cycles, while computational secrecy is measured in terms of time
- Perfect secrecy leaks information with a tiny probability to eavesdroppers with bounded computational power, while computational secrecy leaks absolutely no information about an encrypted message
- Perfect secrecy leaks absolutely no information about an encrypted message, while computational secrecy leaks information with a tiny probability to eavesdroppers with bounded computational power (correct)
- Perfect secrecy guarantees security against realistic adversaries, while computational secrecy does not
What does a (t, ϵ)-secure scheme guarantee?
What does a (t, ϵ)-secure scheme guarantee?
- The scheme can be broken with probability at most ϵ in time t
- Any adversary running for time at most t can break the scheme with probability at most ϵ
- No adversary running for time at most t can break the scheme with probability at most ϵ (correct)
- The scheme can be broken with probability at least ϵ in time t
Why is it more convenient to measure running time in terms of CPU cycles for (t, ϵ)-secure schemes?
Why is it more convenient to measure running time in terms of CPU cycles for (t, ϵ)-secure schemes?
- It aligns with the practical implementation of cryptographic schemes (correct)
- It allows for a more accurate measurement of time compared to traditional time units
- It provides a standardized measurement across different computing systems
- It simplifies the calculation of success probability for adversaries
Which block cipher mode is deterministic and cannot be CPA-secure?
Which block cipher mode is deterministic and cannot be CPA-secure?
In which block cipher mode is a uniform initialization vector (IV) of length n chosen?
In which block cipher mode is a uniform initialization vector (IV) of length n chosen?
Which block cipher mode has ciphertext length double the plaintext length in a CPA-secure construction?
Which block cipher mode has ciphertext length double the plaintext length in a CPA-secure construction?
Which block cipher mode involves encrypting a message of length l using a length-preserving block cipher?
Which block cipher mode involves encrypting a message of length l using a length-preserving block cipher?
Which block cipher mode uses an initialization vector (IV) for encryption?
Which block cipher mode uses an initialization vector (IV) for encryption?
What is the key space size for a private-key encryption scheme using a 128-bit key?
What is the key space size for a private-key encryption scheme using a 128-bit key?
For c = 1 and n = 64, how many years does a 4 GHz processor with 16 cores require at most to break the scheme?
For c = 1 and n = 64, how many years does a 4 GHz processor with 16 cores require at most to break the scheme?
How are realistic adversaries modeled in cryptographic schemes?
How are realistic adversaries modeled in cryptographic schemes?
Which of the following is a characteristic of a pseudorandom function?
Which of the following is a characteristic of a pseudorandom function?
In the context of distinguishing pseudorandom functions, what does the theorem state about the construction's security?
In the context of distinguishing pseudorandom functions, what does the theorem state about the construction's security?
What is a characteristic of a strong pseudorandom permutation?
What is a characteristic of a strong pseudorandom permutation?
What is the definition of EAV-security in private-key encryption?
What is the definition of EAV-security in private-key encryption?
What is the key characteristic of a pseudorandom generator used in EAV-secure encryption schemes?
What is the key characteristic of a pseudorandom generator used in EAV-secure encryption schemes?
What is the role of semantic security in private-key encryption?
What is the role of semantic security in private-key encryption?
In the experiment PrivKA,Î (n), what is A given and what does it output?
In the experiment PrivKA,Î (n), what is A given and what does it output?
What does CPA-Security for Multiple Encryptions involve?
What does CPA-Security for Multiple Encryptions involve?
What is the property of pseudorandom functions?
What is the property of pseudorandom functions?
Computational secrecy requirement: Information about the encrypted message is leaked with a tiny probability to eavesdroppers with bounded computational power
Computational secrecy requirement: Information about the encrypted message is leaked with a tiny probability to eavesdroppers with bounded computational power
Upper bounds the success probability of an adversary running for some specified time. A concrete definition of security takes the following form. A scheme is (t, ϵ)-secure is any adversary running for time at most t succeeds in breaking the scheme with probability at most ϵ.
Upper bounds the success probability of an adversary running for some specified time. A concrete definition of security takes the following form. A scheme is (t, ϵ)-secure is any adversary running for time at most t succeeds in breaking the scheme with probability at most ϵ.
How large can t be. How small should ϵ be.
How large can t be. How small should ϵ be.
CPA-secure private-key encryption scheme uses ______ function F
CPA-secure private-key encryption scheme uses ______ function F
Distinguisher has no access to the key k
Distinguisher has no access to the key k
Strong pseudorandom ______ cannot be efficiently distinguished from a random ______
Strong pseudorandom ______ cannot be efficiently distinguished from a random ______
An event that occurs with probability $2^{-60}$ each second is expected to occur once every ______
An event that occurs with probability $2^{-60}$ each second is expected to occur once every ______
A scheme is secure if for every probabilistic polynomial-time adversary A, the probability of A succeeding in the attack is ______
A scheme is secure if for every probabilistic polynomial-time adversary A, the probability of A succeeding in the attack is ______
Both PPT adversaries and ______ probabilities of success are needed to allow practical encryption schemes
Both PPT adversaries and ______ probabilities of success are needed to allow practical encryption schemes
Semantic security is the analog of perfect secrecy for computationally bounded adversaries and is the first definition of computationally secure encryption to be proposed
Semantic security is the analog of perfect secrecy for computationally bounded adversaries and is the first definition of computationally secure encryption to be proposed
______ is a form of security in private-key encryption where an adversary behaves the same, regardless of whether it observes an encryption of m0 or m1
______ is a form of security in private-key encryption where an adversary behaves the same, regardless of whether it observes an encryption of m0 or m1
A ______ is a polynomial-time deterministic algorithm for transforming a short, uniform bitstring called the seed into a longer, 'uniform-looking' output string
A ______ is a polynomial-time deterministic algorithm for transforming a short, uniform bitstring called the seed into a longer, 'uniform-looking' output string
CPA-Security for Multiple Encryptions is stronger than ______
CPA-Security for Multiple Encryptions is stronger than ______
The LR-Oracle Experiment involves A being given 1 and oracle access to LRk,b (â‹…, â‹…) and outputs a bit ______
The LR-Oracle Experiment involves A being given 1 and oracle access to LRk,b (â‹…, â‹…) and outputs a bit ______
The private-key encryption scheme has indistinguishable encryptions under a chosen-plaintext attack if for all PPT adversaries A there is a negligible function ______
The private-key encryption scheme has indistinguishable encryptions under a chosen-plaintext attack if for all PPT adversaries A there is a negligible function ______
ECB is deterministic and cannot be ______
ECB is deterministic and cannot be ______
Let F be a length-preserving block cipher with block length n. A uniform initialization vector (IV) of length n is ______. c0 = IV. For i = 1, … , l, ci := Fk (ci−1 ⊕ mi )
Let F be a length-preserving block cipher with block length n. A uniform initialization vector (IV) of length n is ______. c0 = IV. For i = 1, … , l, ci := Fk (ci−1 ⊕ mi )
Let m = m1 , m2 , … , ml where mi ∈ {0, 1}. n Let F be a length-preserving block cipher with block length n. A uniform initialization vector (IV) of length n is ______.
Let m = m1 , m2 , … , ml where mi ∈ {0, 1}. n Let F be a length-preserving block cipher with block length n. A uniform initialization vector (IV) of length n is ______.
Let m = m1 , m2 , … , ml where mi ∈ {0, 1} n Let F be a length-preserving block cipher with length n To encrypt a message of length l
Let m = m1 , m2 , … , ml where mi ∈ {0, 1} n Let F be a length-preserving block cipher with length n To encrypt a message of length l
Fortunately, there exist secure constructions based on block ciphers that have lower ______
Fortunately, there exist secure constructions based on block ciphers that have lower ______
Study Notes
Security Notions in Private-Key Encryption Schemes
- One-time pad scheme with length l(n) has a view eav ~ (n) of A identical to the view of A in PrivKA,Î when w is chosen uniformly from {0, 1}l(n).
- When w is generated by choosing k uniformly from {0, 1}n := G(k), the view of A is identical to the view of A in PrivKA,Î (n) and setting w.
- In the experiment PrivKA,Î (n), A is given 1, outputs pairs of equal-length message lists, and a key k is generated using Gen.
- The one-time pad does not have indistinguishable multiple encryptions in the presence of an eavesdropper.
- Chosen-plaintext attacks allow an adversary to influence honest parties sharing the key to encrypt messages of its choice.
- Chosen-plaintext attacks are modeled by giving the adversary A access to an encryption oracle.
- The private-key encryption scheme has indistinguishable encryptions under a chosen-plaintext attack if for all PPT adversaries A there is a negligible function negl.
- CPA-Security for Multiple Encryptions extends the CPA indistinguishability experiment to multiple encryptions using lists of plaintexts.
- The LR-Oracle Experiment involves A being given 1 and oracle access to LRk,b (⋅, ⋅) and outputs a bit b′.
- A private-key encryption scheme is CPA-secure for multiple encryptions if for all PPT adversaries A there is a negligible function negl.
- CPA-Security for Multiple Encryptions is stronger than EAV-security.
- Pseudorandom functions are "random-looking" functions, and pseudorandomness is a property of a distribution over functions.
Security Notions in Private-Key Encryption Schemes
- One-time pad scheme with length l(n) has a view eav ~ (n) of A identical to the view of A in PrivKA,Î when w is chosen uniformly from {0, 1}l(n).
- When w is generated by choosing k uniformly from {0, 1}n := G(k), the view of A is identical to the view of A in PrivKA,Î (n) and setting w.
- In the experiment PrivKA,Î (n), A is given 1, outputs pairs of equal-length message lists, and a key k is generated using Gen.
- The one-time pad does not have indistinguishable multiple encryptions in the presence of an eavesdropper.
- Chosen-plaintext attacks allow an adversary to influence honest parties sharing the key to encrypt messages of its choice.
- Chosen-plaintext attacks are modeled by giving the adversary A access to an encryption oracle.
- The private-key encryption scheme has indistinguishable encryptions under a chosen-plaintext attack if for all PPT adversaries A there is a negligible function negl.
- CPA-Security for Multiple Encryptions extends the CPA indistinguishability experiment to multiple encryptions using lists of plaintexts.
- The LR-Oracle Experiment involves A being given 1 and oracle access to LRk,b (⋅, ⋅) and outputs a bit b′.
- A private-key encryption scheme is CPA-secure for multiple encryptions if for all PPT adversaries A there is a negligible function negl.
- CPA-Security for Multiple Encryptions is stronger than EAV-security.
- Pseudorandom functions are "random-looking" functions, and pseudorandomness is a property of a distribution over functions.
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Test your knowledge of security notions in private-key encryption schemes with this quiz. From one-time pad schemes to chosen-plaintext attacks and CPA-security for multiple encryptions, this quiz covers a range of concepts essential for understanding encryption security.
