48 Questions
Which of the following is a precise definition of computational security?
There is no efficient algorithm that can be used by the attacker to succeed with reasonably high probability.
What is the difference between computational security and unconditional security?
Computational security depends on the currently available algorithms and computing power, while unconditional security is impossible to break even with unlimited time and resources.
What is perfect secrecy in cryptography?
Guessing the plaintext has the same chances of success after having seen the ciphertext as it had before seeing it.
What is the main difference between computational security and perfect secrecy?
Computational security allows for some information leakage, while perfect secrecy leaks no information about the plaintext.
What is the definition of unconditional security?
It is impossible (even with unlimited time/resources) to break the cipher.
Which type of attack assumes that the attacker has unlimited computational power?
Ciphertext-only attack
What is the difference between provable security and computational security?
Provable security has a mathematical proof that there is no efficient algorithm to break the cipher, while computational security has no such proof.
Which type of cryptography has provable security?
Public key cryptography
What is the definition of computational security in terms of the probability of success for the attacker?
Reasonably high probability usually means 1/(polynomial in n)
What is the one-time pad?
A cipher with perfect secrecy
What is the difference between computational security and provable security?
Computational security has a mathematical proof that there is no efficient algorithm to break the cipher, while provable security has no such proof.
Which type of cryptography has no provable security?
Symmetric cryptography
Which of the following is a precise definition of computational security?
There is no efficient algorithm that can be used by the attacker to succeed with reasonably high probability.
What is the difference between computational security and unconditional security?
Computational security depends on the currently available algorithms and computing power, while unconditional security is impossible to break even with unlimited time and resources.
What is perfect secrecy in cryptography?
Guessing the plaintext has the same chances of success after having seen the ciphertext as it had before seeing it.
What is the main difference between computational security and perfect secrecy?
Computational security allows for some information leakage, while perfect secrecy leaks no information about the plaintext.
What is the definition of unconditional security?
It is impossible (even with unlimited time/resources) to break the cipher.
Which type of attack assumes that the attacker has unlimited computational power?
Ciphertext-only attack
What is the difference between provable security and computational security?
Provable security has a mathematical proof that there is no efficient algorithm to break the cipher, while computational security has no such proof.
Which type of cryptography has provable security?
Public key cryptography
What is the definition of computational security in terms of the probability of success for the attacker?
Reasonably high probability usually means 1/(polynomial in n)
What is the one-time pad?
A cipher with perfect secrecy
What is the difference between computational security and provable security?
Computational security has a mathematical proof that there is no efficient algorithm to break the cipher, while provable security has no such proof.
Which type of cryptography has no provable security?
Symmetric cryptography
Which type of attack does a ciphertext-only attack refer to?
An attack where the attacker has access to the ciphertext only
What does it mean for a cipher to have perfect secrecy?
The ciphertext leaks no information about the plaintext except the length
What type of security is dependent on the currently available algorithms and computing power?
Computational security
What is the difference between computational security and unconditional security?
Computational security is dependent on the currently available algorithms and computing power, while unconditional security is not
What is the main difference between provable security and computational security?
Provable security means that it is unfeasible to break the cipher, while computational security means that no attack has succeeded in a reasonable amount of time
What does it mean for a cipher to have unconditional security?
The cipher is impossible to break even with unlimited time/resources
What is the difference between computational security and provable security?
Computational security means that no attack has succeeded in a reasonable amount of time, while provable security means that it is unfeasible to break the cipher
What is one possible precise mathematical definition of computational security?
There is no efficient algorithm that can be used by the attacker to succeed with reasonably high probability
What is one example of a cipher that has perfect secrecy?
One-time pad
For which type of cryptography does provable security exist?
Public key cryptography
What is the difference between computational security and perfect secrecy?
Computational security is impossible to break even with unlimited time/resources, while perfect secrecy is unfeasible to break
What is the difference between provable security and unconditional security?
Provable security means that it is unfeasible to break the cipher, while unconditional security means that no attack has succeeded in a reasonable amount of time
What are the different levels of knowledge the attacker can have in terms of breaking a cipher?
Ciphertext only, known plaintext, chosen plaintext, chosen ciphertext, samples of previous signatures or message authentication codes.
What does it mean to 'break' a cryptosystem?
Finding the plaintext, key, creating a digital signature, creating a message authentication code.
Does obtaining partial information about the plaintext/key count as 'breaking' a cryptosystem?
It depends on the specific definition of 'breaking' used.
What is computational security?
It is unfeasible (too time/resource consuming) to break the cipher; this depends on the currently available algorithms and computing power.
What is unconditional security?
It is impossible (even with unlimited time/resources) to break the cipher.
What is the difference between computational security and unconditional security?
Computational security is unfeasible to break, while unconditional security is impossible to break.
What is provable security?
There is no efficient algorithm that can be used by the attacker to succeed with reasonably high probability.
What is the definition of perfect secrecy/information-theoretic security?
The ciphertext leaks no information about the plaintext (except the length).
What is the one-time pad?
A cipher that has perfect secrecy, but is expensive and not used in practice.
Which type of cryptography has provable security?
Public key cryptography.
Which type of cryptography has no provable security?
Symmetric cryptography.
What is the status of computational security for most ciphers in use today?
They only have computational security in the sense that no attack has succeeded in a reasonable amount of time, but there is no proof that no efficient attack will be found.
Test your knowledge on the security of ciphers with this quiz! Learn about what it means for a cipher to be secure and the different levels of knowledge an attacker may have. Get precise definitions for terms such as ciphertext only, known plaintext, chosen plaintext, and chosen ciphertext. See if you know what it means to "break" a cryptosystem and what an attacker could potentially obtain. Sharpen your understanding of security definitions with this informative quiz.
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