Network Security: Random Numbers and Hashing
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Questions and Answers

Which requirement ensures that a random number generator can produce every number from 0 to m-1 before repeating?

  • It should use a nonlinear function.
  • It should generate numbers efficiently in 64-bit arithmetic.
  • It should have multiple seeds.
  • It should be a full-period generating function. (correct)

    • What does the linear congruential generator formula Xn+1 = (a・Xn + c) mod m utilize?

  • It is based on random sampling techniques.
  • It requires prime numbers for m.
  • It generates numbers using Fibonacci series.
  • It incorporates an increment and a multiplier. (correct)

    • Which method of pseudorandom number generation utilizes the least significant bit for output?

  • Linear Congruential Generator
  • Counter Mode
  • Blum Blum Shub Generator (correct)
  • Output Feedback Mode

    • What is a notable characteristic of a non-deterministic random bit generator?

    <p>It is based on unpredictable physical processes. (C)</p> Signup and view all the answers

    In the context of pseudorandom number generators, what does 'm' typically refer to?

    <p>The modulus value. (B)</p> Signup and view all the answers

    Which of the following is not a characteristic of a good random number generator?

    <p>Can be initialized with multiple seeds. (C)</p> Signup and view all the answers

    Which of the following PRNG modes is known for generating pseudorandom bits by combining a counter and a value?

    <p>Counter Mode (C)</p> Signup and view all the answers

    What is the main drawback of deterministic random number generators compared to non-deterministic ones?

    <p>They can produce predictable sequences. (A)</p> Signup and view all the answers

    What is a key characteristic of a Pseudorandom Number Generator (PRNG)?

    <p>It produces periodic sequences. (C)</p> Signup and view all the answers

    Which of the following statements best describes the purpose of a hashing function?

    <p>To transform a long message into a fixed-size hash output. (D)</p> Signup and view all the answers

    What does the term 'collision resistant' refer to in cryptographic hash functions?

    <p>It should prevent finding any two distinct original messages yielding the same hash. (D)</p> Signup and view all the answers

    Which type of generator is generally considered inefficient for producing random numbers?

    <p>True Random Number Generator (TRNG) (B)</p> Signup and view all the answers

    What is a potential issue with using XOR for hashing?

    <p>It can lead to predictably formatted data outputs. (B)</p> Signup and view all the answers

    Which of the following is NOT a security requirement for cryptographic hash functions?

    <p>High computational inefficiency (C)</p> Signup and view all the answers

    In hashing, what is one purpose of using 'rotated XOR'?

    <p>To enhance the randomness of the hash output. (B)</p> Signup and view all the answers

    What does the fixed output size of a cryptographic hash function ensure?

    <p>The hash value will always have the same length regardless of input size. (A)</p> Signup and view all the answers

    What is the formula used to calculate the probability of at least two people sharing a birthday in a group of n persons?

    <p>$p = 1 – (365・364・363・…・(365 – (n-1))) / 365n$ (A)</p> Signup and view all the answers

    In the context of SHA-512, what does the function Ch(e, f, g) evaluate?

    <p>The XOR operation between e AND f and NOT e AND g (C)</p> Signup and view all the answers

    What is one of the features of the Encrypt-then-MAC method in authenticated encryption?

    <p>It is the only method that can be proven to achieve the highest level of security. (A)</p> Signup and view all the answers

    What is a key component of the SHA-3 hashing algorithm's iteration function?

    <p>A combination of theta, rho, pi, chi, and iota functions (B)</p> Signup and view all the answers

    What can be inferred about SHA-512 and its use in secure hashing?

    <p>It features functions like Ch and Maj to enhance security. (C)</p> Signup and view all the answers

    Which of the following statements is true regarding the applications of hash codes?

    <p>MAC is one of the applications for message integrity verification. (C)</p> Signup and view all the answers

    Which statement accurately describes the encrypt-and-MAC method?

    <p>It is adequately secure and used in protocols like SSH. (A)</p> Signup and view all the answers

    How many different birthday combinations are possible for n persons?

    <p>365n (D)</p> Signup and view all the answers

    What is the significance of the condition H(M) = h in the context of hashing?

    <p>It demonstrates the pseudo-randomness of the hash function. (B)</p> Signup and view all the answers

    What makes a hash function 2nd pre-image resistant?

    <p>It prevents the discovery of an alternative message with the same hash given the original message. (C)</p> Signup and view all the answers

    How does the effort for brute-force attacks compare among different types of pre-image resistance?

    <p>First and second pre-image resistance both require 2m efforts, while collision resistance requires 2m/2. (D)</p> Signup and view all the answers

    What is the core focus of cryptanalysis when evaluating hash functions?

    <p>To find effective methods to produce collisions in hash functions. (B)</p> Signup and view all the answers

    In the context of the Birthday Attack, how does the probability of encountering a repeated element relate to the number of attempts?

    <p>It exceeds 0.5 after approximately √(k-1) attempts. (D)</p> Signup and view all the answers

    What does the Birthday Paradox illustrate in terms of hash function security?

    <p>It demonstrates how easily collisions can be found despite a large number of possible outputs. (D)</p> Signup and view all the answers

    How many attempts would typically be required to find a second message that produces the same hash as an m-bit hash value?

    <p>√(2m) = 2m/2 attempts. (C)</p> Signup and view all the answers

    What is the expected number of pairs of inputs needed to potentially find a matching hash output, given n inputs?

    <p>n(n-1)/2 pairs. (C)</p> Signup and view all the answers

    What is one primary use of random numbers in network security?

    <p>Session key generation (D)</p> Signup and view all the answers

    Which criterion ensures that the frequency of occurrence of bits is approximately equal?

    <p>Randomness Criteria (D)</p> Signup and view all the answers

    What should be unpredictable in the context of forward unpredictability?

    <p>Next output (B)</p> Signup and view all the answers

    Which of the following is a source of true randomness for a TRNG?

    <p>Sound and video input (B)</p> Signup and view all the answers

    In which type of generator is the output stream deterministic based on a seed?

    <p>Pseudorandom Number Generator (PRNG) (C)</p> Signup and view all the answers

    What is meant by backward unpredictability in random number generation?

    <p>Seed should not be predictable from any output value. (B)</p> Signup and view all the answers

    Which of the following describes a pseudorandom function?

    <p>Uses a seed to create a random bit stream. (C)</p> Signup and view all the answers

    What is a common source of entropy for true random number generation?

    <p>Disk drives with random fluctuations (D)</p> Signup and view all the answers

    Study Notes

    Network Security: Random Numbers and Hashing

    • This document details random numbers and hashing, core concepts in network security.
    • It covers true random number generators (TRNGs) and pseudorandom number generators (PRNGs), exploring their uses and characteristics.
    • The document also discusses cryptographic hash functions, their requirements, and potential attacks.

    Random Numbers

    • Randomness Criteria: Two key criteria are uniform distribution (frequency of bits is approximately equal) and independence (no subsequence can be inferred from another).
    • Unpredictability Criteria: Forward unpredictability (next output is unpredictable if the seed is unknown), and backward unpredictability (seed is not predictable from any output value).
    • Random Number Generation: A diagram illustrates the process, differentiating between true random number generators (TRNGs) drawing from real-world randomness (e.g., thermal noise), and pseudorandom number generators (PRNGs) that produce deterministic sequences using algorithms and seeds.
    • TRNG Entropy Sources: Various sources of entropy for TRNGs are listed, including sound/video input, thermal noise, fluctuations in disk drive speeds, and clock timings.

    Hashing

    • Goal of a Hash Function: To map long messages to short, fixed-size hash values (digests). These are useful for integrity checks and digital signatures.
    • Hashing Using XOR: A simplified method initially used for integrity checks and block-level hash function generation; XOR operations across blocks and bits are emphasized. This type is not as complex or secure when compared to more established hashing functions.
    • Cryptographic Hash Function Requirements: Emphasis is on variability in input size, fixed output size, and efficiency for hardware and software implementations.
    • Security Requirements for Cryptographic Hash Functions: Includes: pre-image resistance (one-way property), 2nd pre-image resistance (weak collision resistance), and strong collision resistance.
    • Relationship among Hash Function Properties: A Venn diagram visually shows relationships between collision resistance, 2nd pre-image resistance and preimage resistance.
    • Brute-Force Attacks on Cryptographic Hash Functions: Effort for these attacks corresponds to the number of possible hash values; 1st pre-image resistance is 2m; 2nd pre-image resistance is 2m; collision resistance is 2m/2.

    PRNGs

    • Linear Congruential Generators (LCGs): Details of LCG parameters including modulus (m), multiplier (a), increment (c), and seed (x0), are provided.
    • Blum Blum Shub Generator: The generation method is outlined—initializing with a seed, calculating (x2 mod n), and selecting the least significant bit.
    • PRNGs using Block Cipher Modes of Operation: Two cipher modes are described (counter mode and output feedback mode), using pseudo-random bits to generate random values.
    • PRNG based on RSA: The method uses RSA to encrypt the seed and generate pseudo-random bits in a cyclic fashion, emphasizing the use of encryption/decryption procedures for cryptographic security.

    PRNG Comparison:

    • Efficiency & Determinism of PRNGs vs. TRNGs: PRNGs are very efficient, deterministic, and periodic; TRNGs are generally inefficient, non-deterministic, and aperiodic.

    Hashing Applications

    • Message Authentication Code (MAC): Methods of adding MACs to messages are introduced, along with diagrams illustrating the processes involved. Different methods include encrypt-then-MAC, encrypt-and-MAC, and MAC-then-Encrypt.
    • Digital Signatures: The use of a hash function and associated cryptographic functions to generate and verify digital signatures is illustrated, using one-way functions.
    • Message Digest Implementation (e.g., MD5): Steps involved are outlined (padding to a fixed length, appending length information, initializing a buffer, and processing in blocks).
    • MD5 Implementation Details: Specific details about the MD5 algorithm are provided, outlining how parameters are initialized and manipulated for various rounds of processing.
    • Iteration Function(f) for SHA-3: Various cryptographic functions used are discussed (theta, rho, pi, chi, iota) focusing on the different functionalities each performs. This function takes various inputs and outputs results based on the current values.
    • SHA-3 Sponge Construction: A detailed outline of the SHA-3 structure emphasizing the sponge construction, showing input message processing, the state, and the output value, with illustrations of the absorption and squeezing phases.

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    Network Security: Random Numbers and Hashing PDF

    Description

    This quiz covers essential concepts of random numbers and hashing in network security. Explore the differences between true random number generators (TRNGs) and pseudorandom number generators (PRNGs), along with cryptographic hash functions. Understand the criteria for randomness and the implications of various attacks on these systems.

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