Cryptography & Network Security: Introduction to Number Theory

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Questions and Answers

What does the notation 'b | a' mean?

  • b is a remainder of a
  • b is a divisor of a (correct)
  • b is a multiple of a
  • b is a factor of a

Which of the following properties of divisibility is NOT mentioned in the text?

  • If b | g and b | h, then b | (mg + nh) for arbitrary integers m and n
  • If a | b and b | c, then a | c
  • If a | 1, then a = ±1
  • Any b ≠ 0 divides 0 (correct)

What is the purpose of the example with $b = 7, g = 14, h = 63, m = 3, n = 2$ in the text?

  • To demonstrate that 7 is a divisor of $3 * 14 + 2 * 63$ (correct)
  • To demonstrate that 7 is a factor of $3 * 14 + 2 * 63$
  • To demonstrate that 7 is a multiple of $3 * 14 + 2 * 63$
  • To demonstrate that 7 is a divisor of 14 and 63

What is the meaning of the statement '$13 | 182$' in the text?

<p>13 is a divisor of 182 (B)</p> Signup and view all the answers

Which of the following statements about divisibility is NOT mentioned in the text?

<p>If a | b and b | c, then a | (b + c) (B)</p> Signup and view all the answers

What is the significance of the statement '$17 | 0$' in the text?

<p>17 is a divisor of 0 (D)</p> Signup and view all the answers

If 24 = 9 (mod n), what is the possible value of n?

<p>3 (B)</p> Signup and view all the answers

Given 57 = 6 (mod m), what could be a possible value for m?

<p>7 (B)</p> Signup and view all the answers

What is the value of m if 83 = -2 (mod m)?

<p>6 (D)</p> Signup and view all the answers

If 90 = 6 (mod p), what are the potential values for p?

<p>20 (B)</p> Signup and view all the answers

For which of the following equations does the given congruence hold? 25 = 4 (mod x)

<p>$x = 6$ (D)</p> Signup and view all the answers

If $64 = -3$ (mod y), what is a possible value for y?

<p>$11$ (D)</p> Signup and view all the answers

What is the relationship between a positive integer a and a nonnegative integer n when divided, according to the Division Algorithm?

<p>a = qn + r, where 0 ≤ r &lt; n (D)</p> Signup and view all the answers

What is the general relationship given in the Division Algorithm?

<p>a = qn + r (A)</p> Signup and view all the answers

What is the Euclidean Algorithm primarily used for in number theory?

<p>Determining the greatest common divisor of two positive integers (C)</p> Signup and view all the answers

When are two integers considered relatively prime?

<p>When their only common positive integer factor is 1 (B)</p> Signup and view all the answers

How is the greatest common divisor (GCD) of two numbers defined?

<p>The largest integer that divides both numbers (D)</p> Signup and view all the answers

What does gcd(0,0) equal according to the content provided?

<p>0 (A)</p> Signup and view all the answers

What algorithm, developed in 2002, efficiently determines whether a given large number is prime?

<p>AKS algorithm (C)</p> Signup and view all the answers

Who is believed to have discovered the Chinese Remainder Theorem (CRT) around 100 A.D.?

<p>Sun-Tsu (D)</p> Signup and view all the answers

Which theorem provides a way to reconstruct integers in a certain range from their residues modulo a set of pairwise relatively prime moduli?

<p>Chinese Remainder Theorem (CRT) (D)</p> Signup and view all the answers

What property must be known beforehand for the Chinese Remainder Theorem (CRT) to be applied when dealing with potentially very large numbers?

<p>Factorization of M (D)</p> Signup and view all the answers

Which of the following algorithms produces a probabilistic result for proving the primality of very large numbers?

<p>Fermat's Primality Test (C)</p> Signup and view all the answers

What theorem does not appear to be as efficient as the Miller-Rabin algorithm for determining whether a given large number is prime?

<p>AKS algorithm (A)</p> Signup and view all the answers

What is the result of [(11 mod 8) + (15 mod 8)] mod 8?

<p>2 (C)</p> Signup and view all the answers

Which property of modular arithmetic is demonstrated by the expression [(11 mod 8) - (15 mod 8)] mod 8?

<p>Additive inverse (B)</p> Signup and view all the answers

What is the result of [(11 mod 8) * (15 mod 8)] mod 8?

<p>5 (C)</p> Signup and view all the answers

According to the information provided, what is the unique way that any integer a > 1 can be factored?

<p>a = p1^a1 * p2^a2 * ... * pn^an (A)</p> Signup and view all the answers

What is the result of the Extended Euclidean Algorithm example provided?

<p>d = 1; x = -111; y = 355 (B)</p> Signup and view all the answers

Which property of prime numbers is mentioned in the text?

<p>Prime numbers only have divisors of 1 and itself (D)</p> Signup and view all the answers

Flashcards

Divisibility

For integers a, b, and nonzero b, b divides a if a = mb for some integer m.

What does b | a mean?

If b divides a, written as b | a, then b is a divisor of a.

If a | 1, what is a?

If a | 1, then a must be either 1 or -1.

If a | b and b | a...

If a | b and b | a, then a and b are equal in magnitude but may differ in sign i.e. a = ±b.

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Which numbers divide 0?

Any nonzero integer b divides 0.

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Transitivity of divisibility

If a divides b and b divides c, then a divides c.

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Divisibility of linear combinations

If b divides both g and h, then b divides any linear combination of g and h (i.e., b | (mg + nh)).

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Congruence modulo n

Integers a and b are congruent modulo n if they have the same remainder when divided by n.

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What does a ≡ b (mod n) mean?

The notation a ≡ b (mod n) means a and b are congruent modulo n.

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If a ≡ b (mod n)...!

If a ≡ b (mod n), then n divides the difference between a and b.

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Symmetry of congruence

If a ≡ b (mod n), then b ≡ a (mod n).

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Transitivity of congruence

If a ≡ b (mod n) and b ≡ c (mod n), then a ≡ c (mod n).

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Division Algorithm

Given a positive integer n and a nonnegative integer a, the division algorithm states that a = qn + r, where 0 ≤ r < n.

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Greatest Common Divisor (GCD)

The greatest common divisor (GCD) of a and b is the largest integer that divides both a and b.

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What does gcd(a, b) mean?

The notation gcd(a, b) represents the greatest common divisor of a and b.

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Chinese Remainder Theorem (CRT)

The Chinese Remainder Theorem allows reconstructing integers within a range from their residues modulo a set of pairwise relatively prime moduli.

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Prime Numbers

Prime numbers are numbers greater than 1 that are only divisible by 1 and themselves.

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Unique Prime Factorization

Any integer a > 1 can be uniquely factored as a = p1^a1 * p2^a2 * ... where p are prime numbers.

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Study Notes

Divisibility

  • A nonzero b divides a if a = mb for some m, where a, b, and m are integers.
  • b divides a if there is no remainder on division.
  • Notation b | a means b divides a.
  • If b | a, then b is a divisor of a.
  • Example: 1, 2, 3, 4, 6, 8, 12, and 24 are divisors of 24.

Properties of Divisibility

  • If a | 1, then a = ±1.
  • If a | b and b | a, then a = ±b.
  • Any b ≠ 0 divides 0.
  • If a | b and b | c, then a | c.
  • If b | g and b | h, then b | (mg + nh) for arbitrary integers m and n.

Modular Arithmetic

  • Two integers a and b are congruent modulo n if (a mod n) = (b mod n).
  • Notation a = b (mod n) means a and b are congruent modulo n.
  • Example: 73 = 4 (mod 23); 21 = -9 (mod 10).

Properties of Congruences

  • If a = b (mod n), then n | (a - b).
  • If a = b (mod n), then b = a (mod n).
  • If a = b (mod n) and b = c (mod n), then a = c (mod n).

Division Algorithm

  • Given positive integer n and nonnegative integer a, dividing a by n gives quotient q and remainder r such that a = qn + r.
  • 0 ≤ r &lt; n.

Greatest Common Divisor (GCD)

  • The GCD of a and b is the largest integer that divides both a and b.
  • Notation gcd(a, b) represents the GCD of a and b.
  • gcd(a, b) is the largest c such that c divides a and b.
  • gcd(a, b) = max[k, such that k | a and k | b].

Chinese Remainder Theorem (CRT)

  • The CRT states that it is possible to reconstruct integers in a certain range from their residues modulo a set of pairwise relatively prime moduli.
  • The CRT can be stated in several ways.
  • It provides a way to manipulate large numbers modulo M in terms of tuples of smaller numbers.

Prime Numbers

  • Prime numbers only have divisors of 1 and themselves.
  • Prime numbers are central to number theory.
  • Any integer a &gt; 1 can be factored in a unique way as a = p1^a1 * p2^a2 * ....

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