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Pollard's p-1 Method
Pollard's p-1 MethodPollard's p-1 method is a prime factorization algorithm discovered by John Pollard in 1974. Limited by the algorithm, the Pollard's p-1 method is only work for integers with specific factors. If the number n has a prime factor p such that p-1 can be expressed in terms of a product of primes, the finding of prime factor p is based on the selected boundary B of the B-smooth number. The algorithm fails when the selected boundary B is smaller than the B-smooth number of p-1. Pollard's P-1 Methed by Smooth NumberPollard's P-1 Methed by Smooth Number Example 2For example: n=667=p*q=23*29; let B=5 imply
Therefore for B=5, k5 or (p5-1)m5 is equal to 77760000. Fermat's Little Theoremlet a=2, by Fermat's little theorem, let p be one of the prime factors of n, imply p idivides ak-1. ![]() Greatest Common DivisorSince ak-1 is a very large number, before finding the greatest common divisor of n and ak-1, ak-1 can be raised to the high power modulo n. Imply Using squarings modulo
and using the residue to calculate the greatest common divisor. Imply ![]() The greatest common divisor of n and ak-1 is Using Euclid's algorithm
Imply ![]() The algorithm fails because the greatest common divisor of n and ak-1 is equal to 1. The number n does not have prime divisor p with p-1 is 5-smooth. Therefore the bound B equals to 5 fails, a larger bound B' should be used. Let B=7, imply
Therefore for B=7, k7 or (p7-1)m7 is equal to 77760000*343 = 26671680000. Imply k7 = k5 * 343. And the new ak can be expressed as ![]() And ak can be raised to the high power modulo n, imply ![]() Using squarings modulo
and using the residue to calculate the greatest common divisor. Imply ![]() The greatest common divisor of n and ak-1 is Using Euclid's algorithm
Imply ![]() Integer 29, the greatest common divisor of n and ak-1 is also the prime divisor of n. And p-1 is 7-smooth.
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