Williams’ p+1 factorization algorithm for Bitcoin

BY KEYHUNTER 03.03.2024
Williams’ p+1 factorization algorithm for Bitcoin

Python code for Williams’ p+1 factorization algorithm for Bitcoin:

def p_plus_1(n):
    gcd = 2
    while gcd == 2:
        gcd = gcd_euc(n, gcd)
    return gcd

def gcd_euc(a, b):
    while b = 0:
        a, b = b, a % b
    return a

The p_plus_1 function takes an input n and returns the gcd of n and 2. It does this by repeatedly calling gcd_euc, which is a function that implements the Euclidean algorithm for finding the gcd of two numbers. If gcd is equal to 2, the function will continue to call itself with the new value of gcd.

The gcd_euc function takes two numbers a and b and returns their gcd. It does this by repeatedly replacing a and b with b and the remainder of a divided by b, until b is equal to 0. At that point, a is the gcd of the original a and b.

Williams’ p+1 factorization algorithm is an algorithm that is used to factorize large integers, which is a crucial step in the RSA encryption algorithm. The algorithm works by first selecting a prime number p, and then computing the square root of the number being factorized modulo p. The algorithm then uses a mathematical formula to compute the value of x, which is a factor of the original number.

This algorithm is used in Bitcoin to generate public and private keys. The public key is generated by selecting two large prime numbers and multiplying them together, while the private key is generated by factoring the product of the two prime numbers using Williams’ p+1 factorization algorithm.

code for the williams’ p+1 factorization algorithm in python. here it is:

import math

def p_plus_one_factorization(n, b):
    if b == 2 or b == 3:
        return "not prime"

    if n == 1:
        return b

    if n % 2 == 0:
        return "not prime"

    if n % b == 0:
        return b

    k = 0
    while k < 20:
        a = (b - 1) // 2
        s = (b + 1) // 4
        t = (b - 1) // 4

        if t < 2:
            break

        if n % a == 0:
            return a

        k += 1

    return "not prime"

this code implements the algorithm for finding the factors of a number n, given a base b. it returns “not prime” if the number is not prime, or the factor if it is.

Python implementation of the Williams’ p+1 factorization algorithm:

import math

def factorize(n):
    # Choose a random value for x
    x = math.sqrt(n) + math.floor(math.sqrt(n))

    # Find a value for y that makes x^2 - ny = 1
    y = 1
    while True:
        if x**2 - n * y == 1:
            break
        y += 1

    p = x
    q = y
    return p, q

This function takes an integer n as input and returns two integers p and q such that n = p * q + 1. It uses the algorithm you mentioned, which is also known as the Williams’ algorithm or the Williams’ p+1 factorization algorithm.

Williams’ p+1 factorization algorithm is an algorithm used to solve the discrete logarithm problem in finite fields. It is based on the fact that if we have a prime number p and a generator g of the multiplicative group Zp, then we can factorize any number in the field Zp into its prime factors using the algorithm.

The algorithm works by repeatedly computing the discrete logarithm of a number in Z*p with respect to the generator g, until we reach a number that is a power of g. At this point, we have found the prime factors of the original number.

The algorithm is used in cryptography for breaking certain types of cryptographic algorithms, such as the Diffie-Hellman key exchange and the ElGamal encryption scheme. However, it is not considered secure for modern cryptography as it can be easily broken with modern computers.

 example implementation in Python:

from Crypto.Util.number import long_to_bytes, bytes_to_long
from Crypto.PublicKey import RSA

def p_plus_1(n):
    p, q = n // 2, n - p - 1
    return p, q

def williams_p_plus_1_factorization(n):
    if n % 2 == 0:
        raise ValueError("n must be odd")
    p, q = p_plus_1(n)
    while True:
        d = RSA.number.gcd(p - 1, q)
        if d == 1:
            return p, q
        p -= d
        q -= d

def williams_discrete_logarithm(n, x, y):
    p, q = williams_p_plus_1_factorization(n)
    x = long_to_bytes(x)
    y = long_to_bytes(y)
    k = RSA.number.inverse(x, p)
    u = k * (y % p) % p
    v = (y - u) // p
    u += v * p
    u %= p
    v = (v - 1) // q
    u -= v * q
    u %= q
    v = (v - 1) // p
    u += v * p
    u %= p
    return u

The p_plus_1 function takes an odd integer n and returns the factors p and q of n such that n = p + 1 = q + 1. The williams_p_plus_1_factorization function applies the Williams’ p+1 algorithm to find the factors p and q. The williams_discrete_logarithm function applies the Williams’ p+1 algorithm to solve the discrete logarithm problem given n, x, and y.

Python code for the williams’ p+1 factorization algorithm, but i need to clarify that this algorithm is used to factorize large numbers into their prime factors, and not specifically to solve the discrete logarithm problem. here’s a possible implementation:

import math

def p_plus_1(n, a, b):
    """
    williams' p+1 factorization algorithm.
    """
    m = int(math.sqrt(n))
    for i in range(2, m+1):
        while n % i == 0:
            n = n // i
            a = a + i
            b = b - 1
    if n > 1:
        a = a + n
        b = b - 1
    return a, b

# example usage:
n = 123456789
a, b = p_plus_1(n, 0, 0)
print(f"{n} = {a} * {b}")

this code takes as input a positive integer n, and two integers a and b representing the current factors of n. it returns the final factors of n. the algorithm works by repeatedly dividing n by prime factors until only two factors remain, and then using the relationship n = p + 1 to find the factors p and q of n. the a and b variables keep track of the current factors of n as the algorithm proceeds.

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