block17.ruby

EC_Gx = 0x79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798
EC_Gy = 0x483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8
EC_p = 2**256 - 2**32 - 2**9 - 2**8 - 2**7 - 2**6 - 2**4 - 1
EC_n = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141

def extended_euclidean_algorithm(a, b)
  s, old_s = 0, 1
  t, old_t = 1, 0
  r, old_r = b, a
  while r != 0
    quotient = old_r / r
    old_r, r = r, old_r - quotient * r
    old_s, s = s, old_s - quotient * s
    old_t, t = t, old_t - quotient * t
  end
  [old_r, old_s, old_t]
end
def inverse(n, p)
  gcd, x, y = extended_euclidean_algorithm(n, p)
  (n * x + p * y) % p == gcd || raise('invalid gcd')
  gcd == 1 || raise('no multiplicative inverse')
  x % p
end
def ec_double(px, py, pn)
  i_2y = inverse(2 * py, pn)
  slope = (3 * px**2 * i_2y) % pn
  x = (slope**2 - 2 * px) % pn
  y = (slope*(px - x) - py) % pn
  [x, y]
end
def ec_add(ax, ay, bx, by, pn)
  return [ax, ay] if bx == 0 && by == 0
  return [bx, by] if ax == 0 && ay == 0
  return ec_double(ax, ay, pn) if ax == bx && ay == by

  i_bax = inverse(ax - bx, pn)
  slope = ((ay - by) * i_bax) % pn
  x = (slope**2 - ax - bx) % pn
  y = (slope*(ax - x) - ay) % pn
  [x, y]
end
def ec_multiply(m, px, py, pn)
  nx, ny = px, py
  qx, qy = 0, 0
  while m > 0
    qx, qy = ec_add qx, qy, nx, ny, pn if m&1 == 1
    nx, ny = ec_double nx, ny, pn
    m >>= 1
  end
  [qx, qy]
end