counter.py 文件源码

def noise(sigma, sum_of_sq, p_exit):
    '''
    Sample noise from a gussian distribution
    the distribution is over +/- sigma, scaled by the noise weight, which is
    calculated from the exit probability p_exit, and the overall sum_of_sq
    bandwidth
    returns a floating-point value between +sigma and -sigma, scaled by
    noise_weight
    '''
    sigma_i = p_exit * sigma / sqrt(sum_of_sq)
    # the noise needs to be cryptographically secure, because knowing the RNG
    # state could allow an adversary to remove the noise
    random_sample = SystemRandom().gauss(0, sigma_i)
    return random_sample