from machine import ADC
import utime
import uhashlib

adc = ADC(26)


def get_entropy(samples: int = 512):
    entropy = bytearray()
    
    for _ in range(samples):

        value = adc.read_u16()
        
        mixed = (
            value ^
            (value >> 2) ^
            (value >> 5) ^
            utime.ticks_cpu()
        ) & 0xFF
        
        entropy.append(mixed)
        
        utime.sleep_us(5)
        
    return entropy

def secure_random(num_bytes: int = 32):
    entropy = get_entropy()
    
    digest = uhashlib.sha256(entropy).digest()
    
    output = bytearray()
    
    while len(output) < num_bytes:
        digest = uhashlib.sha256(digest).digest()
        output.extend(digest)
        
    return bytes(output[:num_bytes])