They are called 'natural' rights and 'natural' law because they are things that human beings have the capability to conceive of out of pure reason, absent of an existence of authority, government or society. They exist whether or not one *believes* in them consciously. It's one of the defining characteristics of human beings that set us apart from other species. And every human has the capability to conceive of such things.
In one branch of Hindu thought, examples of these conceptions would be 'Ṛta' and 'Dharma'.
'Yugams' are cycles that the world goes through.
Kali yugam, in my interpretation is when people have to be forced to abide by the natural law by an authority, force or government. It is when people forget about the moral and ethical principles that govern their behaviour.
Satya yugam on the other hand is an age of total anarchy, where everyone can reason out for themselves the moral and ethical code and there is no need for an authority.