just buy bitcoin and hodl long term. If the price increases in time, you get the passive income. In that case it can't really get more passive than that 
there are many other ways you can make som income in crypto though, bounty signatures included. It's almost oassive too
there are many other ways you can make som income in crypto though, bounty signatures included. It's almost oassive tooHodling Bitcoin is actully uncertain passive income. And it's a one-time interest, which means if you are not a trader - you will sell it only once.