Actually its a bit of an headache if we do speak about marriage contracts or whatsoever but in general we do know that once both had been that shackled out with marriage then all of their assets whether they have acquired it on their pre-marriage then it would be turned out to be conjugal. I dont know totally if there would be other terms or conditions in other marriage on such aspect but since you have mentioned about these kind of arrangement about having that financial infidelity on which it shocks me that you can potentially be imprisoned just because of becoming a fraud or whatever it called. Why people are just that too serious about acquiring or knowing all the money that you've been that holding? Its understandable that there shouldnt be something be hidden but if there's one then its up into someones personal choice into this aspect because if we do tend to look up on the reasons such as this then it falls down into that personal reason too on which we do commonly known issues in between relationships specially if we are talking or speaking about financial aspects. Humans are naturally greedy but not all but majority will be always that securing themselves and thats why they would be fighting into something just for the sake of money or getting their part specially on the issue of divorce on which they would be trying out to dig on whatever things that could be possibly dig. In regarding about crypto holdings then as long that your partner isnt aware then you can totally be able to keep it hidden unless if there's someone who knows about your holding but if you are honest and transparent into your partner and telling about your crypto investment then expect that he/she would be including it out when it comes into the time of separation.