Since I don't get enough reputation to comment, I'll leave a new answer here.
know the result 0101 & 1100 = 0100 without revealing anything as stated above?
The answer to this question is NO. No matter how fancy the crypto tricks are, the truth still holds: ONCE one party knows the final result, the privacy of the other party's input will be compromised. Because together with his input(let's say Alice knows the result )
holds:0101 get: 0100
we all know that 0&0=0 0&1=0 1&1=1 1&0=0
So it's clear that Alice can definitely recover some bits of Bob's input where a bit 1 occurs in the result.
And the sad news here is that MPC does NOT work at all. Of course, it's well known that MPC guarantees the privacy of input of both parties. BUT MPC fails when the result itself leaks information about parties' data. In fact, the security definition of MPC indicates what I mentioned above is not complete, the latter half of the definition is:
except what be derived from the output.
Note information leaked from the result does not contradict the security definition of MPC. The reason is what can be learned from REAL world can be learned from IDEAL world(computation is done by a trusted third party)
So when we utilize MPC as a privacy tool, it's crucial that the first step to asking whether utilizing MPC brings privacy or NOT. A bad concrete example to calculate the sum of two numbers by MPC: a+b=c. An easy invert algorithm simply calculates b=c-a can get the genuine input of Bob.