Considering that the entirety of the blockchain is public, its impossible to actually put secrets into a smart-contract. You have to make the data available to all nodes that are actually running the smart contract data.

An interesting approach to solving this is homomorphic encryption. This allows for alice to give Bob to encrypted numbers A and B. Bob can then compute an encrypted version of A + B using only the encrypted versions of A and B. This could be used by putting an encrypted secret on the blockchain, after which everyone can compute using that secret, but cannot see the actual outcome.

This still won't help with random number generation though, because it remains deterministic.