I am looking for a one-directional encryption algorithm that preserves the size of the input. Then I would like to be able to mix an encrypted with original data and to be able to receive the same result. It is probably hard to grasp, let me try to explain with an example: Let's say I have the input:
This is some text to encrypt and the encrypted result with the same size says:
xxxxxxxxxxxxxxxxxxxxxxxxxxxx. The algorithm should be able to calculate the same result from any input that mixes the original unencrypted bytes with the encrypted result:
This is xxxx text to encrypt or
This is some text xx xxxxxx. Note that providing a protocol that describes which area is the original and which is already encrypted is ok. It does not need it to determine this on its own.
An example use case that illustrates an application of such an algorithm: Alice and Bob play battleship. When Alice makes her choices, she encrypts them and sends them to Bob. Bob cannot make any sense of the data, else he will know where to attack. When bob plays his move, Alice reveals the field. Bob does not trust Alice that she did not change the order of the ships after he already told her his move - this is why Alice sends the board encrypted again with already stricken fields revealed. Bob now can apply the algorithm that can encrypt the revealed part to make sure that he will get the same result as the original send from Alice. NOTE: this is illustration use case - I am not looking for alternatives to solve this problem.
Can you give me ideas of algorithms that already provide this or something that I can base such thing on?