I'm looking for a resource (possibly CPP) for which I could do the following on a windows and linux machine:

1) type a string message into a GUI control (or some other input that can be accessed by the resource).

2) run a resource script that puts the message through a hash function (or a custom hash function) and outputs the hash string.

3) have a reverse function available in order to decrypt the message in an input fashion just like step #1.

can someone tell me what open-source resource might be the best for this? Right now I am imagining typing a message into a text file, saving the file to a hard drive location, running a script on it replacing the old file with a new file that just has a hash string in it, then using that hash string for the encoded message.

does this sound feasible to anyone? can anyone suggest a better way to do this?