How to certify a secret decision revealed in a delay in a game by game?

In a game-by-game game that requires a player to commit to a secret decision and then reveal it publicly, how can a player certify that he did it honestly without just trusting in good faith? Consider the following example.

  1. Alice is committed to making a decision, such as preprogramming an action she will take. A spectator might notice that he is doing something but they would not know the details.
  2. Although Bob does not know exactly what Alice is doing, he is committed to making a decision in response to that, like reacting to stop her. Resolving your decision will depend on resolving your decision.
  3. Alice has to reveal what her decision was after the fact to resolve it at this point along with Bob's reaction. If you are being honest or have a way to certify what your decision was, that's fine. If she is capable of lying, she could change her decision retroactively.

Are there common tools, techniques or conventions to support this? At a table, Alice could simply write her decision on a folded note card and reveal it later; or in a board game, she could play her facedown card and reveal it later. These common table conventions do not translate well into the online game. So, how can Alice certify her secret decision to be revealed in a delay?