We need a few more details than what you've offered so far, and if you can take/post pics that would even be better.
Regardless, we need to know the following things:
1. The shape of the lock.
2. Anything you can see inside the lock.
3. If you know, how the latch operates on the inside
4. Age of the furniture.
5. condition of the lock.
6. Anything you can recall about the key including shape, color, size, etc.
This will help us in identifying it and better addressing your request.
*insert witty comment here*