Squeeze
If you want to fit your fingers into a key hole, you have to squeeze them in. Fingers aren't exactly supposed to fit in key holes... they're for keys, after all. But you want to squeeze your finger on in there anyway to unlock the door.
Imagine what it would be like to squeeze your fingers into a keyhole. Maybe try squeezing one finger really tight first. Did that hurt? Well it's going to be a lot worse in that key hole.
さく
しぼ
None
Once you've squeezed your finger in the key hole to unlock this door you squeeze all the money and jewels and treasures you can fit into your sack (さく). Your stealing sack.
You have the ability to squeeze your fingers into locks to open them, so of course you're stealing. And you squeeze those stolen goodies into your sack so you can take them with you.