How would I use this keypad and a shift register to make a door lock?

So I was following this instructable to make a simple lock that opens when the correct key is entered, but I accidentally ordered the wrong keypad. Here is the keypad I ordered. It has a pin for each key instead of the matrix style setup. Since there are so many pins, I'm going to need to use a shift register, I think but I don't know anything about them. Any advice for how to wire this keypad would be greatly appreciated. Like do I use the Arduino pins for outputs or inputs and where to put the resistors is mainly what I'm confused about.

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spycatcher2k: Find the common pin (or find the datasheet) - thats 12 inputs, the UNO has 17 available for use, so pleanty left over.

My problem is that I know how to wire a regular push button, but that uses the Arduino pins as grounds to tell when the button has been pressed. The keypad I ordered only has 1 ground for all the keys, so how do I differentiate which key is being pressed. There is no data sheet as far as I can find.

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