How to remember all your PIN numbers (Projects)

One PIN To Rule Them All, One PIN To Find Them, One PIN To Bring Them All And In The Memory Bind Them

Like me, you probably have a half dozen credit, debit and bank cards in your wallet, all with different PIN numbers. Now, I have trouble remembering my address, not to mention my wife's birthday (07/28, dear), and the only way I remember our anniversary is by scheduling my yearly checkup for same day (nothing like a prostate exam to remind you it's a special day!)

So remembering a half-dozen different PINs is out of the question. As is writing the PINs on the cards themselves, which my friendly neighborhood banker frowns upon. And yet, that's exactly what I do – without in any way compromising the security of the PIN. In fact, all I have to do is remember one 4-digit number, my Secret PIN (or SPIN for short).

It all works through the magic of modular arithmetic – which is just like regular arithmetic, except without all that annoying carrying and borrowing.

The first step is to decide upon, and memorize, your SPIN number. This should be a 4 digit number you will never forget, yet is hard for thieves to guess. Obviously, it shouldn't be 0000 – if you chose this as your SPIN then you are DIM.

For the purposes of illustration, let's assume my SPIN is 0728 (it isn't, sorry dear…)

Now let's say that Conglomerated MegaBankCorp issues you a bank card with at PIN of 1234. What you do is modularly subtract 0728 from 1234 – with no borrows, as follows:

1234 PIN
0728 SPIN
----
1516 CODE

This generates the card's CODE (Completely Obfuscated Digits of Encryption – OK, it's a lame acronym, come up with something better if you don't like it).

The CODE is what you write on the back of your card. And then, when you drive up to the CashPoint machine, all you ever have to remember is your SPIN. You just modularly add it to the CODE written on the back of the card to get your PIN.

0 + 1 = 01 -> 1
7 + 5 = 12 -> 2
2 + 1 = 03 -> 3
8 + 6 = 14 -> 4

Why, it's so easy, even a child can do it – in fact, both of my kids have had cash cards, and have used this system, since they were pre-teens. As a side note, getting your kids checking accounts with cash cards is an excellent way to introduce them to financial matters. You just fund them with their allowance once a quarter, and if they blow it the first week buying Super Smash Mario Brothers World of Warcraft, that's their problem. It also completely eliminates the dreaded “Daddy, buy it for me!” – it's amazing how that wonderful and expensive toy isn't so wonderful when it's their money that pays for it. And finally, it makes holiday season a lot simpler, because all they'll ever want for Xmas is cold, hard cash – both my kids are trying to get their overseas relatives to do wire transfers this year, to minimize the currency exchange losses…

Finally, it is, of course, asking way far much of our Hallowed Financial Institutions to publicize this simple technique, and to program their systems to sound the alarm and let loose the hounds when some moron thief gets hold of your card, sees the number on the back, and enters it, thinking it's your PIN – home alarm systems have panic codes, why not bank cards? Not to mention that if a lot of people did this, slightly less moronic thieves would be less likely to risk trying out a card with a “PIN” on it, which would confer some herd immunity onto the legions of people who, unable to remember 6 different PIN numbers, just write them down on the backs of the cards, or on a handy slip of paper they keep in their wallets…