Jigar Mehta’s WebBlog

June 26, 2007

Why are ATM PINs 4 digits long?

Filed under: Uncategorized — jigarme @ 2:51 pm

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Why are ATM PINs 4 digits long?

via Matasano Chargen by Dave G. on Jun 25, 2007

The answer is best summed up in this article about the ATM Machine turning 40 years old. They quote John Shepherd-Barron, the inventor of the ATM:

Mr Shepherd-Barron came up with the idea when he realised that he could remember his six-figure army number. But he decided to check that with his wife, Caroline.

“Over the kitchen table, she said she could only remember four figures, so because of her, four figures became the world standard,” he laughs.

If you had asked me how they had come up with the length requirements, I would have thought that somewhere, someone might have tried to run some basic statistics, figure out acceptable losses based on likelihood of a PIN number getting guessed. Then try and balance that user requirements.

Nope. That wasn’t (isn’t?) how decisions and standards are made. And even today, MOST PINs are four digits in length. Policies are well documented inside of the enterprise. One thing that usually doesn’t get well preserved is why those policy decisions were made.

The other choice quote from this article:

“Money costs money to transport. I am therefore predicting the demise of cash within three to five years.”

While I can appreciate anyone who tries to predict the future, we should remember there is a reason why we say most of them are insane. I can see a future without cash, but even if we all said right now that it is time to move away from cash, it would take more than five years to execute on that.

Finally, Mr Shepherd-Barron, is working on a new invention. One to scare salmon-stealing seals away from his salmon farm:

“I invented a device to scare them off by playing the sound of killer whales, but it’s ended up only attracting them more.”

It’s clearly an uphill battle to top the invention of the ATM.


Things you can do from here:


1 Comment »

  1. RIP – John Shepherd-Barron, 84, found his bank closed 45 years ago & thought: “What if you could get cash, anywhere in the world, from a machine, as easy as you can a candy bar.” And so the ATM (& PIN numbers you can’t remember) was born. http://urdead2me.wordpress.com/2010/05/15/rip-john-shepherd-barron/

    Comment by urdead2me — May 21, 2010 @ 5:44 pm

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