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September 23, 2011

The secret sauce of ATM machines


From page 140 of Vlatko Vedral's superb book, "Decoding Reality":

Have you ever wondered why your PIN (personal identification number) is secure when you withdraw money from an ATM machine (automatic teller)? How come neither the bank staff nor the bank manages to know you PIN? Why they do not obtain it when you type it into the ATM and then steal your money?

The reason is that the ATM machine performs the following operation: When you type in your PIN with the intention of withdrawing the money, the PIN (usually a four-to-six-digit number) gets multiplied by a huge (say a 500 digit) number. The resulting number (a number 504 digits long) is then checked by the bank. And if it is in the database, you will be allowed to proceed with your transaction.

But — and this is the crucial but — the bank cannot figure out your PIN from the 504-digit-long number that they have in their database. It would simply take them a very long time – longer than the age of the universe with current [2010] computers!

The punch line of all this is that, using a quantum computer, we can factorize numbers very quickly. If we have a quantum computer with 10,000 quantum bits, we could factor a 504-digit number in a few seconds. And that would be the end of most current security!

September 23, 2011 at 12:01 PM | Permalink


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