How can two debit cards share same PIN

usignuolo

I destroyed my bank debit card by mistake and have been sent a replacement. The last four digits are different to the previous card but the pin is the same. How does that work? Why isn't it a different pin? Just interested in how these things work?

MrSilk

... From the chip on the card, and the strip on the back. Magic aye?

CKhalvashi

As above.

The bank can't see what it is, though.

thenudeone

If your car has been accidentally damaged (rather than lost or stolen), it is more secure simply to keep the same PIN.
That way, anyone who intercepts your post can't use your card in a shop, because they don't have a PIN.

If they had to send out a new card plus a new PIN, there is a greater risk that interception could lead to the new card being used fraudulently.

MrSilk

thenudeone wrote: »

If your car has been accidentally damaged (rather than lost or stolen), it is more secure simply to keep the same PIN.
That way, anyone who intercepts your post can't use your card in a shop, because they don't have a PIN.

If they had to send out a new card plus a new PIN, there is a greater risk that interception could lead to the new card being used fraudulently.

Unless you're with Natwest/RBS when you have to activate a new debit card on your internet banking

grumbler

MrSilk wrote: »

... From ... the strip on the back.

:huh:
What do you mean?

Cornucopia

The PIN is encrypted on the card.

PINs seem to be widely misunderstood.

There are 4 digits. That means less than 10000 unique combinations of numbers, once invalid combinations are weeded-out. So even if they were randomly distributed, you'd share the same PIN as a number of other people (maybe 6000 in the UK).

But that's okay, because the PIN is not intended as a unique identifier (the card number does that). It's a password. And as long as you keep it secret, the chances of anyone guessing it are slim.

grumbler

Cornucopia wrote: »

There are 4 digits. That means less than 10000 unique combinations of numbers, once invalid combinations are weeded-out.

Which are invalid?

Paul_Herring

usignuolo wrote: »

The last four digits are different to the previous card but the pin is the same. How does that work? Why isn't it a different pin? Just interested in how these things work?

The PIN is stored within the chip on the card.

The bank knows what your PIN is and programs it in before sending it out (unless you requested a change in which case they select another number and send out a separate letter.)

Changing it at an ATM also sends the change back to the bank so they know what the current PIN is.

When using the card, depending on whether the terminal being used is online or offline, when the PIN is entered, it is either sent back to the bank for verification, or the card itself can verify correct entry.

Yolina

grumbler wrote: »

Which are invalid?

I'd guess stuff like 0000

Paul_Herring

grumbler wrote: »

Which are invalid?

More like disallowed (if in fact they are,) rather than invalid, but as pointed out, 0000 certainly, 1234 and maybe any of the other 20 most common pins found elsewhere.