debit card : Java Glossary


debit card

Debit cards are like credit cards, except you pay by electronic transfer at the time of purchase. You can’t use them over the phone or over the Internet. They have an invisible PIN (Personal Identification Number) (4-digit password). They are more secure than credit cards, since the card number alone is not sufficient to make a purchase.

There are no transaction fees or interest charges to the user. The fees to the vendor are much smaller than for credit cards. The vendor gets his money right away. If there are insufficient funds the vendor declines the sale without loss.


Debit cards that have a 4-digit PIN are not as vulnerable as credit cards, but they still are vulnerable. Happily, thieves can’t use them on the Internet, even if they steal both the card and PIN. Sophisticated thieves replace the reader units or insert extra electronics into gas pump units to record account numbers and PINs (Personal Identification Numbers). They then can wipe out your account at any ATM (Automated Teller Machine) in the world.

Thankfully, the PIN is not stored inside the card where it could be extracted by thieves. It is stored in the bank’s server.

Mag Stripe

The original debit cards had mag stripes that were read by pulling them through a mag stripe reader in only one of four plausible orientations pulling toward or pushing away from you. The problem was the stripes were easily erased by stray magnetic fields, and the magnetic material gradually rubbed off. Even the cards made in 2017 have a stripe as a backup.

Gold Bump

The next generation of cards had a gold-plated bump debit gold contact near the left end of the card. This allowed electric signals to pass through to a computer chip embedded in the card. You had to insert it into a slot flanked by two decoys, in only one of four plausible orientations. You inserted the card with the gold bump up, with the bump end first into the slot. The problem was the conducting gold plate was very thin and easily wore off. Further, finger grease on the contact stopped the card from working. You can sometimes revive a card by cleaning the bump with DeOxit Red. Even the cards made in 2017 have a gold bump as a backup.


The latest generation of card has a symbol touchless symbol usually on the upper right corner of the card. All you have to do is slowly tap that symbol onto a matching one on the vendor’s terminal. They don’t even have to touch. For sales under $100 you usually don’t even need to enter a PIN. The disadvantage is a thief can use your card until you report it lost or stolen. The advantage is the whole sale is much faster, and not just because you do not have to enter a PIN. Even if you have a touchless card, you can still make your purchases via the gold bump. There is an idiotic flaw in the design. The cashier must ask the customer if they have a credit or debit card. She must enter that choice into the cash register which then primes the reader to accept the correct type. It should figure it out for itself.


We need to invent a debit card that works over the Internet. It could look like a standard debit card. You would insert it into a card reader attached to your computer. It could also look like a USB (Universal Serial Bus) fob. It might even be done purely with software. It would work using digital certificates.

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