Card-related protocols

Magstripe

A magnetic stripe card, a.k.a. swipe card, is much like a piece of audio tape on a card. The prototype basically was that.

Orders of magnitude

• There may be multiple tracks, on the order of 3mm wide
• densities like 75 or 210 bits per inch
• often storing 5 or 6 bit codes

A lot of uses write them just once, with what amounts to a token. A few repeat their code.

They store a handful of numbers, so are usable similar to barcodes.

They should not store anything of value, and typically should point to a database, e.g. they should identify you, but the database should keep track of your money.

There are systems that ignore this, which sometimes makes sense, and is sometimes rather insecure.

Cloned cards can potentially be detected if the entire setup is designed up for it, but it's a bit of security-by-obscurity, isn't the most effective, or very common.

The magnetic material varies in coercivity.

HiCo (Higher coercivity) requires more energy to encode, and that encoding will last longer.

LoCo is perfectly fine for things like one-use hotel room keys, transit tickets, day passes for theme parks, and such.

Smart cards

https://en.wikipedia.org/wiki/Smart_card

CCID: USB-smart card interface https://en.wikipedia.org/wiki/CCID_(protocol)