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SIM / Smart Card Deep Dive – Part 1 – Introduction to Smart Cards

Getting up close and personal with Smart Card / SIM Cards

I know a little bit about SIM cards / USIM cards / ISIM Cards.
Enough to know I don’t know very much about them at all.

So throughout this series of posts of unknown length, I’ll try and learn more and share what I’m learning, citing references as much as possible.

So where to begin? I guess at the start,

A supposedly brief history of Smart Cards

There are two main industries that have driven the development and evolution of smart cards – telecom & banking / finance, both initially focused on the idea that carrying cash around is unseemly.

This planet has – or rather had – a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn’t the small green pieces of paper that were unhappy.

Douglas Adams – The Hitchhiker’s Guide to the Galaxy

When the idea of Credit / Debit Cards were first introduced the tech was not electronic, embossed letters on the card were fed through that clicky-clacky-transfer machine (Google tells me this was actually called the “credit card imprinter”) and the card details imprinted onto carbon copy paper.

Customers wanted something faster, so banks delivered magnetic strip cards, where the card data could be read even more quickly, but as the security conscious of you will be aware, storing data on magnetic strips on a card to be read by any reader, allows them to be read by any reader, and therefore duplicated really easily, something the banks quickly realised.

To combat this, card readers typically would have a way to communicate back to a central bank computer. The central computer verified the PIN entered by the customer was correct, confirmed that the customer had enough money in their balance for the transaction and it wasn’t too suspicious. This was, as you would imagine in the late 1980’s early 1990’s, rather difficult to achieve. A reliable (and cheap) connection back to a central bank computer wasn’t always a given, nor instant, and so this was still very much open to misuse.

“Carders” emmerged, buying/selling/capturing credit card details, and after programming a blank card with someone else’s fraudulently obtained card details, could write them on a blank card before going on a spending spree for a brief period of time. Racking up a giant debt that wasn’t reconciled against the central computer until later, when the card was thrown away and replaced with another.

I know what you’re thinking – I come to this blog for ramblings about Telecommunications, not the history of the banking sector. So let’s get onto telco;

The telecom sector faced similar issues, at the time mobile phones were in their infancy, and so Payphones were how people made calls when out and about.

A phone call from a payphone in Australia has sat at about $0.40 for a long time, not a huge amount, but enough you’d always want to be carrying some change if you wanted to make calls. Again, an inconvenience for customers as coins are clunky, and an inconvenience for operators as collecting the coins from tens of thousands of payphones is expensive.

Telcos around the world trailed solutions, including cards with magnetic strips containing the balance of the card, but again people quickly realised that you could record the contents of the magnetic stripe data of the card when it had a full balance, use all the balance on the card, and then write back the data you stored earlier with a full balance.

So two industries each facing the same issue: it’s hard to securely process payments offline in a way that can’t be abused.

Enter the smart card – a tiny computer in a card that the terminal (Payphone or Credit Card Reader) interacts with, but the card is very much in charge.

When used in a payphone, the caller inserts the smart card and dials the number, and dialog goes something like this (We’ll assume Meter Pulses are 40c worth):

Payphone: “Hey SmartCard, how much credit do you have on you?”

Smart Card: “I have $1.60 balance”

*Payphone ensures card has enough credit for the first meter pulse, and begins listening for Meter Pulses*

*When a meter pulse received:*

Payphone: “Please deduct $0.40 from your Balance”

Smart Card: “Ok, you have $1.20 remaining”

This process repeats for each meter pulse (Payphone metering is a discussion for another day) until all the credit has been used / Balance is less than 1 meter pulse charge.

While anyone could ask the smart card “Hey SmartCard, how much credit do you have on you?” it would only return the balance, and if you told the smart card “I used $1 credit, please deduct it” like the payphone did, you’d just take a dollar off the credit stored on the card.

Saying “Hey SmartCard set the balance to $1,000,000” would result in a raised eyebrow from the SmartCard who rejects the request.

After all – It’s a smart card. It has the capability to do that.

So in the telecom sector single use smart cards were rolled out, programmed in the factory with a set dollar value of credit, sold at that dollar value and thrown away when depleted.

The banking industry saw even more potential, balance could be stored on the card, and the PIN could be verified by the card, the user needs to know the correct PIN, as does the smart card, but the terminal doesn’t need to know this, nor does it need to talk back to a central bank computer all the time, just every so often so the user gets the bill.

It worked much the same way, although before allowing a deduction to be made from the balance of the card, a user would have to enter their PIN which was verified by the card before allowing the transaction.

Eventually these worlds collided (sort of), both wanting much the same thing from smart cards. So the physical characteristics, interface specs (rough ones) and basic communications protocol was agreed on, and what eventually became ISO/IEC 7816 was settled upon.

Any card could be read by any terminal, and it was up to the systems implementer (banks and telecos initially) what data the card did and what the terminal did.

Active RFID entered the scene and there wasn’t even a need for a physical connection to the card, but the interaction was the same. We won’t really touch on the RFID side, but all of this goes for most active RFID cards too.

Enter Software

Now the card was a defined standard all that was important really was the software on the card. Banks installed bank card software on their cards, while telcos installed payphone card software on theirs.

But soon other uses emerged, ID cards could provide a verifiable and (reasonably) secure way to verify the card’s legitimacy, public transport systems could store commuter’s fares on the card, and vending machines, time card clocks & medical records could all jump on the bandwagon.

These were all just software built on the smart card platform.

Hello SIM Cards

A early version Smart card was used in the German C-Netz cellular network, which worked in “mobile” phones and also payphones, to authenticate subscribers.

After that the first SIM cards came into the public sphere in 1991 with GSM as a way to allow a subscriber’s subscription to be portable between devices, and this was standardised by ETSI to become the SIM cards still used in networks using GSM, and evolved into the USIM used in 3G/4G/5G networks.

Names of Smart Cards & Readers

To make life a bit easier I thought I’d collate all the names for smart cards and readers that are kind of different but used interchangeably depending on the context.

Smart Card|Terminal
UICC (Universal Integrated Circuit Card) – Standards name for Smart CardCard Reader (Generic)
SIM (Mobile Telco application running on UICC)Phone (Telco)
USIM (Mobile Telco application running on UICC)SIM Slot (Telco)
Credit / Debit / EFTPOS Card (Banking)UE (Telco)
Java Card (Type of Smart Card OS)EFTPOS Terminal (Banking)
Phone Card (Telco / Payphone)

And then…

From here we’ll look at various topics:

  • Introduction to Smart Cards (This post)
  • Meet & Greet (The basics of Smart Cards & their File System)
  • APDUs and Hello Card (How terminals interact with a smart cards)
  • (Interacting with real life cards using Smart Card readers and SIM cards)
  • Mixing It Up (Changing values on Cards)

Other topics we may cover are Javacard and Global Platform, creating your own smart card applications, a deeper look at the different Telco apps like SIM/USIM/ISIM, OTA Updates for cards / Remote File Management (RFM), and developing for SimToolkit.

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