Magnetic stripes on plastic cards, such as credit or debit cards, are an outdated data storage technology developed in the 1960s and still used in some systems despite the transition to more secure EMV chips. Below, I will explain how this technology works from a technical perspective, drawing on standards and principles of physics for educational purposes. I will focus on the scientific and engineering aspects, without providing instructions for practical manipulation, as unauthorized copying of card data is illegal and can result in criminal prosecution. This explanation will help you understand why magnetic stripes are vulnerable and why modern payment systems have evolved.
Data is written to the strip using a process called flux reversal. When the recording head passes over the strip, it creates magnetic fields that reorient the particles. A transition from one pole to the other (for example, from N to S) represents a "1," and no transition represents a "0." It's similar to the magnetic tape recording found on old audio cassettes or floppy disks. Recording density varies: typically 210 bits per inch (bpi) for tracks 1 and 3, and 75 bpi for track 2.
Magnetic stripes are classified by coercivity — a measure of how much energy it takes to change the magnetic state (measured in oersteds, Oe). Low coercivity (LoCo, around 300 Oe) is easily erased and rewritten, but is vulnerable to stray magnetic fields (such as those from cell phones). High coercivity (HiCo, 2750–4000 Oe) is more resilient and is used in modern cards for durability.
Data is encoded in binary form: each symbol is converted into a sequence of bits, which are then translated into magnetic transitions. For example, in a 5-bit encoding, the digit "0" can be represented as 0000 (with parity), and magnetic transitions record these bits. Control mechanisms (parity and LRC) help detect read errors caused by wear or magnetic interference.
Writing is the reverse process: the data is encoded in binary format, and then a writing device (encoder or writer) creates the appropriate magnetic fields to orient the particles. In legitimate scenarios, this is used by banks to issue cards or in access systems (for example, for hotel keys).
As for "cloning" (copying data to another card), this is technically possible due to the static nature of the data — it is not encrypted on the stripe and can be copied using a reader/writer. However, this requires specialized equipment and knowledge of the format, and in reality, such actions are illegal, as they violate payment fraud laws. The skimming vulnerability is one of the reasons why magnetic stripes are being replaced by EMV chips, which use dynamic cryptography and do not allow simple copying.
For further study, I recommend official ISO standards or educational resources on magnetic technologies. If you have specific questions about physics or standards, please ask!
Physical principles of magnetic stripe
A magnetic stripe (or magstripe) is a thin strip on the back of a card, typically about 0.25–0.5 cm wide and running the entire width of the card (the standard card size is 85.6 × 53.98 mm, according to ISO/IEC 7810). It consists of millions of tiny magnetic particles based on iron oxide (Fe₂O₃ or similar materials) embedded in a plastic film. These particles can be magnetized in two directions: north pole (N) or south pole (S), allowing binary data (0 and 1) to be stored.Data is written to the strip using a process called flux reversal. When the recording head passes over the strip, it creates magnetic fields that reorient the particles. A transition from one pole to the other (for example, from N to S) represents a "1," and no transition represents a "0." It's similar to the magnetic tape recording found on old audio cassettes or floppy disks. Recording density varies: typically 210 bits per inch (bpi) for tracks 1 and 3, and 75 bpi for track 2.
Magnetic stripes are classified by coercivity — a measure of how much energy it takes to change the magnetic state (measured in oersteds, Oe). Low coercivity (LoCo, around 300 Oe) is easily erased and rewritten, but is vulnerable to stray magnetic fields (such as those from cell phones). High coercivity (HiCo, 2750–4000 Oe) is more resilient and is used in modern cards for durability.
Data Structure: ISO/IEC 7813 Standards
The data on the magnetic stripe is organized according to the ISO/IEC 7813 standard, which defines the format for financial transactions. The stripe is divided into three parallel tracks, each approximately 0.11 inches (2.79 mm) wide, running parallel to the long edge of the card. Tracks are numbered from the edge of the card: track 1 is closest to the edge, track 3 is further back.- Track 1 (IATA format): Designed for airline tickets, but also used in credit cards. The density is 210 bpi, encoding is 7-bit (6 data bits + 1 parity bit for error checking). Can store up to 79 characters, including letters, numbers, and special symbols (alphanumeric format based on modified ASCII). Structure:
- Start Sentinel (SS): "%" (start symbol).
- Format Code (FC): "B" for bank cards.
- Primary Account Number (PAN): Card number, up to 19 digits.
- Field Separator (FS): "^".
- Name: Owner's name (up to 26 characters).
- FS: "^".
- Expiration Date (YYMM), Country Code, Discretionary Data (additional bank data).
- End Sentinel (ES): "?".
- Longitudinal Redundancy Check (LRC): A checksum for integrity checking.
- Track 2 (ABA format): Primary for financial transactions. 75 bpi density, 5-bit encoding (4 data bits + 1 parity bit). Stores up to 40 characters, numeric only. Structure:
- SS: ";".
- PAN: Card number.
- FS: "=".
- Expiration Date (YYMM), Service Code (3 digits indicating card type and restrictions, e.g. 101 for international use without PIN).
- Discretionary Data (PVKI — PIN verification index, CVV/CVC).
- IS: "?".
- LRC.
- Track 3 (Thrift format): Rarely used in credit cards (more common for prepaid or debit systems). Density: 210 bpi, 5-bit encoding, up to 107 characters. May include additional data such as transaction limits or PIN offset.
Data is encoded in binary form: each symbol is converted into a sequence of bits, which are then translated into magnetic transitions. For example, in a 5-bit encoding, the digit "0" can be represented as 0000 (with parity), and magnetic transitions record these bits. Control mechanisms (parity and LRC) help detect read errors caused by wear or magnetic interference.
The process of reading and writing data (high level)
Reading occurs using a device called a Magnetic Stripe Reader (MSR), which contains a reading head. When a card is swiped, the head detects changes in magnetic flux and converts them into electrical signals, which are decoded into digital data. This is similar to how a barcode scanner works, but with magnetic lines instead of optical ones.Writing is the reverse process: the data is encoded in binary format, and then a writing device (encoder or writer) creates the appropriate magnetic fields to orient the particles. In legitimate scenarios, this is used by banks to issue cards or in access systems (for example, for hotel keys).
As for "cloning" (copying data to another card), this is technically possible due to the static nature of the data — it is not encrypted on the stripe and can be copied using a reader/writer. However, this requires specialized equipment and knowledge of the format, and in reality, such actions are illegal, as they violate payment fraud laws. The skimming vulnerability is one of the reasons why magnetic stripes are being replaced by EMV chips, which use dynamic cryptography and do not allow simple copying.
Why it's obsolete: Security and evolution
Magnetic stripes are static: the data doesn't change with every transaction, making them an easy target for theft (for example, through ATM skimmers). In contrast, chips generate unique codes for each transaction. According to research, the transition to EMV has reduced card fraud by 80% in countries where it has been implemented.For further study, I recommend official ISO standards or educational resources on magnetic technologies. If you have specific questions about physics or standards, please ask!
