Magnetic stripe cards are tokens used for authentication and access control in many security environments. Magnetic stripe card readers can be interfaced with a variety of access control equipment, including locally controlled electrical locks, or centrally controlled security databases. Magnetic stripe cards are identical in composition and appearance to bank or credit cards. The stripe normally contains about 140 digits and characters, divided among one to three tracks in a proprietary format. They can double as identification cards or badges when they are printed or embossed with the user’s name, identification number, imprints of corporate or organizational logos, and a photograph.
Magnetic stripe cards must be either swiped through a reader track, or fully inserted and then removed from a reader in order to cycle a lock. Card readers can be mounted to adjacent walls, doorframes, or any convenient surface. Many systems include red and green LEDs on the lock face to indicate the state of the lock. When a valid card is detected, the green LED illuminates and the electric lock opens. When an invalid card is detected, the red LED illuminates and the electric lock will not open. Depending on the system, the control of the lock can be located at the door, at an intermediate control panel, or at a central control station to manage authentication processes for a large facility with many authorized users. Systems can be programmed so that an alarm is generated after a preset number of failed access attempts.
Magnetic stripe readers detect the points on the stripe where the magnetic encoding reverses polarity. Areas where two north magnetic poles or two south poles are adjacent cause a small voltage transient in the card reader. These transients, used in combination with clocking and error checking algorithms, produce a series of binary digits that can be used to represent binary coded decimals, a limited set of American National Standards Institute (ANSI) alphanumeric characters, or information in another proprietary or encrypted format. Caution should be used when selecting a magnetic stripe card reader, because many readers only read track one or track two, but not both. Encoding a magnetic stripe card is normally accomplished when a card is issued, using a card printer with the appropriate capabilities. Card printers are widely available.
Magnetic stripe systems are used throughout the public and private sectors, because of their relatively low cost and versatility. They are much more versatile than keycard systems. Essentially keycard systems provide local control of an access point, but lack the capability of centralized control. Often, keycard systems also lack recordkeeping capability; however, magnetic stripe systems offer both fine-grained control of access points and detailed, real-time record keeping capability.
Magnetic stripe systems achieve this using centralized system control. In centralized systems, the security manager maintains a computerized database of authorized permissions for each cardholder. When a cardholder operates a reader, the reader sends a signal back to the controller, which identifies the card-bearer and access point. If a card-bearer has permission for the door, then the access point opens. Another advantage of centralized control is that the list of permissions for each user can change according to the situation. For example, the permissions of every user could be revoked if it became necessary to lock everyone out of a facility.
Permissions for a single user could be revoked or modified during planned periods of absence such as vacation, holidays, business travel, or at certain times of the day. Automated, centralized access control also provides more accurate record keeping.
Centralized control offers advantages in emergencies. Access for fire and emergency crews can be coordinated and granted to affected areas quickly. Fine-grained access control systems can be used in schools, colleges, hospitals, public and private office buildings, and residences.
Like other electrical lock systems, the performance of magnetic stripe systems can be measured by the number of cycles performed before corrective maintenance is required or a card must be re-issued. Vendors and manufacturers often advertise high performance values; however, sitespecific conditions (e.g., extreme heat, dust, high humidity) can cause the actual performance to be much lower.
Equipment used to copy and encode magnetic stripe cards is commercially available; therefore, magnetic stripe cards can be copied and forged with relative ease. Additional features imprinted on the card such as identification photographs, corporate logos, and holograms all help to minimize the chance of an effective forgery. The information encoded on the magnetic stripe should differ from the information on the face of the card to prevent forgers from simply encoding the information from the card face.
There have been concerns about the privacy of information on magnetic stripe cards; however, many systems now encrypt personal information, leaving only the access code and possibly the individual’s name encoded on the card. Relatively weak magnetic fields can corrupt the encoded information on some cards, particularly the cards used with low-energy encoding devices. Cards that use high energy encoding have a magnetic medium with greater permanence and resistance to ambient magnetic fields.
- Access Control Technologies Handbook
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