Magnet information cards

Magnetic cards are provided with unique card signatures which include a number of bits, some of which have intermediate magnetic levels. As a result a card reader allocates randomly either a one or a zero to the intermediate level bits. The random allocation provides a test for the genuineness of the card. The intermediate level bits are formed as a result of inherent inconsistencies in the characteristic of a normal magnetic stripe along its length. It is not possible therefore to readily, if at all, reproduce patterns of intermediate level bits in a duplicate because the stripe on the duplicate will have differently arranged inconsistencies along its length.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
The invention relates to magnetic cards. 
2. Description of Prior Art 
The invention relates more particularly to magnetic cards in the form of 
credit cards, automatic teller machine cards, membership cards guest 
cards, pre-paid cards for telephones and the like. Such cards are 
generally formed of plastic and carry a one or more magnetic tracks which 
carry binary codes. The codes are normally for identifying the issuer or 
system and the user as well as a pin number or user signature. It is 
normal also to provide information about the expiry date, the credit limit 
or credit currently available for the user and so on. The card often 
carries a cipher which is a compilation of the system code and the pin 
number. Generally, the cards are used automatically and card readers 
provided a points-of-need which are capable of reading the binary codes 
and controlling an entry terminal to dispense cash or simply identify that 
the card is genuine and in force, at a point-of-sale for example. 
Generally stated, problems arise because such cards are relatively simple 
to copy or to re-produce and so represent a risk for both issuers and 
users. Methods of "protection" have therefore been developed already to 
reduce these problems but most current methods concentrate on making the 
card itself more difficult to duplicate. Such protection methods include 
adding a hologram, using especially fine printing, ultraviolet ink, 
photographs and incorporating active integrated circuit chips (sometimes 
called "smart" cards). The main disadvantages of these solutions is that 
they inherently add to the cost of producing genuine cards and in some 
cases also require generally more sophisticated card readers in use for 
satisfactory checking of the cards. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide `protected` cards and 
methods for producing such cards which remove or at least reduce the above 
disadvantages. 
According to one aspect of the invention, there is provided a magnetic card 
having normal coded information carried on the card, each bit of the code 
information being formed by a magnetic value representing either a one or 
a zero for detection by a card reader arranged to normally allocate either 
a one or a zero to each bit, including a card signature formed by bits 
positioned at fixed relative positions on the card having intermediate 
magnetic values in which in use the reader randomly allocates a one or a 
zero. 
The signature bits may be positioned at fixed relative positions relative 
to one or more bits of the normal coded information bits and/or to a 
signature marker bit carried on the card. 
The signature bits are preferably carried on the card in a first magnetic 
track extending along the card. 
The magnetic card may have normal coded information separately 
representative of a system signature and a user signature, and include a 
cipher of normal coded information formed by a compilation of the system 
and user signatures and the card signature. 
The magnetic card may have three magnetic tracks in which the card 
signature is formed in a first track, the cipher is formed in a second 
track, and the user signature is formed in a third track. 
The card signature is preferably formed in a normally unused part of a 
magnetic track on the card. 
According to another aspect of the invention there is provided a method of 
forming a magnetic card in which a card signature is formed by writing 
either ones or zeros onto a part of a magnetic track of a blank card, 
covering the part of the track with thin masks, and writing either zeros 
or ones respectively onto the part of tracks to form a number of bits 
having intermediate magnetic values to form the card signature. 
The method may include covering the card signature with a protective thick 
mask, writing normal coded information on to the card, and then removing 
the protective mask.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to the drawings, in FIG. 1 a stripe 9, which is a strip of 
magnetic material carrying machine readable bits forming binary codes, is 
provided on a plastic card 10. The data or bits, typically carried on each 
of three tracks 9A, 9B and 9C, represents the name of the card holder in 
track 9A, an account number in track 9B and the issuer code in track 9C. 
The normal coded information also includes cash amounts authorised by the 
card. In all cases and according to International Standards ISO 7811 none 
of the tracks are fully used. ISO 7811 defines that the maximum number of 
bits normally used for each of three tracks leaves parts of each track 
blank consisting of about a quarter length of each track, which formerly 
has been normally unused. 
Thus parts of the normal coded information includes a "system signature" 
representing the card issuer and a "user signature" (PIN). In accordance 
with embodiments of the invention the magnetic cards also have a unique 
"card signature". The special card signature is provided to prevent 
duplication of the magnetic cards and depends on the unique magnetic 
characteristics of each genuine card supplied by the issuer. The card 
signature is conveniently located at the right hand end or region of track 
9A. 
In the production of the stripe 9, the physical and chemical consistency of 
the stripe is rendered as consistent as reasonably practical along its 
length. However, that consistency is not completely uniform and in 
producing cards of the present invention the inconsistencies are relied 
upon or used to generate cards having a unique code representing the card 
signature. In other words, each card itself when made up and coded has a 
card signature which is unique for a particular card because its signature 
depends on the random inconsistencies in the magnetic properties along the 
stripe on each particular card. Even if the same method of producing two 
cards is repeated, the two cards will in practice not have the same 
signature because the relative positions of the normal inconsistencies 
along the stripes will be different. Thus different signatures will always 
be formed. In providing magnetic cards according to the invention, the 
relative physical disposition of the bits of information forming the card 
signature on the card which exhibit so-called "intermediate magnetic 
values" are used or made use of the qualify the genuineness of each card. 
In practice or use of a magnetic card, a normal card reader is programmed 
to read bits of information at various positions on magnetic cards. At 
each position the card reader must allocate either a zero or a one to the 
bit formed on the stripe instantaneously then opposite a reading head of 
the reader. International Standard (ISO) 7811 para 6.2.1 lays down the 
Industry requirements for magnetically recorded data. Thus a binary one is 
identified by producing a current of 500% of a reference current and 
binary zero is identified by producing a current of 350%. These values, 
with specified tolerances either side, will be allocated by a card reader 
as either ones or zeros accordingly. Should the current produced by a data 
bit be, say, around 425% of the reference current, which value would be 
included in this application as having a so-called "intermediate" value, 
the card reader in practice will randomly allocate either a one and or a 
zero. The fact that the normal reader inconsistently allocates different 
binary numbers to such a bit identifies that the card is a genuine card. 
The positions of the random bits or numbers, as it were, relative either 
to other normal information on the card, or to a normal bit provided as a 
card signature marker, is used to check the genuineness of the magnetic 
card. 
Thus a simple test for magnetic cards of the present invention is to pass 
the card through a reader twice. If the card signature bits read out as 
the same code, the card can be presumed not to be genuine. 
In a practical situation, it is not normally enough to read the card twice 
and simply to ascribe genuineness to a change anywhere in the card 
signature region of track 9A, the physical position of any changes in 
reading must also be monitored. Of course as these changes are random, it 
is statistically possible that a change will not take place at one 
specific intermediate value bit location. Therefore in order to determine 
the actual card signature in the beginning, the card is normally read say 
50 times. This will locate all the intermediate value bits. 
The total signature typically consists of 30 to 50 bits and has around 25 
to 30 intermediate value bits respectively. Further as already explained, 
the establishment of the special or intermediate value bits depends on 
variations in the physical/chemical inconsistencies of the stripe 
material, and so the special bits will tend to occur in practice in 
sequences or batches along the card signature region. It is therefore 
necessary in practice to identify physically with respect to the signature 
marker bit, say, where the batches are. Whenever the signature is read, 
one at least of each batch is likely to change each time according to any 
read out and so in practice, it is sufficient to determine that one change 
at least has taken place in each sequence or batch location. Thus, it is 
quite clear that if the card signature does not change at all even when 
read only twice that the card is not genuine. (This could serve as a first 
or point-of-use test.) On the other hand to test a card for genuineness, 
that is to test more positively, if a card is read say four or five times 
and all read out changes lie within the batch locations, the card could 
reasonably be regarded as genuine. 
The card normally has a cipher at a right hand end part of track 9B. The 
cipher is formed as normal coded information and represents a compilation 
of the system signature (issuer's code), the PIN number and the card 
signature. The card signature information used for the compilation 
contains the relative physical positions or regions of the intermediate 
value bits on the card. Compilation means simply that the information 
identifying the system signature, the PIN number and the card signature 
are put together by a system program to produce the cipher code. When a 
card is checked, the information must match. Compilation techniques as 
such are already used for magnetic cards to provide ciphers. 
In one method to form the special card signature on the stripe 9, a write 
logic "1" is written in to all available data bits of a card signature 
region. A thin (0.05 cm) plastic mask is or number of thin masks are 
placed over the region on the magnetic stripe. A series of logic "0" is 
then written on to the stripe. The thin mask or masks are then removed. 
See FIG. 3. 
The card signature region is then covered with a thick (0.2 cm) plastic 
mask and the normal information written onto the stripe in the usual way. 
The protective mask is then removed. 
Each signature comprises a unique pattern of bits for each particular card. 
Due to inherent non-uniform magnetic properties of the stripe 9 some bits 
are converted in the method more towards an `0` magnetic value than other 
bits by the write over of the series of logic "0" signals with the, thin 
masks in place. As a card reader must allocate either a logic "1" or a 
logic "0" to each bit, some bits are read with uncertainty, as they 
exhibit an intermediate magnetic value. The reader will therefore as a 
matter of practice allocate `0` sometimes and `1` at other times. 
The unique card signature bits therefore owes their form and position to 
the non-uniform characteristics of the magnetic stripe 9. In order to 
check further that the card is genuine a fixed mark, formed by a normal 
bit, is positioned on the stripe 9 and distances or positions determined 
as to where the `uncertain` bits are relative to the fixed mark. Thus the 
signature can be checked by the positions of these "uncertain" or 
intermediate unique bits. 
As the formation of the intermediate magnetic level bits is inherently 
somewhat random, a card signature may be formed by the method with too 
many intermediate level bits per card signature for practical purposes. 
This can be overcome by using a number of thin masks instead of a thin 
single mask. It may also be overcome by writing over the thin mask with 
the series of logic `0` more than once, or deliberately (or otherwise) 
varying the precise thickness of the thin mask along its length. 
It will also be noted in this context that the magnetic level exhibited by 
each bit is dependent on a magnetic hysteresis effect and so there is less 
tendency than normally would be the case for the magnetic level to be set 
at a, say, truly intermediate or central level (that is to produce 425% of 
the reference current). This is because the bits formed after the write 
over with the series of logic "0" will tend to remain either somewhat 
nearer the "1" level or be converted nearer towards the `0` level than 
would be the case without the practical hysteresis effect. This leads in 
practice to the likely formation of fewer intermediate level bits than 
would otherwise be naturally the case in the method described. 
Further, the method is much more dependent, again as a matter of practice, 
to form the intermediate card signature bits in dependence upon the random 
inconsistencies in the magnetic properties of the stripe 9 along its 
length. Thus and importantly, as the card signature bits at least 
partially derive their uncertain characteristic by the imperfections of 
the stripe itself they cannot be repeated or reproduced in practice on a 
different length of stripe 9. 
In practice therefore a genuine card is first provided with a unique 
signature and the positions of the uncertain bits (at the intermediate 
level) recorded and a code identifying those positions is generated. That 
code is combined (compiled) with the issuer's signature and the user's 
personal signature (PIN) in a chosen format using a suitable software 
program and a (cipher) security code representing is generated and written 
on to the end of the track 9B. 
A card reader is shown in FIG. 2, in which rollers are provided at an entry 
housing 11 and driving sets of rollers 12 and 13 are positioned to take 
the card past a pair of reading heads 14 and 15. The reading heads are 
electrically connected to a processor 16. With the reader in FIG. 2, data 
or bits on the card are read twice in succession as the card passes 
adjacent the heads 14 and 15. Thus, a card may be passed through the card 
reader in one direction and the data, especially the card signature can be 
read twice to determine immediately as described above immediately, or as 
a first appraisal at least, whether the card is genuine. That is to say, 
if the card signature appears to be the same when read by the two heads 14 
and 15, it can be presumed that the card is not genuine. The card can of 
course be read twice again, as the card passes back towards and out of the 
housing 11. See FIG. 4. 
It will be appreciated that the intermediate level bits may be provided by 
a method which includes writing a series of zeros onto a card, covering or 
part of the card signature region with a thin mask or masks, and then 
writing a series of ones onto the card signature region. 
In another method, the card signature can be first written with a write 
head set to write either logic "1" or logic "0" at respective saturated 
signal energy levels. The write head is then set at an unsaturated signal 
energy level and either logic "0" or logic "1" is written respectively on 
the card over the first written data. This provides the special card 
signature with the appropriate intermediate magnetic values as required. 
It will be noted that in embodiments of the invention the inherent 
inconsistencies of a magnetic stripe are used to form a unique card 
signature. These inconsistencies occur as a matter of practice even when 
present day quality controlled stripes are manufactured. The magnetic 
recording level is then set up so that a manageable number of 
inconsistencies will show up when the card is read, and information about 
the physical positions of the inconsistencies is noted and stored. To 
check a card signature for genuineness, the reader is checked to see 
whether it is "confused" when reading one, or usually several, of the 
points. This means that every card in practice will have a unique 
signature that can be verified for genuineness. One advantage in practice 
is that a simple first appraisal test is to read the card twice. Two 
consecutive identical card signature read-outs indicates immediately that 
the card is almost certainly not genuine. In terms of security, this 
offers an easy and reliable point-of-use or point-of-sale test. Also, as 
is clear and has been explained already, it is virtually impossible to 
produce a fake card having the same signature because it would mean 
establishing corresponding inconsistencies at many physical positions 
along the length of the card signature, certainly in order to satisfy a 
full test of a card.