GB2279477A

GB2279477A - Security/access system

Info

Publication number: GB2279477A
Application number: GB9404929A
Authority: GB
Inventors: Robert John Baldwin
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-28
Filing date: 1994-03-14
Publication date: 1995-01-04
Anticipated expiration: 2014-03-14
Also published as: GB9404929D0; GB9313332D0; GB2279477B

Abstract

A security system has a substrate 2 carrying a plurality of electrical elements 4a - 4j, and a reading device. The reading device indicates if one or more of the electrical elements 4a - 4j has been rendered inoperative after it accepts an identification code and applies a specific current or voltage to each of the electrical elements. The current or voltage applied to each element 4a - 4j is determined by the identification code, such that if an incorrect identification code has been supplied, one or more of the elements 4a - 4j will be rendered inoperative. <IMAGE>

Description

SECURITY/ACCESS SYSTEM This invention relates to a security/access system and particularly, but not exclusively, to a security system suitable for use in conjunction with a transaction card.

Transaction cards such as credit cards, debit cards or cheque guarantee cards are used extensively and have well recognised advantages over the use of cash.

Unfortunately, however, these cards are becoming increasingly abused when they fall into criminal hands.

A criminal can use a card in a number of ways. It is known for a criminal to purchase goods at a level below that at which a merchant is required to gain authorization from the office which issues the card.

Alternatively, it is known for a criminal to persuade a merchant to process transaction coupons made out using the card, whilst actually selling no goods or goods of a lesser value than the coupon/receipt indicates. The proceeds are then split between the criminal and the merchant. Using these two methods it is possible to use a stolen card fraudulently until its expiry date.

There are known measures which can be taken in order to combat illegal use of a card. These measures are implemented at the point of sale by the merchant. The measures include but are not limited to the following: i) telephoning the issuing office for verification of the card and/or authorization of the transaction; ii) checking the card number against lists of stolen and/or lost cards which are produced by the card-issuers; iii) use of a "hot-card" file which is electronically up-dated on a daily basis and contains the identification numbers of stolen or lost cards; iv) checking the signature on the card against that on the signed receipt.

All of these measures have drawbacks.

Making a telephone call for verification or authorization can cost the merchant up to 2 and it is often difficult to get through to the issuing office.

These factors tend to be dissuasive.

The lists of stolen and/or lost cards are usually long out of date, slow to use and depend upon the merchant being bothered to check the list properly. Furthermore, when reading a list quickly, it is easy to misread a number.

The latest technology in "hot-card" files will only take the details of about 15,000 cards. This is roughly the number of cards issued by a single well-known issuing office alone which are stolen every three weeks. This means that a criminal would only need to wait for one or two weeks before being relatively sure that the stolen card in his possession is unlikely to be identified.

Fraudulent use no longer relies upon stolen or found cards. It has now become common practice to re-load the magnetic strip on a card with details copied from another card. A system that will do this can be legally purchased by anyone for as little as 500. By use of this system, a card need not be stolen in order to have costs charged to the account to which it pertains.

Cards of this type are widely used by long-distance trucking companies throughout Europe, and their production has become a cottage-industry in the Far East.

The above problems are exacerbated by the fact that completely false or obviously altered cards may quite deliberately not be noticed by an honest merchant or cashier because he receives little reward from the issuing office, yet risks physical violence from the card-presenter. In any case, if the merchant claims that the card was correctly presented, he will be paid by the issuing office.

Several physical modifications of transaction cards have been suggested as solutions to the above described problems.

Cards employing laser-engraved signature verification systems have been proposed. These have questionable reliability and are expensive.

IC cards, which contain a processor which identifies itself and can pass the necessary details to electronic terminal equipment at the point of sale are known. The processor inside the card also registers all purchases.

It has been found that criminals can circumvent the system by stamping on the card in order to smash the processor; the merchant or cashier then takes down details from the front of the card in the old fashioned way. These cards are also expensive to produce.

It has been proposed that the card could carry a processor which generates a picture of the card-holder which the merchant or cashier may compare with the card presenter. This system is expensive and, in any case, a person' s appearance can change depending upon the style of their hair and clothing, etc.

Another type of card incorporating an electronic water-mark has been proposed. Such a card would be undesirably expensive to produce.

Alternative systems, which include voice pattern details, retina-pattern details and/or finger-print details held within the card and accessed by a processor, have been considered. However, such systems have questionable reliability and are expensive to implement.

Quite apart from the obvious expense, all the above systems could be circumvented by a skilled fraudster who could re-load the card with new details. Such fraud is extremely unlikely to be detected.

The present invention sets out to provide a system which is simple and inexpensive to manufacture and which does not require a significant alteration of the structure of the card or the like in which the system is provided.

In addition, the invention sets out to provide a system which is tamper-proof and which could prevent use of the card or the like in which the system is provided after any attempt to alter or tamper with the structure of the card or the like or with the information contained therein.

According to one aspect of the invention there is provided a security system comprising a substrate, a plurality of electrical elements situated on the substrate, and a reader; the reader comprising means for indicating that one or more of the electrical elements have been rendered inoperative and being adapted to accept an identification code and apply a specific current or voltage to each of the electrical elements, the current or voltage applied to each element being determined by the identification code, such that if an incorrect identification code has been supplied to the reader, one or more of the elements will be rendered inoperative.

The electrical elements may be rendered temporarily or permanently inoperative. If temporarily inoperative, the operative state may be restored automatically after an interval, or by an externally applied resetting action.

Preferably, the electrical elements are fuses and the reader is adapted to apply a number of predetermined currents in sequence and the identification code causes the reader to select the order of the fuses to which the predetermined sequence of currents is applied.

The reader may be capable of applying one of a number of predetermined current or voltage sequences. The particular current or voltage sequence used can be determined by some characteristic of the item on which the substrate is situated. This characteristic can be automatically discovered by interrogation by the reader or can be manually entered.

The reader may be arranged to activate a time-lock or alarm (or other responsive device such as an immobiliser) if an incorrect identification number has been supplied.

The substrate may be situated in a transaction card or a key or the like and may be in the form of a wafer.

Throughout this specification, the expression 'key' is not limited in the traditional sense, but is used to describe anything used to gain access to something or somewhere.

The fuses may be situated in conductors, each of which has a specific resistance; the specific resistances may all be equal. The reader may also comprise means for verifying the resistance of conductors.

In a preferred embodiment, the reader includes means for blowing all of the fuses, should one of the fuses be detected as blown.

The reader may be programmed only to accept certain items carrying a substrate at certain times, or to accept only certain identification codes at certain times.

The reader may also be programmed to add or subtract a value from an entered identification number to generate a true identification number - which is then used as the basis for validation. Other mathematical operations may be used rather than only addition or subtraction.

The reader may detect data on the card which it will use as the basis for programming itself to adjust the identification number entered by certain factors to generate a true identification number. The data on the card may be permanently set or capable of being altered.

Most people are able to recall their identification number correctly and to enter it accurately on a keypad, first time, every time. However, there are occasions when a person will accidentally enter the wrong identification number, either due to a momentary mental aberration or hitting the wrong key without noticing. At this point a reader in accordance with a preferred embodiment of the invention will destroy the fuses in the wafer. To reduce the incidence of this occurrence in circumstances where the card is being used legitimately, it may be desirable to enter the identification number twice. The processor will compare the two identification numbers, and if they match, will pass the currents accordingly. If the identification numbers do not match, the card-user will be asked to start again, and hopefully the identification numbers will match this time.The number of such tries could be limited or unlimited as required by the needs of the application in which the system is operating. This will reduce the number of cards which are destroyed whilst being used legitimately.

The reader may contain an integrated circuit comprising a control unit to permit possible multiple attempts for entering a identification number, as described above.

The substrate may be covered with a thin sheet of dense material in order to prevent examination by X-ray or some similar device.

The reader may be arranged to destroy the electrical elements if the resistance of a wire is found incorrect.

When identification number is entered, the reader may instruct a video camera (or similar device) to film the card presenter for a limited period.

To maintain clean electrical contacts on cards and reader, an ultra sonic cleaning device may be built into the reader.

According to a further aspect of the invention there is provided a method of verifying the eligibility of a user of an object comprising: i) accepting an identification code from the user; ii) applying a plurality of specific currents or voltages to a plurality of electrical elements situated in the object, the value of the current or voltage applied to each element being determined by the identification code; iii) checking to see if any of the elements have been rendered inoperative; iv) indicating whether or not any of the elements have been rendered inoperative.

Preferably the elements are fuses and specific currents are applied. In a preferred embodiment, the method includes the additional steps of checking the integrity of the fuses prior to applying currents to them and blowing all of the fuses if, at any stage, a fuse is detected as blown.

In the aspects of the invention set out above, the reader tests the resistance of each wire in the card wafer and passes currents though them in accordance with the identification code entered by the user (and possible other information carried on the card).

According to yet another aspect of the invention, the reader performs such a resistance test, but does not follow this by making any of the wires inoperable. The identification code is used to notify the reader as to which wire is expected to have which resistance value.

Since the reader does not pass significant currents through the wafer, the latter is not required to contain fuses. Such an arrangement may be appropriate, for example, where the card is to be an electronic key.

In unattended/unobserved situations, the need for the wires in cards to be made inoperable may be diminished.

The reader may be programmed to accept cards with certain resistances in their wires. The reader is programmed to accept identification numbers, the digits of which correspond to the wires bearing certain resistances, in accordance with the resistances that the reader has been programmed to identify.

Further preferred features of the invention are set out in the claims.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a wafer for use in a system according to the invention; and Figure 2 is a schematic diagram of circuitry of a reader for use in a system according to the invention.

This embodiment of the invention comprises four main physical elements. Namely, (i) a plastic transaction card; (ii) a wafer 2 which is installed within the plastic card and acts as a substrate; (iii) a reader 10 into which the card is entered for verification; and (iv) a processor, which controls the actions of the reader.

Each element will be described and the operation of the system will then be explained.

The card is a slightly adapted version of a conventional transaction card such as a credit card. It is to be understood that this invention may be employed equally successfully in another structure such as an ignition key for a car or a door key.

The wafer 2 comprises ten fuses 4a-4j, each of which is electrically connected to opposite ends of the card by means of a wire 6a-6j.

The fuses are used to record a personal identification number on the card. Fuse 4a relates to the digit "1", fuse 4b relates to the digit "2", and so on. Where a digit does not form part of the personal identification number (PIN), the fuse relating to that digit has a rating of 13 Amps. The first digit in the PIN is identified by a 5 Amp fuse in the corresponding wire, the second digit in the PIN is represented by a 7 Amp fuse in the corresponding wire, the third digit in the PIN is represented by a 9 Amp fuse in the corresponding wire and the fourth digit in the PIN is represented by an 11 Amp fuse in the corresponding wire.

In the embodiment shown in Figure 1, it can be seen that the PIN of the card is "1357". This is because wire 6a, which corresponds to digit "1", has the 5 Amp fuse; wire 6c, which corresponds to the digit "3" has the 7 Amp fuse; wire 6e, which corresponds to the digit II "5", has the 9 Amp fuse; and wire 6g, which corresponds to the digit II "7", has an 11 Amp fuse. Of course different cards will have different fuses in the wires and will therefore have different PIN numbers. The PIN number 1357 is here merely used as an example.

The resistance of each wire is 2 Ohms, taking into account the fuse. This makes the wires indistinguishable. Preferably, the wires and fuses also appear identical when viewed by X-ray apparatus and the like.

The reader 10 comprises a resistance meter 12 which can measure the precise resistance of an electrical circuit.

The reader 10 also comprises seven part-circuits 14a-14g. The part-circuits each have a different resistance and form complete circuits with the wires 6a-6j and fuses 4a-4j when connected to the wafer 2.

The resistance of each of the part-circuits is as follows: 14a - 78 Ohms 14b - 58 Ohms 14c - 38 Ohms 14d - 28 Ohms 14e - 22 Ohms 14f - 18 Ohms 14g - 8 Ohms.

When the reader 10 is connected to the wafer 2 so as to form complete circuits, the 2 Ohm resistance of each wire 6a-6j and fuse 4a-4j in the wafer plus the resistance of the connected part-circuits 14a-14g produces circuits with the following resistances: Circuit including 14a : 80 Ohms Circuit including 14b : 60 Ohms Circuit including 14c : 40 Ohms Circuit including 14d : 30 Ohms Circuit including 14e : 24 Ohms Circuit including 14f : 20 Ohms Circuit including 14g : 10 Ohms.

When a voltage of 240 volts is delivered from the mains (this is the mains voltage in the UK - the mains voltage will vary from country to country) and sent through each of the circuits, the following currents will be produced: Circuit including 14a : 3 Amps Circuit including 14b : 4 Amps Circuit including 14e : 6 Amps Circuit including 14d : 8 Amps Circuit including 14e : 10 Amps Circuit including 14f : 12 Amps Circuit including 14g : 24 Amps.

These currents are easily calculated using Ohm's law.

The processor is configured to connect and disconnect the part-circuits 14a-14g of the reader 10 to the wires 6a-6j of the card in a specific order determined by the PIN number entered.

The PIN number of the wafer 2 and, therefore, the card is dependent upon which wire 6a-6j holds which fuse 4a-4j. The PIN number is unalterable. The PIN number must be known to the person presenting the card to prevent the card from being made invalid.

Operation of the device will now be explained.

The card is placed in the reader 10, thereby connecting the wires 6a-6j in the wafer with corresponding nodes built into the reader 10. Thus, the wafer 2 is joined into the circuitry of the reader 10.

A PIN number is entered.

The reader 10 then performs a series of checks and actions as outlined below.

Resistance Check - The reader 10 verifies that the resistance of each wire 6a-6j is correct.

Integrity Check - The reader 10 passes a small current through each wire 6a-6j to ensure that they will all take a current.

PIN Number Check - The reader 10 passes a specific current through each wire 6a-6j as identified by a digit used in the PIN number; a different specific current is used for each wire 6a-6j, depending upon whether and where it appeared in the PIN number.

Cross Check - The reader 10 passes a greater specific current through all the wires 6a-6j other than those that were identified in the PIN number.

Verification - The reader 10 passes a small current through each wire to ensure that they will all still take a current.

Invalidation - In the event that the PIN number offered is incorrect, the reader 10 then passes sufficient current through each wire 6a-6j to blow all the fuses 4a-4j, thus rendering the card useless for future such tests.

Confirmation - The reader 10 signals that the card is valid or invalid.

This process will now be illustrated using the embodiment of the card discussed above, which has the PIN number 1357.

Procedure When The Correct PIN Number is Entered Resistance Check - The reader 10 checks that the resistance of each wire is 2 Ohms.

Integrity Check - The reader 10 connects wire 6a to part-circuit 14a, which will allow 3 Amps to flow. Once current flows, the reader 10 connects wire 6b to part-circuit 14a. This is done for each wire in turn until they have all be checked to ensure that they will allow a current to pass. When all wires have shown that they will carry a current, the reader 10 moves onto the next stage.

PIN Number Check - (i) The reader 10 connects wire 6a to part-circuit 14b, thus allowing 4 Amps to flow. Once current flows, the reader 10 moves onto the next stage.

(ii) The reader 10 connects wire 6c to part-circuit 14c, thus allowing 6 Amps to flow. Once current flows, the reader 10 moves onto the next stage. (iii) The reader 10 connects wire 6e to part-circuit 14d, thus allowing 8 Amps to flow. Once current flows, the reader 10 moves onto the next stage. (iv) The reader 10 connects wire 6g to part-circuit 14e, thus allowing 10 Amps to flow. Once current flows, the reader 10 moves onto the next stage.

Cross Check - The reader 10 connects wires 6b, 6d, 6f, 6h, 6i, and 6j in turn to part-circuit 14f, thus allowing 12 Amps to flow. Once current has been shown to flow through each of these wires, the reader 10 moves onto the next stage.

Verification - The reader 10 connects wire 6a to part-circuit 14a, which allows 3 Amps to flow. Once current flows, the reader 10 then connects wire 6b to part-circuit 14a. This is done for each wire in turn until they have all been checked to ensure they will still allow a current to pass. This is done just in case a wire carried a current for long enough to register before its fuse blew. When all wires 6a-6j have shown that they will still carry a current, the reader 10 moves onto the next stage.

Invalidation - Not applicable when the correct PIN number is offered.

Confirmation - The reader 10 signals that the PIN number offered is correct.

Procedure When an Incorrect PIN Number (say 1354) is Entered Resistance Check - The reader 10 checks that the resistance of each wire 6a-6j is 2 Ohms and then moves onto the next stage.

Integrity Check - The reader 10 connects wire 6a to part-circuit 14a which will allow 3 Amps to flow. Once current flows, the reader 10 connectes wire 6b to part-circuit 14a. This is done for each wire in turn until they have all been checked to ensure that they will allow a current to pass. When all wires 6a-6j have been shown that they will carry a current, the reader 10 then moves onto the next stage.

(ii) The reader 10 connects wire 6c to part-circuit 14c, thus allowing 6 Amps to flow. Once current flows, the reader 10 moves onto the next stage. (iii) The reader 10 connects wire 6e to part-circuit 14d, thus allowing 8 Amps to flow. Once current flows, the reader 10 moves onto the next stage. (iv) The reader 10 connects wire 6d to part-circuit 14e, thus allowing 10 Amps to flow. Once current flows, the reader 10 moves onto the next stage.

Cross Check - The reader 10 connects wires 6b, 6f, 6g, 6h, 6i and 6j in turn to part-circuit 14f, thus allowing 12 Amps to flow. Whilst all the other wires will accept this current, the fuse 4g in wire 6g will be blown as it can only take 4 Amps. The reader 10 will then detect that current will not flow through wire 6g. The reader 10 then moves onto the next stage.

Verification - The reader 10 connects wire 6a to part-circuit 14a which will allow 3 Amps to flow. Once current flows, the reader 10 connects wire 6b to part-circuit 14a. This is done for each wire in turn until they have all been checked to ensure that each will still allow a current to pass. This is done just in case a wire carried a current for just long enough to register before its fuse blew. The reader 10 will once again detect the blown fuse 4g in wire 6g. The reader 10 moves onto the next stage.

Invalidation - Having established that the PIN number is incorrect and that one fuse (4g) has been blown, the reader 10 connects each wire 6a-6j in turn to part-circuit 14g which passes 24 Amps. Each fuse 4a-4g will blow, rendering the card useless for future such tests. The reader 10 moves onto the next stage.

Confirmation - The reader 10 signals that the card is invalid.

From the foregoing, it will be clear that it is impossible to establish the PIN number of the card. Any attempt to use the card without using the correct PIN number will not only be denied but will also result in the card being made useless for future such tests and therefore of no value to the criminal.

A criminal might attempt to establish the PIN number of a stolen card by testing it with an electric current.

However, the moment he passes too large a current through any wire, the card becomes useless for future such tests. As all the wires in the wafer offer the same resistance to current, the only time that the criminal can know which wire is intended to take a given current is when that current is exceeded, thus destroying the fuse in that wire and making the card useless for future such tests.

For PIN numbers using a particular digit more than once, the lower amperage fuse in the wire that corresponds to that digit is not fitted. It would be no easier to establish the PIN number without invalidating the card.

The PIN number could be composed of any amount of digits, letters and/or symbols as required; provided that each digit, letter and/or symbol could be related to a wire by the reader 10 which has sufficient part-circuits and an appropriate processor.

The electrical qualities of the wires, fuses and part-circuits can be varied; for example the sizes of the resistors could be different from the above example as could the currents and voltages applied.

The purpose of checking the resistance of each of the wires is to reduce the very slight chances of professional tampering. As previously mentioned, card producers consider that it is virtually impossible to split a card open or drastically alter it without easy detection.

By entering miniture switches into the wafer, it would be possible to allow the card-holder to make a number of attempts to enter the correct PIN number before the card is destroyed by the reader.

The system may be operated in isolation or in conjunction with other systems.

The wires may be in the form of microwires or conductive paint. Any appropriately sized electrical conductor will suffice. Any appropriate conductive substance may be employed. The fuses will ideally be microfuses.

The fuses may be replaced by any other electrical component which is rendered inoperative after a specific voltage or current has been applied to it.

The part-circuit pattern shown in Figure 2 is simply one particular arrangement, which is given as an example.

The reader may include several different arrangements of part-circuits. Each of the part-circuits will, therefore, apply different currents in a different order. The reader may be programmed to select the particular part-circuit pattern which is to be applied during a validation operation. The particular part-circuit pattern which is to be used can be based upon some feature of the card. This feature could be the first letter of the card-holder's name, the expiry date of the card or simply some other code stored on the substrate. If the pattern is selected in dependence upon an obvious feature such as the first letter of the card-holder's name or the expiry date of the card, this information could be entered manually by the reader operator. Alternatively, this information could be automatically read when the card is entered into the reader.The information could be stored magnetically, for instance. In this case, it would not be possible for the reader/operator to enter the information manually.

There is no need for the holder of the transaction card to actually know the positions of the fuses within the wafer. The card holder must simply know the PIN number of the card. On this basis, the reader could also be programmed to instruct the processor to alter the allocation of the digits on the wires according to a pre-set formula.

The features set out in the two paragraphs immediately above would make the criminal' s task considerably harder.

The fuse sizes and resistance of the wires need not be the same in cards to which different reader patterns apply. As long as the correct pattern is selected, the reader will know which resistance to expect from which wire and will generate the correct current/voltage to pass through the wire. The resistance of every wire in any given card could be different if a sufficiently complex pattern were designed. The more variables which are used, the more complex the pattern(s) will be.

Under some circumstances, such as where access is limited or restricted, it may be necessary to program the reader only to accept certain card numbers at certain times.

As well as destroying the card, the reader may be called upon to instigate a secondary action such as operating a time-lock or an alarm after a set number of unsuccessful attempts to access a system have been made.

To make the system even more difficult for a criminal to overcome, the reader can be programmed to expect the PIN number entered to be different from the PIN number relating to the card. For instance, the reader might be programmed that it will add "4" to every digit entered.

Therefore if the number of the card is 5678, the numbered entered into the reader would be 1234 because 1 + 4 = 5, 2 + 4 = 6, etc. Anyone seeing a person using this system to operate, for example, an electric gate in this way would not be able to open the gate even if they had seen the number 1234 typed into the reader and were able to obtain a card with that number.

It is desirable that the card cannot be read by the use of X-ray apparatus or some similar device. To this effect, the substrate may be coated with a thin sheet of dense material (e.g. lead).

As an added precaution, the reader can be programmed to destroy the fuses of all the wires of the card in the event that the resistance of the wires found to be incorrect by the reader.

Additional electrical components (such as switches, for example) may, of course, be added to the substrate.

"Non-contact" connections may be used for passing the voltage/current from the reader to card and vice versa.

This may be done by electromagnetic induction, in which case the resistance meter in the reader may be replaced by an operational amplifier comparator circuit, with the corresponding changes in the tests performed. The voltage/current may be adjusted by the primary and induction coils.

As already mentioned, in certain applications the reader identifies and accepts cards with certain resistance patterns but does not render the card inoperable if the resistance pattern does not match the identification number. As already mentioned, this modification is appropriate to electronic keys.

e. g. The reader operating a pair of electric doors or gates may be programmed to accept cards having either (a) 1 Ohm resistance in wire 1, 2 Ohms resistance in wire 2, 3 Ohms resistance in wire 3, etc, OR (b) 10 Ohms resistance in wire 1, 9 Ohms resistance in wire 2, 8 Ohms resistance in wire 3, etc.

The reader is programmed so that it will accept identification numbers which identify the wires containing resistances 1 Ohm, 3 Ohms, 5 Ohms, and 7 Ohms.

For card (a), the identification number is therefore 1357, whilst for card (b) it is 0864.

If the card, identification number, and 11reader-expectation11 are not compatible, then the reader will reject the card. After a limited number of unsuccessful attempts, a time lock/alarm/responsive device may operate, which may be disarmed e.g. by entering the correct card/identification number five times, followed by 0000 or some similar arrangement.

Codes such as data stored on the card may still be used, and where the voltage/current is induced, the operational amplifier comparator circuit would be in operation as opposed to the resistance meter, in which event the test is not of resistance but of alteration effected in the -sltage/current resultant from being induced into and then out of the curd.

Many further modifications and adaptations of the invention will suggest themselves to those versed in the art upon making reference to the foregoing description which is given by way of illustrative example only.

Claims

1. A security system comprising a substrate, a plurality of electrical elements situated on the substrate, and a reader; the reader comprising means for indicating that one or more of the electrical elements have been rendered inoperative and being adapted to accept an identification code and apply a specific current or voltage to each ofthe electrical elements, the current or voltage applied to each element being determined by the identification code, such that if an incorrect identification code has been supplied to the reader, one or more ofthe elements will be rendered inoperative.

2. A security system according to Claim 1, wherein one or more ofthe electrical elements is or are rendered temporarily inoperative when an incorrect identification code is supplied to the reader.

3. A security system according to Claim 2 wherein the or each electrical element is automatically restored to an operative state after an interval of time.

4. A security system according to Claim 2, wherein the or each electrical element is adapted to be restored to an operative state by means of a re-set command input from outside the substrate.

5. A security system according to Claim 1, wherein one or more ofthe electrical elements is or are rendered permanently inoperative when an incorrect identification code is supplied to the reader.

6. A security system according to Claim 5, wherein the electrical elements are fusels, each of which is blown if a current higher than its threshold value is applied.

7. A security system according to any preceding claim wherein the reader is adapted to apply a number of predetermined currents or voltages in sequence and the identification code causes the reader to select the order ofthe electrical elements to which the predetermined sequence of currents or voltages is applied.

8. A security system according to Claim 7, wherein the reader is adapted to apply one of a number of predetermined current or voltage sequences.

9. A security system according to Claim 8, wherein the voltage or current sequence selected is determined on the basis of a characteristic ofthe electrical elements, the substrate or an article on which the substrate is situated.

10. A security system according to Claim 9, wherein the reader is adapted to determine the said characteristic by interrogation.

11. A security system according to Claim 9, wherein the reader is adapted to receive the said characteristic from manually operable means.

12. A security system according to any preceding claim, wherein the reader is arranged to activate a security device such as a time-lock, alarm or immobiliser if an incorrect identification code has been supplied.

13. A security system according to any preceding claim wherein the substrate is in the form of a wafer.

14. A security system according to any preceding claim wherein the substrate is provided on a transaction card, or is part of a transaction card.

15. A security system according to any preceding claim, wherein the substrate is provided on a key, or defines part of a key.

16. A security system according to any preceding claim, wherein the reader is programmed to accept a substrate or an item carrying a substrate only at certain times, or is adapted to accept only certain identification codes at certain times.

17. A security system according to any preceding claim, wherein the reader is programmed to alter the supplied identification code in order to generate a true code, which is used to determine the current or voltage applied to each electrical element.

18. A security system according to Claim 17, wherein the code is altered on the basis of data provided on the substrate or an article carrying the substrate.

19. A security system according to Claim 17 or 18, wherein the supplied code is modified by a mathematical computation.

20. A security system according to Claim 19, wherein the mathematical computation is an addition or subtraction process.

21. A security system according to any preceding claim, wherein the reader is adapted to recognise an incorrect identification code and request the input of the correct code before proceeding with using the code to apply a current or voltage to the electrical elements.

22. A security system according to Claim 21, wherein the reader is adapted to use the input code to apply a current or voltage to the electrical elements only when the correct code has been input twice.

23. A security system according to Claim 21, wherein the reader will only allow an incorrect code to be entered a limited number times.

24. A security system according to any preceding claim wherein the substrate is covered with a layer of dense material in order to reduce the possibility that the structure ofthe substrate could be examined by means of X-rays or other examination means.

25. A security system according to any preceding claim, wherein the reader is arranged to instruct a visual device to observe the presenter ofthe substrate for an interval oftime.

26. A security system according to any preceding claim, wherein the reader comprises an ultrasonic cleaning device for cleaning electrical contacts provided on the reader and/or the substrate or article supporting the substrate.

27. A security system according to any preceding claim, wherein the electrical elements are each situated in a respective conductor and the total resistance of each conductor and its respective electrical element is substantially the same value.

28. A security system according to Claim 27, wherein the reader comprises means for checking the resistances of the respective conductor and electrical element combinations.

29. A security system according to Claim 27, wherein the reader is adapted to render the electrical elements inoperative should one of the detected resistances not equal an expected value.

30. A security system according to any preceding claim, wherein the reader comprises means for rendering all of the electrical elements inoperative if the reader detects that any one of the electrical elements has been rendered inoperative.

31. A security system according to any preceding claim, wherein each electrical element corresponds to a digit or character of the range of digits or characters from which the identification code is selected and the electrical elements corresponding to digits or characters forming the identification code have characteristics which serve to prevent them from being rendered inoperative when the said specific currents or voltages are applied to the elements in the event that a correct identification code is input to the reader.

32. A security system according to any preceding claim, wherein current or voltage is transferred between the reader and the substrate in a non-contact manner.

33. A security system according to Claim 32 comprising induction coils for the transfer of current or voltage between substrate and reader.

34. A security system substantially as hereinbefore described with reference to Figures 1 and 2 ofthe accompanying drawings.

35. A method of verifying the eligibility of a user of an object comprising: i) accepting an identification code from the user; ii) applying a plurality of specific currents or voltages to a plurality of electrical elements situated in the object, the value ofthe current or voltage applied to each element being determined by the identification code; iii) checking to see if any of the elements have been rendered inoperative; iv) indicating whether or not any ofthe elements have been rendered inoperative.

36. A method according to Claim 35, wherein the operability ofthe electrical elements is checked beforehand and all ofthe elements are rendered inoperative if any ofthe elements is discovered to be inoperative.

37. A method according to Claim 35 or 36, comprising: i) passing a specific current through each electrical element, the value of each current depending upon (a) whether a digit or character assigned to the respective electrical element is one ofthe characters or digits defining the identification code and (b) the position ofthe digit or character within the code; ii) passing a greater specific current through all ofthe electrical elements having a digit or character assigned thereto which is not one ofthe digits or characters forming the identification code;; iii) passing a small current through each electrical element to determine if any of the electrical elements has been rendered inoperative by the currents passed in steps (i) and (ii); iv) if any ofthe electrical elements is found to be inoperative in step (iii), applying a current to all ofthe electrical elements to render them inoperative; and v) signalling whether the verification was successful or unsuccessful.

38. A method according to Claim 35, 36 or 37 comprising initially checking the resistance of each one of a respective number of conductors in which the electrical elements are situated.

39. A method according to any one of Claims 35 to 38 for use in conjunction with a security system according to Claims 1 to 30.

40. A method of veriting the eligibility of a user of an object substantially as hereinbefore described with reference to the accompanying drawings.

41. A security system comprising a substrate provided with a number of electrical elements and a reader; the reader being adapted to accept an identification code, interpret the identification code in order to determine the expected resistance of each electrical element, check that the respective actual resistances of the electrical elements correspond with the expected resistances, and perform an operation depending upon the outcome ofthe check.

42. A security system according to Claim 37, wherein the substrate is a key, part of a key, or provided in a key.

43. A security system according to Claim 41 or 42, wherein the reader is adapted to alter the supplied code in order to generate a true code, which is used to determine the expected resistance of each electrical element.

44. A security system according to Claim 43, wherein the code is altered on the basis of data provided on the substrate or an article carrying the substrate.

45. A security system according to Claim 43 or 44, wherein the supplied code is modified by a mathematical computation.

46. A security system according to Claim 45, wherein the mathematical computation is an addition or subtraction process.

47. A security system according to any one of Claims 41 to 46, wherein current or voltage is transferred between substrate and reader in a non-contact manner.

48. A security system according to Claim 47, comprising induction coils for the transfer of current or voltage between substrate and reader.

49. A security system according to any one of Claims 32, 33, 47 and 48, wherein the reader comprises a comparator circuit for enabling the reader to compare voltages or current input to and output from the substrate.