Registers – Records – Magnetic
Reexamination Certificate
1998-12-08
2001-01-30
Le, Thien M. (Department: 2818)
Registers
Records
Magnetic
C235S380000
Reexamination Certificate
active
06179211
ABSTRACT:
This invention relates to a method of identifying a data carrier, and particularly, though not exclusively, to reading codes stored in a security element attached to a card or document as a permanent pattern of a magnetic property detectable, for example, as a variation of remanent magnetisation along the element.
A data carrier of this kind is described in GB-A-1,331,604 in which in spaced regions of an element anisotropic magnetic particles are dispersed and fixedly aligned in a binder along a preset direction, whilst in remaining regions the particles are not so aligned or are aligned along a substantially different preset direction. This arrangement is commonly described as a magnetic “watermark” or as forming a “permanent magnetic structure” since unlike conventional magnetic recordings the pattern of remanent magnetisation revealed by uniaxially magnetising or “developing” the document can be restored by re-magnetisation even after erasure by the application of an a.c. erase field, for example. A magnetic “watermark” is particularly well suited to recording data in digital form since each alignment direction may be assigned a different significance i.e. a binary “ONE” or a binary “ZERO”.
Due to the “built-in” nature of the recording, a security element may conveniently be prepared as a single “watermarked” tape comprising strings of binary coded numbers (usually grouped in characters) which provide a security feature when cut from the tape and applied to a support to form a document or card. Typically each string of numbers is separated by a marker or “sentinel” comprising a unique sequence of bits which itself never appears in the security data. For this reason the “sentinel” can always be identified so that by reference to its position on the document the bits chosen to represent the security data (a particular set of characters appearing on the document, for example) can always be recovered.
However, due to tolerancing problems during manufacture of the tape and problems of registration between the tape and the support it is not possible without recourse to the use of expensive equipment, to ensure that a “sentinel” or “sentinels” always appear in the same position on the document.
In practice, when one “sentinel” appears at each end of the document the bits between the “sentinels” are chosen represent the security data. It sometimes occurs, however, that only one “sentinel” appears on the document so that depending upon the exact location an appropriate number of bits, selected from both sides of the “sentinel”, are chosen to represent the security data identifying that document. Thus for each position of the first detected “sentinel” there is a different bit selection rule for choosing the bits constituting the security data. The sequence of bits representing the security data may then be used as verification information, or may be used to derive verification information, which for example, the user may have to supply before the card is validated.
This technique, however, has a weakness for the case when the first “sentinel” on the card is close to its edge. In such a case it is possibly for the card reader to fail to detect the first “sentinel” and instead pick up the second “sentinel” on the card. Thus there is always the possibility of an ambiguity. For instance suppose that a card is made in a factory, and a piece of magnetic tape is attached to the card, the tape having the number 300 together with parts of the numbers 299 and 301. The card is read in the factory and the identification number 300 is obtained. Without knowing how the “sentinels” lie with respect to the edge of the card, it is possible for card readers in the field to recognise the identification number of the card as 299, 300 or 301. This is clearly undesirable for cards for use in financial transactions, as it might be possible to confuse two cards having adjoining lengths of “watermarked” tape attached to them. It is also undesirable for cards used for claiming benefit, or access control, or identification, or having a stored value such as prepaid fare cards.
In order to solve this problem, “WATERMARK” tape made by THORN Security Science Ltd, Swindon, England, is often applied to cards in a registered fashion such that the “sentinels” always occur at the same point on a card. Increased production costs are associated with such registered cards. An alternative solution, described in GB-A2,021,835, is to erasably record the position of the marker
According to the invention, there is provided a method of identifying a data carrier according to the claims. This can provide the advantage of identifying the data carrier uniquely without having to resort to expensive registration schemes to ensure that the markers are always at exactly the same position on the data carrier.
In order to guarantee that the data carrier will be identified uniquely, it is necessary that each rational number in the sequence should not be repeated and the difference between successive numbers must be equal to or greater than one. In practice, it is sufficient to have a long enough sequence so that in use the card or document becomes outdated before the sequence is repeated. Successive markers are most conveniently arranged to be displaced in a single given direction. Preferably successive markers are equally spaced from one another.
Preferably, the data carrier comprises a document or card carrying a security element having data encoded thereon as a permanent pattern of a detectable magnetic property, and the fixed point on the data carrier is constituted by an edge of the document or card. This simplifies the measurement of the distance in part a) of the above mentioned method.
REFERENCES:
patent: 4469937 (1984-09-01), Stockburger et al.
patent: 4645916 (1987-02-01), Raisleger
patent: 4707593 (1987-11-01), Murata et al.
patent: 4992646 (1991-02-01), Collin
patent: 4998009 (1991-03-01), Iijima et al.
patent: 5151582 (1992-09-01), Toshinori
patent: 1 331 604 (1973-09-01), None
patent: 2 021 835 (1979-12-01), None
patent: 2 272 092 (1994-05-01), None
Green Ian MacDonald
Willcock Simon Nicholas Murray
Central Research Laboratories Limited
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Le Thien M.
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