GB2331171A

GB2331171A - A method of labelling an article

Info

Publication number: GB2331171A
Application number: GB9723732A
Authority: GB
Inventors: Richard Waltham
Original assignee: Thorn Secure Science Ltd
Current assignee: Thorn Secure Science Ltd
Priority date: 1997-11-10
Filing date: 1997-11-10
Publication date: 1999-05-12
Also published as: MY123889A; GB9807341D0; TW392125B; GB9723732D0

Abstract

A method of labelling an article includes the steps of: a) choosing a first character string to represent a given class of articles of value, b) expressing this first character string as a sequence of binary digits, the sequence being periodic, having a period of less than 64 binary digits, and having a length greater than or equal to one period, c) storing at least one period of the sequence in a data store 1, and d) attaching the data store to, or incorporating the data store in, an article of value 2. The data store 1 may comprise a data-carrying layer which includes anisotropic magnetic particles having a permanent non-random orientation in predetermined spaced regions.

Description

A METHOD OF LABELLING AN ARTICLE This invention relates to a method of labelling an article of value, and to a method of authentication for an article of value. It also relates to an identification means or label for use in such a method.

Magnetic tape having a permanent pattern of a detectable magnetic quantity is known from GB1331604A, which is incorporated herein by reference, and GB2309568A. Such tape is available from Thorn Secure Science Limited under the UK registered trade mark "WATERMARK" tape, and is used as an identification or authentication means on articles of value such as bank cards or credit cards.

Such tape is difficult to manufacture, and thus fairly expensive when compared to normal magnetic tape. Another drawback with the tape is that because of the difficulties in manufacture it has not been possible to achieve data packing densities on this tape of better than about 39 bits per inch (1.53 bits per mm) using industry standard F2P coding. The data format used in Watermark tape requires marker portions, known as "sentinels", with a binary digit string between successive sentinels. Each sentinel comprises 10 bits, with the data between sentinels typically comprising 60 bits. The data between sentinels may be incrementing or non-incrementing. If the data is non-incrementing, then the data stored on the tape is periodic, having a period of 70 binary digits. At a data packing density of 1.3 bits per rum, this implies that over 53 mm of tape must be applied to an article of value in order to identify it correctly, and if part of the tape gets damaged, or the read head bounces at the edge of the label then there is no redundancy, and so the data cannot be read correctly. Thus Watermark tape is not particularly convenient for use on small articles or documents of value.

According to a first aspect of the invention, there is provided a method of labelling an article of value as claimed in claims 1-18.

According to a second aspect of the invention, there is provided a method of authenticating an article of value as claimed in claims 21 and 22.

According to a third aspect of the invention, there is provided an apparatus for performing the said method of labelling or authenticating an article of value.

According to a fourth aspect of the invention, there is provided an identification means for labelling an article of value.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which Figure 1 shows an article of value labelled according to the invention, Figure 2 shows a block diagram of a method of identification according to the invention, and Figure 3 shows a block diagram of a method of authentication according to the invention.

In Figure 1, an identification means (1) labelling an article(2) is shown.

The identification means comprises a data-carrying layer (in the present example a magnetic tape laminated to the article of value) having a permanent pattern of a detectable magnetic property. The data being carried by the layer comprising a sequence of binary digits, the sequence having a period of less than 60 binary digits, and having a length greater than or equal to one period. In the example shown in Figure 1 the data comprises marker portions or sentinels (3) with four other portions or characters (4, 5, 6, 7) located between successive marker portions. Each sentinel comprises the binary digit string, in the present example 1010000. Other binary digit strings can be used as an alternative, for example 0010100, or 0101111, etc., but 1010000 has been chosen because it is one of the strings which is least likely to be confused with other binary digit (bit) strings when read.

Each of the other characters comprises a 7 bit number. The four character string (4, 5, 6, 7), comprising 28 bits, is chosen to represent a given class of articles, for example a document of value such as a share certificate or gift voucher issued by a company. In the present example these four characters give 2,214,841 possible different "first" character strings (i.e. "key differs"), as will be explained below.

The "first" character string in the present example comprises four characters. Each of the four characters is represented by a 7 bit number which is found from a predetermined look-up table such that the marker character (1010000) does not appear if the sequence of bits is read in either direction, except at a marker. The marker character is preferably not palindromic so that reading apparatus can work out which way up the character string has been presented to it in use. Each of the characters, being 7 bits in length, can take 128 potential values. The value 1010000 and its reverse 0000101 must be excluded as these would be confused with a marker. The number 0101xxx must also be excluded as it could combine with xxxx000 in an adjacent character to produce a "phantom" marker. Numbers containing long runs of zeros must also be avoided, as this can confuse F2F decoding and/or the ability of a reader to differentiate between the method of the present invention and that of normal "WATERMARK" tape. The numbers which must be excluded at characters 2, 3 and 4 are shown in Table 1, whilst additional numbers which must be excluded at the first character position are shown in Table 2. The actual complete look up table used in the present embodiment is shown in Table 3.

D Exclusion D Exclusion D Exclusion 0 xx(000-0000000) 26 001(1010-000)xx 65 xx(10-10000)01 1 xx(0000-000000)1 32 xx(1-010000)0 66 xx(10-10000)10 2 x(00000-00000)10 33 xx(1-010000)1 67 xx(10-10000)11 3 x(00000-00000)11 40 xx(000-0101)000 74 100(1010-000)xx 4 xx(101-0000)100 41 xx(000-0101)001 80 (1010000) 5 (0000101) 42 xx(000-0101)010 84 10(10100-00)xx 6 xx(101-0000)110 43 xx(000-0101)011 90 101(1010-000)xx 7 xx(101-0000)111 44 xx(000-0101)100 96 110(0000-101)xx 10 000(1010-000)xx 45 xx(000-0101)101 97 11(00001-01)xx 11 xx(0-000101)1 46 xx(000-0101)110 104 1(101000-0)xx 16 001(0000-101)xx 47 xx(000-01O1)111 106 110(1010-000)xx 20 00(1010o00)xx 48 011(0000-101)xx 112 111(0000401)xx 21 001(1010-000)xx 52 01(10100-00)xx 116 11(10100-00)xx 22 xx(00-00101)10 58 011(1010-000) 122 111(1010-000)xx 23 xx(00-00101)11 64 100(0000-101)xx Table 1 - Codewords excluded at characters 2, 3 & 4 D = decimal value of the excluded codeword

D Exclusion D Exclusion D Exclusion 81 101(0000-101)0001 87 101(0000-101)0111 93 101(0000-101)1101 82 101(0000-101)0010 88 101(0000-101)1000 94 101(0000-101)1110 83 101(0000-101)0011 89 101(0000-101)1001 95 101(0000-101)1111 85 101(0000-101)0101 91 101(0000-101)1011 86 101(0000-101)0110 92 101(0000-101)1100 Table 2- Additional codewords excluded at character 1 Table 3- Binary Table n = input, unencoded value (b, D, H) = output, encoded value in binary, decimal and hex respectively.

n b D n b D H n b D H n b D H 0000000 0 0 0100000 32 20 1000000 64 40 1100000 96 60 0000001 1 1 0100001 33 21 1000001 65 41 1100001 97 61 0000010 2 2 16 0100010 34 22 1000010 66 42 46 1100010 98 62 0000011 3 3 17 0100011 35 23 1000011 67 43 47 1100011 99 63 0000100 4 4 18 0100100 36 24 35 1000100 68 44 48 1100100 100 64 0000101 5 5 19 0100101 37 25 36 1000101 69 45 49 1100101 101 65 0000110 6 6 20 0100110 38 26 37 1000110 70 46 50 1100110 102 66 0000111 7 7 21 0100111 39 27 38 1000111 71 47 51 1100111 103 67 0 0001000 8 8 0101000 40 28 39 1001000 72 48 1101000 104 68 1 0001001 9 9 0101001 41 29 40 1001001 73 49 52 1101001 105 69 0001010 10 A 0101010 42 2A 1001010 74 4A 1101010 106 6A 0001011 11 B 0101011 43 2B 41 1001011 75 4B 53 1101011 107 6B 2 0001100 12 C 0101100 44 2C 42 1001100 76 4C 54 1101100 108 6C 3 0001101 13 D 0101101 45 2D 43 1001101 77 4D 55 1101101 109 6D 4 0001110 14 E 0101110 46 2E 44 1001110 78 4E 56 1101110 110 6E 5 0001111 15 F 0101111 47 2F 45 1001111 79 4F 57 1101111 111 6F 0010000 16 10 0110000 48 30 1010000 80 50 1110000 112 70 6 0010001 17 11 22 0110001 49 31 71 1010001 81 51 58 1110001 113 71 7 0010010 18 12 23 0110010 50 32 72 1010010 82 52 59 1110010 114 72 8 0010011 19 13 24 0110011 51 33 73 1010011 83 53 60 1110011 115 73 0010100 20 14 0110100 52 34 1010100 84 54 1110100 116 74 0010101 21 15 25 0110101 53 35 74 1010101 85 55 61 1110101 117 75 0010110 22 16 26 0110110 54 36 75 1010110 86 56 62 1110110 118 76 0010111 23 17 27 0110111 55 37 76 1010111 87 57 63 1110111 119 77 9 0011000 24 18 28 0111000 56 38 77 1011000 88 58 64 1111000 120 78 10 0011001 25 19 29 0111001 57 39 78 1011001 89 59 65 1111001 121 79 0011010 26 1A 0111010 58 3A 1011010 90 5A 1111010 122 7A 11 0011011 27 1B 30 0111011 59 3B 79 1011011 91 5B 66 1111011 123 7B 12 0011100 28 1C 31 0111100 60 3C 80 1011100 92 5C 67 1111100 124 7C 13 0011101 29 1D 32 0111101 61 3D 81 1011101 93 5D 68 1111101 125 7D 14 0011110 30 1E 33 0111110 62 3E 82 1011110 94 5E 69 1111110 126 7E 15 0011111 31 1F 34 0111111 63 3F 83 1011111 95 5F 70 1111111 127 7F Binary numbers shown in bold in Table 3 are excluded for all character places. Binary numbers shown in italics in Table 3 are excluded from character position 1. It will be noted that the numbers n in table 3 do not form a monotonically increasing sequence. This is in fact of no consequence as it is a look up table. Thus any value could appear at any place in the look up table as long as the place is the same for both the encode and decode operations.

Only 84 of the possible 128 possible values available with a 7 bit string are used in the encode direction. The 44 excluded values become parity errors if found in the reverse (decode) application of the look-up table shown as Table 3.

To avoid generating phantom markers, values of n above 70 must be avoided in the character 1 position. This is done by keeping the maximum possible number used to 2,214,840 or less. The total number of possible combinations or "key differs" is (71 x 84 x 84 x 84) / 19, which rounds down to 2,214,841.

Having now described in some detail what format the data carried by the identification means takes in the preferred embodiment, the method of providing the data will be explained.

First, the person desiring to label the artide of value must choose a characters string from the 2,214,841 combinations possible when using 4 characters from Table 3. In the present example this will be a decimal number, which we shall call N, which lies between zero and 2,214,841. This step is shown as block 20 in Figure 2.

The steps in the method are then as follows, with steps a to h being represented in Figure 2 by blocks 21 to 28 respectively:- a). Check that N lies between zero and 2,214,841. b). Multiply N by a numerical factor, in the present example the integer 19. This factor is known as the longitudinal redundancy check factor, or LRC. c). Convert the result (i.e. 19N) to the number base of the look up table (84 in the present example) giving a 4 digit number in base 84, d). Take this 4 digit number and using the look up table of Table 3 encode the digits sequentially into characters 1-4, each character comprising a 7 bit number, e). Add the marker 101000 to one end of the data, f). Send the resulting 35 bit sequence through a circuit of known form which applies F2F encoding to the binary data, g). Embody the code as a permanent structure of a detectable magnetic property in an identification means as previously described, h). Repeat steps f) and g) to provide a periodic sequence of binary digits in the identification means.

This completes the encoding part of the labelling or identification method.

The identification means is then applied to or incorporated in an article of value such as a document of value. This may be achieved by simply laminating the identification means, in the present example magnetic tape, to the article, or by a transfer method in which an adhesive layer is applied to the surface of the tape, the article affixed to this adhesive layer, and the substrate tape is removed leaving the upper layer of what was originally the tape bonded to the surface of the article of value.

In order to authenticate the article of value, the identification means applied to the article as described above must be read and decoded. This may be performed according to the following method, which is represented in Figure 3 as a flow diagram in which blocks 30 to 41 correspond to the following steps a -1 respectively:- a) Move a reader or scanning means past the identification means, or vice versa, b) Apply a F2F decoding algorithm to the scanned data, c) Test for the presence of leading or trailing zeros, which would indicate the presence of the usual "WATERMARK" data format, if found decode as a normal "WATERMARK" record. If not found, continue as described below, d) Find 35 contiguous bits which are free from read or F2F decode errors, using known error detection techniques, and/or authentication techniques, e) Check for errors in the 35 contiguous bits by storing them in a shift register such as, for example, a ring or rotating barrel shifter, and rotate the digits one place in either direction, checking in both cases that the 35 bits contain exactly one marker or sentinel - any other result signifying the presence of an error, f) Arrange the digits by rotation and, if necessary, by inverting the order of the digits, such that the marker appears at the head of the character string and character 4 appears at the tail, g) Remove the bits corresponding to the marker, leaving 28 bits corresponding to data consisting of 4 characters, each character comprising 7 bits, h) Apply the look-up table of Table 3 in reverse to each of the 4 characters to give 4 numbers in base 84. If the look-up table does not contain an entry matching one or more of the numbers this indicates the presence of an error, i) Convert the number to a number base which matches the desired output, such as, for example, base 10 in the present example, j) Divide the number obtained in step i above by the LRC (19 in the present example), k) Compare the result with N, the number characteristic of a genuine article of value. If they are the same, then the article is genuine, l) Signal the result of this comparison.

In the above encode and decode sequence, it is not convenient to use a binary checksum as an error protection feature. The use of multiplication and division by the LRC factor has similar error protection properties to that of a checksum. A random error on, for example, a modulo 19 multiplication and division error protection scheme has only a 1 in 19 chance of producing a codeword which passes the test.

The reasons for choosing the LRC factor to be 19 are as follows. The LRC factor chosen should share as few common factors as possible with the number base of the look-up table (84 in the present example). Being a prime number a little above 16 makes 19 a good candidate. It would be possible to use LRC factors of 17 or 13, these would provide slightly worse error protection but numbers which are slightly easier to work with. It would also in theory be possible to use the numbers 16, 15, or 14- however, this would make for rather more interaction between the LRC factor and the number base of the look up table, and hence rather more exdusions from the look-up table.

In addition to the 19 multiply/divide LRC factor, substantial error detection is achieved in the present method by use of the character look up table and by the F2F coding.

Although in the above example 4 characters each comprising 7 bits are used, more or less characters may be employed in the scheme if desired, and each character may comprise more or less than 7 digits in a predetermined number base which need not be equal to 2.

The use of the method described above enables an identification means or label having a pitch of 30 mm to be produced having 2,214,841 possible "key differs". In comparison, a standard"WATEREARK"tape record with similar key differs has at least a 45 mm pitch, assuming that both are encoded at 1.53 bits per mm. it is anticipated that this invention will find wide application in areas such as: a) Provision of sets of identical tokens, such as event tickets, gift tokens, share certificates, promissory notes, bank notes, and signatures to authenticate that a given organisation or person has stamped or sealed the document. b) Cost critical applications, where conventional'WATERMARK"technology is too expensive. An important factor in cost control is minimisation of surface area. This is also desirable for aesthetic considerations.

As a further aspect of the invention, the above method may be applied in an analogous way to the case where the successive character strings having a sentinel or marker therebetween are not identical but increment or decrement. In this case the binary digit sequence will not in general be periodic. In this case the digit sequence will be applied to the article, for example a document, in a registered position so that the marker is in a known position on the document.

This slightly simplifies the decoding described above, which no longer requires the rotating barrel shifter. This registration process is known in the industry, although in this particular embodiment the registration can be sensed by magnetic means. More conventional optical sensing can be used at registration if suitable optical features are included during the manufacture of the magnetic foil. In general, application needing incrementing numbers are likely to need more than four of the 7 bit characters. For example, if the embodiment shown in the example is extended from 35 to 63 bits it generates 1.1 x 1014 "key differs", whereas "WATERMARK" would require 90 bits to encode this.

Claims

CLAIMS 1. A method of labelling an article, including the steps of a) choosing a first character string to represent a given class of articles, b) expressing this first character string as a sequence of binary digits, the sequence being periodic, having a period of less than 64 binary digits, and having a length greater than or equal to one period,

c) storing at least one period of the sequence in a data store comprising a layer of material having a permanent pattern of a detectable magnetic property, and d) attaching the data store to, or incorporating the data store in, an article.
2. A method as claimed in claim 1 in which the sequence has a period of less than 60 binary digits.
3. A method of labelling an article, including the steps of a) generating a first character string comprising a sequence of incrementing or decrementing numbers, each number comprising fewer than 64 binary digits,

c) storing at least one said number of the sequence in a data store comprising a layer of material having a permanent pattern of a detectable magnetic property, and d) attaching the data store to, or incorporating the data store in, an article.
4. A method as claimed in claim 3 in which each number comprises fewer than 60 binary digits.
5. A method as claimed in any preceding claim, in which the characters comprising the first character string each consist of one or more digits.
6. A method as claimed in any preceding claim, in which the sequence of binary digits comprises identical marker portions with an given binary digit string being located between successive marker portions.
7. A method as claimed in claim 6, in which each given binary digit string being located between successive marker portions is identical to the others.
8. A method as claimed in claim 6, in which the marker portion is not palindromic, and is different to the given binary digit string.
9. A method as claimed in claim 8, in which the marker portion comprises the binary digit string 1010000.
10. A method as claimed in claim 7,8 or 9 in which the given binary digit string is generated by coding of the first character string.
11. A method as claimed in claim 10, in which the coding includes multiplication of the digit or digits comprising each character in the first character string by an integer, followed by substitution of the resultant number by a number expressed in a larger number base.
12. A method as claimed in claim 11 in which the substitution of the resultant number is performed using a look-up table, the look-up table omitting binary digit strings which may cause confusion with the marker portion.
13. A method as claimed in claim 11 or 12 in which the integer lies in the range 13to20.
14. A method as claimed in claimed in claim 11 or 12 in which the integer is equal to 19
15. A method as claimed claim 14 in which the look-up table is as shown in Table 3.
16. A method as claimed in any preceding claim in which the data store comprises a layer of anisotropic magnetic particles having a permanent non-random orientation in predetermined spaced regions.
17. A method of authenticating an article labelled in accordance with any preceding claim, including the steps of: reading the sequence of binary digits; extracting therefrom the first character string; comparing the extracted character string with a predetermined character string; and signalling the result of said comparison.
18. A method as claimed in claim 16 appended to claim 11, in which the first character string is obtained by decoding the given binary digit string, the decoding including using the said look-up table in reverse, and subsequently dividing each number derived therefrom, corresponding to one character in the first character string, by the said integer.
19. An article labelled in accordance with a method as claimed in any preceding claim.
20. An apparatus for performing a method as claimed in any one of claims 1 18.
21. An identification means for labelling an article in accordance with a method as claimed in any one of claims 1 - 18, comprising a data-carrying layer having a permanent pattern of a detectable magnetic property, the data being carried by the layer comprising a sequence of binary digits, the sequence having a period of less than 64 binary digits, and having a length greater than or equal to one period.
22. An identification means for labelling an article in accordance with a method as claimed in claim 1 or dependent claims, comprising a data-carrying layer which includes anisotropic magnetic particles having a permanent non random orientation in predetermined spaced regions, the data being carried by the layer comprising a sequence of binary digits, the sequence having a period of less than 64 binary digits, and having a length greater than or equal to one period.