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Claims  |
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What is claimed is:
1. A method for authenticating a printable item made of a medium subject to
physical damage and having an irregular random surface and a
machine-readable uniqueness characteristic over a specified are of the
item, the method comprising the steps of:
applying a magnetic composition onto a part of the irregular surface of the
item, the magnetic composition forming a magnetic stripe having a
non-uniform magnetic characteristic along the surface of the item;
encoding the item according to the substeps of:
reading the uniqueness characteristic along the specified area of the item
to define an identifier;
writing the identifier value onto the magnetic stripe to thereby encode the
item; and
authenticating the encoded item according to the substeps of:
reading the uniqueness characteristic along the specified area of the item
to obtain a verification value;
reading the magnetic stripe to obtain the identifier written thereon by
substeps of:
sensing the magnetic flux variations along the magnetic stripe and
generating therefrom an analog data signal characterized by peaks in the
analog data signal;
conditioning the analog data signal by obtaining a uniform amplitude of the
peaks and filtering of noise from the signal;
detecting the position of the peaks, whether of negative or positive
polarity, of the conditioned analog data signal;
sensing the differential position between successive peaks;
sensing the polarity of each peak;
processing the differential positions and polarity information to assign a
first value representative of a "0" to a bit when there is a first
differential position value, to assign a second value representative of a
"1" when there is a second differential position value, to assign a third
value representative of a non-data character when there is a third
differential position value, and assigning values other than the first,
second or third values to peaks whose differential position is other than
the first, second or third differential positions;
recovering the values of the data bits whose value could not be defined in
the step of processing by applying predefined error correction criteria to
a data bit string of the assigned values; and
comparing the verification value and the identifier read from the magnetic
stripe according to a predefined comparison criterion, the item being
authenticated when the verification value and the read identifier compare
according to the predefined comparison criterion.
2. The method of claim 1 wherein the step of encoding comprises a further
substep of encrypting the identifier according to a predefined encryption
key.
3. The method of claim 2 wherein the step of authentication comprises a
further substep decrypting the encrypted identification value stored on
the magnetic stripe according to a decryption key prior to comparing the
decrypted identifier with the verification value to authenticate the item.
4. A method for authenticating a printable item made of a medium subject to
physical damage and having an irregular random surface and a
machine-readable uniqueness characteristic over a specified area of time,
the method comprising the steps of:
applying a magnetic composition onto a part of the irregular surface of the
item, the magnetic composition forming a magnetic stripe having a
non-uniform magnetic characteristic along the surface of the item;
encoding the item according to the substeps of: reading the uniqueness
characteristic along the specified area of the item to define an
identifier;
writing the identifier value onto the magnetic stripe to thereby encode the
item by substeps of:
defining a first string of bits each bit having a value of "1" or "0"
representative of a data bit string;
defining a second string of bits each bit having a value of "1" or "0"
representative of a start sentinel;
defining a third string of bits, each bit having a value of "1" or "0"
representative of a stop sentinel;
representing each bit of the first, second and third string of bits by a
predefined time period between flux changes along the magnetic stripe, a
"0" being represented by a first time period and a "1" being represented
by two consecutive second time periods, each second time period equal to
1/2 the duration of the first time period;
defining a framing character having two consecutive third time periods,
each equal to 3/2 the duration of the first time period;
effecting magnetic flux changes along the magnetic stripe in accordance
with the time period representation for "1's", "0's" and framing
characters to store first the second string, next the first string and
last the third string, with framing characters being interposed at
predefined intervals in the first string; and
authenticating the encoded item according to the substeps of:
reading the uniqueness characteristic along the specified area of the item
to obtain a verification value;
reading the magnetic stripe to obtain the identifier written thereon; and
comparing the verification value and the identifier read from the magnetic
stripe according to a predefined comparison criterion, the item being
authenticated when the verification value and the read identifier compare
according to the predefined comparison criterion.
5. The method of claim 4, wherein the step of encoding comprises the
further substep of encrypting the identifer according to a predefined
encryption key.
6. The method of claim 5 wherein the step of authentication comprises a
further substep of decrypting the encrypted identification value stored on
the magnetic stripe according to a decryption key prior to comparing the
decrypted identifier with the verification value to authenticate the item.
7. A method for authenticating a document or the like having a
machine-readable uniqueness characteristic, comprising the steps of:
applying a magnetic composition onto a part of said document;
sensing said uniqueness characteristic from said document to define an
identifier;
encoding said identifier onto said magnetic composition according to a
predefined format to define a string of bits; and
authenticating said document according to the substeps of:
reading said magnetic composition to retrieve said identifier encoded
thereon;
processing said encoded identifier by identifying the differential
positions and polarity information of signal peaks from said coded
identifier and assigning a first value representative of a "0" to a bit
when there is a first differential position value, assigning a second
value representative of a "1" when there is a second differential position
value, assigning a third value representative of a nondata character when
there is a third differential position value, and assigning values other
than the first, second or third values to peaks whose differential
position is other than the first, second or third differential positions;
applying error correction techniques to correct errors in said identifier;
freshly sensing said uniqueness characteristic to define a verification
identifier; and
comparing said corrected identifier with said verification identifier
according to a predefined comparison criterion to authenticate said
document.
8. The method according to claim 7 wherein said step of encoding further
includes encrypting said identifier.
9. The method according to claim 8 wherein said step of comparing further
includes decrypting said identifier.
10. The method according to claim 7 wherein said substep of reading
comprises steps of:
identifying the location of flux changes along said magnetic composition
corresponding to the identifier encoded thereon;
identifying the polarity of said flux changes;
determining the space between said flux changes; and
determining the value of the bits of said encoded identifier by comparing
said space and polarity data against a set of predefined conditions.
11. The method according to claim 7 wherein said step of applying a
magnetic composition comprises printing said magnetic composition on said
document.
12. The method according to claim 7 wherein said applied magnetic
composition exhibits a nonuniform magnetic characteristic.
13. The method according to claim 7 wherein said step of encoding comprises
encoding said identifier on said magnetic composition by defining a bit
string wherein each bit is representative of a data bit string, or a start
sentinel, or a stop sentinel and each bit of said bit string is
represented by a predefined time period bteween magnetic flux changes.
14. A method for authenticating a document or the like having a
machine-readable uniqueness characteristic comprising the steps of:
applying a magnetic composition onto a part of said document;
sensing said uniqueness characteristic from said document to define an
identifier;
encoding said identifier onto said magnetic composition according to a
predefined format to define a string of bits; and
authenticating said document according to the substeps of:
sensing the magnetic flux variations from said magnetic composition
corresponding to said identifier encoded thereon to generate an analog
data signal;
conditioning said signal by obtaining a uniform amplitude of peaks in said
signal and filtering noise from said signal;
detecting the position of said peaks, regardless of polarity, of said
conditioned signal;
sensing the differential position between successive peaks;
processing the differential positions and polarity information to assign a
first value representative of a "0" to a bit when there is a first
differential position value, assigning a second value representative of a
"1" when there is a second differential position value, assigning a third
value representative of a nondata character when there is a third
differential position value, and assigning values other than the first,
second or third values to peaks whose differential position is other than
the first, second or third differential positions;
recovering data values for data whose value could not be defined in said
processing step by applying error correction criteria to said data with
assigned values to correct said identifier;
freshly sensing said uniqueness characteristic from said document to define
a verification identifier; and
comparing said verification identifier characteristic and said corrected
identifier according to a comparison criterion to authenticate said
document.
15. The method according to claim 14 wherein said step of encoding further
includes encrypting said identifier.
16. The method according to claim 15 wherein said step of comparing further
includes decrypting said identifier.
17. The method according to claim 14 wherein said step of applying a
magnetic composition comprises printing said magnetic composition on said
document.
18. The method according to claim 14 wherein said applied magnetic
composition exhibits a nonuniform magnetic characteristic.
19. The method according to claim 14 wherein said step of encoding
comprises encoding said identifier on said magnetic composition by
defining a bit string wherein each bit is representative of a data bit
string, or a start sentinel, or a stop sentinel and each bit of said bit
string is represented by a predefined time period between magnetic flux
changes. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a system for self authenticating an item
of value, and in particular, to a system for authenticating items by
retrieving authenticating data from a storage medium such as a magnetic
stripe disposed on the item of value, even if the storage medium has been
physically damaged.
Numerous systems have been devised for authenticating articles,
particularly those vulnerable to being counterfeited. Examples include
imprinting an object with a difficult to copy pattern, application of
holographic tape and marking the item with secret identification indicia.
One particularly effective method and apparatus for authenticating articles
is described in U.S. Pat. No. 4,423,415, issued Dec. 27, 1983, to Goldman
and entitled "Non-Counterfeitable Document System." Although, the Goldman
system is effective, additional security may be desired if the item to be
authenticated is a high value document such as a stock certificate or
bond. One means of increasing security is to encrypt the identifier in a
manner such as described in U.S. Pat. No. 4,405,829 entitled
"Cryptographic Communications System and Method" issued Sept. 20, 1983, to
Rivest et al.
Of specific interest is the method of encrypting using a private key known
only to the source, i.e., the entity issuing the stock or bond, but
decrypting using a public key known to the public and indeed which may
even be identified on the document itself. Successful decryption using the
public key will only be possible if the encryption was initially done
using the private encryption key. Therefore, successful decryption will
indicate the document indeed originated with the stock or bond issuer and
is genuine.
Unfortunately, this and other useful encryption techniques result in very
large encrypted identifiers which would have to be printed on the
document. However, printing such numbers on the document so as to be
manually readable is impractical because of the inherent space limitations
on the document as well as the difficulty in manually reading such a long
number. Therefore, alternative means of storing the anticipated large
string of numbers defining the encrypted data on the document are desired.
One means of storing very large quantities of information in a small space
is to place a machine readable magnetic stripe on the item itself.
However, practical use of a magnetic stripe to store data on a document
presently requires that the stripe be printed directly onto the document.
Because documents are generally made out of paper and paper has a highly
irregular surface contour, a printed magnetic stripe will exhibit a highly
irregular geometry which cause wide variations in the magnetic flux
characteristic along the length of the stripe. Heretofore, such wide
variations in magnetic flux characteristics have resulted in the inability
to retrieve data accurately or reliably - an essential requirement when
encrypted data is stored to verify authenticity.
Mangetic stripes as well as other storage medium disposed directly onto
paper documents such as stock certificates, would in any event be subject
to physical damage such as tearing, folding or scratching thereby adding
to the difficulty of reliably retrieving data from the document's storage
medium. Further exacerbating the problem is the fact that encrypted data
must be stored and retrieved without errors. Indeed, any error in reading
encrypted data will cause the result of decryption to be "garbage".
Therefore, authentication of documents by storing authenticating data on a
storage medium disposed directly on the document, particularly where the
document must be authenticatable in the presence of possible physical
damage, has not heretofore been possible even though use of a storage
medium, such as a magnetic stripe, imprinted directly on the document is
desired.
Efforts to overcome non-uniform magnetic flux problems so as to enable use
of a printed magnetic stripe have included making the magnetic stripe more
uniform by improving the method of applying the magnetic composition and
by improving the ink formulations. Such efforts have been unsuccessful
and, in any event, have not addressed the problem of reliably reading the
magnetic stripe in the presence of physical damage.
Another suggested approach has been to attach a strip of magnetic tape over
the surface of the document since magnetic tape exhibits uniform magnetic
characteristics and can be made strong enough to resist most physical
damage. However, overlaying tape on the document is incompatible with
current document printing specifications. In any event, application of
magnetic tape would make a genuine document vulnerable to damage by
removal of the tape.
Therefore, there is a need for an authentication system which includes a
document with a storage medium such as a magnetic stripe printed directly
on its surface and capable of storing large quantities of data, at least a
portion of which data is preferably encrypted, and from which the stored
data can be retrieved without errors, even in the presence of physical
damage such as tears, folds or scratches, thereby enabling decryption and
authenticity verification. The storage medium (stripe) is preferably of
the type that is applied by offset printing so as to be highly compatible
with the printing of the remaining information on the document of value.
SUMMARY OF THE INVENTION
In accordance with the present invention, a document, such as a stock
certificate or bond having a significant value, may be authenticated as
being genuine by first providing a storage medium, preferably machine
readable, such as by printing a magnetic composition (e.g. ink) onto a
part of the irregular surface of the item so as to form a storage area on
the document. The document (item-of-value) will generally be made of a
fibrous medium, such a paper, which exhibits a highly irregular surface
contour characteristic. In the case of a magnetic stripe, a magnetic
composition, used to form the magnetic stripe, will flow over and follow
the irregular surface giving the resultant magnetic storage stripe a
highly irregular geometry, surface contour and magnetic particle
concentration characteristic resulting in a non-uniform, difficult to
read, magnetic flux characteristic along the stripe.
In the case of a magnetic stripe, the magnetic stripe is next encoded with
a suitable identifier such as a number. With other mediums, e.g., bar type
codes or imprinted readable patterns, the encoding of the identifier
occurs as part of the process of applying the storage medium to the
document.
The identifier may be selected and associated with the document to be later
authenticated by any suitable means. However, a preferred means of
selecting an identifier is to select a document with a medium which has a
uniqueness characteristic. The uniqueness characteristic is sensed and
used to derive an identifier such as in the manner described in U.S. Pat.
No. 4,423,415. The identifier value is next encrypted, preferably in
accordance with the encryption algorithm described in U.S. Pat. No.
4,405,829 issued Sept. 20, 1986, to Rivest et al. which patent is hereby
incorporated by reference. The encrypted identifier is then processed to
define an error correction code. A preferred error correction code may be
derived in accordance with the teaching of Error-Correcting Codes, by
Peterson and Weldon, MIT Press at page 269 et seq.
The error correction code and the encrypted identifier, each in the form of
a string of digital data bits, are combined in accordance with a
predefined format to form a bit string. According to a preferred
predefined format, the bit string starts with "1's" and ends with an
indefinite number of repetitions of a predefined bit sequence referred to
herein as a "framing character." Following the repetition of "1's" on one
end of the bit string is a predefined recognizable bit sequence defined as
a "start sentinel" followed by a data field which starts with a framing
character and is followed, in any predefined order, by the encrypted
identifier, the error correction code, a public decryption key, any other
desired data (optional) and ending with another framing character.
Following the data field is another predefined recognizable bit sequence
defined as a "stop sentinel" followed by the ending repetition of framing
characters. Additional framing characters are interspersed at defined bit
intervals in the data field. The framing characters are recognizable and
enable the location and quantity of erroneous, missing, or lost data to be
identified and in some instances enable the value of the missing,
erroneous or lost data to be recovered. When a magnetic stripe is used,
the resultant formatted bit string is written onto the non-uniform
magnetic stripe by altering the magnetic flux along the length of the
magnetic stripe in accordance with a selected data storage convention used
for magnetic stripes such as the F2F convention.
The document is authenticated by first obtaining a verification value which
is to be compared against the stored identifier. A match will indicate the
document is authentic. In the preferred system, the uniqueness
characteristic along a predefined, specified area of the document is
sensed and a verification value derived from the sensed data. Reading
apparatus next reads the data on the storage medium such as by sensing the
flux variations representative of the bit string previously stored along
the non-uniform magnetic stripe. However, because of the non-uniform
magnetic characteristic of the magnetic stripe and because of scratches,
folds, tears and other defects or damage to the document, the previously
stored bit string will include errors and missing data. Therefore, the
present invention includes novel methods of processing the signal
representative of the data read from the storage medium to read those bits
in the bit string which can be read despite the non-uniformities,
irregularities and damage, and recover and replace data which was
erroneously read, lost or otherwise made unreadable due to folds, tears or
other damage to the document itself. Such methods includes local signal
processing and local and global error correction techniques to correct
erroneous or missing data; to identify the locations and quantity of other
missing or erroneous data using, inter alia, the framing characters; and,
using the information as to the location and quantity of missing or
erroneous data in conjunction with the error correction code, to recover
the value of the remaining missing or erroneous data. The present
invention has been found to enable recovery of the originally stored bit
string from the storage medium, and in particular, non-uniform magnetic
stripes, without error in almost all cases, even when the document has
significant physical damage.
The resulting recovered portion of the bit string which is the encrypted
identifier, is then decrypted and compared with the obtained verification
value according to a predefined compare criterion. The item is
authenticated when the vertification value and the decrypted identifier
value compare according to the predefined compare criterion. The
verification value and the decrypted identifier do not need to match
exactly for the document's authenticity to be assured. The number of
errors which can be accepted and still result in a positive authentication
indication are predefined and are part of the predefined compare
criterion.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which constitute a part of the specification, exemplary
embodiments are set forth as follows:
FIG. 1 is a partial cutaway perspective of a document with a storage medium
thereon and specifically a magnetic stripe storage medium;
FIG. 2 is a top partial view of a document showing an area characterized by
a uniqueness characteristic and a magnetic stripe storage medium;
FIG. 3 is a simplified block diagram illustrating a system, including an
optional write subsystem, in accordance with the invention;
FIG. 4 is a pictorial representation of a bit string formatted for storage
on a storage medium, such as a magnetic stripe, on a document;
FIG. 5 is a simplified block diagram showing a write subsystem such as that
depicted in FIG. 3;
FIGS. 6A, 6B and 6C illustrate various waveforms, timing relationships and
binary bit string data illustrating the operation of the authentication
system in accordance with the invention;
FIG. 7 is a simplified block diagram of a read subsystem useful in reading
flux changes from a magnetic stripe;
FIG. 8 is an illustration of various address, bit data, write and read
signals at various locations in the authetication system of FIGS. 3, 5 and
7;
FIG. 9 is a series of waveforms illustrating the operation of the
correlator and peak and polarity detector blocks of FIG. 7;
FIG. 10 is a partial flow chart illustrating a means of recovering the
number of data bits in a bit string and computation of data frame offsets;
and
FIG. 11 is a flow chart illustrating one means of identifying the number
and location of bits in a section of the bit string identified as
containing erroneous bit values.
DETAILED DESCRIPTION
Although the present invention contemplates the use of various storage
mediums on a document, the following detailed description is given with
reference to a magnetic stripe as the preferred storage medium.
Referring initially to FIG. 1, an item 100, such as a document made out of
a fibrous medium 102 such as paper, as a surface 106 on which a magnetic
stripe 104 is disposed such as by offset printing. The paper medium from
which most documents of value such as stocks or bonds are made result in a
highly irregular surface geometry. When a composition such as a magnetic
ink is applied to such a surface to form a magnetic stripe, the resultant
stripe assumes a similar irregular geometry. The magnetic stripe 104
consequently has a highly irregular geometry exhibiting a non-uniform
magnetic flux characteristic along its length. Such a stripe is
nevertheless the preferred authenticity verification storage medium for
such documents of value.
Referring to FIG. 2, the system in accordance with the invention comprises
a printable item 10 made of paper or any other printable medium such as
that described in conjunction with FIG. 1. Matter readable by an observer
such as words, designs, pictorial representations and the like 12 may be
printed across the surface of the document 10 using any desired method
such as offset printing. For example, the printing may be such as to
identify the document as a stock or bond which may be of considerable
monetary worth and indeed may be a negotiable instrument. In order to
provide additional protection against counterfeiting, a space 14 on the
surface of the document 10 is set aside to define a field of sensible
locations. A corner indicia 16 is positioned about the edge of the space
14 to define the space and enable alignment of a uniqueness characteristic
reader 30 (FIG. 3) with the space for subsequent repetitive reading such
as in the manner set forth in U.S. Pat. No. 4,423,415. The space 14
defines a specified area of the item which has, for example, a random but
substantially non-changing transparency variation over its surface. That
random transparency defines a uniqueness characteristic which is machine
readable in accordance with U.S. Pat. No. 4,423,415. Once sensed, an
identifier representative of that uniqueness characteristic is derived and
assigned. Of course, any other uniqueness characteristic of the document
which can be sensed and referenced by an identifier value, can be utilized
without departing from the present invention.
The document 10 further includes a storage medium, which in the illustrated
embodiment is a magnetic stripe 18 disposed over a portion of the
irregular, random surface 19 of the document 10 by printing and preferably
by offset printing. The magnetic stripe 18 will generally have non-uniform
geometric and magnetic flux characteristics such as those described in
conjunction with FIG. 1.
Referring to FIG. 3, a simplified block diagram of an authentication system
in accordance with the invention includes the document 10 of FIG. 2 having
the magnetic stripe 18 to provide an escort memory on the document 10. The
uniqueness characteristic (such as transparency) is sensed from region 14
by a uniqueness characteristic sensor 40. The uniqueness characteristic
reader 30 is coupled to the sensor 40 to receive a signal representative
of the sensed uniqueness characteristic and therefrom define the
identifier such as a binary number. Apparatus and methods for reading and
deriving an identifier representaitve of the uniqueness characteristic are
fully described in U.S. Pat. No. 4,423,415, which patent is hereby
incorporated by reference. A control processor 32 receives the identifier
from the reader 30 and preferably encrypts the identifier and then
processes the encrypted identifier to generate an error correction code
for the encrypted identifier. In the preferred embodiment, the error
correction code is a Bose-Chaudhure-Hocquenghem code whose derivation is
fully described at page 269 et seq. in Error Correcting Codes by Peterson
and Weldon published by MIT Press. The encrypted identifier and the error
correction code, both digitized, are combined with any other desired data,
such as a public encryption key, to form a coded identifier.
Before being stored on the storage stripe, the coded identifier is
formatted in accordance with a predefined format selected to facilitate
authentication and data recovery. The result is a bit string which is sent
to a write subsystem 34. The write subsystem 34 generates a "write
current" signal 212 (FIG. 6A) representative of the bit string 214 (FIG.
6A). the write current signal 212 is provided to a write head 38 which,
when positioned in close proximity to the magnetic stripe 18, will cause
flux changes along the length of the stripe 18 as the stripe 18 moves
past. In order to write the bits of the bit string 214 onto the stripe 18
at the correct location, a transport mechanism 36, under control of the
control processor 32, causes the document 10 to physically pass beneath
the write head 38 so that the write subsystem 34 will cause flux changes
representative of individual bits in sequence to occur at predefined
spacings along the magnetic stripe 18. A transport mechanism, useful in
such a configuration, is described in the aforementioned U.S. Pat. No.
4,423,415. Of course, the invention is equally applicable if the document
10 remains stationary and the write head 38 moves across the document.
To verify the authenticity of the document 10, the information stored on
the magnetic stripe 18 is read as the document is moved by the transport
mechanism 36 past a second head 39 under control of the control processor
32. The resultant signal (ideally appearing as the signal 228 of FIG. 8
but in reality having the | | |
