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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of data processing, and in
particular, to a method and apparatus for controlling the dissemination of
digital information. Furthermore, the present invention provides
transparent access to uncontrolled digital information together with
controlled digital information with the same access apparatus.
2. Description of the Related Art
The distribution of original works--whether be it text, graphics,
animation, video or audio--in magnetic, electronic, optical or any other
medium is becoming popular. Advances in digital compression technology and
improvement in the price/performance ratio of computers have made it
economical and feasible to disseminate digital information in such "soft"
forms. However, original works encoded in digital medium can be easily
duplicated, encrypted, transmitted via communication networks and
destroyed. For the remainder of the description of the present invention,
original works encoded in digital medium shall be referred to as digital
information. The push factors, i.e., easy access and manipulation, that
make digital information a rival to the traditional hard copy forms, i.e.,
books, newspapers or microfiches, have also made it difficult to establish
evidence of illegal usage of such information.
With respect to the distribution of hard copies of original works,
copyright and publishing laws strike a balance between the twin goals of
compensating the publisher/author and of maintaining reasonable cost to
the end users. It is straightforward to establish evidence of making
illegal copies of hard copy of original works. The main thrust of
copyright and publishing laws is to establish evidence of illegal
possession.
In contrast, evidence of illegal possession of digital information is
difficult at best and at worst impossible to obtain. The present invention
proposes to control the usage of distributed digital information as an
alternative. By usage, the present invention refers to the number and
timing of the accesses specified by the information provider.
Prior art controls the dissemination of software programs only with copy
protection schemes. Copy protection relies on hardware or software
artifacts to detect and prevent illegal copying of software programs.
Encryption is sometimes used to provide copy protection. Some recent
examples of copy protection schemes are U.S. Pat. No. 4,866,769 to Karp
and U.S. Pat. No. 4,903,296 to Chandra et al.
U.S. Pat. No. 4,903,296 claims copy protection of software on magnetic
medium with a special key having two marks made on the surface of the
medium. These marks are in the form of absence of material and domains
that cannot be formed by conventional magnetic disk write heads.
Additionally, an encrypted key which is critical for running the
application is built into a special purpose hardware subsystem. Finally
the hardware subsystem is required to decrypt the key.
U.S. Pat. No. 4,866,769 teaches a method of copy protection of personal
computer software distributed in diskettes through the use of a unique
identification stored in read only memory of a personal computer. A source
ID is provided with every software distributed. The personal computer ID
is used with the source ID on the distribution diskette to produce an
encoded check word, using any available encryption method. This check word
is then used to verify that the software is being used on the designated
personal computer.
While U.S. Pat. Nos. 4,903,296 and 4,866,769 disclose off-line schemes for
controlled dissemination of software, U.S. Pat. No. 4,999,806 describes a
central station distributing software over telephone lines--an on-line
scheme for software dissemination. The central station transmits an
acceptance code to a caller and then terminates the call. After verifying
the caller's credit information, the central station calls the purchaser
back and continues with the transaction only after receiving the
acceptance code. The central station then transmits a Control Transfer
Program and Initialization Program to the purchaser. The purchaser
executes the Initialization Program to turn over control of the
purchaser's computer to the central station. The Control Transfer Program
makes sure that no memory resident copying programs are running before
transmitting over the telephone line the purchased/leased program to the
purchaser's computer. Thereafter the various transmitted programs are
erased, leaving only a copy of protected version of the purchased program
on the purchaser's disk.
To prevent unauthorized copying and use of information, prior art copy
protection schemes require either introducing artificial indica as
software keys or requiring special hardware subsystems. Not only are these
solutions costly to both the information providers and the end users as
they require additional processing steps, but they are also incompatible
with the trend of encouraging concurrent use of different types of
information in a network environment. Furthermore, the prior art copy
protection schemes provide limited control over the dissemination of
digital information in that they prevent unauthorized copying of software
but not "uses" of such information.
Absent from the prior art is the dissemination of uncontrolled information.
By uncontrolled information, the present invention refers to a portion of
the information which the information provider has decided to let the end
user view without registering it as a "use" of the controlled information.
Typically, the uncontrolled information is either at a lower resolution
compared with the controlled information or it comprises a selected
portion of the controlled information which allows the end user to make an
informed decision whether to subscribe or use the controlled information.
Examples of uncontrolled information are the preview of a movie, or a
demonstration version of the controlled software, or even an abstract of a
patent document. Hitherto, prior art information dissemination system does
not permit the transparent access of uncontrolled digital information with
the same access device as that for accessing the controlled digital
information.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for controlling the
dissemination of digital information. Digital information is structured
logically to incorporate usage history and allowable access window before
it is encrypted in a header portion and a body portion. The end user
accesses the digital information with a tamper-proof controlled
information access device by decrypting the digital information. A
controller disposed in the controlled information access device permits
end users to access transparently uncontrolled information. Controlled
digital information will be accessed as long as the conditions specified
by the information provider are met. In one embodiment of the present
invention, controlled information is disseminated in an off-line manner
while the second embodiment of the present invention disseminates
controlled digital information in an on-line manner.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a model of information dissemination.
FIG. 2 illustrates a logical structure of a Sealed Controlled Information
(COIN) according to a first embodiment of the present invention.
FIG. 3 shows the architecture of a device used by an information consumer
for accessing the controlled information according to the first embodiment
of the present invention.
FIG. 4 illustrates the logical flow of how the Sealed COIN is prepared by
an information provider.
FIGS. 5A & 5B show the logical flow of the controller in the access device
according to the first embodiment of the present invention.
FIG. 6 illustrates the architecture of an access device for a system for
controlled dissemination of digital information according to the second
embodiment of the present invention.
FIG. 7A illustrates a possible format of the logical structure of Sealed
COIN used in a second embodiment of the present invention.
FIG. 7B illustrates a possible format of the logical structure of the
Sealed Opener which cooperates with the Sealed COIN used in the second
embodiment of the present invention.
FIG. 8 illustrates the flow diagram of the information provider used in the
second embodiment of the present invention where a Sealed COIN is
generated.
FIG. 9 shows the flow diagram of the information provider used in the
second embodiment of the present invention where an opener for accessing
the sealed COIN in FIG. 8 is generated.
FIG. 10 illustrates the logical flow of the overall process of on-line
controlled dissemination of information according to the second embodiment
of the present invention.
FIGS. 11A and B illustrate the flow diagram of the controller in the access
device according to the second embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A method and apparatus for controlling the dissemination of digital
information is described. In the following description, numerous specific
details are set forth such as logical structures of digital information
and program steps, etc. in order to provide a thorough understanding of
the present invention. It will be obvious to one skilled in the art that
the present invention may be practiced without these specific details. In
other instances, well-known steps such as those involved with encryption
and decryption of data are not shown in order not to obscure the present
invention.
Notation and Nomenclature
The detailed description with respect to the controlled dissemination of
digital information is presented partially in terms of algorithm and
symbolic representation upon operation on data bits within a computer
memory. These algorithmic descriptions and representations are the means
used by those skilled in the data processing art to convey most
effectively the substance of their work to others skilled in the art.
An algorithm is here, and generally, conceived to be a self-consistent
sequence of steps leading to a desired result. These steps require
physical manipulation of physical quantities. Usually, though not
necessarily, these quantities take the form of electrical, optical or
magnetic signals capable of being stored, transferred, combined, and
otherwise manipulated. It proves convenient at times, principally for
reason of common usage, to refer to these signals as bits, values,
elements, symbols, characters, numbers or the like. It should be borne in
mind, however, that all of these and similar terms are to be associated
with the appropriate physical quantities and are merely convenient labels
applied to these quantities.
Further, the manipulations performed are often referred to in terms such as
adding or comparing, which are commonly associated with the mental
operations performed by a human operator. No such capability of a human
operator is necessary, or desirable. In most cases, in any of the
operations described herein which form part of the present invention, the
operations are machine operations. Useful machines for performing the
operations of the present invention include general purpose digital
computers or similar devices. In all cases, it should be borne in mind
that there is a distinction between the method operation in operating a
computer or other apparatus and the method of computation itself. The
present invention relates to method steps for providing better control
over the dissemination of digital information.
The present invention also relates to an apparatus for performing these
operations. This apparatus may be specially constructed for the required
purpose or it may comprise a general purpose computer as selectively
activated or reconfigured by a computer program stored in the computer.
The algorithms presented herein are not inherently related to any
particular computer or other apparatus. In particular, various general
purpose machines may be used with programs written in accordance with the
teachings herein, or it may prove more convenient to construct specialized
apparatus such a dedicated processor to perform the required method steps.
The required structure for a variety of these machines would appear from
the description given below.
GENERAL SYSTEM CONFIGURATION
A general model of information dissemination is shown in FIG. 1. Here, the
Information Provider 10 refers to a supplier of all types of information
including but not restricted in form to text, graphics, animation, video,
audio, software, or any combination thereof. The transmission channel 20
represents the means and more specifically the media through which
information is delivered to the Information Consumer 30 over paths 15 and
25. The transmission channel 20 includes but is not limited to any
communication means or media such as computer networks, satellite links,
diskettes, optical disks or other storage medium. It should also be
understood by one skilled in the art that Information Consumer 30 is used
interchangeably with one or more end users of information. The present
invention chooses the word "information consumer" to highlight the
use-once nature of the controlled information. In other words, once
controlled information is consumed, the original information no longer
exists in a usable form and the re-access to the same information is not
automatic. The use-once nature can be generalized to use-n-time, i.e.,
once the controlled information has been used for n times, it no longer
exists in a usable form.
This invention teaches methods and apparatus for an information provider to
prepare information packaging for dissemination. These methods are going
to be described in specific steps of manipulating information. For one
skilled in the art, it is obvious that some of these steps shall be best
automated by, for example, implementing them as a special purpose
software, which is normally called a server, running on general purpose
computers. It is also clear that an information provider could
simultaneously instantiate multiple executions of the server to serve
multiple information consumers. For clarity of presentation, the
description below shall elaborate on the model having one provider and one
consumer in our description. It is also clear that an information consumer
may also be another information provider.
FIRST EMBODIMENT OF THE PRESENT INVENTION
1. Preparation of distribution package
FIG. 2 illustrates a logical structure of a Sealed Controlled Information
(COIN) according to a first embodiment of the present invention. The
Sealed COIN is prepared by an information provider once the information
consumer agrees to the terms of an information distribution contract. The
first embodiment of the present invention describes an off-line scheme
where the transmission channel 20 comprises any kind of non-volatile
storage medium such as a floppy disk, a hard disk, an optical disk and
other non-volatile semiconductor storage devices. An information
distribution contract contains at a minimum the identity of controlled
information, the number of accesses, and the type of transmission medium
20.
Referring again to FIG. 2, the logical structure of the Sealed Controlled
Information (COIN) comprises a header 35 and a body 40. COIN refers to the
original information encoded in some "soft" form (e.g., electronic,
magnetic or optical) that the Information Provider 10 shall provide to the
Information Consumer 30 for his access for a predetermined number of
times. COIN is encoded or sealed by using some scheme such that accessing
the COIN without a valid decryption key is computationally intractable.
The header 35 further comprises a plurality of fields: a medium signature
36, an access window 37 (AW), total number of legal accesses allowed 38
(TAL), the number of legal accesses left 39 (LAL), and TAL number of
encryption/decryption keys 41 (K.sub.1 to K.sub.TAL). The medium signature
36 refers to any scheme which allows a distribution medium, such as a
floppy disk, to have a unique identification. Preferably, this signature
depends upon the characteristics or nonuniformities of the distribution
medium. For an example of a suitable medium signature, please refer to the
pending U.S. application Ser. No. 08/120,969, filed 13 Sep. 1993, by the
same assignee as the present invention, now U.S. Pat. No. 5,412,718. The
AW 37 refers to a specified time period within which a legal access is
granted to the information consumer for accessing the COIN. A start and
end time is given as the boundary of the access window in which the
Information Consumer 30 can access the disseminated information legally.
TAL 38 is the total number of legal accesses to the COIN granted by the
Information Provider 10 to the Information Consumer 30 under an
information dissemination contract. LAL 39 is the number of legal accesses
left; it is the difference between TAL and the number of accesses already
granted. When LAL is equal to zero, access to COIN shall be denied.
K.sub.1 to K.sub.TAL 41 are keys used for decrypting the COIN in the body
40. Preferably the encryption and decryption scheme of K.sub.1 to
K.sub.TAL 41 is based on Public Key Cryptography (PKC) which allows the
information provider to transmit secret messages to the access device
without prior transmission of a secret key. Under PKC, each party has a
pair of keys--one secret (known only to itself) and one public (known to
everyone like a telephone number in a telephone directory). In other
words, the information provider has a secret key (SSK) and a public key
(SPK) while the access device has a secret key (DSK) and a public key
(DPK). When the information provider sends a secret message to the
information consumer, the information provider uses the access device's
public key (DPK) to encrypt the message. Only the access device can
decrypt the encrypted message by using its own secret key (DSK). For
further reference on PKC, see R. L. Rivest, A. Shamir and L. Adleman: "A
Method for Obtaining Digital Signature in Public-Key Cryptosystems"
Communications of the ACM, Vol. 21, No. 2, February 1978, pp. 120-126.
Also see D. E. R. Denning, Cryptography and Data Security,
Addision-Wesley, Reading, Mass., 1983.
Once the Information Consumer 30 agrees with the Information Provider 10 on
the terms of the distribution contract, Information Provider 10 executes a
procedure as outlined in FIG. 4 beginning with step 60 to produce a
distribution medium incorporating the sealed COIN. In step 62 TAL number
of keys, K.sub.1 to K.sub.TAL, are generated for encrypting COIN in the
body 40. Although PKC is referred in the embodiment of the present
invention, any method of encryption is applicable. Next, a medium
signature 36 is created from the particular distribution medium on which
COIN is to be distributed. Pending U.S. application Ser. No. 08/120,969,
filed 13 Sep., 1993, and assigned to the same assignee as the present
invention exemplifies one of many ways of generating a medium signature.
In step 66, COIN is encrypted with K.sub.1. It follows that the body 40 of
the sealed COIN is generated. In step 68, the header 35 is prepared next.
Initially the value LAL 39 is set to be identical with that of TAL 38. By
concatenating AW 37, TAL 38, LAL 39, K.sub.1 to K.sub.TAL 41, and medium
signature 36 as illustrated in FIG. 2, the header 35 is then encrypted in
step 68 using the public key DPK of the information consumer's access
device. The encrypted header 35 and the encrypted body 40 constitutes the
sealed COIN and is written onto the distributed medium in step 70.
2. Access of information
It is assumed that the Information Consumer 30 has some device, for example
a computer, to access the information in the distributed medium. The
minimum enhancements to such a device for accessing COIN are shown in FIG.
3. A Controller 45 is coupled at its input to an information input channel
27 for receiving disseminated information from the read device (not shown)
of distributed medium. The Controller 45 is also coupled at one of its
outputs to an information output channel 29 for transmitting re-encrypted
information to the write device (not shown) of the distributed medium. The
function of Controller 45 shall be described below in the description of
FIG. 5. It should be understood by one skilled in the art that the
Controller 45 can be implemented fully in hardware or by a general purpose
processor with the appropriate software. The controller 45 is also coupled
at the other output to an output unit 50 over a link 47 for displaying the
disseminated information. The output unit 50 could be a display unit for
text/graphics/animation/video or a transducer for audio information. The
output unit 50 could itself be a device for distributing controlled
information to other information consumers. The controller 45 is also
coupled to a clock 55 over link 49 for counter-checking whether the real
time is within the boundary of the access window AW 37. Preferably, the
clock 55 and the access device are tamper-proof such that the information
consumer may not tap into the link 47 nor alter the value of the clock 55.
It should be understood by one skilled in the art that the controller has
means to interact with the user, the details of which are omitted in order
not to obscure the description of the first embodiment of the present
invention.
FIGS. 5A & 5B summarizes the logical flow of the Controller 45 of the
access device in accordance to the first preferred embodiment of the
present invention. When the Information Consumer 30 wishes to access the
sealed COIN, he or she loads in step 80 the medium read/write device with
the distribution medium (not shown) containing the sealed COIN. The
Controller 45 of the access device is presented with the information read
from the medium read/write device via the input channel 27. The Controller
45 checks in step 82 whether the information at the input channel 27 is
encrypted. If the information is unencrypted, i.e., uncontrolled
information, the Controller 45 allows the information at the input channel
27 to pass directly in step 84 to the output unit 50 over the link 47.
However, if the information at the input channel 27 is encrypted or
controlled, the Controller 45 decrypts the header 35 of the sealed COIN by
using in step 88 the secret key DSK of the access device. As mentioned
above, the secret key DSK is unknown to the Information Consumer 30. Next
in step 90, the Controller 45 checks whether there are any legal access
left by testing the value of LAL 38 for zero. If there are no legal
accesses left, the value of LAL 38=0 and an evade processing module is
invoked in step 92 which either denies the information access or erases
the contents of the medium. The specific action depends on a particular
embodiment of the invention. Should the value of LAL be greater than zero,
then the Controller 45 compares in step 94 the value of the access window
AW 37 with the time of the clock 55. If the current time falls outside of
the boundary of the AW 37, the evade processing module in step 92 is
invoked. Otherwise, the Controller 45 checks in step 96 whether the medium
signature 36 corresponds with the signature read from the input channel 27
and that of the output channel 29. If the medium signature 36 does not
match, the sealed COIN is stored on a copied medium. An evade processing
module as in step 92 is invoked. Otherwise, the Controller 45 confirms
that the Information Consumer 30 has a right to access the sealed COIN on
the distribution medium.
It should be obvious to those skilled in the art that the controller of the
access device of the present invention permits the information consumer to
access transparently uncontrolled and controlled information in an
off-line manner by using the same access device. While the present
invention obviates the task of switching back and forth between at least
two access devices, it also allows the information provider to distribute
uncontrolled and controlled information in one package. With greater
information at the disposal of the information consumer, usage of
controlled information under the terms of the information provider is
encouraged.
After the Controller 45 determines that the Information Consumer 30 has a
right to access the sealed COIN on the distribution medium in FIG. 5A, the
controller extracts in step 95 the encryption/decryption key
K.sub.TAL-LAL+1 from the header 35. The Controller 45 disables dumping of
decrypted information via the output channel 29. The Controller 45 then
decrypts the sealed COIN by using the key K.sub.TAL-LAL+1 in step 98. The
decrypted information, COIN, is provided in step 100 in FIG. 5B as output
to the output unit 50 over the link 47. It follows that the Information
Consumer 30 accesses the COIN transparently while the Controller 45
checks, validates, encrypts and decrypts the appropriate controlled
information automatically. In step 102 the Controller 45 decrements the
value of the LAL by one. The header 35 thus become modified header 35'.
Should the value of LAL equals zero as tested in step 104, then a "disable
information access" module is invoked in step 106 which for example,
erases the sealed COIN from the distribution medium. If the value of LAL
is >0, then the Controller 45 extracts the encryption/decryption key
K.sub.TAL-LAL+2 and encrypts the COIN in step 108. The Controller 45 then
encrypts the modified header 35' by using the public key DPK of the access
device. Finally the Controller 45 writes the new sealed COIN generated by
this encrypted COIN 40 and the encryption of the modified header 35' onto
the distribution medium via output channel 29 in step 110. Thus, the
procedure described in FIGS. 5A and 5B implements a "use-n-times"
controlled information scheme that give the information provider enhanced
control over the dissemination of digital information.
SECOND EMBODIMENT OF THE PRESENT INVENTION
1. Overall system set-up and operations
The second embodiment of the present invention describes an online scheme
for controlled dissemination of digital information. Referring once again
to FIG. 1, the transmission channel 20 comprises a variety of
communication links between the Information Provider 10 and the
Information Consumer 30. For instance, the transmission channel 20 could
include a computer network or even telephone lines.
The architecture of an access device modeling the Information Consumer 30
for an on-line scheme is illustrated in FIG. 6. Controlled information
from the transmission channel 20 is presented to the Information Consumer
30 over an input channel 27 which is coupled to a Controller 48. The
functions of the Controller 48 shall be elaborated in connection with the
description of FIG. 11. The Controller 48 can be implemented either in
hardware or by a general purpose processor with proper software. Referring
again to FIG. 6, the Controller 48 is coupled to an output unit 50 over a
clear channel 47. Just as in the first embodiment of the present
invention, the output unit 50 comprises a device for outputting controlled
information or a mechanism for distributing controlled information to
others. The Controller 48 is also coupled to a memory storage 52 and a
clock 55 for reasons which shall be explained below. The Controller 48 is
coupled to an output channel 29 for outputting re-encrypted controlled
information. Preferably, the various channels coupled to the Controllers
48 are tamper-proof. This will make it impossible for users to tap into
the clear channel 47, to access the Controller 48, to alter the value of
the memory storage 52, or to change the value of the clock 55. It should
be understood by one skilled in the art that the controller has means to
interact with the user, the details of which are omitted in order not to
obscure the description of the second embodiment of the present invention.
The objective of the on-line scheme of controlled dissemination of digital
information is to achieve improved control of the delivery of information
so that once the information is accessed by the information consumer for a
specified number of times, the information no longer exists in a usable
form without authorization from the information provider. The enhanced
control of information dissemination is achieved by using encryption and
by limiting an information consumer's access at a designated legal access
device during an access window.
In order to achieve the above mentioned controls, the encrypted COIN is
packaged with some control data, which is called the "header" while the
encrypted COIN is called the "body". The header and body together are
called the Sealed-COIN. A user presents the Sealed-COIN together with a
ticket to the access device in order to access the COIN. This ticket is
called "Seal Opener" or just "Opener" for short. The Openers are issued by
the Information Provider at user's request. FIGS. 7A and 7B illustrate
possible logical structures of Sealed-COIN and Seal Opener for realizing
the second embodiment of the present invention. Below are definitions of
specific terms and acronyms needed in the rest of the description:
COIN Original information encoded in some digital form; identified by
unique identification, IID.
TAL Total number of legal access to the COIN allowed by the information
provider to information consumer.
LAL Number of legal access left.
LAD The device on which the COIN can be accessed legally.
PID Unique identification number of information provider.
UID Unique identification number of information consumer.
CID Unique identification of a contract of information dissemination.
Logically, a contract associates PID, IID, TAL, LAD and UID.
AW Access window is the time during which a legal access is granted to
COIN.
An agreement or contract of information dissemination (CID) between an
information provider and an information consumer provides at a minimum
that the information provider shall provide some COIN to the information
consumer for TAL number of legal accesses on certain LAD. As such, CID
associates with PID, IID, TAL, LAD and UID respectively. In the simplest
form, a CID is formed by concatenating PID, IID, TAL, LAD and UID as
illustrated logically in FIG. 7A. It should be understood by one skilled
in the art that although the fields 121 to 129 in FIG. 7A are drawn in
some order, the structure of CID 120 in any implementation is not bound by
this order and arrangement. Similarly, the generality of the preceding
comments applies to FIG. 7B. CID 120 expires when all of TAL 125 number of
accesses have been made.
Referring again to FIG. 7A, a Sealed-COIN comprises a header 119 and a body
130. As mentioned above briefly, body 30 is the original COIN which has
been encoded by using some encryption scheme so that obtaining the COIN
without a valid decryption key is computationally intractable. The
decrypted header 119 further comprises three fields: CID 120, LAL 122 and
keys 124. Keys 124 consist of TAL number of keys K.sub.1, K.sub.2, . . . ,
K.sub.TAL. They are used to decrypt the body and further encrypt the COIN
to form new Sealed-COIN.
FIG. 7B shows the logical structure of a Seal Opener. It too has a header
140 and a body 145. The header 140 has two fields: CID 131 and AW 142. CID
131 of the Opener is identical to the CID 120 of the Sealed-COIN. The AW
142 holds a number of access windows during which the information consumer
may access the COIN. The body 145 contains a decryption key K.sub.H for
the header 119 of the Sealed-COIN in FIG. 7A. The key K.sub.H is
maintained for the life of contract CID. For the second embodiment of the
present invention, a Public Key Cryptography scheme as well as a
conventional secret key scheme are used to illustrate the on-line scheme
of information dissemination. With respect to a Public Key scheme, the
present invention denotes the secret and public keys of Information
Provider 10 by PSK and PPK, respectively, and the secret and public keys
of the access device by DSK and DPK, respectively.
FIG. 10 illustrates the logical flow of the overall process of on-line
controlled dissemination of information of the present invention. The
on-line scheme of the present invention commences with the establishment
of a contract between an Information Provider 10 and an Information
Consumer 30 in step 168 of FIG. 10. At this juncture, a CID and its
associated fields PID 121, IID 123, TAL 125, LAD 127 and UID 129 are
stipulated in the contract. Based on this information, the Information
Provider 10 generates a Sealed-COIN as illustrated in FIG. 8, and
transmits it over the transmission channel 20 to the information consumer
in step 170 of FIG. 10. The information consumer then makes an request to
the Information Provider 10 over the same channel in step 172 of FIG. 10.
After verifying the information consumer's request in step 174 of FIG. 10,
the Information Provider 10 generates an Opener as outlined in steps
160-166 of FIG. 9 and transmits the Opener to the information consumer in
step 174 of FIG. 10. The information consumer presents the Sealed-COIN
received earlier and the Opener to Controller 48 for accessing the COIN in
step 176.
In determining whether to grant the information consumer's request for
access in step 178, the Controller 48 applies the logical sequence of
steps as outlined in FIGS. 11A and 11B details of which shall be
elaborated below. Should an access be granted, the Controller 48 checks if
the CID contract has expired in step 182 of FIG. 10, i.e., whether all the
TAL number of accesses have been made by the information consumer. If not,
the COIN is re-sealed as described below and the outcome is made available
to the information consumer through the Information Output Channel 29. The
information consumer saves the re-sealed COIN for future access in step
184. For subsequent accesses, the information consumer starts from step
172 by making another access request to the Information Provider 10. This
continues until the expiration of the contract as in step 180.
2. Preparation of Sealed-COIN and Seal Opener
FIG. 8 describes how an information provider generates a Sealed-COIN. The
information provider is ready to generate a Sealed-COIN in step 150 if it
has the CID and the values of the associated quantities, namely, PID, IID,
TAL, LAD and UID. The information provider first generates TAL number of
keys, K.sub.1, K.sub.2, . . . , K.sub.TAL in step 152. Next, in step 154,
the information provider forms the header fields 119 of the Sealed-COIN by
combining the CID for field 120, the value of TAL for field 122 and the
keys for field 124. Then the body 130 of the Sealed-COIN is formed by
encrypting the COIN identified by IID with key K.sub.1. The header fields
119 in turn are encrypted in step 156 to form the header with a new key
K.sub.H which the information provider maintains in association with the
contract CID during the life time of the contract. As mentioned earlier,
the key K.sub.H forms part of the body of the Opener. Finally, the
information provider forms the Sealed-COIN by concatenating the header and
the body in step 158.
FIG. 9 illustrates in detail the steps in which the information provider
generates an Opener. The process starts with an information consumer
making an access request with a valid CID and a number of valid access
windows AW in step 160. With the CID, the information provider finds the
corresponding key K.sub.H, which it used in step 156 to encrypt the header
fields 119 of the Sealed-COIN, and encrypts K.sub.H using the information
provider's secret key PSK in step 162. The information provider then forms
the Opener by using the CID for field 131, AWs for field 142 and the above
encrypted K.sub.H for field 144 in step 164. Finally, the Opener is
generated by encrypting the above outcome with the access device's public
key DPK in step 166.
3. Access to Sealed-COIN
As mentioned briefly above, FIGS. 11A and 11B describes the controller's
logical steps in determining whether to grant the information consumer its
access request. Step 200 checks whether the input is uncontrolled
information. An example of uncontrolled information is catalog information
for the user to browse. If it is uncontrolled information, it is outputted
to the output unit 50 over the clear channel 47. Otherwise, the Controller
48 asks the information consumer for an Opener in step 204. The controller
uses its own (i.e., the Access Device's) secret key DSK to decrypt the
Opener to extract CID and AWs from field 131 and field 142 in step 206.
From the CID, the controller extracts the LAD from field 127. The
controller checks whether the LAD matches with its own (i.e., the Access
Device's) identification, and verifies whether the current time according
to Clock 55 is within one of the AWs found in field 142. If any of these
checks fails, access to controlled information is denied in step 210.
If the checks in step 208 are successful, the controller extracts the PID
from field 121, and thus the information provider's public key PPK in step
212. With this key, the controller decrypts the body 145 of the Opener to
obtain K.sub.H in step 214. Using K.sub.H, the controller then, in step
216, decrypts the header 119 of the Sealed-COIN presented earlier by the
information consumer. Then it extracts the value of TAL from field 125 of
the header in step 218. The controller then checks in step 220 whether T
(denoting the value of TAL-LAL+1) is within the range of [1, TAL]. In step
222, the access is denied if T is not within the range. W | | |
