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Claims  |
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What is claimed is:
1. A document delivery system, comprising:
a broadcast center that repeatedly sends a document as a plurality of
encrypted packets;
a communication link connected to the broadcast center for carrying the
packets;
a receiving computer, connected to the communication link, and including a
memory and a broadcast receiver wherein the broadcast receiver decrypts
each packet as it is received and stores only the decrypted packets that
are not duplicates of previously received packets in the memory.
2. The document delivery system of claim 1, where the sent document
consists of two or more from the following group: software, images, text,
and full-motion video.
3. The document delivery system of claim 1, wherein the communication link
includes a hybrid link, allowing fast broadcast communication from the
broadcast center to the receiving computer and slower communication from
the receiving computer to the broadcast center.
4. The document delivery system of claim 1, wherein the communication link
is an satellite broadcast link with a dial-up modem return link.
5. The document delivery system of claim 1, wherein the system is a Local
Area Network.
6. The document delivery system of claim 1, wherein the broadcast center
also sends an unencrypted packet containing a catalog, and the receiving
computer further includes a file browser, and wherein the file browser
receives the catalog, stores the catalog in the memory, displays the
stored catalog, and receives user input indicating a requested document in
the catalog.
7. The document delivery system of claim 6, further comprising:
a security engine containing a number of keys;
means in the receiving computer to send a load request to the security
engine when the file browser receives input indicating the requested
document in the catalog.
8. The document delivery system of claim 7, further comprising:
means in the security engine to send a key corresponding to the requested
document to the broadcast receiver,
wherein the broadcast receiver discards received data which does not
correspond to the key.
9. The document delivery system of claim 7,
wherein the broadcast center includes means for sending an announcement
message announcing that a specific document is about to be broadcast by
the broadcast center; and
wherein the means for sending a load request sends a load request if the
document request received by the browser corresponds to the document
announced by the announcement message.
10. The document delivery system of claim 6, wherein a security engine
sends billing information to the broadcast center on a predetermined
periodic basis.
11. The document delivery system of claim 6, wherein a security engine
sends encrypted billing information to the broadcast center on a
predetermined periodic basis.
12. The document delivery system of claim 1, wherein the broadcast center
includes means for sending an announcement message that a specific
document is about to be broadcast by the broadcast center.
13. A document delivery system, comprising:
a broadcast center that sends a document as a plurality of encrypted
packets;
a communication link connected to the broadcast center for carrying the
packets;
a receiving computer, connected to the communication link, and including a
memory and a broadcast receiver, wherein the broadcast receiver decrypts
each packet as it is received and stores only the decrypted packets in the
memory; and
a security engine, wherein the broadcast center includes means for sending
account information to the security engine and the security engine uses
the account information to generate keys used by the broadcast receiver to
decrypt the received packets and wherein the account information includes
key seeds and the security engine uses a one-way hashing method based on
an identification of the sent document and one of the key seeds.
14. The document delivery system of claim 13 wherein the account
information includes billing information.
15. The document delivery system of claim 13, wherein the account
information includes an engine private key for encrypting billing
information sent to the broadcast center on a periodic basis.
16. A receiving computer in a document delivery system having a broadcast
center that sends a document as a plurality of encrypted packets and sends
account information including key seeds to the receiving computer, the
receiving computer comprising:
a memory;
a broadcast receiver that decrypts a packet as it is received and stores
only the decrypted received packet in the memory; and
a security engine that generates keys used by the broadcast receiver to
decrypt the received packets in accordance with a one-way hashing method
based on a document ID of the sent document and one of the key seeds.
17. The receiving computer of claim 16, further comprising:
a file browser for receiving a catalog, storing the catalog in the memory,
displaying the stored catalog, and receiving user input indicating a
document in the catalog.
18. The receiving computer of claim 17, further comprising:
means in the file browser to send a load request to the security engine
when the file browser receives input indicating a document in the catalog.
19. The receiving computer of claim 18, further comprising:
means in the security engine to send a key corresponding to the requested
document to the broadcast receiver,
wherein the broadcast receiver discards received data which is not part of
the document corresponding to the key.
20. The receiving computer of claim 18, wherein the means for sending a
load request sends a load request if the document request received by the
file browser corresponds to a document announced by an announcement
message received from the broadcast center.
21. The receiving computer of claim 16, wherein the security engine sends
billing information to the broadcast center on a predetermined periodic
basis.
22. The receiving computer of claim 16, wherein the security engine sends
encrypted billing information to the broadcast center on a predetermined
periodic basis.
23. The receiving computer of claim 16, wherein communication between the
broadcast center and the receiving computer occurs via a communication
link that includes a hybrid link, allowing fast broadcast communication
from the broadcast center to the receiving computer and slower
communication from the receiving computer to the broadcast center.
24. A method for document delivery in a network system, including the steps
of:
sending, by a broadcast center in the network, a document as a plurality of
encrypted packets;
connecting a communication link to the broadcast center;
decrypting a received packet, in a receiving computer connected to the
communication link, the receiving computer including a memory and a
broadcast receiver, wherein the broadcast receiver performs the decrypting
step on the packet as it is received and stores only the decrypted
received packet in the memory;
sending, by the broadcast center, account information including key seeds
to a security engine in the receiving computer; and
generating, by the security engine, keys used by the broadcast receiver to
decrypt the received packets in accordance with a one-way hashing method
based on a document number of the sent document and one of the key seeds.
25. A document delivery system, comprising:
a broadcast center that sends a documents as a plurality of encrypted
packets;
a communication link connected to the broadcast center for carrying the
packets;
a receiving computer, connected to the communication link, and including a
memory and a broadcast receiver, wherein the broadcast receiver decrypts
each packet as it is received and stores only the decrypted packets in the
memory; and
a tamper-resistant security engine, wherein the broadcast center includes
means for sending account information to the security engine and the
security engine uses the account information to generate keys used by the
broadcast receiver to decrypt the received packets.
26. A method for receiving documents by a receiving computer in a network
system, including the steps of:
connecting a communication link to a broadcast center in the network;
receiving from the broadcast center, by a broadcast receiver, a document as
a plurality of encrypted packets;
decrypting a received packet as it is received and storing only the
decrypted received packet in a memory in the receiving computer;
receiving from the broadcast center, by a security engine in the receiving
computer, account information including key seeds; and
generating, by the security engine, keys used by the broadcast receiver to
decrypt the received packets in accordance with a one-way hashing method
based on a document identification of the sent document and one of the key
seeds.
27. A method for receiving documents by a receiving computer in a network
system, including the steps of:
connecting a communication link to a broadcast center in the network;
receiving from the broadcast center, by a broadcast receiver, more than one
copy of a document as a plurality of encrypted packets; and
decrypting a received packet as it is received and storing only the
decrypted received packet in a memory in the receiving computer if the
decrypted received packet is not a duplicate of a previously received
packet.
28. The method of claim 27, further including the steps of:
receiving, by a file browser, a catalog;
storing the catalog in the memory;
displaying the stored catalog; and
receiving user input indicating a document in the catalog.
29. The method of claim 28, further including the steps of:
sending a load request from the file browser to a security engine when the
file browser receives input indicating a document in the catalog;
sending from the security engine to the broadcast receiver a key
corresponding to a requested document, and discarding received data which
is not part of the document corresponding to the key.
30. The method of claim 27, further including the step of sending an
announcement message from the broadcast center that a specific document is
about to be broadcast by the broadcast center. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This application relates to a computer network and, more specifically, to a
method and apparatus for implementing an electronic document delivery
system where both documents and billing information are encrypted during
transmission.
An electronic document delivery system transmits documents from a central
depository to individual nodes or receiving computers. In some
conventional document delivery systems, a user accesses a computer at the
central depository, examines a list of available documents stored at the
central depository, and requests that one or more of the documents be
transmitted to him. In other conventional document delivery systems, a
predetermined group of documents are sent from the central depository to
the user and stored on the user's system. The user is then free to examine
documents in the predetermined group. Still other conventional electronic
document delivery systems can be used to send only certain types of
documents, such as text-only documents.
Some electronic document delivery systems transmit documents to the user in
encrypted form. The encrypted documents are received at the receiving
computer and stored in a memory. Thereafter, the documents are decrypted
and the decrypted form of the documents are also stored in a memory. Such
double storage of documents is wasteful of memory and storage space.
What is needed is an electronic document delivery system in which a user
can determine which documents he wishes to receive and in which the user
is charged only for those documents that he receives. It is also desirable
to allow the user to designate which documents he wishes to receive
without having to access a central computer to view a list of available
documents. Furthermore, it is desirable that such a system use encryption
for all critical information passing between the central computer and the
receiving computer. It also is desirable to avoid having both an encrypted
and a decrypted version of a document stored at the receiving computer, as
this is wasteful of memory space.
SUMMARY OF THE INVENTION
The present invention overcomes the problems and disadvantages of the prior
art by having a central computer (or "broadcast center") periodically send
a "catalog" of available documents to a receiving computer. The user can
then browse through the available documents without having to access the
broadcast center. The documents are transmitted as packets, and the
packets are decrypted as soon as they are received, eliminating the need
to store both an encrypted and a decrypted version of the documents at the
receiving computer. Moreover, the invention is not limited to text-only
documents and can receive all types of documents, such as software,
images, text, and full-motion video. The receiving computer periodically
receives information allowing it to decrypt received documents and to
encrypt billing information to be sent to the broadcast center.
A purpose of the present invention is to allow all forms of electronic
documents to be distributed in a cost-effective manner using broadcast
technology in a way that prevents access to a document without paying for
it.
In accordance with the purpose of the invention, as embodied and broadly
described herein, the invention resides in a document delivery system
comprising:
a broadcast center that sends a document as a plurality of encrypted
packets;
a communication link connected to the broadcast center for carrying the
packets;
a receiving computer, connected to the communication link, and including a
memory and a broadcast receiver, wherein the broadcast receiver decrypts
each packet as it is received and stores only the decrypted packets in the
memory.
In further accordance with the purpose of the invention, as embodied and
broadly described herein, the invention resides in a document delivery
system in a network, comprising:
a broadcast center that sends a catalog containing a list of documents to
be sent by the broadcast center;
a communication link connected to the broadcast center for carrying the
catalog;
a receiving computer, connected to the communication link, and including a
memory and a file browser, wherein the file browser receives the catalog
and stores the catalog in the memory, displays the stored catalog, and
receives user input indicating a document in the catalog.
In further accordance with the purpose of the invention, as embodied and
broadly described herein, the invention resides in a method for document
delivery in a network system, comprising:
the steps of sending, by a broadcast center in the network, a document as a
plurality of encrypted packets;
connecting a communication link to the broadcast center;
decrypting a received packet in a receiving computer connected to the
communication link, the receiving computer including a memory and a
broadcast receiver, wherein the broadcast receiver performs the decrypting
step on the packet as it is received and stores only the decrypted packet
in the memory;
sending, by the broadcast center, account information including key seeds
to a security engine in the receiving computer; and
generating, by the security engine, keys used by the broadcast receiver to
decrypt the received packets in accordance with a one-way hashing method
based on a document ID of the sent document and one of the key seeds.
It is understood that both the foregoing general description and the
following detailed description are exemplary and explanatory and are
intended to provide further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of this specification, illustrate several embodiments of the invention
and, together with the description, serve to explain the principles of the
invention.
FIG. 1 is a hardware block diagram of a preferred embodiment of the
invention;
FIG. 2 is a detailed hardware block diagram of a broadcast center of FIG.
1;
FIG. 3 is a detailed hardware block diagram of a security engine of FIG. 1;
FIG. 4 is a detailed hardware block diagram of a receiving computer of FIG.
1;
FIG. 5 is a timing chart showing the overall operation of the present
invention;
FIG. 6 is a flowchart of steps performed by the broadcast receiver of FIG.
1 in the function of receiving and decrypting packet information;
FIGS. 7(a) and 7(b) are flowcharts of steps performed by the file broadcast
receiver of FIGS. 1 and 4 in the functions of receiving an announcement
message and sending a load request, and receiving and processing a
decrypted packet from the broadcast receiver;
FIG. 8 is a flowchart of steps performed by the security engine of FIG. 3
in the function of receiving and processing a load request from the file
broadcast receiver; and
FIG. 9 is a flowchart of steps performed by the file browser of FIGS. 1 and
4 in the function of displaying a catalog and processing document requests
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments of the
invention, examples of which are illustrated in the accompanying drawings.
Wherever possible, the same reference numbers will be used throughout the
drawings to refer to the same or like parts.
a. General Overview
The following is a general discussion of networking hardware used in a
preferred embodiment of the present invention.
In a preferred embodiment of the present invention a communication link
between a broadcast center computer and a plurality of document receiving
computers is implemented using satellite technology to implement a
high-speed one way link between the document receiving computer and the
broadcast center. This high-speed link is used to download documents and
data from the network. The receiving computer also has a conventional link
such as a dial-up modem and telephone line sending data to the network.
The invention can use various forms of high-speed, one-way links, such as
satellites, and cable television lines. The invention can use various
forms of low-speed networks, such as TCP/IP networks, dial-up telephones,
ISDN D-channel, CPDP, and low-speed satellite paths.
The described embodiment of the present invention uses satellites to
provide a high-speed one-way link. Satellites can cover large geographical
areas and are insensitive to the distance between a transmitter and a
receiver. In addition, satellites are very efficient at point-to-point
applications and broadcast applications, and are resilient and resistant
to man-made disasters. Two-way satellites are expensive to use, however,
because of the costs involved in purchasing an installing satellite ground
terminal hardware. In the past, these costs have placed satellite
communications outside the reach of an individual consumer.
The present invention allows a personal computer to receive downloaded
information from the network via a satellite at a very practical cost. In
the present invention, the cost of satellite communications is reduced
because a one-way satellite link is used. Receive-only earth station
equipment is cheaper to manufacture because it requires less electronics
than send/receive antennae.
b. The Electronic Document Delivery System
The following paragraphs present a brief overview of a preferred embodiment
of the present invention. A more detailed description follows thereafter.
The present invention is an electronic document delivery system in which a
central broadcast center broadcasts documents on a predetermined schedule.
Documents can include various types of files or data, including software,
images, text, and full-motion video. Periodically, a catalog of documents
to be sent during an upcoming time period is sent by the broadcast center
to a plurality of receiving computers. Users of the receiving computers,
either human beings or other computers, designate which documents in the
catalog they wish to receive. Sometime later, the broadcast center
broadcasts, in encrypted form, each of the documents listed in the
catalog. As each document is received by a receiving computer, the
receiving computer determines whether one or more of its users have
designated the document as a document from the catalog that they would
like to receive. If the document was designated by the user, the receiving
computer decrypts the document and stores billing information about the
received document. The billing information will be transferred back to the
broadcast center at a later time.
The following paragraphs provide a more detailed description of a preferred
embodiment of the present invention. FIG. 1 is a hardware block diagram
100 of a preferred embodiment of the invention. FIG. 1 includes a
receiving computer 110, which is one of the plurality of receiving
computers, a broadcast receiver 120, a security engine 130, a
communications link 140, and a broadcast center 150. Receiving computer
110 includes a file broadcast receiver 112 and a file browser 114.
Communications link 140 preferably is a combination of a satellite
broadcast channel plus a dial-up telephone line. Another embodiment of the
invention uses a vertical blanking interval of broadcast television to
carry the broadcast data.
In FIG. 1, communications link 140 includes an incoming link 142 carrying
encrypted and non-encrypted data packets and an outgoing link 144 carrying
encrypted billing information as discussed below.
FIG. 2 is a detailed hardware block diagram of broadcast center 150 of FIG.
1. As shown in FIG. 2, broadcast center 150 is preferably a general
purpose computer including a CPU 202 and a memory 204. CPU 202 can be any
type of known CPU that is capable of performing the functions described
below in connection with broadcast center 150. Similarly, memory 204 is a
generally known type of memory capable of holding information, such as
RAM, ROM, a floppy disk, a hard disk, etc.
Memory 204 includes a software program that is executed by CPU 202 to
perform functions F1, F2, F3, and F4, as described in connection with the
table below. Memory 204 also includes a plurality of documents capable of
being sent to ones of the receiving stations over communication link 140.
Memory 204 also includes information about all documents available to be
sent by broadcast center 150, such as document name, document length,
origin of the document, ownership of the document, schedule on which the
document is to be transmitted (e.g., periodically, or at a predetermined
time or date), cost to a user of receiving the document, access control
information indicating which receivers are authorized to receive the
document, etc. The specific data and the format of the data stored in
memory 204 may vary without departing from the spirit and scope of the
invention. Memory 204 also includes a set of key seeds to be sent to
security engine 130 of receiving computer 110, as described below.
FIG. 3 is a detailed hardware block diagram of security engine 130 of FIG.
1. As shown in FIG. 3, security engine 130 is preferably a general purpose
computer including a CPU 302 and a memory 304. CPU 302 can be any type of
known CPU that is capable of performing the functions described below in
connection with security engine 130. Similarly, memory 304 is a generally
known type of memory capable of holding information, such as RAM, ROM, a
floppy disk, a hard disk, etc.
Security engine 130 preferably is a physically secure computer. Thus, it is
physically locked or otherwise rendered physically inaccessible to
unauthorized persons and its memory is not accessible to other computers
or CPUs. Ensuring that security engine 130 is physically secure ensures
that people only receive documents they will be billed for because the
master key used to decrypt key sets and the key sets themselves are
physically secure. A smart card is an example of such a security engine.
Dallas Semiconductor "DS2252T Secure Micro Stik" is another. In one
implementation of the invention, to reduce cost, link 144 is omitted and
billing information is sent to broadcasting center 150 by way of receiving
computer 110. In yet another implementation, the security engine may be
integrated with the receiver to reduce cost and to maintain the secrecy of
the keys.
Memory 304 includes a software program that is executed by CPU 302 to
perform functions F10, F11, and F12 described in connection with the table
below. A preferred embodiment of the present invention uses software based
encryption because the amount of data to be encrypted and decrypted by the
security engine is relatively small and relatively slow encryption and
decryption is acceptable. In contrast, broadcast receiver 120 preferably
implements a decryption algorithm in hardware using a symmetrical encoding
scheme, such as the Data Encryption Standard (DES) Electronic Codebook
implemented under Federal Standard 10-26, as shown in Telecommunications:
Compatibility Requirements for Use of Data Encryption Standards, published
Dec. 11, 1978 by the General Services Administration.
Memory 304 also includes an engine ID (a code uniquely identifying the
security engine), an engine master key (for decrypting the account status
information received from broadcast center 150 and for encrypting billing
information and checksum to be sent to broadcast center 150), document ID
data identifying a document requested by the user from the catalog
(received as part of a load request), key seeds for generating keys to
decode the documents listed in the catalog, account information received
from broadcast center 150, billing information for documents received
since billing information was most recently received from broadcast center
150, and a credit limit received from broadcast center 150. The specific
data and the format of the data stored in memory 304 may vary without
departing from the spirit and scope of the invention.
FIG. 4 is a detailed hardware block diagram of receiving computer 110 of
FIG. 1. As shown in FIG. 4, receiving computer 110 is preferably a general
purpose computer including a CPU 402 and a memory 404. CPU 402 can be any
type of known CPU that is capable of performing the functions described
below in connection with receiving computer 110. Similarly, memory 404 is
a generally known type of memory capable of holding information, such as
RAM, ROM, a floppy disk, a hard disk, etc.
Memory 404 includes a plurality of software programs that are executed by
CPU 402 to perform functions F7, F8, F9, F13, and F14 described in
connection with the table below. As can be seen from FIG. 1, receiving
computer 110 includes both file broadcast receiver 112 and file browser
114. Both file broadcast receiver 112 and file browser 114 preferably are
implemented as a plurality of software programs stored in memory 404 that
are executed by CPU 402. As also shown in FIG. 1, file broadcast receiver
112 performs all interfacing to the "outside world" that is performed by
receiving computer 110. File browser 114 only receives data from and sends
data to file broadcast receiver 112 (although browser 114 also receives
data from users during times when users are designating documents from the
catalog).
Memory 404 also stores received documents and catalog data (including the
document name, the document length, the origin of the document, the
ownership of the document, the schedule on which the document is to be
transmitted, e.g., periodically, or at a predetermined time or date, the
cost to a user of receiving the document, a description of the document
sufficient to allow a user to determine whether he desires the document,
etc.). Memory 404 also stores a list of "documents of interest" which are
the names of the documents designated by users browsing the catalog, and
the account status (whether there is any credit remaining) of the
receiving computer's account. The specific data and the format of the data
stored in memory 204 may vary without departing from the spirit and scope
of the invention.
The following paragraphs present an overview of the operation of the
present invention with reference to the timing chart of FIG. 5. At a
predetermined time interval, broadcast center 150 broadcasts the catalog
"in the clear," i.e., in unencrypted form, to the plurality of receiving
computers including receiving computer 110 using multicast addressing. The
catalog preferably is broadcast in packet format. The described embodiment
sends all packets in accordance with the IEEE 802.2 data communication
standard. Broadcast receiver 120 receives the catalog and passes it to
receiving computer 110. In receiving computer 110, the catalog is stored
in memory 404, e.g., a hard disk. When a user, using file browser 114,
designates a document from the catalog, broadcast file receiver 112 stores
a document ID, e.g., a number or an unambiguous document name, in the list
of "documents of interest" in memory 404.
Broadcast center 150 then proceeds to broadcast the documents listed in the
catalog using multicast addressing. For each document, broadcast center
150 first multicasts an announcement message identifying the document to
be sent next. The announcement message also includes a key seed ID
identifying the key seed needed to decrypt the document. The announcement
message is received and decrypted by broadcast receiver 120 and passed to
file broadcast receiver 112. If the announced document is on the list of
documents of interest, file broadcast receiver 112 sends a load request
including the key seed ID to security engine 130. Security engine 130
determines if the user has sufficient credit and authorization to receive
the document. If so, security engine 130 sends the key (obtained in
accordance with the key seed ID) for the document to broadcast receiver
120.
After broadcast center 150 sends the announcement message for a document,
it prepares to send the document itself. The document is packetized,
encrypted, and broadcast over communications link 140. As broadcast
receiver 120 receives each encrypted packet, it determines whether it is a
packet for which broadcast receiver 120 has a key. Each document sent from
broadcast center 150 is decrypted with a different key. If broadcast
receiver 120 has received a correct key from security engine 130, it
decrypts the packet and passes it to file broadcast receiver 112, where
the packets of the received document are assembled in their correct order
and stored in memory 404, e.g., on a hard disk. File broadcast receiver
112 then informs the user that the requested file has been received. In a
preferred embodiment, all encryption is done using a symmetrical encoding
scheme, such as the Data Encryption Standard (DES) method. Other
embodiments may use a private key scheme for non-document data, e.g.,
billing information and key sets, sent between the broadcast center and
the receiving station.
Another type of data transmitted by broadcast center 150 is account
information. Account information is transmitted "in the clear," i.e., in
unencrypted form, at least to the extent that broadcast receiver 120 does
not decrypt it. The account information is passed through file broadcast
receiver 112 and is passed to security engine 130 as account information.
Security engine 130 decrypts the account information using a master key
stored in memory 304. The account information includes key, seed, credit
limit, etc. Since the account data is encrypted in a way that only the
security engine 130 can decrypt, there is no need for the data to be
further encrypted for transmission to the broadcast receiver 120. This
allows for easier transmission of account information (the broadcast
receiver 120 does not require a key to receive the account information)
without compromising the security of the information (the data is still
encrypted in a way that only the security engine 130 can decrypt).
Periodically, e.g., once a month, security engine 130 encrypts its billing
information concerning documents received by receiving computer 110 during
the past month and sends the encrypted billing information to broadcast
center 150. This encryption is performed using a master key of broadcast
center 150 that is stored in memory 304. This information may be encrypted
using a symmetrical encryption method, such as DES or a private key
method. Broadcast center 150 decrypts the received billing information
using the master key and uses the decrypted information to send yet
another updated account status to receiving computer 110.
The following table provides a list of the functions performed by the
electronic document distribution system, according to which particular
subsystem performs the function. These functions will be described in the
following paragraphs, with reference to FIGS. 1-5.
______________________________________
FUNCTIONS PERFORMED BY
ELECTRONIC DOCUMENT DISTRIBUTION SYSTEM
SUB-SYSTEM FUNCTION
______________________________________
BROADCAST Send catalog (non-encrypted)
(F1)
CENTER
Receive and decrypt billing
(F2)
information
Periodically send account status
(F3)
(non-encrypted) and key seeds
(encrypted)
Send announcement message, and
(F4)
packetize, encrypt, and send
document
BROADCAST Receive and store key from
(F5)
RECEIVER security engine
Receive packet and decrypt
(F6)
it if key is correct
FILE BROADCAST Receive announcement message
(F7)
RECEIVER and load request
Receive document request and
(F8)
store document ID on list of
documents of interest
Receive and process decrypted
(F9)
packet from broadcast receiver
SECURITY Receive accounting statistics
(F10)
ENGINE and key seeds and store them
in memory
Periodically send billing
(F11)
information to broadcast
center (encrypted)
Receive and process load request
(F12)
from file broadcast receiver
CATALOG Receive and store new catalog
(F13)
BROWSER
Display catalog and process
(F14)
document requests
______________________________________
Functions F1, F2, F3, and F4 are performed by the broadcast center 150 of
FIG. 2. In executing function F1, broadcast center 150 broadcasts to all
potential receiving computers a catalog listing all documents to be sent
during an upcoming predetermined time period, e.g., over the next week.
The catalog is sent "in the clear," i.e., unencrypted, because none of the
receivers are charged a fee to receive the catalog and there is no reason
to limit access to the catalog.
In executing function F2, broadcast center 150 receives encrypted billing
information from security engine 130. Broadcast center 150 receives
similar billing information from each receiving computer on the network.
The billing information details which documents were received during | | |
