KR20030048464A - Data scrambling system for a shared transmission media - Google Patents

Abstract

The present invention is directed to a method for providing additional security for communication between a server 36 and a particular client modem 70 on a shared communication medium 50. The method is then passed over a communication comprising the scrambled key to be used to form a scrambling seed for scrambling subsequent messages. In a preferred embodiment, server 36 and client modem 70 generate and hand over a key to be used for communication between server 36 and client modem 70 to implement a dynamic dual key scrambling system.

Description

DATA SCRAMBLING SYSTEM FOR A SHARED TRANSMISSION MEDIA}

[CROSS REFERENCE TO RELATED APPLICATION]

This application claims priority to provisional applications filed November 8, 2000, US Application No. 60 / 246,684. This application extends the concepts described in the related application assigned to the general assignee "coaXmedia". The application (hereinafter referred to as "'845 application") is PCT / US01 / 09845 and entitled "Architecture and Method for Automatic Distributed Gain Control for Modem Communication over Passive Multipoint Networks." for Modem Communications Over Passive Multipoint Networks, "published on WO 11/76142 on October 11, 2001.

The related application by general assignee "coaXmedia" is U.S. Application No. 09 / 908,754, which discloses "Telephony, latency sensitive data, best effort data and Priority Packet Transmission System For Telephony, Latency Sensitive Data, Best Efforts Data and Video Streams in a Shared Transmission Media Such as Passive Coax Distribution, "US, filed July 21, 2000. Based on provisional application No. 60 / 219,886.

This application shows an improvement over the already filed application. Therefore, there is a contradiction between the preceding application and the content and drawings of the present application, and of course the content of the present application is superior.

For the convenience of the reader, various abbreviations and other terms used in the present invention are defined at the end of the contents as glossaries. Other terms used by the present application to define the operation of the inventive system are defined throughout the specification. For the convenience of the reader, Applicants add a number of subject headings to clarify the internal structure of the present specification and to assist in locating specific discussions. These subject headings are for convenience only and are not intended to be limited to the statements in that particular subject.

For clarity, the terminology for components is used. The use of specific terms for a component that is suitable for the purpose of carrying out any object within the disclosed invention is to be construed as including all technical equivalents used to achieve the same purpose, whether the internal working principle of the named component or other component is the same. It doesn't matter. Unless expressly limited by the following detailed description or claims, limitations for clarity as described above should not be misinterpreted as limiting the scope of the specification to named components.

The present invention relates to data communication. More specifically, the present invention addresses the use of branch coaxdistribution systems and trees for upstream and downstream data communications between a hub-server and two or more client modem sets. One of the things that continues to improve in the field of data communications. Preferably, the client modems should allow for a plug and play connection or other easy connection between a laptop and a tree and branch network. The tree branch network is preferably connected to the Internet. Thus, the present invention can be used for plug and play access to the Internet through existing coaxial television networks in hotels or multiple dwelling units (MDUs) or similar buildings.

The '845 application describes a system that allows devices such as personal computers to be connected to a special modem connected to an existing tree-branch coaxial network in a hotel, MDU or similar building. The system uses a frequency range bandwidth in one of two ranges outside the range used for cable TV. Thus, the system will have a frequency range for the downstream channel and a frequency range for the upstream channel. Since this is a tree-branched network, all communications going downstream must identify which modem device is being addressed, since all modems receive information through the communication. On the other hand, communication from many individual modems to the upstream end of the network must be controlled so that only one modem device can transmit upstream data at some point to avoid bus contention. The control method used in the reference application is based on a polling and response model.

The situation addressed by the '845 application and the present invention is outlined in FIG. 1 can be further divided into four clusters of components. The first cluster is the head end equipment 10 of the cable TV. The second cluster is a hybrid fiber-coax (HFC) distribution network 20. The third cluster is the premises coaxial distribution equipment 30 and it may exist in a similar state such as an MDU or a hotel. The final cluster is the equipment cluster 40 in the user's room. Clusters 30 and 40 contain the components of the present invention. In accordance with industry practice, cable TV headends and the Internet are located at the upstream end of FIG. 1 for cable TV and IP data, respectively. The TV set or computer in the user's room is a downstream point. The upstream data transmission goes up towards the upstream end and the downstream data transmission goes down towards the downstream end. Thus, the component on the data path receives downstream data transmissions from the upstream end and upstream data transmissions from the downstream end.

The cable TV head-end equipment 10 has been described in the referenced '845 application and need not be repeated here. In general, the cable TV signal is provided to the HFC distribution network 20. Digital communication signals from the Internet 15 travel through the cable TV headend equipment 10 to the HFC distribution network 20. The components selected at the cable TV headend are examples for the invention only and do not have any limitations or mandatory components.

In the cluster 30, the signal coming from the HFC distribution network 20 is carried on the cable 31 to the splicer device 32. The junction device 32 is connected to the input of a TV channel amplifier 33. The output of the TV channel amplifier 33 is passed to the second splicer device 34 and then to one or more splicer devices. Techniques for tree-branch networks suitable for distributing cable TV signals of one or more splicer devices forming a tree-branch distribution network 50 ending in a series of TV coax receptacles (not shown) are described in the above description. It is well known to those skilled in the art. Thus, in order to avoid unnecessary congestion, the tree branch network 50 has only been shown with a few junction devices and connecting cables, and is not a full set of components for the tree branch network.

The junction devices 32 and 34 form a bypass around the TV channel amplifier 33. The bypass loop has a cable modem 35 at the upstream end and a data hub 36 (also called a "hub" or "server") at the downstream end of the bypass loop. As described above in the '845 application, server 36 is comprised of a number of components, such as RF modem 37, protocol converter 38, and NIC unit 39. The operation of the component is described in the '845 application and need not be repeated here. Coaxial tree-branch network 50 connects head-end 42 of the tree-branch network to a set of splitter devices.

Some sets of splitting devices are shown as dividers 52, 54, and 56 in FIG. 1. The signal from headend 42 is thus present at the input to client modem devices 60, 62, 64, 66, 68, and 70. The output jacks on the client modem device are devices such as personal computers 72, 81, 87 and 92, telephones 74, 77, 78, 82, 85 and 88 and televisions 71, 75, 80, 84, 86 and 90) are allowed. Note that two phones 77 and 78 are connected to modem device 64. The two phones are each connected to their own phone port. Since the cable TV signal does not need to be processed within the modem device, the signal may be taken from an external diplexer located upstream of the modem device rather than from an output on the modem device. Note that components 94 and 96 will be discussed below.

The '845 application includes an RF coaxial transmission system, where the information flowing from all the downstream [“42” to client modem devices 60, 62, 64, 66, 68 and 70] is DVB / MPEG-2. Formatted according to the structure to facilitate the use of multimedia applications.

To help illustrate the concept of the present invention, the preferred format used for downstream and upstream transmission in a particular " coaXmedia " system is shown in FIG. The details of the data structure are included in the examples, which do not represent an essential form of the invention.

The downstream transmission frame 100 is a 204-byte MPEG / DVB frame. The downstream transmission frame 100 appears after the SYNC byte 104 (of 47 hex and B8 hex values for frame or packet start-up confirmation (e.g., 47 hex for multi-frame confirmation)). 2 bytes 108 used by MPEG2 for packet identification (" PID "), followed by an additional byte 112 and 16 bytes of FEC field 120 preserved for packet type identification of the 184 byte payload that follows. It is composed of The SYNC byte 104 appears in the next frame of the FEC field 120.

Any downstream data (IP, voice, video, etc.) may be located in one or more data subpackets 130. One or more data subpackets are carried in the MPEG frame payload 116. The detailed configuration of the data subpackets is not important in the present invention, but the data subpackets generally consist of a subpacket header 134 and a subpacket payload 136. The sub packet header contains a target and addresses of various control fields. The address used for the target may be the MAC address of the client modem, a portion of the MAC address, an alias for the client modem, a broadcast group address, or some other form of address, whereby the client modem may have some subpackets sent to the client modem. It can recognize whether it is addressed. The subpacket payload includes a CRC value 140 added to the end of the data 138 within the subpacket payload 136.

Upstream data frame 150 consists of an 8-byte preamble 152, a SYNC byte 154, and a data packet 160. The details of the data packet are not critical but can be usefully divided into a data packet header 166 and a data packet payload 168. The data packet payload 168 has various lengths and includes a CRC value 170. 1 includes an idle period 180.

The upstream data header 166 includes control fields for communicating the lengths of the various payloads with each other and confirming the type of transmission. The particular system used by " coaXmedia " uses a polling scheme, so that client modems 60, 62, 64, 66, 68, and 70 use time slots for using upstream channels for communication with server 36. (time slot) is guaranteed. Thus, in this system, there is no need to identify the upstream communication source and source address. In other systems that use conflict detection and correction to share the upstream channel, the upstream data header 166 is likely to include a source address.

Upstream and downstream data flows occur simultaneously, and both transmit data using a single frequency. For example, downstream communication from the server to the client modem may be present in the first frequency channel with upstream data carried on the second frequency channel. Thus, a client modem listening to the first channel and making a call on the second channel cannot decrypt a message sent by another client modem because it is not equipped to decrypt the message on the second channel.

Although the client modem intended for use in the system is not capable of listening to the upstream channel and is designed to only listen to downstream messages addressed to a particular client modem, the buyer prefers an additional level of security to protect data communications. The additional protection may be achieved despite attempts by unauthorized parties using unauthorized equipment that modifies the client modem to listen to downstream traffic that is not addressed to the client modem or attempts to eavesdrop on upstream or downstream traffic. It will make the communication more secure. To illustrate the problem, FIG. 1 includes an unauthenticated device 94 connected to the tree-branch network 50 between the divider 54 and the authenticated client modem 70.

The actual location of the connection is not critical to the invention. The main concern is that any connection to the tree branch network accesses all downstream communications to all connected computers 72, 81, 87 and 92. Fortunately, tree-branched networks operate against eavesdropping over the full range of upstream communications. Even if an unauthorized device 94 attempts to listen for upstream communications from the client modem to the server 36 on the upstream channel, eavesdropping will be difficult as a general technique since the tree branch network will attenuate the upstream signal on parallel branches. The amount of attenuation increases with the number of divider devices that must be located between the transmitting client modem and the unauthorized device 94. Thus, the unauthorized device 94 may be able to receive a strong signal on the upstream channel from the communication originating at the client modem 70, but the communication on the upstream channel from the client modem 66 will be attenuated. Communication on the upstream channel from the client modem 64 will be more attenuated because the client modem is separated by two splitter devices 52 and 54 from the unauthorized device 94. .

The '845 application recognized that the user would prefer a system with additional security. The '845 application addressed this desire by suggesting that other client modems use different randomization sequences for DVBspectral shaping. Variations between the randomization sequences used by the various client modems will add complexity to someone attempting to eavesdrop on communications. The '845 application contains the teaching that the sequence starting point for each client modem and each direction may vary. Information communications initiating DVB spectral shaping are transmitted under communications security, including encrypted sessions with public keys / private keys or other means known to those skilled in the art.

Implementing the method proposed in the '845 application will make it difficult to use a mass produced DVB randomizer that does not allow individualization of DVB sequences or DVB start points. In order to implement a secure connection using conventional techniques such as public key / private key encryption, it is necessary for the client modem to have the additional capability to support the simply encrypted session. Encrypted sessions passing the information needed to individualize DVB randomization will cause a delay on the processor adding the client modem to the network. As a result, once a client modem is added to the network, the '845 application does not pass new changes or new sequence start points to the randomization sequence. Thus, for a particular client modem, the DVB randomization process continues along the set sequence after receiving the initial randomization sequence and / or sequence start point.

It is an object of the present invention to provide additional security for carrying upstream and downstream data between a client and a server.

Another object of the present invention is to make it very difficult for an eavesdropper to access information on an upstream channel in order to eavesdrop on the downstream channel, thereby obtaining access to downstream data.

Yet another object of the present invention is to make it more difficult to obtain access to downstream data without much addition to the hardware required by the client modem.

1 is a schematic diagram in the form of a network for a system using the present invention comprising a tree-branch network connected to a series of client modem devices, wherein the client modem device is connected to a combination of a television and a device such as a personal computer and a telephone; has exist.

2 is a schematic diagram illustrating downstream and upstream transport formats used herein to describe certain embodiments of the present invention.

3 is a conceptual diagram illustrating a process of scrambling and unscrambling a portion of a binary message.

4 is a conceptual diagram illustrating various logical components included in the sequence of events arranged in Table A. FIG.

The present invention presents various methods for providing additional security for communication on a shared transmission medium. More specifically, the present invention provides a method of using a scrambling seed based on a key that is preferably handed over in a scrambled communication. The preferred embodiment of the present invention provides one new key for each upstream transmission from the client modem, and one new key for each downstream transmission to the client modem, thereby allowing each transmission between the client modem and the server. Provide two scrambling seeds based on the key.

The present application teaches how to initiate a process of handing over a key under a personalized but static seed and a change addressing a request to send a multicast message under a personalized but static regime.

The method and other embodiments provide a necessary solution to the desire to improve communication security on shared media.

The above and other advantages of the present invention will become apparent from the following drawings and detailed description.

Prior to adding the present invention, a typical operation for a network such as that shown in FIG. 1 is for the server 36 to transmit downstream data, which may include client modems 60, 62, 64, 66, 68 or 70) randomization for spectral shaping (DVB disturbance) is performed. DVB randomization is often called DVB scrambling. Unlike the alternative method of DVB randomization proposed in the referenced '845 application, conventional DVB randomization is not scrambling in that it is intended to improve security. Conventional DVB randomization is performed through standard processes to enhance data transmission making it easier to receive transmitted information without transmission errors. Thus, if the unauthenticated device 94 has chosen to capture downstream transmissions for a session in communication with the device 72 addressed to the client modem 60, the communication may result in the unauthenticated device ( Can be read by device 96 after 94 transfers the downstream transmission to data communication via a standard DVB sequence that switches spectral shaping DVB randomization (currently the MPEG / DVB protocol excludes the FEC field from DVB randomization). Note). In order to avoid confusion in the specification and claims that follow, all references to scrambling refer to scrambling for the purpose of adding security rather than DVB randomization.

The conventional DVB randomization process is part of the transmission process and is described herein as part of the context for the present invention. The present invention does not require DVB randomization. As described below, the present invention can be combined with an alternative DVB randomization method proposed in the '845 application to provide an additional layer of security.

In order to add additional protection to prevent unauthorized devices from acquiring unscrambled communications, the improved method requires that both upstream and downstream data be scrambled for security. While the preferred embodiment adds two scrambling / unscrambling levels for the selected communication portion, the specification shows how to add only one additional scrambling / unscrambling level. You can make simple changes to add additional scrambling / unscrambling behavior.

As described above, the sub packet 130 transmitted downstream includes a sub packet payload including a data sub packet header 134 and a sub packet data 138 and a sub packet CRC field 140 as necessary. 136). The downstream "coaXmedia" header consists of the destination device address and several control fields.

The purpose of the scrambling is to protect the sub packet data 138. Thus, the bit receives scrambling for security purposes. CRC field 140 also receives the scrambling so that more complex effort is required when eavesdropping downstream communications. In a very preferred embodiment of the present invention, certain control fields of the subpacket header also receive scrambling.

Similarly, the upstream message will be sent with the scrambled data packet payload 168. In a very preferred embodiment, some or all of the data packet headers 166 will also be scrambled. Scrambling certain or all headers adds another obstacle to those attempting to eavesdrop on the transmission, since the length of the variable length payload is scrambled. In a commercial embodiment of the "coaXmedia" system, the upstream transmission has padding to achieve a minimum transmission length. Thus, the lack of an unscrambled length indicator makes it difficult to distinguish between the end of data and the start of padding.

Pseudo Random Binary Sequence (PRBS) constructor is used to scramble data at the sender and unscramble data at the receiver. One suitable constructor is known to the person skilled in the art, a linear feedback shift register. The PRBS generator performs a series of manipulations on individual bits or sets of bits in the seed value, starting with the seed value. This process then provides a repeatable sequence of mock random numbers. A well designed linear feedback shift register will have a sequence of numbers equal to N squared of two if N is the size of the shift register. A typical use case of a feedback shift register for scrambling bits is to provide a seed value to the feedback shift register and to cause the feedback shift register to perform manipulations of the register contents to move to the next number in the sequence. The specific bit from the feedback shift register is used in an exclusive OR operation with the first bit being scrambled. The output of the exclusive OR operation will replace the scrambled bits. Therefore, the output scrambled according to the shift register bit value may be the same as the value in the unscrambled bit or inverted. The feedback shift register performs manipulation of register contents and performs an exclusive OR operation on the next bit that is scrambled. At the receiving end, the process can be repeated. If the corresponding feedback shift register and equivalent seed are used, the scrambled message is subjected to the same pattern of inversion and non-inversion on the individual bits, so that the message received after unscrambled is the same as the message sent before it was scrambled. .

Thus, as shown in FIG. 3, a portion of the unscrambled message 204 is subjected to a bit-by-bit exclusive OR operation 206 along with the bit sequence 208 generated by the feedback shift register. The resulting sequence of scrambled bits is transmitted as part of the scrambled message 212. After receiving the same seed as used at the transmit end, a feedback shift register that performs the same internal operation on the same number of iterations will generate a bit sequence 216 at the receive end. Performing the bit-by-bit exclusive OR operation 206 with the received scrambled message is repeated to generate a received unscrambled message 220 that matches the unscrambled transmitted message 204.

One of the problems overcome by the present invention is a scrambling seed (initial content) that can be used in the PRBS producer without allowing other client modems and unauthorized devices 94 to access the seed, and both ends of the link. It is necessary to synchronize (client modem and server). Often, the actual seed is not passed, except for the key used to generate the seed. Thus, in the following specification and claims, the seed is the actual value supplied to the scrambling device and is a function of the key (including the case where the seed is the same as the key). The key must remain confidential to protect the scrambled data and must be handed over between the client modem and the server so that each of them can scramble the incoming scrambled communication.

The solution to synchronizing both ends is to screen each client modem with its own key and give the upstream channel's server the ability to pass the key. The upstream channel (client modem to server) is in a different frequency band than the downstream channel and cannot be received by any other client modem. Thus, the fact that a client modem cannot receive any upstream RF channel prevents one client modem from eavesdropping on the upstream messages and keys of another client modem. As mentioned above, the use of an upstream channel adds technical difficulties to any attempt to eavesdrop downstream data transmissions, even if there is unauthorized listening on the upstream channel. These problems include the need to decode upstream transmissions to eavesdrop on attenuation and downstream transmissions that exist in attempts to listen to remote branches.

The sequence of events for the preferred embodiment is as described below. Table A provides a summary of the sequence steps (Table A is located after the glossary and before the claims). 4 shows the relationship between logical components of a system performing various steps. Since one or more logical functions may be performed by one physical device, the actual physical layout may differ from FIG. 4. To shorten the length of the names of the various components, US stands for upstream and DS stands for downstream. 4 does not include other functions performed in server 36 or client modem 70 that are not relevant to the discussion of the present invention.

In power-up, certain default seed words can be used for both upstream and downstream scramblers. In a preferred embodiment, the seed is based on the MAC ID for each client modem, but other values may be used to generate the seed if the value is known to the client modem and server. The overall MAC ID may be used within the scope of the present invention, but shorter seeds based on the MAC ID are more likely to be used. Since the seed is based on the MAC ID, this would mean that each client has a single scrambling sequence at power-up. The MAC ID for each client modem is known to the server by entering the MAC ID with a keyboard connected to the server when the client modem is added as an authenticated device. A more creative method of identifying the MAC ID of a newly discovered client modem is described in co-pending application [US Application No. 60 / 309,809; A method for Efficiency Dectecting and Polling Downstream Modems in a Shared Transmission Media Such as Passive Coax Distribution on a Tree and Branch Network).

In step 410, a frame comprising one or more subpackets intended to be sent to one or more client modems arrives in the DS data buffer 508. The subpacket receives the CRC value 140 calculated by the CRC calculator 510 based on a portion of the subpacket. The CRC value is one of the well known ways of providing a transmission check word. The transfer check word is used to detect whether the transfer process changes the communication. Ideally, all modified communications should be detected and discarded. By calculating the transfer check word and transmitting it in a transfer, one can check the integrity of the transfer process by calculating the transfer check word on the relevant portion of the received communication and checking this value against the transmitted value of the transfer check word. .

One known method of generating a CRC value is to treat the message as a long binary word, divide the word by a fixed number and send the remainder as the CRC value. Other methods of generating a CRC value can be used as long as both the client modem and the server generate or check the CRC value using the same algorithm. As mentioned above, the CRC value is transmitted as a means for detecting errors in the transmission process. CRC calculation is performed on the received data and the data is discarded if the CRC value for the received data does not match the transmitted CRC value.

Continuing at step 410, after the server 36 has the MAC address of the target client modem (step '400'), the seed may be sent from the key generator 516 to the DS layer 2 scrambling block 520. . The outgoing downstream message is scrambled based on the seed supplied to the feedback shift register, where the seed is a known change in the client modem MAC address. Thus, the message sent to the client modem will receive first level scrambling using the seed based on the MAC ID. As described above, some of the scrambled subpackets may be the subpacket payload 136 or the payload added to a certain control field of the subpacket header 134. Fortunately, one field of subpacket header 134 can be used to indicate that the message is using a seed based on the MAC ID as the scrambling seed. If this option is selected, the portion of the sub packet header 134 should not receive scrambling, so that the field can be read before any attempt to unscramble the scrambling level. As an alternative to the unscrambled field, noting the use of a seed based on MAC ID, the client modem does not have a different seed value or the last received seed value does not provide an unscrambled message that matches the transmitted CRC code. In this case, the seed used based on the MAC ID may be the default seed used to unscramble the message.

In a preferred embodiment of the present invention, the process is repeated at DS level 1 scrambling 524. Again, the seed is based on the MAC ID for the destination client modem, and the information is passed from the key generator 516 to block 524. In a preferred embodiment, the second set of scrambling based on the MAC ID will not be the same as the first set of scrambling (otherwise the first set will be restored). By using another method of calculating the seed based on the destination client modem MAC ID, one can make a difference in scrambling. Alternatively, the difference in scrambling may be implemented by placing a difference in the operation of the two feedback shift registers or by both the pitback shift register and the way the seed is calculated. If desired, the system may initially operate with one level scrambling at block 520 or 524.

DS DVB randomization block 528 is added to the conventional DVB randomization for spectral shaping. The message is modulated and sent to the client modem on the downstream channel.

In step 414, all client modems receive the message and switch RF modulation. Next, each client modem removes the DVB randomization indicated by block 632. In the preferred embodiment, the client modem reads a field in the header of the subpacket indicating that the client modem should use the MAC ID as the basis for the two seeds to scramble the scrambled information. In a preferred embodiment, unscrambling is performed sequentially in the DS layer 1 scrambling block 636 and the DS layer 2 scrambling block 640. The CRC value is calculated at CRC verification 614. If the CRC of the unscrambled subpacket calculated at block 614 of the client modem matches the CRC value passed from block 510, the message at DS data buffer 608 is still held and used. If not, the message is discarded. The client formulates its response (such as a response that there is no data to send or initiates the process of sending data from the client modem). The response is generated and placed in a frame located in US data buffer 612.

In step 420, CRC value 170 is calculated in CRC Calc block 610 and added to the upstream packet. The CRC value is passed to the seed / key generator 616 for use in the future at steps 434 and 440. The client modem first performs scrambling in US Layer 2 scrambling 620 and again uses the seed based on the MAC modem of the client modem in US Layer 1 scrambling 624. As mentioned above, the two scrambling operations may use other methods of calculating the seed based on the MAC ID, and manipulate the seed differently in the feedback shift register, or both.

In one possible embodiment, part of the upstream data packet header 166 receives scrambling and the unscrambled field will inform the server whether the upstream transmission is using scrambling based on MAC ID. However, the use of these fields is not necessary in the above preferred embodiment because the server interprets the response in the client modem as the next logical step in the initialization sequence and operates properly. In the preferred embodiment, the server only starts a new attempt to connect with the client modem. Thus, only the client modem should identify which communication is the continuation or restart of the previous sequence of communication.

US DVB randomization is added to block 632 and the frame is transmitted with RF modulation on the upstream channel.

In step 424, the server receives the frame and modulates it. The US DVB randomization is removed at block 532. The US layer 1 scrambling is removed with a seed based on the MAC ID of the client modem at block 536.

The second round of unscrambling occurs at block 540. Again, a seed based on the MAC ID of the client modem is used. The transmitted CRC code 170 is checked against a calculated CRC code based on the received data packet of the CRC verification block 514. If the CRC code is matched, the data packet is accepted and the CRC code is sent to the key generator 516 to continue to be used as the key for the seed value. If the CRC code does not match, the received data packet is discarded.

In step 430, the process of transmitting downstream subpackets is repeated. The random number generated by the key generator 516 is added to the data payload of the downstream data subpacket of the CRC Calc block 510 before the CRC value 140 is recalculated in the CRC Calc block 510. An initial level of scrambling based on the MAC ID occurs at DS layer 2 scrambling block 520. DS layer1 scrambling is added at block 524 using a seed based on the most recent CRC code from the last upstream data packet received from the destination client.

In step 434, the process of receiving downstream subpackets is repeated at each client modem. After DS DVB randomization is removed at block 632, DS layer 1 scrambling is removed at block 636 using a seed based on the final CRC code for the final upstream transmission from the client modem. In a preferred embodiment, the client modem reads an unscrambled field of the downstream data subpacket indicating that the downstream subpacket is scrambled in combination with a seed based on the CRC code and a seed based on the MAC ID. The field value tells the client modem that the final CRC code was correctly received by the server and that the final upstream CRC code 170 should be used as the key for the seed to scramble the next upstream message, which in turn passes the new CRC value.

Seed based scrambling based on the MAC ID is removed in the DS layer 2 scrambling block 640. The unscrambled data subpacket is used to generate another CRC value at CRC verification block 614. For all but one client modem, this arrives at an unscrambled data packet with the correct downstream CRC code 170 that matches the CRC code generated for the received data and a downstream address associated with the client modem. I will not. The destination client modem will correctly unscramble the data subpackets and find that both the CRC code and address are good. CRC verification block 614 then passes the received random number to key generator 616.

Step 440 repeats the process of transmitting the data packet upstream. The new CRC code 170 is generated in the CRC Calc block 610 and located in the upstream data packet 160. The upstream data packet is scrambled with the seed based on the random numeric key received in the last downstream transmission in US Layer 2 scrambling block 620. The scrambled data packet is scrambled again in US layer 1 scrambling block 624 using a seed based on a CRC code from a previous upstream data packet. US DVB randomization is added to block 628.

Step 444 repeats the process of receiving an upstream transmission. After US DVB randomization is removed at block 532, US layer 1 scrambling is removed at block 536 with a seed based on the CRC code of the previous upstream transmission from the particular client modem. After US layer 1 scrambling is removed, US layer 2 scrambling is removed at block 540 with a seed based on a random numeric key passed with the final downstream transmission to the particular client modem.

As described above, for the CRC code calculated based on the data packet received in CRC verification block 514, the transmitted CRC code 170 is checked. If the CRC code is matched, the data packet is accepted and the CRC code is sent to the key generator 516 to be used for subsequent seed values. If the CRC code does not match, the received data packet is discarded.

Step 450 repeats the process of transmitting subpackets downstream. A new random number is generated at the seed / key generator 516 and passed to the CRC Calc block 510 so that the data portion of each downstream subpacket before the CRC value 140 is calculated and added to the downstream subpacket 130. Is inserted. The random number is stored in key generator 516 for use in unscrambled the next upstream transmission from this particular client modem. DS layer 2 scrambling occurs at block 520 using a seed based on a random number previously sent to the destination client modem. DS layer1 scrambling occurs at block 524 using a seed based on the most recent CRC code from the final upstream transmission from the destination client modem.

Step 454 repeats the process of receiving a downstream transmission. DS layer 1 scrambling is correctly removed from the client modem block 640 through the use of a seed based on the CRC code for the final upstream transmission. DS layer2 scrambling is correctly removed at block 636 through the use of a seed based on previously transmitted random numbers. The new random number sent by the server is taken from the properly unscrambled message in Calc verification block 614 and stored in seed / key generator 616.

In step 460 the process continues with US Layer 1 scrambling based on the most recent upstream CRC code from the particular modem and US Layer 2 scrambling based on the most recent random number sent by the server to the particular client modem. . This process continues until there is an interruption that causes the process to restart with the use of a seed based on the MAC ID.

As will be apparent to those skilled in the art, the server must manage the CRC code and associated random number for each client modem. By modifying the preferred embodiment, a seed based on the manipulation of the key sequence can be obtained. Thus, the key for DS layer1 scrambling may be based on several least significant bits (LSBs) of the sum of the last 6 digits stored CRC value for a particular client modem. Alternatively, a set of CRC values and random numbers can be accumulated for a particular client modem before being exchanged from the seed based on the MAC ID. Accumulation of these values will allow the use of a lag between the transmission or random number of CRC values and their use. These concepts can be mixed, and since DS layer 1 scrambling can use CRC values from the latest second and fourth communications from the client modem, the seed is a function of the most recent second and fourth CRC codes for a particular key. to be. The same kind of operation can be applied to key values generated by the server.

[Restart]

After the server 36 receives the seed from the client modem, a restart will be required if the server later sends a poll message or sends a packet to the client modem and does not receive a response from the client modem. In this situation, the server will soon use the power-up scrambling seed again, in which case the power-up scrambling seed is based on the MAC ID. The downstream data subpacket will have an associated header field indicating that a seed based on the MAC ID is used for the packet, which will instruct the client modem to use the seed based on the MAC ID. Thus, if the downstream message becomes cloudy and the client modem does not respond, the process will simply return to reinitializing the communication using the MAC ID seed. Likewise, if an upstream message becomes cloudy, the server will simply return to reinitializing the communication using the MAC ID seed.

[Prevention of seed value becoming 0]

The preferred embodiment adds a small difference to prevent scrambling from being initialized with all zero seeds (some feedback shift registers do not effectively change all zero seeds). One way to prevent all zero seeds is to create a real scrambler seed that is at least one bit longer than the seed supplied. The extra bit is always set to 1 so that the seed used for scrambling is always initialized to a non-zero number. Using a feedback shift register that changes all zero seeds or using a seed and key generator that does not generate all zero seeds are other ways to avoid the problem of all zero seeds.

[Other Embodiments]

As mentioned above, the new method can be applied to various aspects by those skilled in the art.

The preferred embodiment uses two levels of scrambling. Those skilled in the art can use the means described above to initiate one level of scrambling based on the upstream CRC code as described above and not add a second level of scrambling based on a random number generated at the server.

Alternatively, those skilled in the art can use the random number generated in the server in the next step after scrambling using the seed based on the MAC ID, and use it as one level scrambling.

Those skilled in the art can replace the use of the random CR downstream code generated by the server with two levels of scrambling. Accordingly, the downstream CRC code 170 is passed to the seed / key generator 516 instead of passing the random number from the seed / key generator 516 to the CRC Calc block 510. This has the advantage of saving bandwidth since the CRC code is already in the downstream data and no additional bits need to carry a random number generated by the server. The system may enable the use of downstream CRC codes and random numbers generated by the client modem. Similarly, one of ordinary skill in the art can apply the teachings of the present invention to a system using random numbers generated by a client modem and random numbers generated by a server. The disadvantage of using random numbers is that this increases the overhead that must be passed with the data.

Those skilled in the art can change the order in which scrambling based on CRC and scrambling based on random numbers are applied to each message. The order need not be symmetrical between upstream and downstream processes. Thus, the upstream message is first scrambled by the seed based on the CRC and then scrambled by the seed based on the random number with the downstream message first scrambled by the seed based on the random number, and then scrambled by the seed based on the CRC. do.

In summary, it should be noted that the dual set of seeds for each server for client link communication is single for each client (except for the multicast message described below) and for each packet. Once scrambling based on random numbers is added to scrambling based on upstream CRC codes, the scrambling pattern will change dynamically with every packet.

A variant of the present invention is a method of improving the improved security method disclosed in the referenced '845 application by adjusting the sequence starting point for DVB randomization by handing over the key using the method disclosed above. This can be used in addition to one of the scrambling steps or as an alternative step. This improves the method proposed in the '845 application in that it can provide a dynamic change of the sequence start point for DVB randomization. Using the disclosed method to provide a DVB sequence start point alleviates the need to establish a secure communication session under conventional methods before crossing the sequence start point for DVB randomization. Alternatively (or additionally), the disclosed invention can be used to pass a static key or a set of dynamic keys to select a particular DVB randomization scheme from various possible DVB randomization schemes.

Although the preferred embodiment of the present invention does not combine the proposal of the '845 application that provides additional security through specially modified DVB randomization based on static inputs, the method of the' 845 application uses a dual key double scrambling method as described above. By adding a security layer to the system.

[Multicast message]

Multicast messages are downstream sent in data packets sent to a given set of client modems. This may be all client modems, or one or more sets of one or more. Multicast messages can be used in a variety of applications, such as conferences, where more than one phone needs to receive signals, broadcasting to multiple subscribers, multiplayer games, or other applications. Since the multicast message is generally sent to one or more clients, neither client can return a response to the server or a response message will crash. The data sent downstream must still be scrambled, but the seed word cannot be dynamically selected by the upstream message since the client modem cannot respond to the multicast message.

Instead, the server generates one or more multicast scrambling seeds for a given multicast group, and sends a key or seed for seeding to a client modem that is a member of each multicast group through a special message that is essentially protected by the scrambling technique by scrambling. something to do. To make it more difficult to unscramble messages that do not have a dynamic seed, the system is set to hand over two seeds and thus the multicast message is protected by two levels of scrambling. Thus, transmissions to a multicast group are protected by double scrambling but no dynamic and single packet to packet scrambling occurs.

Systems using multicast messages tend not to scramble some of the addresses of downstream data subpackets. The client modem may scrambling to determine whether to use a regular key for messages from the server to the client modem or a special multicast key for a specific multicast group that generates a seed to unscramble some of the scrambled communications. It is necessary to read an address that is not present.

[Etc]

Those skilled in the art will recognize that the methods and apparatus of the present invention can be applied in many respects and are not limited to the specific embodiments intended to facilitate the understanding of the present invention. In addition, the scope of the invention encompasses the scope of modification, modification and replacement of the system components disclosed herein, as known to those skilled in the art.

The legal limitations of the scope of the claimed invention are set forth in the claims which follow, and extend to their legal equivalents. Those who are not familiar with the legal standards for equivalence should consult with those registered with the US Patent Office or its equivalent, or with the patent authorities granting this patent.

[Glossary]

FEC: Forward Error Correction

IP: Internet Protocol

MPEG: Motion Picture Experts Group: Digital Video Standards

DVB: Digital Video Broadcast

CRC: Cyclic Redundancy Check

PID: Packet Identifier

PRBS: Pseudo Random Binary Sequence

RF: Radio Frequency

US: Upstream or United States

DS: Down Stream

TABLE A

Claims (23)

A method of maintaining additional security for communication between an upstream server and at least two downstream client modems on a shared communication medium through the use of a dynamic key generated by a particular client modem, the method comprising: A. the server receiving scrambled upstream communication from a first client modem; B. The server includes a new key for the first client modem using a transfer seed for the first client modem based on the transfer key for the first client modem received in a previous upstream communication from the first client modem. Unscrambled scrambled portion of upstream communication; C. storing sufficient information for the server to generate a new seed for the first client modem based on the new key for the first client modem based on the unscrambled content of upstream communication; D. the server scrambling at least a portion of the next downstream communication to the second client modem with scrambling based on a seed for the second client modem based on a key for a second client modem, wherein the second client modem The key is independent of the key for the first client modem; E. scrambling, by the server, at least a portion of a next downstream communication to the first client modem with scrambling based on the new seed for the first client modem based on the new key for the first client modem; F. the first client modem receiving a next downstream communication to the first client modem; G. unscrambled scrambled portion of the next downstream communication to the first client modem with a new seed for the first client modem based on the new key for the first client modem; H. generating, by the first client modem, a next upstream communication comprising a next key for the first client modem; I. storing information sufficient for the first client modem to generate a next seed for the first client modem based on a next key for the first client modem; And J. Maintaining security comprising the first client modem scrambling at least a portion of a next upstream communication using the new seed for the first client modem based on a new key previously delivered for the first client modem. Way. 2. The method of claim 1, wherein the new seed for the first client modem is the same as the new key for the first client modem. The method of claim 1, wherein the new key for the first client modem is a transmission check word used to test the accuracy of the upstream transmission, and the new key for the first client modem is transmitted with upstream communication without overloading. . 2. The method of claim 1 wherein the new key for the first client modem is a random number generated by the first client modem and not a transmission check word. The method of claim 1, wherein the scrambled portion of the upstream communication comprises a portion of a data packet header. 6. The method of claim 5, wherein the scrambled portion of the upstream communication comprises a field carrying a length of a data packet of variable length. 2. The method of claim 1, wherein the first client modem is for the first client modem based on the new key for the first client modem only when the field of the next downstream communication lacks a signal to use a default seed based on a default key. Maintaining the scrambled portion of the next downstream communication to the first client modem with the new seed. 8. The method of claim 7, wherein said default key is based on an address of said first client modem. 8. The method of claim 7, wherein a previous key for a first client modem received in a previous upstream communication from the first client modem is transmitted while being scrambled based on the default key. 2. The method of claim 1, further comprising a preliminary step of exchanging communication between the server and the first client modem, wherein the server is sufficient to generate an initial first client modem seed based on an initial first client modem key. The portion of the preliminary communication is scrambled with the default seed until the data is stored. 2. The scrambled value is passed along with one communication and the value is used to change the DVB randomization of the next communication, so that the eavesdropper uses the passed value to switch non-standard DVB randomization. As needed, a controlled change in the DVB randomization provides a security layer to protect the next communication from an eavesdropper. The method of claim 1, The server transmitting a multicast address key and a multicast in a next downstream communication to the first client modem; The server transmitting the same multicast address key and multicast in a next downstream communication to a second client modem; And The server generating a multicast communication addressed to a multicast group including the first client modem and the second client modem; And sending the multicast communication after the server scrambles a portion of the multicast communication with a seed based on the multicast address key. The method of claim 1, wherein the server scrambles at least a portion of the next downstream communication to the first client modem, wherein the seed A new key for the first client modem; And A method of maintaining security based on a previous key for the first client modem received before a new key for the first client modem. A method of maintaining additional security for communication between an upstream server and at least two downstream client modems on a shared communication medium through the use of a dynamic key generated by the server, the method comprising: A. storing information sufficient for the server to generate a seed for the first client modem based on the key for the first client modem generated by the server, wherein the key for the first client modem is generated in the downstream communication. 1 sent to client modem-; B. a second client modem receiving downstream communication from the server; C. The second client modem includes a new key for the second client modem, using a seed for the second client modem based on the key for the second client modem received in a previous downstream communication from the server. Unscrambled scrambled portion of the downstream communication; D. storing sufficient information for the second client modem to generate a new seed for the second client modem based on the new key for the second client modem received in the unscrambled content of the downstream communication; E. scrambling, by the second client modem, at least a portion of a next upstream communication to the server based on the new seed for the second client modem based on the new key for the second client modem; F. the server receiving a next upstream communication from the second client modem; G. the server unscrambled a scrambled portion of a next upstream communication from the second client modem with the new seed for the second client modem based on the new key for the second client modem; H. generating, by the server, a next downstream communication comprising a next key for the second client modem; I. The second client based on a next key for the second client modem without conflicting with previously stored information sufficient for the server to generate a seed for the first client modem based on the first client modem key. Storing enough information to generate a next seed for the modem; And J. The server comprising scrambling at least a portion of a next downstream communication using the new seed for the second client modem based on the new key previously delivered for the second client modem. A dynamic dual scrambling method of communication transmitted to or transmitted from a specific client modem, the method comprising: A. The server recognizes the presence and address of the original client modem on the shared transmission medium; B. the server generating and sending the downstream communication addressed to the first client modem as part of the two scrambled downstream communications based on the two default scrambling seeds, the downstream communication indicating that a default seed was used. Including a control field; C. the first client modem receiving the downstream communication and recognizing that the default seed has been used; D. the first client modem unscrambled the downstream communication using the default seed; E. The first client modem generates and transmits an upstream communication, wherein prior to transmission the upstream communication is scrambled twice with two default seeds, and the scrambled portion of the upstream communication is generated by the first client modem. Contains an embedded key-; F. receiving, by the server, the upstream communication, unscrambled scrambled portion of the upstream communication using the default seed, and storing a key generated by the first client modem; G. downstream addressed to the first client modem with a control field indicating that the communication is to be scrambled using one seed and one default scrambling seed based on the key generated by the first client modem Generating and transmitting a communication, wherein the portion of the downstream communication is scrambled once with one default seed and scrambled once with one seed based on a key generated by the first client modem. The scrambled portion includes a key generated by the server for communicating with the first client modem; H. receiving, by the first client modem, the downstream communication and reading the control field; I. the first client modem unscrambled the downstream; J. communicating using one default seed and one seed based on the last transmitted key generated by the first client modem; K. storing the key generated by the server for the first client modem to communicate with the first client modem; L. generating and transmitting an upstream communication by the first client modem, wherein the portion of the upstream communication comprising a new key generated by the first client modem prior to transmission is the final transmission generated by the first client modem. Scrambled twice using one seed based on the generated key and one seed based on the last transmitted server generated key generated for communicating with the first client modem; M. The server receives the upstream communication, one seed based on a previously stored key generated by the first client modem and one based on a server generated key last transmitted for communicating with the first client modem. Using the seed to unscramble the upstream communication; N. storing, by the server, the last transmitted key generated by the first client modem; O. The communication is scrambling using one seed based on the last transmitted key generated by the first client modem and one seed based on the last generated server generated key to communicate with the first client modem. Generating and transmitting a downstream communication addressed to the first client modem with a control field indicating which is to be established, wherein a portion of the downstream communication is one seed based on the last transmitted key generated by the first client modem. And scrambled once with a seed based on a server generated key that was last sent to communicate with the first client modem, wherein the scrambled portion of the downstream communication is new for communicating with the first client modem. Contains the server generated key-; P. receiving, by the first client modem, the downstream communication and reading the control field; Q. One seed based on a previously stored server generated key for the first client modem to communicate with the first client modem and one seed based on the last transmitted key generated by the first client modem. Unscrambled the downstream communication; R. storing the last transmitted server generated key for the first client modem to communicate with the first client modem, Repeating steps G through K until an outage is detected in the communication between the first client modem and the server, and going to step B if the outage is detected. 16. The method of claim 15 wherein the key generated by the first client modem is a transmission check word. 16. The method of claim 15 wherein at least one of the default seeds is used solely for communication with the first client modem. 16. The method of claim 15 wherein at least one of the default seeds is derived from an address of the first client modem. A method for updating a key used by a first device of a dynamic dual key scrambling system with a double key of a key generated by a first device and a key generated by a second device, wherein the incoming communication received at the first device is Wherein the update occurs when the incoming communication indicates completion of a startup sequence that establishes dynamic dual key scrambling between the first device and the second device; To A. Unscrambled scrambled portion of the incoming communication with the storage key generated by the first device and the storage key generated by the second device; B. storing a key generated by the second device received at the scrambled portion of the incoming communication; C. generating a key generated by the first device and generating an outgoing communication; D. scrambling a portion of the outgoing communication that includes a key generated by the first device with a storage key from the first device and a storage key from the second device; E. storing a key generated by the first device; And F. Sending the outgoing communication. The method of claim 19, The storage key generated by the first device used for the scrambling and unscrambling operations is the most recent storage key generated by the first device, And a storage key generated by the second device used in the scrambling and unscrambling operations is the most recent storage key generated by the second device. 20. The method of claim 19, wherein the storage key generated by the first device used for the scrambling and unscrambling operations is not the most recent storage key generated by the first device. 20. The method of claim 19, wherein the storage key generated by the second device used for the scrambling and unscrambling operations is not the most recent storage key generated by the second device. The invention described and described in the Detailed Description and Reference Drawings.