# Patent

## Title
Determining HDCP source KSV support

## Abstract

Presented is a method for determining the maximum number of key selection vectors (KSVs) supported by an HDCP source. The method includes transmitting a number of KSVs to the HDCP source, determining whether the HDCP source has entered a failure mode in response to the transmitted number of KSVs, increasing or decreasing the number of KSVs in response to the HDCP source not entering or entering the failure mode, transmitting the increased or decreased number of KSVs to the HDCP source, determining whether the HDCP source has entered the failure mode in response to the transmitted increased or decreased number of KSVs, and repeating the increasing, decreasing, and determining steps until the difference between a lowest number of transmitted KSVs resulting in the HDCP source entering the failure mode and a highest number of transmitted KSVs resulting in the HDCP source not entering the failure mode is one.

## Background
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention generally relates to HDCP Key Selection Vectors (KSVs), and more particularly to determining the number of KSVs that a particular HDCP source can support when connected to an HDCP switch or repeater.
2. Background Art
A typical High-Bandwidth Digital Content Protection (HDCP) system or arrangement, which complies with the High-Bandwidth Digital Content Protection System Specification, the entirety of which is incorporated herein by reference, includes an HDCP source, such as a Blu-Ray player, an HDCP repeater, such as a home theater receiver, and one or more HDCP sinks, such as high definition LCD televisions or monitors.
In operation, protected content (e.g., video from a Blu-Ray disc) is transmitted from the HDCP source (i.e., Blu-Ray player), passed through the HDCP repeater (i.e., home theater receiver), and distributed to the HDCP sinks (i.e., televisions and/or monitors).
In order for the HDCP source to successfully transmit protected content through the HDCP repeater and to the HDCP sinks, an authentication process must first occur. In the authentication process, all devices that are intended to receive protected content (i.e., HDCP sinks) much transmit upstream to the HDCP source a unique ID called a Key Selection Vector (KSV).
In order to deliver the KSVs from the downstream sinks to the upstream source, the HDCP repeater retrieves the KSVs from each of the downstream HDCP sinks and passes these retrieved KSVs to the upstream HDCP source. The HDCP source receives each of the KSVs originating from the downstream sinks and checks these KSVs against an HDCP Revocation List maintained by DCP, LLC (“HDCP blacklist”) in order to determine if each of the downstream sinks are licensed to receive the protected content. If all the downstream sinks are determined to be licensed to receive the protected content, the upstream source transmits the protected content. The protected content is then encrypted for each point-to-point link (source to sink connection) to prevent any external devices from intercepting and copying the protected content.
HDCP specification delineates that HDCP sources should support 127 downstream KSVs and six layers of HDCP repeaters between the source and any HDCP sinks. However, in practice, many sources support far fewer than 127 KSVs. Depending on the particular manufacturer, a typical source will support between 3 and 24 KSVs.
A problem arises when the source receives more KSVs than it can support. Specifically, when a particular source receives more KSVs than it is configured or designed to support, the particular source will stop transmitting content to all downstream sinks. In this case, a user connecting together an HDCP compliant video system is unlikely to realize, or be able to determine, that the reason none of the downstream sinks (e.g., LCDs) display the protected content is because the source cannot support the number of KSVs provided thereto.
Consequently, there exists a need for a system and/or method for determining the number of KSVs a particular HDCP source can support (i.e., the maximum number of downstream HDCP sinks that protected content can be routed to), and routing protected content (i.e., encrypted video) from the HDCP source to no more than the maximum number of supported downstream HDCP sinks so that transmission of protected content to the downstream sinks is not prevented or interrupted.
SUMMARY OF THE INVENTION
It is to be understood that both the general and detailed descriptions that follow are exemplary and explanatory only and are not restrictive of the invention
DISCLOSURE OF THE INVENTION
In one aspect, the invention involves a method for determining the maximum number of key selection vectors supported by a particular HDCP source. The method includes transmitting a number of key selection vectors to the particular HDCP source, determining whether the particular HDCP source has entered a failure mode in response to the transmitted number of key selection vectors, and increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode, or decreasing the number of key selection vectors in response to the particular HDCP source entering the failure mode. The method further includes transmitting the increased or decreased number of key selection vectors to the particular HDCP source, and determining whether the particular HDCP source has entered the failure mode in response to the transmitted increased or decreased number of key selection vectors. The method still further includes repeating steps increasing, decreasing, and determining steps until the difference between a lowest number of transmitted key selection vectors resulting in the particular HDCP source entering the failure mode and a highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode is one.
In one embodiment, determining whether the particular HDCP source has entered the failure mode includes determining if the HDCP source transmits stable encrypted video within a predetermined time window in response to the transmitted number of key selection vectors. In another embodiment, determining whether the particular HDCP source has entered the failure mode includes determining by visual inspection of a display if the HDCP source transmits stable encrypted video in response to the transmitted number of key selection vectors. In still another embodiment, determining whether the particular HDCP source has entered the failure mode includes determining by image analysis if the HDCP source transmits stable encrypted video in response to the transmitted number of key selection vectors.
In other embodiments, the method further includes storing the highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode in a memory as the maximum number of key selection vectors supported by the particular HDCP source.
In another embodiment, the method further includes retrieving the maximum number of key selection vectors supported by the particular HDCP source from a memory in response to the particular HDCP source identifying itself.
In yet another embodiment, the method includes increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode unless the number of transmitted key selection vectors equals 127. If the number of transmitted key selection vectors equals 127 and the particular HDCP source has not entered the failure mode, the rest of the steps are skipped and the number 127 is stored in a memory as the maximum number of key selection vectors supported by the particular HDCP source.
In another aspect, the invention involves a method for determining the maximum number of key selection vectors supported by a particular HDCP source. The method includes sequentially transmitting a plurality of sets of key selection vectors to the particular HDCP source. Each of the plurality of sets of key selection vectors includes a different number of key selection vectors. The method further includes determining which one or more sets of the transmitted plurality of sets do not drive the particular HDCP source into a failure mode, determining which particular set of the one or more sets has the highest number of key selection vectors, and selecting the number of key selection vectors of the particular set as the maximum number of key selection vectors supported by the particular HDCP source.
In still another aspect, the invention involves an HDCP compliant repeater that includes at least one HDCP source interface configured for communicating with an HDCP source, a processor in communication with the at least one HDCP source interface, and a memory in communication with the processor. The processor is configured for transmitting a number of key selection vectors to the particular HDCP source, determining whether the particular HDCP source has entered a failure mode in response to the transmitted number of key selection vectors, and increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode, or decreasing the number of key selection vectors in response to the particular HDCP source entering the failure mode. The processor is further configured for transmitting the increased or decreased number of key selection vectors to the particular HDCP source, and determining whether the particular HDCP source has entered the failure mode in response to the transmitted increased or decreased number of key selection vectors. The processor is still further configured for repeating the increasing, decreasing and determining steps until the difference between a lowest number of transmitted key selection vectors resulting in the particular HDCP source entering the failure mode and a highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode is one.
The memory is configured for storing the highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode as the maximum number of key selection vectors supported by the particular HDCP source.



BRIEF DESCRIPTION OF DRAWINGS
The accompanying figures further illustrate the present invention.
The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is an illustrative schematic diagram of an HDCP repeater in communication with an HDCP source and a plurality of HDCP sinks, according to one embodiment of the invention.
FIGS. 2A-2D are illustrative flow diagrams of steps for determining the number of KSVs that an HDCP source can support, according to one embodiment of the invention.



LIST OF REFERENCE NUMBERS FOR THE MAJOR ELEMENTS IN THE DRAWING
The following is a list of the major elements in the drawings in numerical order.

    
    
        100 HDMI video distribution system
        102 HDCP repeater
        104 HDCP source
        106 HDCP sink
        108 HDCP sink
        110 HDCP sink
        112 HDCP sink
        114 HDCP sink
        116 processor
        118 memory
        202 Turn on source, repeater, and sinks
        204 Repeater drives hotplug signal high
        206 Source authenticates repeater and transmits interrupt signal
        208 User initiates KSV determination routine
        210 Repeater transmits a test set of KSVs
        212 Does source enter failure mode?
        214 Decrease the number of KSVs in the test set
        216 Repeater toggles the hotplug signal
        218 Source authenticates repeater and transmits interrupt signal
        220 Repeater transmits the new test set of KSVs
        222 Increase the number of KSVs in the test set
        224 Repeater toggles the hotplug signal
        226 Source authenticates repeater and transmits interrupt signal
        228 Repeater transmits the new test set of KSVs
        230 Does source enter failure mode?
        232 Lowest # of transmitted KSVs resulting in the source entering failure mode—highest # of transmitted KSVs resulting in the source not entering failure mode=1?
        234 Write the highest # of transmitted KSVs resulting in the source not entering failure mode (the maximum # of supported KSVs) to memory
        236 Does source enter failure mode?
        238 Lowest # of transmitted KSVs resulting in the source entering failure mode—highest # of transmitted KSVs resulting in the source not entering failure mode=1?
        240 Write the highest # of transmitted KSVs resulting in the source not entering failure mode (the maximum # of supported KSVs) to memory
    
    


DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
MODE(S) FOR CARRYING OUT THE INVENTION
The present invention involves a system and method for determining the number of Key Selection Vectors (KSVs) that a particular High-Bandwidth Digital Content Protection (HDCP) source is capable of supporting (i.e., the maximum number of downstream HDCP sinks that protected content can be routed to). The present invention also involves a system and method for routing protected content from the HDCP source to no more than the maximum number of supported downstream HDCP sinks so that transmission of protected content to the downstream sinks is not prevented or interrupted.
Referring to FIG. 1, an HDMI video distribution system 100 employing the method of the present invention is shown. The system 100 includes an HDCP repeater 102 (e.g., a home theater receiver), an HDCP source 104 (e.g., a Blu-Ray player), and a plurality of HDCP sinks 106, 108, 110, 112, 114 (e.g. LCD monitors and/or televisions). The HDCP repeater 102 includes a processor 116 and memory 118. The HDCP repeater 102 is in communication with the HDCP source 104, and each of the plurality of HDCP sinks 106, 108, 110, 112, 114 via High Definition Multimedia Interface (“HDMI”) connections. The program of method steps for determining the maximum number of KSVs supported by the source 104 and for routing protected content to no more than the supported number of sinks is implemented using C and C++ in firmware that is stored on, and executed by, the processor 116, and is described in detail below.
Referring to FIGS. 2A-2D, in one embodiment, flow diagrams of the method steps for determining the number of KSVs that a particular HDCP source can support are shown.
According to the method of the present invention, after the source 104, the repeater 102, and the plurality of sinks 106, 108, 110, 112, 114 are turned on (Step 202), the repeater 102 drives a hotplug signal high to alert the source 104 that there is device (i.e., the repeater 102) connected thereto (Step 204). The source 104 then executes various video start-up routines, authenticates the repeater 102, and transmits to the repeater 102 an interrupt signal that informs the repeater 102 that it can now transmit/report any downstream KSVs (Step 206).
If the source 104 and the repeater 102 are being connected together for the first time and, consequently, the number of KSVs supported by the source 104 is not known, a user would initiate the KSV determination routine via pressing a button on the repeater 102 or on a remote control associated with the repeater 102, for example (Step 208).
In response to receiving the interrupt signal from the source 104 and the indication from the user to start the KSV determination routine, the repeater 102 transmits to the source 104 a first test set of N1 KSVs (Step 210), where N1 can be any number between 1 and 127. Each KSV in the test set is a forty digit binary number that includes twenty “1s” and twenty “0s”. The only requirement for a legitimate KSV is that it not be on the HDCP blacklist.
In the steps described above, the user initiates the KSV determination routine immediately after or during the source 104 transmitting the authentication interrupt signal. It should be noted, however, that the user can initiate the KSV determination routine at any time by pressing a button on the repeater 102 (or remote), as described above. In this case, no matter where the source 104 and repeater 102 are in the authentication or video transmission processes, the repeater 102 will drive the hotplug signal low to simulate a cable disconnect and then drive the hotplug signal high to simulate a cable reconnect. Thereafter, the KSV determination routine will execute as described herein. Additionally, in other embodiments, rather than toggle the hotplug signal to initiate authentication, the receiver sense (RSEN) signal is instead toggled to initiate authentication.
The repeater 102 then determines if the source 104 has entered a failure mode by checking whether the source 104 begins transmitting stable encrypted video within a predetermined time window (e.g., five seconds) (Step 212). If the source 104 does not begin transmitting stable encrypted video within the predetermined time window, the source 104 is assumed to have entered the failure mode.
If the source 104 has entered the failure mode, the repeater 102 decreases the number of KSVs in the test set to N2 KSVs (i.e., N2<N1) (Step 214). The repeater then toggles (i.e., drives low then high) the hotplug signal to simulate a cable disconnect and reconnect to initiate the authentication process once again (Step 216). In response to the hotplug signal being driven high, the source 104 authenticates the repeater 102 and transmits an interrupt signal to the repeater 102 (Step 218). In response to receiving the interrupt signal from the source 104, the repeater again transmits to the source 104 the test set of N2 KSVs (Step 220).
The repeater 102 again determines if the source 104 has entered a failure mode by checking whether the source 104 begins transmitting stable encrypted video within a predetermined time window (Step 230). If the source 104 does not begin transmitting stable encrypted video within the predetermined time window, the source 104 is again assumed to have entered the failure mode, and the repeater 102 again executes Steps 214, 216, 218, 220, and 230, decreasing the number of transmitted KSVs with each iteration, until the source 104 does not enter failure mode. If, however, the source 104 continues to enter failure mode and number of KSVs is decreased to zero, the source 104 is determined to not support any repeater devices, and the KSV determination routine ends.
If during execution of the determination Step 230, the source 104 does not enter failure mode, the repeater 102 determines if the lowest number of transmitted KSVs in a test set that resulted in the source 104 entering the failure mode and the highest number of transmitted KSVs in a test set that resulted in the source 104 not entering failure mode differ by one KSV (Step 232).
If Step 232 is true, the highest number of transmitted KSVs in a test set that resulted in the source 104 not entering failure mode is the maximum number of KSVs supported by the source 104. This number of supported KSVs is stored in memory 118 (Step 234). If Step 232 is not true, the repeater 102 then increases the number of KSVs in the test set as it would if the first test set of N1 KSVs had not forced the source 104 into a failure mode, and is described in detail below.
Referring again to Step 212, if the repeater 102 determines that the source 104 has not entered the failure mode in response to receiving the first test set of N1 KSVs, the repeater 102 increases the number of KSVs in the test set to N3 KSVs (i.e., N3>N1) (Step 222). The repeater then toggles (i.e., drives low then high) the hotplug signal to simulate a cable disconnect and reconnect to initiate the authentication process once again (Step 224). In response to the hotplug signal being driven high, the source 104 authenticates the repeater 102 and transmits an interrupt signal to the repeater 102 (Step 226). In response to receiving the interrupt signal from the source 104, the repeater transmits to the source 104 the test set of N3 KSVs (Step 228).
The repeater 102 again determines if the source 104 has entered a failure mode by checking whether the source 104 begins transmitting stable encrypted video within a predetermined time window (Step 230). If the source 104 begins transmitting stable encrypted video within the predetermined time window, the source 104 is again assumed to have not entered the failure mode, and the repeater 102 again executes Steps 222, 224, 226, 228, and 236, increasing the number of transmitted KSVs with each iteration, until the source 104 enters failure mode.
If during execution of the determination Step 236, the source 104 enters failure mode, the repeater 102 determines if lowest number of transmitted KSVs in a test set that resulted in the source 104 entering the failure mode and the highest number of transmitted KSVs in a test set that resulted in the source 104 not entering failure mode differ by one KSV (Step 238).
If Step 238 is true, the highest number of transmitted KSVs in a test set that resulted in the source 104 not entering failure mode is the maximum number of KSVs supported by the source 104. This number of supported KSVs is stored in memory 118 (Step 240). If Step 238 is not true, the repeater 102 then decreases the number of KSVs in the test set as it would if the first test set of N1 KSVs had forced the source 104 into a failure mode, and is described in detail above.
In other words, in order to determine the maximum number of KSVs supported by the source 102, the repeater 102 increases or decreases the number of KSVs transmitted to the source 104 as necessary until the difference between the lowest number of transmitted KSVs resulting in the source 104 entering the failure mode and the highest number of transmitted KSVs resulting in the source 104 not entering the failure mode is one. The highest number of transmitted KSVs resulting in the source 104 not entering the failure mode is the maximum number of KSVs (and consequently the maximum number of downstream sinks) supported by the source 104.
After the source 104 has been tested, the repeater 102 will not allow content from the source 104 to be routed to more downstream sinks than are supported by the source 104, and therefore will not transmit more downstream KSVs to the source 104 than are supported by the source 104. In doing so, the total number of sinks receiving the protected content is limited, but the source 104 will never enter failure mode because of exceeding its number of supported KSVs limitation.
For example, referring again to FIG. 1, if the maximum number of KSVs supported by the source 104 is three, the repeater 102 will only send three KSVs to the source 104, and only the corresponding three of the five sinks 106, 108, 110, 112, 114 will receive protected content. Even if a user attempts to route content to all five of the sinks 106, 108, 110, 112, 114 connected to the repeater 102, video will still only be routed to three sinks and, therefore, the source 104 will not go into failure mode. The other two sinks will simply receive no video.
Referring to Steps 214 and 222 in FIG. 2B, the number by which the KSVs in the test set are decreased or increased is a matter of choice. However, some choices/methods are more efficient than others.
In one embodiment, the first test set of KSVs includes 127 KSVs. If this first test set of KSVs results in the source going into a failure mode, the number of KSVs in each subsequent test set of KSVs is chosen to be half the number of KSVs in the previous test set until the source 104 does not enter failure mode. Thereafter, the number of KSVs in a particular test set is increased or decreased to a number that is half way between the number of KSVs in the test set of the most recent pass (i.e., source does not enter failure mode) and the number of KSVs in the test set of the most recent fail (i.e., source enters failure mode).
The number of KSVs in a particular test set continues to be increased or decreased as described above until the difference between the lowest number of transmitted key selection vectors resulting in the source entering the failure mode and the highest number of transmitted key selection vectors resulting in the source not entering the failure mode is one
As an example of the above-described KSV determination routine, assume that the number of supported KSVs for a particular source is twelve. In order to ascertain this number of supported KSVs using the KSV determination routine, a first test set of 127 KSVs is transmitted to the particular source. According to the method described herein, this test set of transmitted KSVs results in the particular source entering a failure mode.
Next, a test set of sixty-three KSVs (approximately half the first number of transmitted KSVs) is transmitted to the particular source, which also results in the particular source entering a failure mode. Next, a test set of thirty-one KSVs (again approximately half the number of previously transmitted KSVs) is transmitted to the particular source, which again results in the particular source entering a failure mode. Next, a test set of fifteen KSVs (again approximately half the number of previously transmitted KSVs) is transmitted to the particular source, which again results in the particular source entering a failure mode. Next, a test set of seven KSVs (again approximately half the number of previously transmitted KSVs) is transmitted to the particular source. The test set of seven KSVs results in the particular source not entering a failure mode (i.e., a pass).
Since the test set of seven KSVs resulted in a pass, a test set of eleven KSVs is next transmitted to the particular source. Eleven is the number of KSVs half way between the number of KSVs resulting in the last pass (i.e., seven) and the number of KSVs resulting in the last fail (i.e., fifteen). The test set of eleven KSVs results in the particular source again not entering a failure mode (i.e., a pass).
Next, a test set of thirteen KSVs is transmitted to the particular source. Thirteen is the number of KSVs half way between the number of KSVs resulting in the last pass (i.e., eleven) and the number of KSVs resulting in the last fail (i.e., fifteen). The test set of thirteen KSVs results in the particular source entering a failure mode.
Next, a test set of twelve KSVs is transmitted to the particular source. Twelve is the number of KSVs half way between the number of KSVs resulting in the last pass (i.e., eleven) and the number of KSVs resulting in the last fail (i.e., thirteen). The test set of twelve KSVs results in the particular source not entering a failure mode.
At this point, it can be seen that the difference between the lowest number of transmitted key selection vectors resulting in the particular source entering the failure mode (i.e., thirteen) and the highest number of transmitted key selection vectors resulting in the particular source not entering the failure mode (i.e., twelve) is one. Therefore, the maximum number of KSVs supported by the particular source is twelve. Additionally, the maximum number of downstream sinks that protected content will be routed to by the repeater is also twelve.
It should be noted that if the repeater 102 transmits a test set of 127 KSVs and the source 104 does not enter a failure mode (i.e., pass), the KSV determination routine stops. This is clearly because 127 KSVs are the absolute maximum number of KSVs that can be supported by a source, according to the current HDCP specification.
In still another embodiment, the first test set of KSVs includes 127 KSVs. With each iteration of the KSV determination routine, the number of KSVs in the test set is decreased by one KSV until the source 104 does not go into a failure mode. Thus, the number of KSVs in the test set transmitted to the source 104 that results in the source not going into a failure mode is the maximum number of KSVs supported by the source 104.
In yet another embodiment, the first test set of KSVs includes one KSV. With each iteration of the KSV determination routine, the number of KSVs in the test set is increased by one KSV until the source 104 goes into a failure mode. Thus, the number of KSVs in the test set that is transmitted to the source 104 prior to the transmission of the test set of KSVs that results in the source going into a failure mode is the maximum number of KSVs supported by the source 104
As described in detail above, the KSV determination is manually initiated by the user when the source 104 and repeater 102 are connected together for the first time. Once the maximum number of KSVs supported by the particular source 104 is determined, it is stored in memory 118 and never has to be determined again, even if the source 104 and repeater are powered down, or disconnected and reconnected.
If a new source B is connected to the repeater 102, the KSV determination routine must be executed to determine the maximum number of KSVs supported by that source B. As described above, that maximum number of supported KSVs is stored in memory 118. Thereafter, if the source B is replaced by the original source 104, the KSV determination routine must be executed again to determine the maximum number of KSVs supported by source 104.
The KSV determination routine needs to be re-executed for the original source 104 because there is no way for the repeater 102 to distinguish between the original source 104 and the new source B. It is the responsibility of the user or installation technician to manually execute the KSV determination routine each time the particular source connected to the repeater is changed. As long as the source connected to the repeater remains the same, the KSV determination routine never needs to be executed a subsequent time.
In another embodiment, the repeater 102 is configured to read vendor information, which identifies the particular source, from info frames that are transmitted to the repeater 102 from the source during the startup routines. In this embodiment, in addition to obtaining (and storing) the maximum number of supported KSVs for the particular source from the KSV determination routine, the repeater 102 also stores the particular source identifying information in memory 118. Consequently, if a particular previously identified source, for which the maximum number of supported KSVs has been determined, is replaced by another source, and then later reconnected to the repeater 102, the KSV determination routine need not be executed again since the particular source is already known and the particular source's maximum number of supported KSVs can be retrieved from memory 118.
Additionally, if a particular source is connected to the repeater 102, and the repeater does not recognize the particular source (i.e., there is no corresponding identifying information stored in memory 118), the repeater 102 automatically executes the KSV determination routine as described in detail above.
In still another embodiment, determining if the source 104 has entered a failure mode is accomplished by human visual inspection of video on a display after each transmission of a test set of KSVs. In this embodiment, after a test set of KSVs is transmitted to the source 104, a user or technician would observe a display to determine whether protected content or an error message (or noise) is displayed. If an error message or noise is displayed, the user or technician would execute another iteration of the KSV determination routine.
In yet another embodiment, determining if the source 104 has entered a failure mode is accomplished with image analysis software residing in, and executing on, the repeater 102. In this embodiment, the image analysis software determines whether protected content is successfully being transmitted.
In other embodiments, additional HDCP sources are included in communication with an HDCP repeater that is configured to accommodate such additional HDCP sources. In still other embodiments, more or less HDCP sinks are included.
In still another embodiment, all the HDCP testing functions are implemented as a program of instructions stored on a computer-readable medium such as a floppy disk, compact disk, digital video disk, or other portable or removable drive (e.g., a USB thumb drive). The computer-readable medium is accessible by a computer or other processing device, which is configured to execute the program of instructions stored thereon to perform the HDCP source testing functions described in detail hereinabove.
List of Acronyms Used in the Detailed Description of the Invention
The following is a list of the acronyms used in the specification in alphabetical order.

    
    
        HDCP High-Bandwidth Digital Content Protection
        HDMI High-Bandwidth Digital Media Interface
        KSV Key Selection Vector
        LCD liquid crystal display
    
    


Alternate Embodiments
Alternate embodiments may be devised without departing from the spirit or the scope of the invention.

## Claims

1. method for determining the maximum number of key selection vectors supported by a particular HDCP source, the method comprising:
a) transmitting a number of key selection vectors to the particular HDCP source;
b) determining whether the particular HDCP source has entered a failure mode in response to the transmitted number of key selection vectors;
c) increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode;
d) decreasing the number of key selection vectors in response to the particular HDCP source entering the failure mode;
e) transmitting the increased or decreased number of key selection vectors to the particular HDCP source;
f) determining whether the particular HDCP source has entered the failure mode in response to the transmitted increased or decreased number of key selection vectors; and
g) repeating steps c)-f) until the difference between a lowest number of transmitted key selection vectors resulting in the particular HDCP source entering the failure mode and a highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode is one.

2. The method of claim 1, wherein determining whether the particular HDCP source has entered the failure mode comprises determining if the HDCP source transmits stable encrypted video within a predetermined time window in response to the transmitted number of key selection vectors.

3. The method of claim 1, wherein determining whether the particular HDCP source has entered the failure mode comprises determining by visual inspection of a display if the HDCP source transmits stable encrypted video in response to the transmitted number of key selection vectors.

4. The method of claim 1, wherein determining whether the particular HDCP source has entered the failure mode comprises determining by image analysis if the HDCP source transmits stable encrypted video in response to the transmitted number of key selection vectors.

5. The method of claim 1, further comprising h) storing the highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode in a memory as the maximum number of key selection vectors supported by the particular HDCP source.

6. The method of claim 1, further comprising retrieving the maximum number of key selection vectors supported by the particular HDCP source from a memory in response to the particular HDCP source identifying itself.

7. The method of claim 1, wherein step c) further comprises increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode unless the number of transmitted key selection vectors equals 127.

8. The method of claim 7, further comprising: if the number of transmitted key selection vectors equals 127 and the particular HDCP source has not entered the failure mode, skipping steps d)-g) and storing the number 127 in a memory as the maximum number of key selection vectors supported by the particular HDCP source.

9. A method for determining the maximum number of key selection vectors supported by a particular HDCP source, the method comprising:
sequentially transmitting a plurality of sets of key selection vectors to the particular HDCP source, each of the plurality of sets of key selection vectors comprising a different number of key selection vectors;
determining which one or more sets of the transmitted plurality of sets do not drive the particular HDCP source into a failure mode;
determining which particular set of the one or more sets has the highest number of key selection vectors; and
selecting the number of key selection vectors of the particular set as the maximum number of key selection vectors supported by the particular HDCP source.

10. An HDCP compliant repeater, comprising:
at least one HDCP source interface configured for communicating with an HDCP source;
a processor in communication with the at least one HDCP source interface, the processor being configured for:
transmitting a number of key selection vectors to the particular HDCP source;
determining whether the particular HDCP source has entered a failure mode in response to the transmitted number of key selection vectors;
increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode;
decreasing the number of key selection vectors in response to the particular HDCP source entering the failure mode;
transmitting the increased or decreased number of key selection vectors to the particular HDCP source;
determining whether the particular HDCP source has entered the failure mode in response to the transmitted increased or decreased number of key selection vectors; and
repeating steps c)-f) until the difference between a lowest number of transmitted key selection vectors resulting in the particular HDCP source entering the failure mode and a highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode is one; and
a memory for storing the highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode as the maximum number of key selection vectors supported by the particular HDCP source.

11. The method of claim 5, further comprising i) routing content from the particular HDCP source to a number of HDCP sinks that is less than or equal to the maximum number of key selection vectors supported by the particular HDCP source.

12. The method of claim 9, further comprising routing content from the particular HDCP source to a number of HDCP sinks that is less than or equal to the maximum number of key selection vectors supported by the particular HDCP source.

13. The repeater of claim 10, wherein the processor is further configured for routing content from the particular HDCP source to a number of HDCP sinks that is less than or equal to the maximum number of key selection vectors supported by the particular HDCP source.

14. A method of limiting the number of key selection vectors transmited to an HDCP source from connected HDCP sinks to prevent the HDCP source from entering a failure mode, the method comprising:
a) transmitting a number of key selection vectors to the particular HDCP source;
b) determining whether the particular HDCP source has entered a failure mode in response to the transmitted number of key selection vectors;
c) increasing the number of key selection vectors in response to the particular HDCP source not entering the failure mode;
d) decreasing the number of key selection vectors in response to the particular HDCP source entering the failure mode;
e) transmitting the increased or decreased number of key selection vectors to the particular HDCP source;
f) determining whether the particular HDCP source has entered the failure mode in response to the transmitted increased or decreased number of key selection vectors;
g) repeating steps c)-f) until the difference between a lowest number of transmitted key selection vectors resulting in the particular HDCP source entering the failure mode and a highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode is one,
h) storing the highest number of transmitted key selection vectors resulting in the particular HDCP source not entering the failure mode as the maximum number of key selection vectors supported by the particular HDCP source; and
i) routing content from the particular HDCP source to a number of HDCP sinks that is less than or equal to the maximum number of key selection vectors supported by the particular HDCP source.