KR102008222B1 - Secure KVM Switch - Google Patents

Abstract

The present invention relates to a secure KVM switch. The secure KVM switch comprises: a lower chip reading descriptor and report data of a keyboard and mouse and EDID or DispID data of a display; an upper chip connected to a PC, receiving information of the lower chip, and emulating the keyboard, mouse, and display; a photo interrupter electrically isolating the lower chip and upper chip and connecting the lower chip and upper chip in one-way communication; and a video switch switching an image signal of the display. When a start pattern is received in the upper chip, an instruction packet composed of the start pattern, a header, and data transmitted from the lower chip is interrupted with the highest priority, and the lower chip and upper chip are connected by a common line in one-way communication transmitting a next instruction after a time predicted by a linear prediction function passes.

Description

Secure KVM Switch

The present invention relates to a security KVM switch, and more particularly, to provide a security KVM switch that ensures stable and error-free operation while improving the efficiency of one-way communication.

In recent years, computers and the Internet have become essential to most tasks. Various information necessary for work is obtained from the Internet, and business process is carried out through the Internet beyond information transfer and information sharing. On the other hand, as the number of malicious attackers using hacking or malware technology surges, the leakage of information from individuals and companies has become a serious problem. In order to prevent information leakage, there are increasing cases of separating and operating a network into an internal network and an external network. In case of separate operation between external network and internal network, one person must operate two computers connected to external network and internal network, so KVM (Keyboard, Video) which connects one set of display, keyboard and mouse to two computers display, Mouse) switch is required. Especially in organizations dealing with sensitive information on the internal network, secure KVM switches are important.

In KVM switches, keyboard and mouse data is Universal Serial Bus (USB) communication, and Extended Display Identification Data (EDID) or Display Identification Data (DispID) of the display device is connected to the computer by Display Data Channel (DDC) communication included in the display cable. Is connecting. Since USB communication and DDC communication are two-way communication technologies capable of outputting sensitive information of a computer, a malicious attacker may use them to leak computer information. To prepare for the security risks of KVM switches, more than 30 countries have participated in establishing Common Criteria (CC) criteria for security KVM switches, which are shared by participating countries.

According to the CC evaluation criteria, secure KVM switches require complete blocking of information leakage paths from internal network computers to protect sensitive information of internal network computers. To meet this requirement, data output from a computer must be proved impossible in any case. Since the keyboard and mouse connected to the KVM switch are dedicated to computer input, the one-way communication can be used to prevent data leakage from the computer. In addition, since EDID or DispID information of the display apparatus only needs a computer input, information leakage can be prevented by using one-way communication. The security KVM switch uses one-way communication technology that does not allow data output from a computer, but only allows data input. In addition, the KVM switch is equipped with an electrical isolation device to prevent information leakage by electromagnetic waves.

One-way communication can be implemented simply by using only one line in a communication device in which a transmitting line and a receiving line are separated. USB communication of keyboard and mouse or DDC communication of display device combine transmission and reception by single line, so it is impossible to implement secure one-way communication. For the path that connects the keyboard and mouse to the computer, the secure KVM switch is divided into a USB host device that receives keyboard and mouse data and a USB emulator device that connects to the computer. (Serial Peripheral Interface) communication or UART (Universal Asynchronous Receiver Transmitter) communication is applied and only one way communication is used. The one-way communication path physically breaks one line for complete security, making reverse communication impossible.

For the path that connects the display to the computer, the secure KVM switch separates the DDC host device that reads EDID or DispID from the display and the DDC emulator device that connects the computer, and uses one-way communication between the two devices.

In the one-way communication, various problems occur because the status of the receiving side is unknown to the transmitting side. For example, if a receiving command is being processed and the sender sends the next command without knowing, the receiving party stops processing and generates an error or misses receiving the next command. The prior art is to allow the sender to read the receiver status separately so that the next command is sent after confirming the command end status of the receiver, or the next command is sent after the maximum command processing time has elapsed. .

Reading the status of the receiving side is a violation of the principle of one-way communication, so there is a problem of weak security, and if the command interval is fixed to the maximum command processing time, there is a problem that communication efficiency is lowered because it is not possible to communicate quickly.

An object of the present invention for solving the above problems is to provide a secure KVM switch that ensures stable and error-free operation while improving the efficiency of one-way communication, which is essential for complete security.

Security KVM switch of the present invention for achieving the above object is a down chip for reading the descriptor and report data of the keyboard and mouse, and the EDID or DispID data of the display; An up chip connected to a PC and emulating a keyboard, a mouse, and a display by receiving data of the down chip; A photo interrupter for electrically connecting the down chip and the up chip to one-way communication; And a video switch for switching the image signal of the display, wherein the command packet consisting of a start pattern transmitted from the down chip, a header, and data is interrupted at the highest priority when the start pattern is received from the up chip. It is characterized in that the downlink chip and the uplink chip are connected by a common line in one-way communication to transmit the next command only when the time predicted by the linear prediction function passes.

The down chip reads the descriptor and report data through USB connecting the keyboard and the mouse, and assembles the command packet and assembles the command packet by assembling the command packet by reading EDID or DispID data through the DDC included in the display cable. A controller that assembles a PC change command packet and puts it in a QUE and controls the PC change switch when the DDC host that puts the QUE and the keyboard report read by the USB host detects the PC change request sequence. If the command processing prediction time for the command has elapsed, it may include a transmitter for extracting and transmitting the next command packet from the QUE.

The upstream chip receives a receiver only when the PC number included in the header of the command packet matches its own PC number or when the entire number is received, and the keyboard and the mouse receive data from the keyboard and mouse of the downstream chip. A USB emulator that emulates as if it is actually connected, a DDC emulator that accepts the display data of the down-chip and emulates as if the display is directly connected to a PC, and handles initialization, self-diagnosis, error management and related control commands. It may include a control unit to

The linear prediction function may be a command processing time linear prediction function that models a linear prediction function by distinguishing a memory access case from a flash memory write case and considers a flash memory erase time in a constant term when writing to the flash memory.

The peripheral device of the keyboard, the mouse and the display, the descriptor of the keyboard and the mouse, and the EDID or DispID peripheral device information of the display are stored in both the flash chip of the up chip and the down chip, and the down chip is connected to the peripheral device information of the down chip flash memory. The peripheral device initialization process is started only when the model of the peripheral device is actually changed by comparing the connected peripheral devices, and the upstream chip can operate normally without the initialization process according to the peripheral device information stored in the up-chip flash memory.

Emulates the keyboard, mouse and display in one up chip,

The host function of the keyboard, mouse, and display can be performed by one down chip.

If the number of video switches is added in correspondence with the number of displays, the display can be expanded to two or more using extra DDC ports included in the down-chip and the up-chip without additional hardware.

By adding the number of contacts and the number of up-chips of the video switch corresponding to the number of PCs, the number of PCs can be expanded to two or more.

As described above, according to the present invention, it is possible to guarantee stable and error-free one-way communication, and improve communication efficiency by automatically adjusting an appropriate delay time according to the data size.

1 is a block diagram illustrating a secure KVM switch according to an embodiment of the present invention.
2 is a block diagram illustrating an instruction packet according to an embodiment of the present invention.
3 is a block diagram illustrating a secure KVM switch extending to dual displays according to another embodiment of the present invention.
4 is a block diagram illustrating a secure KVM switch for extending a PC to N according to another embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention.

Next, a security KVM switch according to an embodiment of the present invention will be described.

1 is a block diagram showing a secure KVM switch according to an embodiment of the present invention, Figure 2 is a block diagram showing a command packet according to an embodiment of the present invention.

1 and 2, the secure KVM switch according to the present invention includes a down chip 100 that reads descriptor and report data of the keyboard 10 and mouse 20 and EDID or DispID data of the display 30. , Uplink chips 200 and 300 that are connected to the PC 400 and 500 and emulate the keyboard 10, the mouse 20, and the display 30 by receiving information of the down chip 100, the down chip 100 and the It includes a photo interrupter (50, 60) for electrically connecting the up-chip (200, 300) and one-way communication, and a video switch 40 for switching the image signal of the display (30).

The downlink chip 100 includes a USB host 110, a DDC host 120, a command packet QUE 130, a transmitter 150, and a controller 140.

The USB host 110 reads the descriptor and report data through the USB connecting the keyboard 10 and the mouse 20, and assembles the command packet 600 as shown in FIG. 2 and puts it in the QUE (Queue Buffer) 130. give.

The DDC host 120 reads the EDID or DispID data through the DDC included in the cable of the display 30 and assembles the command packet 600 into the QUE 130.

When the controller 140 detects the PC change request sequence by examining the report of the keyboard 10 read by the USB host 110, the controller 140 assembles the PC change command packet and puts it into the QUE 130 and the PC change switch 40. Also controls.

In addition, the controller 140 assembles the initialization, self-diagnosis, error management and control commands related thereto and puts them in the QUE 130.

When the command processing prediction 160 time elapses for the recently transmitted command, the transmitter 150 removes and transmits the next command packet from the QUE 130.

Since the command packet 600 of the downlink chip 100 is transmitted to all uplink chips 200 and 300, the uplink chips 200 and 300 may be simultaneously received through the respective photo interrupters 50 and 60.

Here, the uplink chips 200 and 300 include receivers 210 and 310, USB emulators 220 and 320, DDC emulators 230 and 330, and controllers 240 and 340.

The receivers 210 and 310 receive only when the PC number included in the header 620 of the command packet 600 matches the PC number of the command packet 600 or when the reception unit 210 or 310 receives the entire PC number. Here, the receivers 210 and 310 transmit to the USB emulators 220 and 320, the DDC emulators 230 and 330 or the controllers 240 and 340 according to the command codes included in the command header.

The USB emulators 220 and 320 receive data from the keyboard 10 and the mouse 20 of the down chip 100 and emulate the keyboard and mouse as if the keyboard and the mouse are actually connected to the PC 400 and 500.

The DDC emulators 230 and 330 also receive the display 30 data of the down-chip 100 and emulate it as if the display is directly connected to the PCs 400 and 500.

The controllers 240 and 340 process initialization, self-diagnosis, error management, and control commands related thereto.

In the present invention, as shown in FIG. 2, the command packet 600 may set the start pattern 610 as a bit pattern having a sufficient length that cannot appear in the header 620 and the data 630. In this case, the header 620 may include a command code 621, a PC number 622, and a data size 623.

The receivers 210 and 310 of the upstream chips 200 and 300 interrupt the highest priority when the start pattern 610 is detected.

Since the command packet 600 always transmits the start pattern 610 first and the header 620 and the data 630, the command packet 600 immediately receives the start pattern 610 regardless of the state of the uplink chips 200 and 300. Stop and receive command packets. In this way, even if the down chip 100 does not know the state of the up chip 200,300, it is possible to control the up chip 200,300 by sending the command packet 600 at any time and guarantee the stable operation of the KVM switch.

The command code included in the header 620 distinguishes types of commands such as descriptors and reports of the keyboard 10 and the mouse 20, EDID or DispID of the display 30, and PC switching of the controllers 240 and 340. .

The uplink chips 200 and 300 may store descriptors and EDIDs in a flash memory in order to shorten the power-on response time of the KVM switch.

In the present invention, since the instruction processing time increases with the size of the data, it can be modeled with a linear function such as ax + b. x is the data size, a is the processing time per byte, and b is the basic processing time. a and b can be calculated from the size of the instruction processing code and the clock speed and memory access time of the microprocessor unit (MPU) used in the up chip. Since the flash memory write time is very long compared to the memory access time, the flash memory write time can be modeled by a linear function such as cy + d. y is the data size to be written to the flash memory, c is the processing time per byte, and d is the basic processing time including the flash memory erase time. Because command processing time can vary considerably depending on other processes or interrupts, ambient temperature, and the physical characteristics of the chip, the basic processing time must be sufficiently considered for stable operation.

The present invention electrically insulates the down chip 100 and the up chip 200 and 300 by inserting photo interrupters 50 and 60 into the one-way communication path. Here, the photo interrupters (50, 60) is one-way communication path is exposed to the air layer can be easily understood by the general public without knowledge of the one-way communication and electrical isolation state can be trusted high security of the security KVM switch of the present invention There is an advantage.

When a peripheral device (keyboard, mouse, video display) is newly connected or powered on to the security KVM switch of the present invention, the peripheral device information (descriptor of keyboard and mouse, EDID or DispID of the display) is newly read to the upstream chip 200,300. During this time, the normal operation of the secure KVM switch will be impossible because of the initialization process required.

In addition, the present invention stores the peripheral device information in both the flash memory of the up chip 100 and the down chip (2000,300), the down chip 100 compares the peripheral device connected to the peripheral information of the down chip flash memory The peripheral initialization process starts only when the model of the peripheral device is actually changed. Since the peripheral devices are hardly changed under normal operating conditions, the uplink chips 200 and 300 operate normally without an initialization process according to the peripheral device information stored in the upchip flash.

On the other hand, the down chip 100 and the up chip (200, 300) of the present invention can be implemented as a single chip, respectively. Here, the down chip 100 is sufficient to have two USB, one I2C, one UART or SPI, and the upper chips 200 and 300 are sufficient to one USB, one I2C, and one UART or SPI.

3 is a block diagram illustrating a security KVM switch that extends to a dual display according to another embodiment of the present invention. If only the video switch 41 is added, the display 30 and 31 may be extended to two. This is because the down chip 100 and the up chip 200 and 300 each have a sufficient number of I2C ports to handle two or more DDCs.

FIG. 4 is a block diagram illustrating a security KVM switch for extending a PC to N according to another embodiment of the present invention. When only a video switch 42 contact point and upstream chip 700 are added, the PC 800 is added. Can be expanded to N. It is very simple to expand the number of PCs because the down chip 100 and the up chip 200, 300, and 700 that handle USB and DDC are the same. Here, the up chip 700 is made of the same configuration as the up chip (200,300), and the reference numeral is omitted in FIG.

As an embodiment of the present invention, one-way communication uses UART and transmits only from the downlink chip 100 to the uplink chip 200,300 using only the TX port of the downlink chip 100 and the RX port of the uplink chip 200,300. Make it possible. The photointerrupters 50 and 60 having a sufficiently fast switching speed for one-way isolation allow high-speed communication. Since normal UART communication cannot have a continuous zero of 10 bits or more, the start pattern 610 of FIG. 2 uses a 13-bit continuous zero pattern. When the UART of the upstream chips 200 and 300 detects a start pattern, the UART interrupts at the highest priority, so that the uplink chips 200 and 300 may receive the header of the command packet in any case.

The instruction processing time prediction function is determined by the following first linear prediction function.

      Delay = a * (datasize) + b

The data size is in bytes and the a and b values are determined by the speed of the microprocessor and the memory storage speed. In the embodiment, stable one-way communication is possible when a = 5 uS / byte and b = 100 uS.

Here, the down chip 100 and the up chip 200 and 300 may be implemented using a common 32-bit MPU, respectively.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

10: keyboard 20: mouse
30: display 40, 41, 42: video switch
50,60,70: Photo interrupt 100: Down chip
200,300,700: Up-chip PC: 400,500,800

Claims (8)

A down chip that reads descriptor and report data of the keyboard and mouse and EDID or DispID data of the display;
An up chip connected to a PC and emulating a keyboard, a mouse, and a display by receiving data of the down chip;
A photo interrupter for electrically connecting the down chip and the up chip to one-way communication; And
And a video switch to switch the video signal of the display.
When a command packet consisting of a start pattern transmitted from the down chip, a header, and data is received from an up chip, an interrupt signal is interrupted with the highest priority, and one-way communication is performed after the time predicted by the linear prediction function has passed. Security KVM switch, characterized in that connecting the down chip and the up chip to a common line. The method of claim 1,
The down chip,
USB host that reads descriptor and report data through USB connecting keyboard and mouse, assembles command packet, and puts in QUE,
DDC host that reads the EDID or DispID data through the DDC included in the display cable and assembles the command packet into the QUE,
A control unit for assembling a PC switch command packet and injecting the PC switch command packet into a QUE and controlling a PC switch switch when the USB host detects a PC switch request sequence by reading the keyboard report read;
And a transmitting unit for extracting and transmitting the next command packet from the QUE when the command processing prediction time for the transmitted command has elapsed. The method of claim 1,
The up chip,
Receiving unit that receives only when the PC number included in the header of the command packet matches the PC number of its own or when the entire reception
A USB emulator that receives data from the keyboard and mouse of the down chip and emulates it as if the keyboard and mouse are actually connected to a PC;
A DDC emulator that receives the down-chip display data and emulates the display as if it is directly connected to a PC, and
Security KVM switch characterized in that it comprises a control unit for processing the initialization, self-diagnosis, error management and control commands related thereto. The method of claim 1,
The linear prediction function is a command processing time linear prediction function that models a linear prediction function by distinguishing a memory access case from a flash memory write case and considers a flash memory erase time in a constant term when writing to the flash memory. Secure KVM Switch. The method of claim 1,
The peripheral device of the keyboard, the mouse and the display, the descriptor of the keyboard and the mouse, and the EDID or DispID peripheral device information of the display are stored in both the flash chip of the up chip and the down chip, and the down chip is connected to the peripheral device information of the down chip flash memory. Compare the connected peripheral devices and start the peripheral device initialization process only when the model of the peripheral device is actually changed.Upper chip operates normally without initialization process according to the peripheral device information stored in the up-chip flash memory. switch. The method of claim 2,
Emulates the keyboard, mouse and display in one up chip,
Secure KVM switch, characterized in that to perform the host function of the keyboard, mouse and display in one down chip. The method of claim 1,
And adding the video switch corresponding to the number of displays to extend the display to two or more displays by using extra DDC ports included in the down-chip and the up-chip without adding hardware. The method of claim 1,
And adding the number of contact points and the number of up-chips of the video switch corresponding to the number of PCs, thereby extending the number of PCs to two or more.

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