GB2228603A - Secure data communication system - Google Patents

Abstract

In a secure data communication system for a security system including a control panel 10 linked to a plurality of information gathering devices 12, 14, 16, each of these devices 12, 14, 16 receives information from e.g. an associated security loop and is identifiable by the control panel 10 by a unique address code. In order to prevent substitution of any one of the devices 12, 14, 16 by a non-functional alien device, provided by an intruder, each device 12, 14, 16 has a predetermined identity code (or password) which is known only to the control panel 10. This code can be predetermined for each device 12, 14, 16 during manufacture thereof or loaded into the devices from a portable instrument during the setting up of the system. The control panel 10 includes means to request the identity code from each device and store same for future reference and comparison to ensure validity of information received by the panel 10. <IMAGE>

Description

SECURE DATA COMMUNICATION SYSTEM This invention relates to a secure date communication system especially in a security system between a central control panel and a plurality of information gathering or interface devices.

Multiplexed security control panels, in general, use two known forms of data communication to link them with various subordinate interface or information gathering devices. In a first known type each device has its own unique address or identity code defined either by the system's user or predetermined for each such device. In this case the central control panel can address each device in turn or randomly, the device then sending information on the status of its inputs to the control panel and/or if necessary receiving information dispensed by the control panel.

A second known type requires that the interface devices are connected to the central control panel as a loop. The control panel initiates an information gathering sequence either in response to a user initiated command or according to a timer control.

Information gathered by each device is transmitted on receiving the appropriate code from the control panel to the next interface device along the loop. Thus a block or pulse of information is generated comprising data from each of the devices which is eventually received by the control panel. A variation on this system is to provide a single directional system whereby the devices are connected in a single series and the data pulse is generated commencing with that device furthest away from the control panel.

Both of these known systems offer a fairly high degree of security against tampering. However, they do not prevent the substitution of one interface or information gathering device for another. If an intruder having a knowledge of the system could gain access to the data communication highway between one or more devices and the control panel he could substitute an alien device which would give predetermined responses to enquiries from the control panel. In this way the system could be defeated by the substitution of false data for accurate data gathered by the security sensors. Where the device has a particular address this information would be required in order to substitute an alien device.

However, this knowledge is relatively easily available.

It is an object of the present invention therefore to provide secure data communication between a control panel and subordinate information gathering devices.

With this object in view the invention provides a secure data communication system comprising a central control panel linked to a plurality of information gathering devices by a data highway, each information gathering device being provided with means for storing and transmitting a predetermined identity code, the transmission means being operative upon a command issued by the control panel which further includes means for storing said identity code upon receipt thereof It will be appreciated that in this way only the control panel has a record of which information gathering device is referred to by a particular identity code. Thus it becomes relatively difficult to determine the particular identity code of any one interface device and hence the code necessary for substitution of an alien device in the system.

Preferably the predetermined identity code is determined during manufacture of each information gathering device.

It is intended that on activation the control panel would send out the command code upon receipt of which the individual devices will respond by transmitting to the control panel their own unique manufacturing identity codes to be stored in the control panel for future comparison or reference. Again in this way only the control panel will have a record of one code referring to each device. An alien device substituted into the system will not have the same unique manufacturing identity code and will therefore be readily perceived by the control panel as the work of an intruder.

Advantageously the predetermined identity code is loaded into the information gathering device from a separate loading device. This device may be carried by, for example, an engineer during installation of the security system so that the identity code may be loaded into each information gathering device at that time.

The invention will be described further by way of example with reference to the accompanying drawings in which: Fig. 1 is a block diagram of a first embodiment of a security system incorporating the invention; and Fig. 2 is a block diagram of a second embodiment of a security system incorporating the invention.

Referring firstly to Fig. 1 a security system comprises a control panel 10 and a plurality of information gathering modules or interface devices 12, 14, 16 of which three such devices are shown representatively. Each of the interface devices 12, 14, 16 is in turn connected to a respective security loop or sensor (not shown) which is responsible for monitoring a specific area or function over which the security system has control.

The interface devices 12, 14, 16 are connected via respective connection means 18, 20, 22 to a central data communication highway 24 which serves to connect all the modules to the control panel 10. It will thus be appreciated that if any one security loop or sensor detects the presence of an intruder or any other alarm signal the interface device to which the security loop in question is connected will output an alarm signal which will be detected by the control panel and brought to the attention of the system's operator.

One common way of defeating such an arrangement is for an intruder to attempt to disable one or other of the security loops or the interface devices themselves. In order to overcome this possibility the control panel 10 is provided with the facility to "poll" each of the interface modules 12, 14, 16 to ascertain the status of the device and its associated input. In order to facilitate such "polling" each interface device 12, 14, 16 is given a unique identity code known as its address.

In this way the control panel can check on the status of any one particular interface device at a given time.

This function is usually controlled either by the system's operator or in response to a timed sequence initiated by the control panel 10 itself.

It would still be possible to overcome the system described and disable, for example, one interface device 12 by breaking the connection 18 between the interface device 12 and the data communication highway 24 and substituting a new, alien interface device provided by the intruder. In this case the new device would be preprogrammed to respond to control panel "polling" with a signal indicative of a correctly functioning interface device whereas it is in fact receiving no inputs from any sensor system. Thus it would be possible for an intruder to gain entry to a protected area through the security loop or sensors to which the original interface device 12 was connected. It will be appreciated however that in order to be correctly identified by the control panel 10 it is necessary in this instance for the alien interface device to respond to the correct address code.However this information is relatively easy to find as it is normally known to the system operator.

The invention provides a means of overcoming such an eventuality by providing each interface device 12, 14, 16 with means for storing a predetermined identity code or password in addition to the defined address for each such device. When the control panel 10 is activated each device 12, 14, 16 is issued a command requesting transmission of the device's password. This code is then stored on the control panel 10 for reference when "polling" the devices for input status the password attached to each status report may be compared with the stored code for validity.

It will be appreciated that in this way only the control panel will have a record of the password or identity code for a particular interface device. Thus it becomes difficult for an intruder to obtain the correct identity code for the substituted interface device to operate correctly.

Fig. 2 illustrates a second embodiment of a known security system to which the invention may be applied.

A security system according to this embodiment includes a control panel 10 and, again, a plurality of information gathering devices or interface modules of which three such devices 32, 34, 36 are shown to represent the entire system. As in the first embodiment each interface device is connected to its own respective security loop or sensor arrangement so as to monitor one particular section of an overall area which is to be protected by the security system. Each interface device 32, 34, 36 is connected to the interface device immediately adjacent to it and in the case of the first interface device 32 and in the case of the final interface device only to interface device 34. In a modified version of this embodiment the interface device 36 is ultimately connected back to the control panel 30.

This arrangement is known as a bi-directional system.

In the arrangement shown in Fig. 2 information on the status of each interface device and its associated security loop is transferred to the control panel 30 along the data highway 38 in response to a control signal either initiated by the system's operator or on a timed basis determined by the control panel. On the issuance of this command information on the status of each device is shifted from one interface device to the next in a direction heading towards the control panel 30. Eventually a block of information comprising a status report from each of the interface devices along the data highway is received by the control panel which can interpret this data and display it as appropriately to the system's operator.

It will be appreciated that it is possible to by-pass this system in a similar manner to that described in respect of the first embodiment. Furthermore if the system is not a bi-directional system but is as depicted in Fig. 2 then breaking the data highway between the control panel and the first interface device 22 effectively removes all the remaining interface devices from the system. Thus an alien device could respond to appropriate instructions from the control panel by indicating that the entire system was in operation when this in fact was not so.

In order to prevent such an occurrence it is intended in accordance with the invention that a unique identity code or password is stored, as previously in each interface device 32, 34, 36 such that information may be positively identified as originating from any one interface device in the system. This code may be loaded into the interface device either by using a portable programming instrument or a key device to be used during installation of the system or by having the address code inserted into the interface device during its manufacture. As in the first embodiment the control panel, on being switched on, would firstly request each of the interface devices to respond to their own unique address codes. These would then be stored for future reference.

Again it will be appreciated that only the control panel will have a record of the address code or identity code for each interface device included in the system.

Thus in order to substitute an alien interface device it would be necessary to know the unique code for each of the devices.

For a higher level of security the interface devices could include time based or dependent encryption means so that the password could be encoded for secure transmission to the control panel 30.

Claims (4)

1. A secure data communication system comprising a central control panel linked to a plurality of information gathering devices by a data highway, each information gathering device being provided with means for storing and transmitting a predetermined identity code, the transmission means being operative upon a command issued by the control panel which further includes means for storing said identity code upon receipt thereof.

2. A communication system wherein the predetermined identity code is loaded into the information gatheing device from a separate loading device.

3. A communication system as claimed in claim 1 wherein the predetermined identity code is determined during manufacture of each information gathering device.

4. A secure data communication system substantially as hereinbefore described.