GB2108358A - Communications security system - Google Patents

Abstract

Communication, eg of a race commentary over telephone lines to a betting shop, is verified by transmitting a verifying data signal of a bandwidth substantially equal to the speech bandwidth. The period between transmission of the verifying data is randomised, eg by transmitting the verifying data signal during the first period of silence in the speech during each of a series of successive time frames, eg of 5 secs duration. In a preferred embodiment the verifying data includes an identity signal and a time reference signal. The receiver compares the received identity signal and time reference signal with respective signals generated by the receiver (4, 5) and an alarm is produced if variance occurs between any of the compared signals. Various aspects of synchronisation between the transmitter and the receiver are disclosed.

Description

SPECIFICATION Communications security system The present invention relates to a communications security system and a method of providing communication security.

Some communications signals have particular importance attached to them in terms of both their content and the time at which they were sent. An example of such a signal is a commentary provided at a race track and conveyed over telephone lines to a betting office where it may be used for judgement of wagers and for settlement of payments. Such commentaries may be conveyed by a line which is capable of transmitting messages in only one direction and cannot be used to verify the commentary.

This type of communication can be used to perpe tratefraud if the telephone line conveying the commentary is intercepted and a false commentary substituted for the genuine one resulting in the settlement of wagers against an erroneous result. A second risk is involved if the commentary is intercepted and delayed by such means as a tape recorder, this delay would allow time for wagers to be placed after the result of the race was known subsequent to which the commentary could be relayed to the betting offices to confirm the result of the race.

One known method of combating these risks is to arrange for positive identification of the commentary at the betting office and by injection of regular time signals into the commentary which can be checked at the betting office terminal. The aural systems currently in use are not totally effective, commenta- tors cannot always be recognised, they can be imitated and the time signals cannot be injected frequently enough to eliminate all possibility of fraud.

According to a first aspect of the present invention there is provided a communications security system comprising a transmitter for transmitting a composite speech and data signal in which the data speed has a bandwidth substantially equal to the speech bandwidth and in which the period between transmission of data is randomised.

According to a second aspect of the present invention there is provided a method of providing communication security comprising the steps of transmitting a composite speech and data signal, selecting the data speed such that the bandwidth of the data is substantially equal to the speech bandwidth and randomising the period between transmission of data.

The present invention mitigates the above described disadvantages by using data signals to confirm an identity and to record the timing of the commentary. The identity is unambiguous and the interval between time checks can be very short-five seconds for example. The nature of the data signal is such that it could not readily be imitated without considerable technical resources.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which; Figure lisa block diagram of a communications system, Figure 2 illustrates a composite speech and data signal, Figure 3 illustrates the data signal in more detail, Figure 4 is a block diagram of a security transmitter, and Figure 5 is a block diagram of a security receiver.

Figure 1 illustrates a system in which a speech transmitter 1 is coupled to a telephone line 3 via a security transmitter 2. The telephone line 3 may be connected to one orto several receiving systems, one of which is illustrated. The speech signals of the commentator are periodically gated out by the transmitter 2 and a brief coded data signal inserted before the commentary is again resumed. The composite signal is transmitted over the telephone line and is received at the bookmaker's premises where it is amplified by the speech receiving equipment 5 in order that it may be heard on a loudspeaker. The data signal is of such short duration, approximately 10 milliseconds, that it is not intrusive to the speech commentary. A security receiver 4 is teed from the telephone line and this receives the data signal.

Figure 2 illustrates a composite speech and data signal while figure 3 illustrates in more detail the characteristics of the data signal. The data signal comprises a brief period of silence followed by binary coded information which represents the system identity followed by a standard coded time signal. The identity is predetermined for the system and can be unique, alternatively it may constitute one of a group of acceptable identities. The standard coded time signal is generated by the transmitter internal clock which has a high order of accuracy such as may be obtained by a quartz crystal oscillator. The security reciver contains a similar clock which is synchronised with that in the transmitter. The receiver aiso contains a reference to system identity.At the receiver, data signals are separated from the composite signal and the content is compared with the local reference of system identity and time. If an identity signal is not received or if the system identity reliably received but the time signal is not confirmed by the receiver internal clock, an alarm is given that a fraud is probably being perpetrated. If neither speech nor identity signal are present, warning is given that the system is unprotected. This condition occurs when the system is disconnected.

The security system has the attribute that speech and data components are not readily separable in either frequency or time domain. This prevents a genuine data signal from being recombined with a fraudulent commentary, a situation which could otherwise remain undetected. This protection is achieved by using a data speed which occupies a bandwidth comparable with that required for the commentary, this eliminates the possibility of frequencyfiltering, and by introducing a random element in the period between transmissions, this prevents time domain gating. The random time element between successive data transmission is derived from the commentary itself, transmissions take place during the first period of silence within the commentary following the commencement of a new time frame.

Figure 4 illustrates the principles of the security transmitter. The speech commentary signal enters the security transmitter 2 at the signal detector 11 which continually scans the signal to identify periods of silence, each silence period is indicated to the signal generator unit 6 which is typically a microprocessor. The identity generator unit 7 of the unit 6 stores information of the system identity or address.

The standard coded time generator 8 of the generator unit t contains a quartz crystal clock which maintains the central time reference. Both identity and standard coded time signals are available to the period and signal gating section 9, of the generator unit 6, which controls the period between successive data signals. Standard time frames are establiohed within the period and signal gating section 9, a typical value being five seconds, and it ip intended that a data signal should be transmitted during each frame period at the first moment of silence which occurs within each frame. The first silence is indicated by the signal detector 11.When conditions are right for the transmission of data, the signal generating unit 6 forms the complete data signal comprising identity and standard coded time together with control signals, all of which pass to the combining unit 10. The combining unit 10 blocks the speech commentary and inserts the data signal at the completion of which the speech commentary is again allowed to pass to line.

The security receiver is illustrated in Figure 5. The incoming signal passes simultaneously to the signal detector 12 and to the signal processing unit 13 which is typically a microprocessor. The signal detector 12 continually scans the incoming signal to identify periods of silence, these are indicated to the period and signal gating section 14 of the signal decoding unit 13. The identity generating component 15 and the standard coded time generator 16 of the processing unit 13 operate in a manner similar to that described for the transmitter unit. The period and signal gating section 14 operates to produce standard time frames in synchronism with those produced at the transmitter unit and uses this information in combination with the output from the signal detector 12 to look for the data signal.The data signal is detected and its content compared with the system identity and the locally generated standard time. When no variance exists between the received data and the locally generated data, this situation confirms that the circuit is genuine.

If the system identity cannot be matched to the received data or if the identity section of data signal is reliably received but the standard coded time signal received are continually at variance with the locally generated time, this can arise only from deliberate interference with the transmission path or with equipment malfunction, this condition is interpreted as a risk of fraud and is used to sound an alarm. The signal processing unit 13 includes a control section 17 from which the alarm or uprotated warning signal is output.

The foregoing describes the normal mode of operation of the system. The method of effecting initial synchronisation between the receivers and the transmitter and the provision to correct for small discrepancies between transmitter and receiver time standards occuring over long periods will now be described.

Initial synchronisation may be effected in a number of ways. A universal time standard may be adopted in which case both transmitter and receivers may be synchronised by reference to it using radio time signals, telephone time signals or a secondary time standard set to universal time. The universal time standard has advantages of simplicity but is less secure since the information is readily available to everyone. If a system time is used, the information for setting time must be available for operatives responsible for that work. One method of achieving this is to generate the system time at the transmitter and to synchronise receivers to the transmission.When this method is used it is necessark to check the authenticity of the transmitted signal by means of either an verbal time announcement which may be checked with universal time or alternativeiy by comparing the commentary from an independent channel with the channel being synchronised.

Small differences between the time standards used in the transmitter and receivers will result in variances in recorded system time, significant variances accumulating over long time periods. One method of overcoming this difficulty is to arrange for receivers to make a small incremental adjustment in orderto align with the transmitted standard coded time. The frequency of resynchronising and the maximum synchronising increment can be arranged to virtually eliminate the possibilities of manipulation, for example it can be arranged to correct discrepancies in locaily recorded time once each day providing that those discrepancies do not exceed 0.25 seconds. It can be arranged for time corrections to be made automatically or they may be initiated manually.In normal operation it is possible for either the identity orforthe standard coded time signal to be wrongly received at the receiver due to low signal levels or due to impulsive noise on the telephone line. It would be inconvenient to raise an alarm where this occurs. One method of minimising the risk of false alarms without reducing security is to allow for such errors to accumulate to a predetermined total before registering an alarm. In such a system a register would be incremented each time a wrong data message was received and would be decremented each time a correct message was received, the register would operate for positive integers only. When the cumulative errcr count exceeds a predetermined level, e.g. four, the alarm would be sounded. Various weightings may be applied to errors or correct code receipts used to update the register. This practice constitutes a simple error correction system.

Claims (19)

1. A communications security system comprising a transmitter for transmitting a composite speech and data signal in which the data speed has a bandwidth substantially equal to the speech band width and in which the period between transmis sionsofdata is randomised.

2. A communications security system as claimed in claim 1,wherein the period between transmissions of data is randomised by the transmitter in accordance with the transmitted speech.

3. A communications security system as claimed in claim 2, wherein the transmitter generates time frames and initiates transmission within a time frame and during the first period of silence, within the speech to be transmitted, following commencement of that time frame.

4. A communications security system as claimed in any preceding claim, wherein transmission occurs between the transmitter and a receiver via a telephone line.

5. A communications security system as claimed in any preceding claim, wherein the transmitter includes a detector, for detecting silences within the transmitted speech, and a signal generator, which provides an identity signal and a time reference signal which are transmitted to a receiver.

6. A communications security system as claimed in any preceding claim, comprising a receiver provided with means for detecting an idenity signal contained within the transmitted signal, means for detecting a time reference signal included in the transmitted signal, means for comparing the received idenity signal with an idenity signal stored in the receiver, means for comparing the received time reference signal with a time reference signal generated by the receiver and means for generating an alarm if variance occurs between any of the compared signals.

7. A communications security system as claimed in claims 5 and 6, wherein the transmitter and receiver comprise respective synchronising means for synchronising generated time reference signals with an independent time reference.

8. A communications security system as claimed in claims Sand 6 or claim 7, wherein the receiver comprises means for re-synchronising the time reference signal generated by receiver with the time reference signal generated by the transmitterwhen a variance of up to a predetermined maximum value occurs within a predetermined period.

9. A communication security system as claimed in claim 6, wherein the receiver comprises means permitting upto a predetermined percentage of occurances of variation between compared signals before an alarm is initiated.

10. A method of providing communication security comprising the steps of transmitting a composite speech and data signal, selecting the data speed such that the bandwidth of the data is substantially equal to the speech bandwidth and randomising the period between transmission of data.

11. Amethod of providing communications security as claimed in claim 10, comprising the step of randomising the period between transmissions of data in accordance with the transmitted speech.

12. A method of providing communications security as claimed in claim 11, comprising initiating transmission within a time frame and during the first period of silence, within the speech to be transmitted, following commencement of that time frame.

13. A method of providing communications security as claimed in any of claims 19 to 12, comprising including an identity signal and a time reference signal in the transmitted signal.

14. A method of providing communications security as claimed 13, comprising the steps of comparing the transmitted identity signal with an identity signal stored in a receiver and comparing the transmitted time reference signal with a time reference signal generated by the receiver and generating an alarm if variance occurs between any of the compared signals.

15. A method of providing communication security as claimed in claim 14, further comprising synchronising the transmitted time reference signal and the receiver generated time reference signal with an independent time reference.

16. A method of providing communication security as claimed in claims 13 and 14 or claim 15, comprising re-synchronising the transmitted time reference signal and the receiver generated time reference signal when a variance of upto a predetermined maximum value occurs within a predetermined period.

17. A method of providing communication security as claimed in claim 14, comprising permitting upto a predetermined percentage of occurances of variation between compared signals before an alarm is initiated.

18. A communications security system substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of providing communication security substantially as hereinbefore described with reference to the accompanying drawings.