Three-way call detection using steganography
View Patent ↗Three-way call detection is an important component of correctional facility telephone equipment because it helps restrict calling access by certain persons to certain restricted telephone numbers. Various three-way call detection methods exist, but all of these implementations suffer from one major limitation-the detection accuracy is not as high as is desired by the industry. The present invention improves detection accuracy, using “steganography.” Steganography involves hiding one set of data or signals within another signal or carrier in such a way that its presence is typically imperceptible to the human ear, and potential even the originator of the carrier signal. The present invention involves a device that connects to a telephone, either at the line or the handset interfaces, and produces a known signal that is steganographically hidden within the user's normal voice signal. Detection equipment, residing at another location, monitors signals on telephone calls and tests for the presence of the hidden signal or data generated by the invention. Once detection is achieved, appropriate action, such as terminating or recording the call, may be taken. Improved accuracy is achieved by choosing the appropriate hidden signal(s). Once detected, the presence of the signal guarantees the call was made to the restricted party from a particular phone line.
1. A three way call detection system for detecting the addition of a third party to an pre-existing telephonic connection between a first party and a second party, said system comprising:
an ID generator for generating identification data;
a spread spectrum modulator for imposing the identification data onto a carrier signal, said modulator outputting a modulated identification signal having frequency components that are capable of being transmitted via a telephonic connection;
a source telephone for participating in a telephone conversation;
a signal combiner for adding the modulated identification signal to the telephone conversation to form an encoded telephone signal, the modulated identification signal being imperceptible to a human listener of the telephone conversation;
a remote telephone for receiving the encoded telephone signal; and
a spread spectrum demodulator for demodulating the modulated identification signal to extract the identification data.
2. The system of claim 1 wherein the identification data is selected from the following: a personal identification number, a user number, an inmate identification number, a user name, data identifying the local telephone exchange of the source telephone, a telephone number of the source telephone, and data identifying the institution where the source telephone is located.
3. The system of claim 1 further comprising a processor for extracting the modulated identification signal from the encoded telephone signal.
4. The system of claim 1 wherein the spread spectrum modulator imposes the identification data onto a carrier signal by subdividing the identification data into a plurality of subdivisions and encoding the plurality of subdivisions on a plurality of frequency bands using a predetermined sequence.
5. The system of claim 4 wherein the spread spectrum demodulator demodulates the modulated identification signal, extracts the plurality of subdivisions of the identification data and assembles the plurality of subdivisions of the identification data into the identification data using the predetermined sequence.
6. The system of claim 4 wherein the predetermined sequence is a predetermined pseudo-random code.
7. The system of claim 4 , further comprising a code generator for generating a pseudo-random code, and wherein the predetermined sequence is a pseudo-random code generated by the code generator.
8. The system of claim 7 wherein the signal combiner passively adds the pseudo-random code to the telephone conversation at a predetermined plurality of frequencies.
9. A system for identifying a source telephone, said source telephone having identification data associated therewith, the system comprising:
a spread spectrum modulator for encoding the identification data into a spread spectrum signal using a spreading code; and
a telephone interface for coupling to a telephone to add the spread spectrum signal to an output of the telephone.
10. The system of claim 9 further comprising a processor for coupling to a telephone to extract identification data using a spread spectrum demodulator and a spreading code.
11. The system of claim 9 wherein the spread spectrum modulator is a selected one of a BPSK modulator, an MPSK modulator, and a QPSK modulator.
12. The system of claim 9 wherein the telephone interface is coupled to a selected one of a telephone handset, a TIP/RING pair of a standard analog POTS line, and a digital telephone interface.
13. The system of claim 9 wherein the telephone interface passively adds the spread spectrum signal to a telephone signal by a selected one of transformer coupling and capacitive coupling.
14. The system of claim 13 , further comprising a processor, coupled to the receiver, for extracting the modulated identification signal from the telephone signal.
15. The system of claim 13 , further comprising:
a comparator for comparing the identification data to a predetermined set of restricted data; and
a restricted call response module for executing at least a selected one of the following responses if the identification data matches any of the predetermined set of restricted data: (1) turning off a microphone of a telephone, (2) disconnecting a telephone call, (3) recording any conversation that may occur on a call, (4) playing a prerecorded message, (5) recording call data, (6) disabling the speaker of a telephone, and (7) adding a disruptive signal to a telephonic connection.
16. The system of claim 13 , further comprising:
a code generator for generating a pseudo-random code;
a spread spectrum modulator for imposing the identification data onto a carrier signal using the pseudo-random code, said modulator outputting a modulated identification signal having frequency components that are capable of being transmitted via a telephonic connection; and
a signal combiner for adding the modulated identification signal to an audio signal of a telephone microphone, said combiner producing a telephone signal as an output.
17. A system for decoding a modulated identification signal imbedded in a telephone signal wherein the identification signal is capable of identifying a source of the identification signal, the system comprising:
a receiver for receiving a telephone signal, which telephone signal comprises an audio signal and a modulated identification signal, said modulated identification signal having identification data embedded therein; and
a spread spectrum demodulator for demodulating the modulated identification signal to extract the identification data.
18. A method for identifying a source telephone, the method comprising:
providing a data identification pattern for identifying a source telephone;
generating a reference spreading code using a random number generator;
encoding the data identification pattern into an identification signal using the spreading code and a spread spectrum modulator, thereby generating a modulated identification signal;
combining the modulated identification signal with an audio signal of a microphone output of a telephone to form a composite telephone signal, the modulated identification signal being imperceptible to a human listener of the composite telephone signal; and
transmitting the composite telephone signal across a telephonic connection.
19. The method of claim 18 , further comprising:
receiving the composite telephone signal from a source telephone at a remote location; multiplying the composite telephone signal by the reference spreading code to form a signal product;
filtering or correlating the signal product to extract the modulated identification signal from the digital data; and
comparing the modulated identification signal with a predetermined set of restricted data signals to determine if the modulated identification signal matches at least one of a predetermined set of restricted data signals.
20. The method of claim 19 further comprising:
performing an envelope detection on the filtered signal product, if needed; and
comparing the output of the envelope detection with a threshold value to determine if the signal product matches at least one of a predetermined set of restricted data signals.
21. The method of claim 19 further comprising:
initiating a restricted call response if the signal product matches at least one of a predetermined set of restricted data signals, the restricted call response being selected from the group of following choices: (1) turning off a microphone of a telephone, (2) disconnecting a telephone call, (3) recording a call, (4) playing a prerecorded message, (5) recording call data, (6) disabling the speaker of a telephone, and (7) adding a disruptive signal to a telephonic connection.
22. The method of claim 19 wherein the step of receiving the composite telephone signal further comprises:
providing an analog-to-digital converter; and
converting the composite telephone signal from an analog signal to a digital signal.
23. The method of claim 18 further comprising:
demodulating the modulated identification signal to extract the data identification pattern using a reference spreading code.
24. A method for identifying a source of a telephone signal received by a remote telephone, the method comprising:
receiving a composite telephone signal from a source telephone at a remote location, the composite telephone signal comprising an audio signal representative of a telephone conversation and a modulated identification signal, the modulated identification signal having identification data that was embedded therein using a reference spreading code;
extracting the modulated identification signal; and
analyzing the extracted modulated identification signal to determine if the identification signal contains data that matches at least one of a predetermined set of restricted data signals.
25. The method of claim 24 wherein the step of extracting the modulated identification signal further comprises:
multiplying the composite telephone signal by the reference spreading code to form a signal product; and
extracting the modulated identification signal.
26. The method of claim 25 further comprising:
initiating a restricted call response if the signal product matches at least one of a predetermined set of restricted data signals, the restricted call response being selected from the group of following choices: (1) turning off a microphone of a telephone, (2) disconnecting a telephone call, (3) recording a call, (4) playing a prerecorded message, (5) recording call data, (6) disabling the speaker of a telephone, and (7) adding a disruptive signal to a telephonic connection.
27. The method of claim 24 wherein the step of receiving the composite telephone signal further comprises:
providing an analog-to-digital converter; and
converting the composite telephone signal from an analog signal to a digital signal.
28. The method of claim 24 further comprising:
demodulating the modulated identification signal to extract the identification data using a reference spreading code.
29. A three way call detection system for detecting the addition of a third party having a third phone to an pre-existing telephonic connection between a first party having a first phone and a second party having a second phone, said system comprising:
an ID generator for generating identification data;
a spread spectrum modulator for imposing the identification data onto a carrier signal, said modulator outputting an identification signal having frequency components that are capable of being transmitted via a telephonic connection;
a signal combiner for adding the identification signal to an output from a microphone of the first phone, thereby producing a combined output signal, said identification signal being added at a level that is imperceptible to a human ear that hears the combined output signal;
a signal receiver coupled to a third phone, for receiving the combined output signal after transmission across a telephonic connection from the first phone to the third phone;
a spread spectrum demodulator for demodulating the identification signal to extract the identification data; and
a processor to analyze the identification data.
30. The system of claim 29 wherein the output from the microphone comprises a digital signal and the signal combiner comprises a selected one of a digital adder or a microcontroller that digitally adds the identification signal to the output from the microphone.
31. The system of claim 29 wherein the output from the microphone comprises an analog signal and the signal combiner comprises a transformer for coupling the identification signal to the output from the microphone.
32. The system of claim 29 further comprising a digital signal processor coupled to the signal receiver for extracting the identification signal from the combined output signal.
33. The system of claim 29 wherein the processor analyzes the identification data to determine whether the connection is authorized.
34. The system of claim 29 wherein the third phone is a component of a local telephone system, and wherein the processor analyzes the identification data and reports its analysis to the local telephone system.
35. The system of claim 29 wherein the combined output signal travels a telephonic connection between the first phone to the second phone, and travels a telephonic connection between the second phone and the third phone.
36. A detection system for detecting a telephonic connection between a first phone and a second phone, said system comprising:
an ID generator for generating identification data;
a spread spectrum modulator for imposing the identification data onto a carrier signal, said modulator outputting an identification signal having frequency components that are capable of being transmitted via a telephonic connection;
a signal combiner for adding the identification signal to an output from a microphone of a first phone, thereby producing a combined output signal, said identification signal being added at a level that is imperceptible to a human ear that hears the combined output signal;
a signal receiver for receiving the combined output signal after transmission across a telephonic connection;
a spread spectrum demodulator for demodulating the identification signal to extract the identification data; and
a processor to analyze the identification data.
37. The system of claim 36 further comprising a digital signal processor coupled to the signal receiver for extracting the identification signal from the combined output signal.
38. The system of claim 36 wherein the first phone is a restricted phone, and the processor determines whether the connection between the restricted phone and the second phone is unauthorized.
39. The system of claim 38 wherein the processor is coupled to the second phone, and upon the detection of an unauthorized connection, the processor causes one or more of the following actions to occur:
a) recording a conversation between the restricted phone and the second phone;
b) terminating the connection between the restricted phone and the second phone;
c) disabling a speaker of the second phone;
d) adding an audible disruptive signal to the telephonic connection; and
e) adding an audible warning message to the telephonic connection.
40. The system of claim 36 wherein the second phone is a restricted phone, and the processor determines whether the connection between the first phone and the restricted phone is unauthorized.
41. The system of claim 40 wherein the processor is coupled to the second phone, and upon the detection of an unauthorized connection, the processor causes one or more of the following actions to occur:
a) recording a conversation between the restricted phone and the second phone;
b) terminating the connection between the restricted phone and the second phone;
c) turning off a microphone of the restricted phone;
d) adding an audible disruptive signal to the telephonic connection; and
e) adding an audible warning message to the telephonic connection.
42. The system of claim 36 wherein the signal receiver is coupled to a third phone that is a component of a local telephone system, and wherein the processor analyzes the identification data and reports its analysis to the local telephone system.