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 virtually imperceptible to the end recipient, and potential even the originator of the carrier signal. Television producers use steganographic methods to encode data in video signals for security, distribution monitoring, piracy-control, and other reasons. The present invention involves a device that connects to a telephone, either at the line or 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)—ones that never occur in the course of normal conversation and never get generated by telephone company equipment. Once detected, the presence of the signal guarantees the call was made to the restricted party from a particular phone line.
1. A method for detecting the addition of a third party to a pre-existing telephonic connection between a first party and a second party, said method comprising:
generating identification data;
subdividing the identification data into a plurality of subdivisions;
encoding the plurality of subdivisions onto a carrier signal to create a spread spectrum modulated identification signal, the spread spectrum modulated identification signal comprising the subdivisions of the identification data encoded on a plurality of frequency bands using a predetermined sequence;
adding the spread spectrum modulated identification signal to a telephone signal to form an encoded telephone signal, the spread spectrum modulated identification signal being imperceptible to a human listener of the telephone signal;
transmitting the encoded telephone signal across a telephonic connection;
receiving the encoded telephone signal at a remote location;
extracting the plurality of subdivisions of the identification data from the spread spectrum modulated identification signal; and
assembling the plurality of subdivisions of the identification data to re-create the identification data using the predetermined sequence.
2. The method according to claim 1 , further comprising comparing assembled identification data to a predetermined set of restricted data to determine if a third party has been added to the pre-existing telephonic connection.
3. The method according to claim 1 , wherein the step of generating identification data comprises inputting at least one alpha-numeric identifier of the first party.
4. The method according to claim 3 , wherein the at least one alpha-numeric identifier of the first party is selected from the group consisting of a personal identification number, a user number, an inmate identification number, a user name, a local telephone exchange, a source telephone number, and any combination thereof.
5. The method according to claim 1 , wherein the predetermined sequence is a predetermined pseudo-random code.
6. The method according to claim 1 , wherein the step of adding the spread spectrum modulated identification signal to a telephone signal comprises passively adding the spread spectrum modulated identification signal to the telephone signal.
7. The method according to claim 2 , further comprising initiating a response upon detecting the addition of a third party to the pre-existing telephonic connection between the first party and the second party.
8. The method according to claim 7 , wherein the response is selected from the group consisting of: turning off a microphone of a telephone; disconnecting the telephonic connection; recording a call; playing a pre-recorded message; recording call data; disabling a speaker of a telephone; adding a disruptive signal to the telephonic connection; and any combinations thereof.
9. A method of monitoring use of a source telephone by a caller, the method comprising:
generating identification data identifying at least one of the caller and the source telephone;
encoding the identification data into a modulated identification signal using a spread spectrum modulator;
combining the modulated identification signal with an audio output signal of the source telephone to form a composite telephone signal;
transmitting the composite telephone signal from the source telephone to a destination telephone;
receiving the composite telephone signal at the destination telephone;
extracting the identification data from the composite telephone signal using at least a spread spectrum demodulator; and
analyzing the extracted identification data to determine if the extracted identification data contains data that matches at least one of a predetermined set of restricted data.
10. The method according to claim 9 , further comprising initiating a restricted call response upon determining that the extracted identification data contains data that matches at least one of a predetermined set of restricted data.
11. A system for detecting unauthorized use of a source telephone to contact a destination telephone by a caller having restricted calling privileges, the system comprising:
a spread spectrum modulator that encodes an identification signal to generate an modulated identification signal, the identification signal including data identifying at least one of the source telephone and the caller;
a signal combiner coupled to an output of the spread spectrum modulator and the source telephone that combines the modulated identification signal and an output signal of the source telephone into a composite telephone signal;
a signal receiver coupled to the destination telephone that receives the composite telephone signal and extracts therefrom the modulated identification signal;
a spread spectrum demodulator coupled to the signal receiver that decodes the identification signal and extracts therefrom the data identifying at least one of the source telephone and the caller; and
a comparator coupled to the spread spectrum demodulator that compares the data identifying at least one of the source telephone and the caller to a predetermined set of restricted data.
12. The system according to claim 11 , further comprising an unauthorized call response processor that initiates an unauthorized call response when the data identifying at least one of the source telephone and the caller matches at least one of the predetermined set of restricted data.