Method and apparatus for communicating secure data over a telephone line using a cellular encryption apparatus

A communication apparatus (100) provides an interface between a cellular encryption and decryption apparatus (150) and a telephone line (91) allowing for communication of secure data of the telephone line using a regular telephone (70). The communication apparatus (100) provides for the receipt of incoming secure data in an unattended data mode, and also allows the telephone to be used in either a secure mode or clear mode. The communication apparatus monitors the telephone line (91) for secure tones while operating in the clear mode. When a secure tone is detected, the communication apparatus (100) breaks the path between the PSTN (90) and the telephone (70) and routes the signals to the cellular encryption and decryption apparatus (150) to establish a secure call.

FIELD OF THE INVENTION 
This invention relates in general to the field of secure communications, in 
particular to the communication of encrypted signals over a telephone 
line. 
BACKGROUND OF THE INVENTION 
There is an increasing need to communicate confidential information over 
the airwaves and telephone lines. The need to secure data from 
unauthorized access is readily apparent. The use of telephones that 
communicate over telephone lines is generally considered more secure than 
cellular and wireless telephones because a court order or physical access 
to equipment is required to "tap" a telephone line. Wireless 
communications, on the other hand, can be intercepted with readily 
available commercial receivers. 
Devices for securing cellular telephone calls are becoming readily 
available. These devices include cellular encryption and decryption 
devices that interface with a cellular telephone. However, no provisions 
are made to allow the security features of these devices to be used over 
the telephone lines. 
Thus, what is needed are a method and apparatus that provides an interface 
between a security device for a cellular telephone, and a telephone line 
allowing for the use of the security features over the telephone line. 
SUMMARY OF THE INVENTION 
The present invention provides, among other things, a method for 
communicating secured data over a telephone line using a cellular 
encryption apparatus. The method comprising the steps of sensing a loop 
current on the telephone line, providing a visible indication that 
non-secure communication is taking place in response to the sensing step, 
notifying the cellular encryption apparatus to enter a secure 
communication mode in response to either an input from a user or in 
response to a secure tone received over the telephone line, coupling the 
cellular encryption apparatus in series with the telephone line providing 
loop current to the telephone line, receiving a notification from the 
cellular encryption apparatus that the cellular encryption apparatus is 
ready for secure information and providing an indication that secure 
communication is taking place in response to the step of receiving the 
notification. The steps of sensing, notifying, coupling, providing loop 
current and receiving, are performed by a communication device coupled in 
line with the telephone line and a telephone set. The communication device 
interfaces with the cellular encryption apparatus and the telephone line 
is decoupled from the telephone set in response to the receiving the 
notification step. 
The present invention also provides, among other things, a communication 
apparatus for interfacing a cellular encryption and decryption apparatus 
between a telephone set and a telephone line. The communication apparatus 
includes a controller, a loop current sensor for sensing a loop current on 
the telephone line, and providing a signal to the controller when the loop 
current is sensed, a first indicator, coupled to the controller, for 
providing a visible indication that non-secure communication is taking 
place, a switch for coupling the telephone line with the cellular 
encryption apparatus, a loop current control circuitry for providing loop 
current to the telephone line, and a second indicator for providing an 
indication that secure communication is taking place. The controller 
notifies the cellular encryption apparatus to enter a secure communication 
mode, and receives notification from the cellular encryption apparatus 
that the cellular encryption apparatus is ready for secure information, 
and the switch decouples the telephone line from the telephone set in 
response to receipt the notification from the cellular encryption 
apparatus.

DETAILED DESCRIPTION OF THE DRAWINGS 
In the preferred embodiments, the present invention provides a method and a 
communication apparatus. The communication apparatus provides an interface 
between a cellular encryption and decryption apparatus and telephone line 
allowing for communication of secure data on the telephone line using a 
regular telephone. The communication apparatus provides for the receipt of 
incoming secure data in an unattended data mode, and also allows the 
telephone to be used in either a secure mode or clear mode. The 
communication apparatus monitors the telephone line for secure tones while 
operating in the clear mode. When a secure tone is detected, the 
communication apparatus breaks the path between the PSTN and the telephone 
and routes the signals to the cellular encryption and decryption apparatus 
to establish a secure call. 
FIG. 1 illustrates a block diagram of a communication apparatus in 
accordance with a preferred embodiment of the present invention. 
Preferably communication apparatus 100 as shown in FIG. 1 is coupled to 
cellular device 150 and is also coupled in series with a telephone set 70 
and the PSTN 90 as shown. Cellular device 150 is suitable for providing 
secure communications for a cellular telephone, included, for example, 
both encryption and decryption of information. Among other things, 
communication apparatus 100 functions as an interface between cellular 
device 150 and telephone line 91. 
In the preferred embodiment, communication apparatus 100 operates in two 
modes: a clear mode and a secure mode. In the clear mode, signaling passes 
from PSTN 90 through apparatus 100 to telephone set 70. In this clear mode 
communication apparatus 100 monitors the telephone line for secured tones. 
When a secure tone is detected or a secure button on keypad 116 is 
pressed, the unit breaks the path between the PSTN and the telephone set 
and routes the signals to the cellular device 150. A secure call may then 
be established. 
Communication apparatus 100 includes port 132 for interfacing with 
telephone line 91, which couples to PSTN 90. Port 132 couples through 
bypass line 152 through relay 114 to port 130. Port 130 interfaces to a 
telephone unit, for example. Port 132 also couples telephone line 91 
through line 154 to ring detector 104. Ring detector 104 includes 
circuitry for detecting rings on line 154 and providing a signal to 
controller 106 indicating the presence of such rings. Line 154 couples 
through ring detector 104 to line isolation circuitry 102 which isolates 
certain signals on line 154 from port 136. Port 136 is the secure 
information port of communication apparatus 100. 
Relay 112 couples line 154 to loop current control circuitry 108. Loop 
current control circuitry 108 provides loop current to PSTN 90 when 
signaled do so by controller 106. Loop current control circuitry 108, 
among other things, keeps the line to PSTN 90 active when bypass line 152 
is opened by relay 114. Communication apparatus 100 also includes keypad 
116 for providing user input to controller 106. In the preferred 
embodiment, keypad 116 has a secure button, a clear button and a data 
button. Pressing these buttons signals controller 106 to perform certain 
operations discussed in more detail below. Communication apparatus 100 
also includes a display 118. In the preferred embodiment, this display is 
comprised of three indicators, such as light emitting diodes, that 
indicate whether or not communication apparatus 100 is in the secure data 
mode, a secure voice mode or a clear voice or data mode. Display 118 may 
alternatively provide similar information by other means. 
Communication apparatus 100 also includes a loop current detector 110 for 
detecting when telephone set 70 is off-hook. Relay 114 switches port 130 
to either bypass line 152 or line 156. Relay 114 is controlled by 
controller 106. Loop current detector 110, upon sensing loop current, 
sends a signal to controller 106. Communication apparatus 100 also 
includes loop current control circuitry 124 for performing loop current 
control functions for telephone set 70. Line isolation circuitry 122 
provides isolation between ports 134 which is the clear voice port and 
telephone set port 130. A suitable procedure performed by communication 
apparatus 100 is described below. 
Cellular device 150 includes modem 182 coupled with encrypted data/voice 
port 162 and encryptor/decryptor 184. Vocoder 186 couples to 
encryptor/decryptor 184, to clear voice port 164 and to clear data port 
166 using data lines 167. Controller 188 interfaces with modem 182, 
encryptor/decryptor 184, vocoder 186 and control port 189. 
FIG. 2 is a flowchart illustrating a process by a communication apparatus 
in accordance with the preferred embodiment of the present invention. 
Procedure 300 is preferably performed by a communication apparatus similar 
to that of communication apparatus 100 (FIG. 1). Those of skill in the art 
will understand that other suitable communication apparatuses may also 
perform procedure 300. Among other things, procedure 300 is used for 
communicating encrypted data over a telephone line using a cellular 
encryption apparatus. Procedure 300, in the preferred embodiment, is a 
procedure for interfacing a cellular encryption apparatus between a land 
line telephone and a telephone line coupled to the PSTN. 
Procedure 300 is also suitable for receiving encrypted data over a 
telephone line using a cellular decryption apparatus. This is referred to 
as the unattended data mode. 
In task 302, the communication apparatus performs steps such as power-up 
initialization and status check. Task 302 is typically performed in 
response to a turn on initiated by a user. However, task 302 may be 
performed in response to signals received over the telephone line from the 
PSTN. In task 304, the communication apparatus waits for an incoming call 
over the telephone line. Also, in task 304, the communication apparatus 
waits for notice of an outgoing call which may be placed by a user of 
telephone set 70 (FIG. 1). For example, an incoming call may be sensed by 
ring detector circuitry which detects a ring signal on the telephone line 
and notifies a controller. An outgoing call may be sensed by a detection 
of loop current when a telephone is lifted off the hook. Alternatively, if 
outgoing data is being sent, a modem for example, provides a signal to the 
communication apparatus which is similar to a telephone on-hook signal. 
When the controller is notified by the ring detector that a call is 
incoming, task 306 is performed. In task 306, the controller counts the 
number of rings and after a predetermined number of rings, the controller 
may determine to answer the incoming call. If prior to the predetermined 
number of rings, loop current is sensed in the telephone line by the loop 
current detector, task 308 determines that the call is being answered by a 
user. For example, telephone set 70 may be lifted off the hook in response 
to the incoming ring. 
When after a predetermined number of rings the phone is not answered, task 
310 is performed. At this point in procedure 300, the communication 
apparatus is planning on receiving secure data over the phone line in the 
unattended data mode. In task 310, the phone line is seized. Relay 112 is 
closed while relay 114 disconnects the telephone set from bypass line 152 
(FIG. 1). Preferably in task 310, the controller verifies that the receive 
data button has been pressed on the communication apparatus. Task 310 also 
involves providing loop current control to the PSTN through loop current 
control circuitry. Task 310 may be viewed as an auto-answering task. 
In task 312, communication apparatus notifies the cellular device 150 (FIG. 
1) that secure data will be coming over the telephone line. Task 312 may 
include the task of controller 106 sending a "go secure" message to the 
cellular device. Task 312 may also involve waiting for a receipt of a 
signal over the phone line that tells the controller that secure data is 
coming. 
After the communication apparatus notifies the cellular encryption device 
that secure data is coming task 314 is performed. In task 314, the 
communication apparatus waits for a notice that call setup is complete. 
This notice preferably comes from the cellular device. Once call setup is 
complete, the clear (non-secure) information indicator is preferably 
turned on indicating that information received over the telephone line is 
not ready to be decrypted. In task 316 communication apparatus waits for a 
notification from the cellular device that it is ready to decrypt the 
incoming data. While waiting in task 316, cellular device performs tasks 
typical in the art for the decryption of information. Once task 316 is 
complete, cellular device 150 is ready to receive encrypted data and ready 
to receive and decrypt such data. 
In task 318, the secure data light is turned on and the clear data 
indicator is turned off. In task 319 the secure data is received through 
the communication apparatus and provides it to the cellular encryption 
device through port 136 (FIG. 1). During the performance of task 319 
cellular device 150 among other things decrypts the encrypted data an 
provides the decrypted data to a clear data port, for example port 166 
(FIG. 1). 
In task 320, communication apparatus waits for a message that says that the 
secure data transmission is complete or alternatively, it may sense that 
the clear button has been pressed on keypad 116. The secure information 
complete message may be provided by the cellular device 150 or it may be 
received over the phone line from PSTN 90. In the unattended data mode, it 
is assumed that in this point in procedure 300 the call is complete and 
task 324 is performed which releases the phone line. Task 324 involves 
recoupling bypass line 152 to telephone set 70 with relay 114 and also 
includes opening relay 112 no longer providing loop current to PSTN 90. 
Task 324 may be viewed as hanging up the line. After task 324 is complete 
communication apparatus returns to task 304 and waits for an incoming or 
outgoing call. 
In task 308, when loop current from the telephone set is sensed, (e.g., 
when the telephone is answered by a user) task 330 is performed. Similarly 
in task 304, loop current detector 110 senses loop current when the 
telephone set is lifted off hook. In this outgoing call situation task 330 
is performed. Prior to task 330, task 328 may turn on the clear 
information indicator indicating that cellular device 150 is not 
encrypting and/or decrypting the information. During the performance of 
task 330, communications are routed between telephone set 70 and PSTN 90 
through bypass line 152 (see FIG. 1). Accordingly, the connection of 
communication apparatus and cellular device 150 to the telephone line is 
virtually invisible to a user. In task 330, controller 106 waits for the 
secure button to be pressed via keypad 116. Alternatively, controller 106 
waits for a secure notice such as a secure tone, over the phone line from 
the other end. Alternatively, controller 106 may be notified by the 
cellular device 150 that it has received a secure tone or secure notice. 
In task 332, the communication apparatus responds to the secure button 
being pressed by notifying the cellular device to go secure. In the 
preferred embodiment, controller 106 sends a control signal to controller 
188. In task 334, the cellular device is switched in line with the 
telephone line. In task 334, relays 112 and 114 are switched and loop 
current control circuitry 108 provides loop current to the PSTN. Relay 114 
provides a connection from telephone set 70 to loop current control 
circuitry 124. Accordingly, PSTN and telephone set 70 are now coupled 
through communication apparatus 100 and through cellular device 150. 
After task 334 switches in the cellular device,-task 314 waits for a call 
setup complete message, preferably from controller 158. When the call 
setup is complete, task 316 is performed in which the communication 
apparatus waits for a secure notification from the cellular device 
indicating that it is ready to decrypt and/or encrypt information. Upon 
receipt of this notification task 318 is performed which turns on the 
secure voice or data indicators. 
In task 319, secure information is communicated between telephone set 70 
and PSTN 90. During task 319, cellular device 150, among other things, 
encrypts and decrypts information provided from ports 134 and 136 of 
communication apparatus 100. During task 319, clear voice data, for 
example, is provided to and from communication apparatus 100 through port 
130 to telephone set 70. Encrypted voice or other information is provided 
to and from PSTN 90 through port 132. Port 134 of communication apparatus 
100 provides a clear voice or other information to cellular device 150 
while port 136 provides the encrypted voice or other information to 
cellular device 150. During task 320, communication apparatus 100 waits 
for the clear data button to be pressed via keypad 116 or waits for a 
secure message complete notice either over the phone line or from 
controller 158. A user of telephone set 70 may press the clear button when 
the user no longer wishes to communicate secure voice over the telephone. 
In task 322, the secure indicator is turned off, the clear indicator is 
turned on and bypass line 152 is coupled into the telephone line through 
relay 114. Furthermore, relay 112 releases the phone line. If task 326 
determines that the call is not complete, the user may wish to continue 
his non-secure telephone call whereby communications are routed through 
bypass line 152. 
During the performance of task 326, clear voice information is communicated 
through bypass line 152. In another embodiment, clear non-encrypted 
information may be routed through cellular device and encryptor/decryptor 
184 acts as a through device without performing an encryption or 
decryption functions. 
Upon completion of the call, task 324, detector 110 senses loop current and 
notifies controller 106 when the user hangs up the telephone. The 
telephone line is released by opening relay 112 and coupling bypass line 
152 to the phone line through relay 114. 
The foregoing description of the specific embodiments will so fully reveal 
the general nature of the invention that others can, by applying current 
knowledge, readily modify and/or adapt for various applications such 
specific embodiments without departing from the generic concept, and 
therefore such adaptations and modifications should and are intended to be 
comprehended within the meaning and range of equivalents of the disclosed 
embodiments. 
It is to be understood that the phraseology or terminology employed herein 
is for the purpose of description and not of limitation. Accordingly, the 
invention is intended to embrace all such alternatives, modifications, 
equivalents and variations as fall within the spirit and broad scope of 
the appended claims.