CA2128307C - Secure telecommunications - Google Patents

Abstract

A security node disposed in the telecommunications network connecting calling and called parties transforms information (which can be voice, data, facsimile, video and other types of calls or messages) encrypted in a first format to (a) encrypted information in a different format or to (b) non-encrypted information, and vice-versa. The node is accessible from any location connected to the network.
By routing calls or messages originated by the calling party and destined for the called party via the security node, and providing appropriate control signals to the node, the information may be encrypted only over a portion of the transmission path between the parties, and clear over the remainder of the transmission path.
Alternatively, the information may be encrypted in different portions of the path using different encryption algorithms. This arrangement enables the parties to obtain relatively secure communications even if only one party has a security device at the originating or terminating end, or if the parties have security devices using different handshaking protocols and encryption algorithms.

Description

212~307 SECURE TELECOMMUNICATIONS
Technical Field This invention relates generally to secure telecomm-lnications involving voice, data, facsimile, video and other information.
s Back~round of the Invention Over the past several years, a great deal of emphasis has been placed on increasing the security of teleco"""llnic~ti-~n~ systems, so that unauthori~d persons cannot intercept and access voice, data, f~simile, video or other information not intended for them. Studies have shown that the commercial markets are well aware10 of the threats to their co,-"--~-nir-ation~ systems and have a clear sense of the business applications which are at risk because of potential breakdowns in security. The reasons for the heightened interest are many, inchl(ling the increased use of cellular telephony in which a portion of the conversation is carried over the air and is thus more susceptible to attack, and the fact that other portions of the teleco--"""r-ir~ion~
5 network can be particularly susceptible to security breaches; i.e., wiring closets, junction boxes, manhole or telephone pole connections, facsimile machines, and especially cordless and cellular phones.
Summary of the Invention In accordance with an illustrative embodiment of the present invention, 20 secure col~ "~ "..~ ic~tions between calling and called parties is accomplished with use of a secure telephone device (STD). An STD disposed between the handset and the base of each party's telephone converts a conventional non-secure telephone call to a secure call by encrypting speech to be tr~n~mittçd to a party and by decrypting speech received from that party. Illustratively, each party's STD comprises a speech 2s coder (and decoder) (codec), a cryptographic system, and a modem. Both the modem and the speech codec are suitably interf~cecl to the telephone base and handset of the party, respectively.
In accordance with the illustrative embodiment, a secure telephone call between two parties having STDs is predicated on an existing non-secure call over a 30 telephone network. Given an STD in combination with a telephone, a calling party establishes a non-secure telephone call in conventional fashion (for example, by generating DTMF signals with the keypad of the telephone base to identify the called party). At the outset of such a call, the STD of each party is in non-secure mode and therefore acts only as a conduit for speech signals to and from a telephone handset.
Either party to the non-secure call may initiate a conversion of the call to a secure 5 call by sign~lling for the initiation of training and cryptographic key exchange - sequences between the cryptographic systems of the two STDs involved in the call.
Such sign~lling is provided with use of a user interface of the STD.
Once in secure mode as a result of such sequences, the speech of each party is encrypted to ensure its security. When a party speaks an utterance, that 0 party's audible words are converted into electrical signals by a microphone in the party's telephone handset. These signals are received by the STD through an appropliate microphone interf~ce and compressed by the STD's speech coder.
Compressed speech signals are then provided to the cryptographic system of the STD. The cryptographic system encrypts the compressed speech signals in 5 accordance with the cryptographic key exchanged between STDs. Encrypted speechsignals output from the cryptographic system are modulated by the modem of the STD. The modulated signals are provided to the telephone base of the speaking party via the telephone base interface of the STD. These signals are then transmitted in conventional fashion over the telephone network to the other party on the call.
Modulated signals received from the network at a party's telephone base are provided to the STD of the party via the STD telephone base interface. Thesereceived signals are first demodulated by the modem of the receiving STD. The resulting clemo~ te,cl signals reflect encrypted com~lessed speech generated by the other party to the call. The encrypted colllplessed speech is then decrypted by the 2s cr,vptographic system of the STD to yield signals reflecting col~l~,ssed speech. The compressed speech signals are then decolllpl~,ssed by a speech decoder of the STD.
Decompressed speech is then provided to the listening party's telephone handset speaker via the handset interface of the STD.
Illustratively, the speech codec of the STD is a CELP speech codec.
30 The cryptographic system conforms to the Federal Information Processing Standard 140-1. The user interface of the STD includes a keypad for generating control orinformation signals to be encrypted; switches to control whether the STD is in secure mode; and a display to indicate, for example, STD status (~ltern~tively, such information could be provided to the user through LEDs or audible messages played 35 through a handset).

212~307 In other illustrative embodiments, the STD may be used to encrypt information signals from various co"~",~ ication devices such as a fax machine, conlpuler, data terminal, etc. Moreover, the STD may be used with conventional speaker phone devices in place of a conventional handset.
s According to one illustrative embodiment, the STD includes a removable interface module. This module contains the intt-rfa~es needed to adaptthe STD for a particular operational environment, such as a particular telephone base and handset which present a particular set of electrical characteristics to the STD. In order that the STD have the capability of functioning with various telephone bases 0 and handsets (i.e., in order that the STD be able to function with devices of varying characteristics), STD interfaces to its environment are contained in the removable (i.e., replaceable) modules. Each module provides a set of interfaces to allow the STD to function with, for example, one or more telephone base and handset combinations of similar characteristics. When a user desires to move an STD to a5 telephone set with base and handset characteristics different from those of the previous telephone set used with the STD, all that is required for STD-telephoneelectrical compatibility is to change in~erf~ce module to one which accommodatesthe new telephone set. Other related embo l i .- ,en~s include removable interface modules for adapting the STD for operation with other devices such as co~ ul~ls,20 fax m~chines, etc.
Various services may be provided with use of the STD. Illustratively, the STD may be used in a "totally secure phone call" service. According to this service, a user who wishes to place a totally secure call to a called party first calls a node of a co--.-"--,-ic~ti~ ns network. The node includes a cryptographic system2s compatible with the user's STD. Once an ordinary non-secure call is established between the calling party and the node, the calling party (or the node) initiates a secure connection with the node (or the calling party) by training and cryptographic key exchange techniques. After the secure connection is established, the callingparty may transmit a telephone number of the called party to the node. This called 30 party telephone number may be entered by the calling party with use of a keypad on a user interface of the STD. The node responds to this information by placing a call to the called party at the number supplied by the calling party. The call to the called party may be a non-secure call or converted to a secure call if the called party has an STD. Once the call to the called party is made, the node may couple (or "bridge") 35 the two calls allowing the calling party and called parties to converse. The phone call is totally secure because not only is the speech of the parties encrypted, but the telephone number of the called party is commllnicated in encrypted form.
Another use for the STD is in the secure communication of personal information. Illustratively, personal infollllation which is to be sent to a system or device over a telephone line may be colll~ at~l in encrypted form with use of an5 STD. A secure connection may be made with the receiving device (which incll1d~s a cryptographic system) by establishing a conventional non-secure connection with the device and then converting the connection to a secure connection by the techniques discussed above. At this point, personal information, which may be, for example, a personal i(lentification number, social security number, or the like, may be 0 comlllunicated to the device via the secure connection. Such personal information may be entered with use of the keypad on the STD.
The STD may also be used in a secure voice messaging system or service. According to an illustrative embodiment, a calling party who accesses avoice m~-ssaging system in conventional fashion may communicate a message in encrypted form. If the voice messaging system includes a cryptographic system which is compatible with the calling party's STD, the calling party (or the system) may initiate a conversion of the non-secure call to the voice messaging system to a secure call as described above. Once the secure call is established, the calling party may leave a message for a recipient knowing that the message has been 20 co. . .~ ated securely to the messaging system. A recipient, using a similar procedure, may securely retneve stored m~-ssagçs at a telephone having an STD.
Brief Description of the Drawin~s In the drawing, Fig. 1 is a block diagram illustrating a security node arranged in 2s accordance with the present invention;
Fig. 2 is a flow diagram illustrating the steps followed in controller 152 of Fig. 1 to set up a "secure-to-clear" commllnication path, i.e., a secure connection between a calling party (CPE 101) and the security node and a clear connection between the security node and the called party (CPE 102);
Fig. 3 is a hardware flow diagram useful in explaining the process for initi~ting secure-to-clear commllnic~tions and illustrating the path through some of the components of Fig. 1 for such calls or messages;
Fig. 4 is a flow diagram illustrating the han-1sh~king steps followed in enciy~ol~ in encryptor bank 170 and in CPE 101 and 102;

212~307 Fig. 5 is a flow diagram illustrating the steps followed in controller 152 in order to set up "secure-to-secure" communication;
Fig. 6 is a diagram similar to Fig. 3 showing the additional elements involved in the setup process for initi:~ting secure-to-secure comrnunication;
Fig. 7 illustrates the path after secure-to-secure co"""ll,-ic~tion has been established using the arrangement of Fig. 6;
Fig. 8 is a block diagram illustrating the elements of typical customer premise equipment, such as CPE 101 of Fig. l;
Fig. 9 is a block diagram illustrating the elements of a typical encryptor, 0 such as en~;ly~ ol~ 172 and 174 within encryptor bank 170;
Fig. 10 is a flow diagram illustrating an alternative process for completing secure-to-clear, clear-to-secure, and secure-to-secure calls using security node 150; and Figs. 11-15 illustrate the hardware arrangements during various steps in 5 the process of Fig. 10.
Fig. 16 presents a flowchart summarizing the illustrative operation of a security node fflcilit:~ting a totally secure telephone call service.
Fig. 17 presents a system for providing secure personal information over the telephone line to an illustrative information service platform.
Fig. 18 presents a system providing secure voice messaging.
Fig. 19 presents a secure telephone device adapted to receive a plug-in telephone handset and base interface moclllle.
Figs. 20 and 21 present schematic diagrams of telephone handset and base interface circuits, respectively, for use in the plug-in module presented in Fig.
2s 19.
Detailed Description Referring first to Fig. 1, there is shown a block diagram illustrating the arrangement of a security node 150 constructed in accordance with the present invention, and its relationship with various components of local and interexchange 30 telecoll~ll~ utions networks. Security node 150 is designed to effect co~ unications such that (a) information carried in a portion of the tr:~nsmi~ion path (e.g., the portion bet~,veen the calling party and node 150) can be secure, while information carried in another portion of the transmission path (e.g., between node 150 and the called party) is clear; or (b) information carried in the portion of the 3s tr~n~mi~sion path between the calling party and node 150 can be encrypted using a first encryption algorithm, while the information carried in the portion of the transmission path between node 150 and the called party is encrypted using a second, different, encryption algoli~
In Fig. 1, coi--"~,lnic~tions originated by a calling party using near side customer premise eyuiplllel-t (CPE) 101 are destined for a called party using far side 5 CPE 102, and vice versa. As used herein, "co.,-",~ ic~tions" may include analog or digital calls or messages that convey voice, data, facsimile, video or other information. Hereinafter, co-~----ll,-i~tions may be referred to simply as calls. CPE
101 and 102 may each include a commercially available secure telephone unit (STU), such as the STU-III telephone available from AT&T, or another secure lo terminal available from a vendor such as Motorola or General Electric. ~lterns~tively, CPE 101 and/or CPE 102 may respectively include a secure telephone device (STD) 191, 192, i.e., an adjunct, that connects to an associated telephone 193, 194, or to a fax machine, data termin~l, or other comml-nication device. Note that there is no re~uirelll~,nl that CPE 101 or STD 191 be of the same type as CPE 102 or STD 192;
5 indeed, they can be obtained from different manufacturers, use different encryption algorithms or han-l~h~king protocols. Also, either CPE 101 or CPE 102 (but not both) can be an ordinary (non-secure) termin~l or device.
For the purposes of further explanation, CPE 101 is assumed to be arranged to transmit and receive outbound (i.e., from the calling party to the security 20 node) and inbound (i.e., from the security node to the called party) calls that can be either clear or secure. Switches in CPE 101 control the mode, clear or secure, in which the e~lui~lllent operates; mode changes are made either locally, under direct user control, by actuating the switches or alternatively, in response to a remotely genel~ted signal. For convenient data entry, CPE 101 may be equipped with a touch 25 tone generator and a keypad; status indications can be given to the user through one or more display indicators, such as LED display lamps. For the purposes of the imm~li~tely following description, it is assumed that CPE 102 is a conventional telephone, since secure-to-clear co-.-..,l.nic~tions are described first. Later in the detailed description, secure-to-secure co,....-,---ic~tions are described.
While teleco.~ -.-ic~tions "access" to security node 150 can be gained by any convenient access mech~ni~m, such as by using (a) a soflwa~ defined network (SDN) access number, or (b) a POTS (plain old telephone service) number in conjunction with a p~e.l~iulll service such as MEGACOM available from AT&T;
or (c) an 800 number, it is assumed, for the purposes of explanation, that a calling party using CPE 101 gains access to node 150 by dialing a predetermined toll-free number, such as 1-800-ENCRYPT. When that number is dialed, the call is routed 212~307 through a switch 107 (e.g., a #SESS ~ electronic switch available from AT&T) in a local exchange carrier (LEC) office 108 serving the calling party, to an interexchange carrier switch 110, typically an AT&T #4ESS Action Control Point (ACP) that is part of a switched teleco~ lni~tions network that is designated generally as 156.
5 Switch 110 responds by gencla~illg a si~n~ling message (usually in the CCS7 sign~ling format) and routing it through a common ch~nnel signaling (CCS) network 115 including a plurality of interconnected Signal Transfer Points (STPs) 116, 117, to an InWATS Data Base (IDB) 120, or to a network control point (NCP) in a software defined network, depending upon the subscription plan of the calling party.
o IDB 120 contains records for each dialed 800 number, and performs a look-up operation in order to generate a routing number associated with the dialed number, which is sent back to switch 110. In response to the routing number, switch 110 in turn routes the call to security node 150, usually through other components of switched telecomlllullications network 156, which may include another ~4ESS
5 switch 125. It is to be noted that a calling party may be connected directly to LEC
office 108, as shown in Fig. 1, or connected via a PBX switch or other customer premises e4ui~ment, not shown. It is also to be noted that other access and signaling arrangements may be used to interconnect CPE 101 with security node 150.
When the call is received in security node 150, the node may also 20 receive from switch 107, 110 or 125, a CCS message containing the dialed number and automatic number identification (ANI) information identifying CPE 101.
However, the availability of such information depends upon the capabilities of the specific switches and si~n~ling e4uip,l,elll being used by LEC office 108 and network 156. For the purposes of the following expl~n~tion, it will be s~s-lm~ that 2s calling party information is not available without plulllp~illg the caller.
As shown in Fig. 1, security node 150 includes a switch 151, which may, for example, be a Definity (TM) digital PBX available from AT&T, that is arranged to connect incoming calls received on trunk 160 to an available port of a switch controller 152, via a line in line group 161. Switch 151 is also arranged to 30 connect calls to available encryptors in an encryptor bank 170, via line group 164. A
bus 162 between switch 151 and controller 152 enables co""",lllic~tion of control signals. Controller 152, which may be a Conversant~ system available from AT&T, includes a voice response unit (VRU) 153 that can transmit voice pro,llp~s to the calling party, in accordance with a script stored in a local database (DB) 154.
3s Controller 152 can also perform a variety of other functions by itself or in combination with switch 151. For example, it can receive and logically process -8- 2I2~307 information entered by the caller in response to ~lulllp~ g, in conjunction withinformation retrieved from database 164. Such information can be entered by the ca71er using the touch tone dialing pad which is no7m~lly part of CPE 101, or via a keyboard or other separate input device. In some cases, information can be input as 5 voice responses that are interpreted using "speech to text" processing capabilities. In addition, controller 152, in conjunction with switch 151, can (a) initiate (or co~ and switch 151 to initiate) calls by generating dialing sequences and applying such sequences to switch 151, (b) ~iml71t~neously receive and process ca71s at several inputs, and (c) bridge (or command switch 151 to bridge) incoming and outgoing 0 calls together. Controller 152 can also remain in the call path for a specified time or interval in order to detect and act upon control signals applied to the call path by either the calling or called parties. All of the foregoing functions are available in the Conversant system mentioned above, and in similar systems available from other vendors.
The process followed in controller 152 when a ca7.1 is received from a caling party that dialed the number of node 150 (e.g., 1-800-ENCRYPT), desiring to effectuate secure-to-clear co, - " "~"-ication (i.e., secure between CPE 101 and security node 150 and clear between security node 150 and the called party), is shown in flow diagram form in Fig. 2 and sl1mm~7i7ec7, as follows:
Upon receipt of a call (step 201), switch controler 152 prolllpls the caller (step 203) for info~ ation needed to complete the call. This may include information identifying the calling party as a subscriber, e.g., a "login"; information verifying the identity of the calling party, e.g., a password; and information identifying the called party, e.g., the telephone number of CPE 102.
At this point in the process, information identifying the "type" of encryption being used by the calling party may also be received in controller 152 in response to a voice prompt. However, it may be preferable to automate the provision of this information, such as by including a code indicative of the encryption type in the "begin secure tr~n~mission" signal exchanged before encryption begins. It is to 30 be observed, however, that the encryption "type" may alternatively be obtained at a subsequent point in the set-up process as discussed more fully below. For the purposes of the following descripdon, it is assumed that the encryption type is obtained in step 205, and stored in database 154. In any event, it is noted here that "type" information is required because node 150 is arranged to support customers3s that use a variety of different CPE that incorporate and use different encryption algorithms. Accordingly, the details of the specific type of encryption used by the 212~307 calling party is required in order to effectuate applopliate processing in node 150.
Upon receipt of caller-entered information, controller 152 checks cl~t~b~ce 155 (step 207) to see if the caller is an authori_ed user. If unauthorized, controller 152 plays a ttormin~ting announcement in step 209 while if ~nthori7~d, S controller 152 continues to collect info~ tion entered in response to the remaining pr~lllpls. In addition, controller 152 sends calling party identificatinn and called party i~lfol~ation to a recording and billing processor 185 in order to initiate the billing process (step 211?. Processor 185 periodically com.~ ates with an automatic bill rating and fol~l~atling system 187 which records call details foro subsequent bill procession (step 213). Call details may include date, time andduration of session, number called, etc. The billing process is shown in Fig. 2 as continuing independently of the "main" call set-up and encryption process involving node 150.
When controller 152 has determined the type of encryption being used 5 in CPE 101, a lookup operation is performed in database 154 (step 215) to determine a hunt group designation associated with selected enc~y~lols within bank of encryptor bank 170 that use encryption algoli~s that can effectively process (i.e., decrypt) encrypted signals generated in CPE 101. Since several calls using the same encryption type can be processed at the same time, encryptor bank 170 contains 20 several such encryptors, each of which has an individual access number in the same hunt group.
Controller 152 then outpulses control signals (generally tones) to switch 151 on line 162, representing the hunt group associated with the selected encryptor type being used by the caller. When the hunt group is called, the next available25 encryptor of the applulJliate type (e.g., encryptor 172 in Fig. 1) is selected by switch 151. However, if no encryptor of the selected type is available (step 217), the process is terminat~l (step 209).
When a particular encryptor is selected, its input end (with respect to calls generated in CPE 101) is connected to switch 151 via line 164 (step 219). Note 30 that in the forward direction, i.e., from CPE 101 to CPE 102, encryptor 172 is actually operating to decrypt calls that have been encrypted in CPE lOl,so that such calls can be extended to CPE 102 from node 150 in the clear.
Because the encly~tol~ within encryptor bank 170 may themselves contain little co"""~ ic~tions ~ign~ling capability, each encryptor, including 35 encryptor 172, can be arranged so that its output end (with respect to calls generated in CPE lOl)is connected to a line side termin;~tion in switch 151, in order to allow 212~30~

signaling to be pelrolllled by controller 152. Specifically, when encryptor 172 is selected, its output end is connected to line 165 in switch 151, thereby supplying dial tone to controller 152.
In response to receipt of dial tone, switch controller 152 is arranged to s generate dialing signals that are applied to switch 151 and cause that switch to initiate a second call to controller 152 (step 221). This call, which is extended from switch 151 to controller 152 via line 166, is desirable since it enables the controller to continue to monitor calls in the clear mode (i.e., not encrypted) after the call setup process has been completed. As explained more fully below, the first connection 10 through controller 152, which is dropped after call setup is completed, places the controller in a position in the call flow sequence such that encrypted (rather than clear) voice/data is received.
Controller 152 is now in a position to complete the call to CPE 102.
This is done by placing the incoming call (i.e., the call from CPE 101 to controller 5 152 via encryptor 172) on hold and init;~ting a new call (step 223) to the called party number that was provided earlier and that is stored in database 154. Routing of this call is from controller 152 to switch 151 via an line 168. From switch 151, the call is routed to switch 125 via trunk 163 and then through telecomml]ni~ations network 156 to the intended destination, CPE 102, using conventional call set-up and 20 ~ign~ling procedures. Egress from security node 150 to the called party may be provided through MEGACOM~ service, SDN, or other outbound service (i.e., PRO
WATS, WATS or Business Long Distance available from AT&T). The connection between teleco~ ic~tinns network 156 and CPE 102 is typically made through a second LEC office 112, which includes a termin~ting #SESS switch 111.
2s When the called party answers, answer supervision is detected in switch 125 and passed through switch 151 to controller 152. In response, controller 152 is arranged to signal switch 151 to bridge (step 225) the call TO controller 152 (on line 161) with the call FROM controller 152 (on line 162). This removes one "appearance" of controller 152 from the call path, but leaves the second appearance intact. This allows controller 152 to continue to "monitor"-the call (step 227) for the occurrence of control signals (touch tone signals or voice, which are clear, rather than encrypted) after an end to end connection is made, so that certain other actions, described below, can be taken during the progress of a call.
Comm~]nic~tiQns in the reverse direction, i.e., from the called party 3s (CPE 102) to the calling party (CPE 101), once the call path has been set up in switch 151, follows the same path and uses encryptor 172 as an encryption (rather -11- 212~307 than a decryption) unit for the return direction.
Before describing the training sequence used to effect secure c~.~.. ni-~tion~ belw~ell the calling party and node 150, it will be instructive to describe the call setup process in an ~ltern~te form, in conjunction with Fig. 3, in s which the same designations are retained for the various components in Fig. 1.However, the call flow is shown in a "linear" form, i.e., the multiple appe~al ces of switch lSl and controller 152 have been "unwrapped".
In Fig. 3, a call initi~to~l by CPE 101 is routed through the local and toll networks, including, for example, ~wi~ches 107, 110 and 125, which are not shownlo in Fig. 3, and arrives at a first input port 301 of switch lSl (step 201), which routes the call to a first input port 311 of controller 152 via its output port 302. After the controller has obtained sufflcient information to determine the type of encryption that may be performed in CPE 101, (steps 203, 205), a connection is made by controller 152 to one of the encl~tols (illustratively encryptor 172) in encryptor bank 170 (steps 207, 215, 217). This connection is made by (1) controller 152, at its output port 312, seizing an available input (port 303) in switch 151, and (2) dialing the hunt group number associated with the ap~ l;ate type of encryptor. This causes switch 151 to route the call from an output port 304 to encryptor 172 (step 219).
The output side of encryptor 172 is connected to an input port 305 of switch 151 (step 221), which provides a dial tone back to controller 152. Upon receipt of this dial tone, controller 152 outputs from port 312 the signals (e.g., digits) required to connect the call to its destin~t~on, via a second connection throughcontroller 152 (step 223). While this connection can be established in several ways, 2s the following procedure is plefell~d: First, the digits output from port 312 cause switch 151 to initiate a call and thereby to connect its input port 305 to an output port 306 that is, in turn, connected to a second input port 313 of controller 152.
Controller 152, in turn, receives the output signals (digits) and initiates a new call through switch 151 by providing the control signals indicative of the dialed number 30 from its output port 314 to an available input port 307 of switch 151. This call is initi~ted when switch 151 connects port 307 to an output port 308 that is in turn connected to switch 125 in the switched telecoll",llll-ic~tions network 156.
When answer supervision is received from the called party using CPE
102, a clear co" " "Il~iç~tion path has been established from CPE 101 through node 3s lS0 to the called party CPE 102. At this point, controller 152 signals switch lSl to bridge the call input at port 301 with the call output at port 304 (step 225). This -12- 212~307 establishes a bypass 350 around one appearance of controller 152, but allows thesecond appearance of that controller to remain in the clear portion of the call path, in order to monitor the call (step 227) and detect control signals or call status conditions and, in response, perform various other call setup and/or m~inten~n~e5 functions.
The process described in conjunction with Fig. 2 establishes a clear c~ ic~tion path between CPE 101 and CPE 102 via security node 150. At some time during the call, the calling party may decide to encrypt the portion of the call between CPE 101 and node 150. The training sequence process by which 0 co",.",l,-i~tion b~,lweell CPE 101 and security node 150 can be switched from clear to encrypted is shown in Fig. 4, which should be read with continuing with reference to Fig. 3. When the calling party wishes to begin encrypted col--"-"~ ation, he or she notifies the destination party of this intent and then institutes transfer to the secure node by, for example, pushing a "secure calling" button on CPE 101 (step 5 401), thereby triggering the encryption unit within CPE 101 to send a message similar to a modem training message to encryptor 172 in encryptor bank 170 (step403). In response, encryptor 172 sends a modem answer signal (step 405) to CPE
101. Some indication at CPE 101, such as a flashing in(iic~tor light associated with the secure calling button, may be used to indic~te that training with encryptor 172 is 20 ongoing.
When the initial training is complete, a key exchange sequence is initi~tyl (step 407), using well known data co,--.,,l~nic~tion~ protocols preparatory to establishing secure c~"....~...-ication~. One such protocol is described in ANSIstandard X9.17, but nume,~us other techniques are well known to persons skilled in 25 the art. If desired, the called party can receive an annonncement, generated by controller 152, during encryption training. Upon successful completion of the key exchange, CPE 101 may be arranged so that the secure in~lir~tor light stops fl~hing and remains lit Controller 152 may detect the completion of training the key exchange sequences, such that an announcement may then be played to the called 30 party (step 409), in(licating that the call is going into the secure mode. Once in the secure mode, the call flow continues through encryptor 172 and controller 152 for the duration of the call (step 411).
If the calling party wishes to change from the secure to the clear mode, the clear button on CPE 101 may be pressed. This signal is detected in encryptor35 172 (step 413), which responds by changing into the clear mode. This change to clear mode may be effected by CPE 101 sending (step 415) a dis~inctive data pattern, -13- 212~,307 normally not occurring in encrypted data (e g a lcpelilive pattern such as 00110011001100110011...), ~ign~ling a request to transfer the call to the clear mode.
Encryptor 172, detecting this unique pattern, may similarly respond with a dirrt;l~nt unique pattern, such as 000111000111, to inflic~te its having received a request from 5 CPE 101 to switch to clear mode. CPE 101 may then respond to the signal returned by encryptor 172 with a third unique pattern, e g. 0101010101010..., completing the secure-to-clear h~n-l~h~ke (step 417). While this h~n~1~h~king is illustrative of a protocol that may be used, other methods will be a~ent to those skilled in the art.
The call then continues until a terrnin~tion or disconnect signal is detected (step 0 419). ~ltern~tively, or in addition, the call may continue until secure co~ nic~tions is again required.
The present invention can also be used to make secure-to-secure calls between a calling party and a called party, when each party uses a dirr~ltnt type of encryptor/decryptor, i e in circumstances in which CPE 101 and CPE 102 do not 5 use the same encryption algolilhms. In this embodiment, security node 150 provides encryption conversion between non-compatible encryption/decryption devices, by using two encryptors available in encryptor bank 170.
The process used to originate a secure call, with encryption conversion at node 150, is illustrated in flow diagram form in Fig.5. The initial steps in this 20 process are the same as those described above in conjunction with secure-to-clear calls; accordingly, the process of Fig. 2 is performed first, to establish a secure path between CPE 101 and node 150 and a clear path from node 150 to CPE 102. Fig. 6 illustrates the hal.lware elements involved in this type of call, and should be consulted in reading the following description.
When co,,,,,,~ ic~tions in the second leg of the call path, (i.e., from node 150 to CPE 102 at the called party location) are also to be encrypted rather than clear, controller 152 is signaled, usually by the called party (step 501). (However, in some arr~ngem~nts, the decision to encrypt both call legs may be signaled by either the calling party using CPE 101 or by the called party using CPE 102.) Upon 30 detection of a control signal in~lic~ting that a second encryptor is needed in the call path, controller 152 queries CPE 102 (step 503) to determine the type of encryptor being used. This interrogation provides controller 152 with information needed to select an applupriate (second) encryptor from encryptor bank 170.
Controller 152 signals switch 151 from a second output port (port 315 in 3s Fig. 6), to establish a second call that is routed through controller 152 (step 505).
This arrangement is used because many PBX switches are not presently capable of "transferring" or "bridging" outgoing calls, and can only transfer or bridge incoming calls. This arrangement is also used so that controller 152 remains in the portion of the call path in which the co,--"~ ic~ti-)ns are clear. This will be appreciated more fully below. Note in Fig. 6 that the second call to controller 152 origin~tes from port 5 315 and extends to input port 601 of switch 151, which connects the call via its output port 602 to controller 152 at a difrel~nt input port 611.
Information identifying the hunt group associated with the particular encryptor type being used by the called party in CPE 102 is determined (step 507) by controller 152, using a look-up in database 154. Controller 152 then initi~tes a call lo to a number associated with the hunt group which is output from port 612 of controller 152 and applied to input port 603 of switch 151, causing the switch to connect (step 513) the call to the next available encryptor in encryptor bank 170 of the a~propliate type (e.g., encryptor 174 in Fig. 6), providing that it is ~etlormin~
(step S09) that an appr~liate encryptor is available. If not, a termin~til n mtoss~e is 15 played in step S l l.
Encryptor 174, like encryptor 172, is arranged so that its output end is connPcte 1 to a line side termin~tion (port 605) in switch lSl. In this instance, however, encryptor 174 is also arranged such that a signal necessary to effectuate a connection in switch lSl between output port 606 to a different input port (port 613) 20 of controller 152 is always produced when encryptor 174 is actuated. This may be accomplished by arranging some encryptors in encryptor bank 170 to be connected to "virtual hot line" connections in switch lSl that autom~ti~lly connect to available ports in controller 152 when that encryptor is activated by receiving a call at its input port. A virtual hot line may be implemPnted by progr~mming switch lS l to detect2s the off-hook condition of one or more of its line side termin~tions and, upondetecting the off-hook condition, a~ltom~ti(~lly routing the call to a preprogrammed destination without any further ~ign~ling from controller 152 or the CPE.
When the "hot-line" call is received by controller 152 at port 613, controller 152 is arranged to transfer (step 517) the connection between its input port 30 313, from output port 314 to output port 315. Concurrently, ports 613 and 314 are connected within controller 152, and ports 602 and 604 are connected within switch lSl. In this status, the call path is a shown in Fig. 7. Note the following:
(a) Two encryptors, 172 and 174 are now in the call path, the first being of the ~pl~liate type to convert encrypted messages received from CPE 101 from 3s secure format to clear format, and the second being of the a~plopliate type to convert encrypted messages received from CPE 102 from secure format to clear format.

- 15 - 2 ~ ~ 8 ~ Q 7 ~

(b) Controller 152 remains in the clear portion of the call path between encryptors 172 and 174. Accordingly, controller 152 can be signaled by parties at either end of the circuit, if desired.
The process of Fig. 5 is completed by monitoring the call (step 519) for 5 control or termination signals. As with the embodiment described earlier, calltermination is effected conventionally, when either CPE 101 or CPE 102 hangs up.In such event, a disconnect signal is detected by switch 151 or controller 152, and the connections are dropped.
Referring now to Fig. 8, there is shown a block diagram illustrating the 10 elements contained within typical customer premises equipment, such as CPE 101 of Fig. 1. Ascllming that CPE 101 is a secure voice terminal, a handset 800 containing a conventional audio input (microphone) and audio output (speaker) is connected to a handset interface 801, which receives and transmits analog (~200 to 300 Hz) signals on lines 802. With respect to outbound signals (generated in CPE 101 and destined 15 for a called party via switch 107), the output of interface 801 is connected to an analog to digital converter 803, which digitizes the audio band signal, illustratively to a 56Kb/s sampled and quantized pulse code modulated (PCM) digital signal. This is done because digital processing in CPE 101 is preferred.
The output of converter 803 is applied to a speech coder/decoder (codec) 20 805, which compresses the received bit stream to a digital word stream, typically at 2400 or 4800 bps. One type of compression can be provided by a code excited linear prediction (CELP) encoder/decoder of the type found in the STU III securevoice terminal available from AT&T; other codecs are also available. Such other codecs include the speech coding systems disclosed in C~n~ n Patent Application 25 Serial No. 2,102,080, filed October 29, 1993 to W. B. Kleijn, directed to generalized analysis-by-synthesis coding. This compression coding is done to facilitate encryption/decryption, which is accomplished in cryptographic module 807. This module may be arranged to perform any well-known translation between clear and secure data, using a stored encryption key. The essence of encryption is to allow 30 only authorized users that have access to an encryption key to then be capable of decrypting the secure data to recover the original information. One example of acryptographic module is described in Federal Information Processing Standard (FIPS) 140-1, "Security Requirements for CryptographicModules", draft dated 7/90.

212~307 The output of cryptographic module 807 is applied to a modem 809 and then to a D/A and A/D converter 811, which together are interposed in the signalpath in order to convert the 2400 bps digital signal output from cryptographic module 807 a sequence of analog modem tones that is suitable for tr~nsmi~sion on5 an analog telephone line. Modem 809 itself pelro~ s the conversion of the modem output at 2400 bps to a digital bit stream, illu~Ll~lively at 56 Kb/s, that is suitable for application to a digital telephone line. This bit steam represents audio tones.
Because the signal has been encrypted (scrambled), the tones are scrambled such that an unauthorized listener would not be able to determine the intelligence contained in o the original voice message.
Because CPE 101 is typically connected to the telecolnlllullications network through a traditional analog subscriber access loop to LEC switch 107, the output of modem 809 is COnvt;l Led back from digital (56Kb/s) to analog forrn in D/A
and A/D converter 811, before being applied to the loop via telephone line interface 5 813. In cases where digital access is provided, D/A and A/D convel~el 811 and/or interface 813 may not be necessary.
With respect to inbound signals (generated in security node 150 and destined for CPE 101 via switch 107), similar conversion is accomplished.
Specific~lly, analog inputs, representing scrambled audio tones, are received via 20 interface 813 and converted to digital form in D/A and A/D converter 811. ThePCM bitstream, representing a series of analog tones is converted to a bit stream at (illustratively) 2400 bps in modem 809, decrypted in cryptographic module 807, and the symbols reconverted to a digital bit stream in codec 805, representing the original analog speech. Finally, the digital bit strearn is converted to intelligible 25 analog form in converter 803 before being applied to handset 800 via interface 801.
The CPE arrangement illustrated in Fig. 8 also includes a front panel interface circuit 820, which receives inputs from clear and secure buttons 821 and 824, a keypad or other input device 822, and is arranged to activate a visual display 823 such as may be provided by a LED, LCD or similar display device. Inputs 30 received in interface 820 may be locally processed in a microprocessor 830, opeld~ g under the control of programs stored in memory 840. Microprocessor 830 also interacts with, and may be programmed to control and coordinate, the operation of D/A and A/D converters 803 and 811, codec 805, modem 809, and, in most instances, cryptographic module 807. This latter interaction may involve secure key 35 storage/retrieval and other encryption related functions.

Fig. 9 is a block diagram illustrating the elements contained within a typical encryptor such as encryptor 172 or 174 within encryptor bank 170. Many of the elements, such as codec 805, cryptographic module 807 and modem 809, are thesame as those described in connection with Fig. 8. However, it will be noted that s each encryptor typically receives inputs from, and supplies outputs to, a PBX or switch, particularly a digital switch 151 of Fig. 1. For this reason, analog to digital conversion (and vice versa) may not be needed, and D/A and A/D converters 803 and 811 are notpresent. Further, the functions Ferform~l by handsetinterf~re 801and telephone line interface 813 are performed by a pair of PBX interface circuits lo 901, 913.
- The encryptor of Fig. 9 also includes a ~ign~ling interf~ce 920 in place of front panel interface 820 of Fig. 8. This is because the encryptor is advantageously positioned within the teleco~ ic~tions network, and is sign~led by calling and called parties using the capabilities of controller 152.
The call origination sequence described above was illustrative, and persons skilled in the art will appreciate various ~ltern~tive processes that may be available where additional intelligence is built into other components of the teleco,-.,....i-i~atirns network. An example will illustrate. Assume that database 120 in Fig. 1 is able to retrieve additional inform~tion about selected calling and called 20 party numbers, and that switches 110 and/or 125 are capable of pclro,millg interactive scripts in response to such information received via sign~ling network 115. In this embodiment, a caller dials the security node 150 access number, and the call is recognized by database 120 as requiring special tre~tment The caller is p~ ed by switch 110 (for example) to identify the call type, i.e., if the call is 2s secure-to-clear, clear-to-secure, or secure-to-secure. For a secure-to clear call, the caller is pr~ pled to input a User I.D. number using the touch tone pad on CPE 101.
Switch 110, in conjunction with database 120, allell~ls to validate the User I.D.
number. If the User I.D. cannot be verified, the caller is informed of the status and asked to re-enter a valid User I.D. #. If the User I.D. number cannot be v~lid~tç-l 30 after two at~m~ , the caller is notified that there is a problem, asked to call a support center with a dirrelGnt telephone number for additional support, and the call is dropped. Thus, portions of steps 203, 205 and 207 of Fig. 2 may be performed outside of node 150.
An alternative process by which the system of Fig. 1 can be used to set 3s up a secure-to-clear call is illustrated in the flow diagram of Fig. 10 and the hardware diagrams of Figs. 11-15. (A sirnilar process would be followed for clear-to secure and secure-to-secure calls.) This process differs from that described above in several important aspects. First, an end to end connection is established between calling and called parties before any encryptors are inserted in the call path. Second, controller 152 is removed from the call path after encryption begins. Third, encryptor "type"
5 inform~iion is provided ~uloma~ically to node 150, at the time when either party desires to begin secure c~ l""~ c~tion.
The process begins upon receipt of a call (step 1001), whereupon switch controller 152 pl~m~ the caller (step 1003) for login, password and called partynumber inrc,lllld~ion needed to complete the call. Encryptor "type" information is 0 not provided at this point. The information is collected (step 1005) and stored in database 154. If the caller is an authorized user (step 1007), controller 152 then places the incoming call (from CPE 101) on hold (step 1015) and transmits calledparty inrol~ Lion previously stored in database 154 to switch 151 in order to initiate a call to CPE 102 in step 217. As with the process of Fig. 2, routing of this call is 5 from controller 152 to switch 151 via line 168, from switch 151 to switch 125 via trunk 163, and then through telecoll~mullications network 156 to CPE 102. If thecaller is authorized, billing and bill processing are initi~ted (steps 1011 and 1013); if the caller is not authorized, a termination announcement is played (step 1009).
When the called party answers, controller 152 signals switch 151 to 20 bridge (step 1019) the call TO controller 152 with the call FROM controller 152.
This establishes a clear co..--~ ication path between both parties and leaves one "ap~alance" of controller 152 temporarily in the path, so that it can continue to t'm~nilo. " the call (step 1021) for the occurrence of control signals indic~ting that either party desires to transfer the call from the clear mode to the encrypted mode.
If it is determined in step 1023 that either party has tr~n~mitted a "begin secure tr~n~mi~sion" signal to controller 152 in(li~ting a desire to encrypt infcrm~tic-n tr~n~mitt~A over the portion of the transmission path between that party's CPE and node 150, a determin~tion is made (step 1025) of the type of encryptor being used in that CPE. Such det~rmin~tion is made "autom~ti~lly" by 30 controller 152, which recognizes a code indicative of the encryption type that is sent together with the "begin secure tr~n~mi~sion" signal. Until a "begin secure tr~n~mi~.cion" signal is detected, step 1021 is repeated.
The training message may include DTMF tones or other ~ign~ling information that specifies the type of encrypting device being used by the calling 35 party. Alternatively, an Adjunct Switch Application Interface (ASAI) in switch 151 can recogni~ DTMF tones generated in CPE 101 during call set-up. In this event, -;
19- 212~ 07 both the encryption type as well as the hunt group number(s) associated with that type of encryptor, can be determined autom~tic~lly and sent to controller 152.
Step 1025 also involves dete. ,..hl~;on of the "hunt group" for the appl~liate en-,lyptol~. Specifically, when controller 152 has determined the type of 5 encryption being used in the CPE that initi~t-.d the "begin secure tr~n~mis~ion"
signal, a lookup operation is pGlrolllled in (l~t~h~e 154 to d~t~.mine the hunt group clesign~tion associated with the appr~liate encly~ within encryptor bank 170.
Controller 152 (step 1027) then signals switch 151 to place one party (i.e., the party that did not generate the "begin encryption signal") on hold, and to initiate a call to the hunt group associated with the selected encryptor type. When that hunt group is called, the next available encryptor of the ap~ropliate type (e.g., encryptor 172 in Fig. 1) is selected by switch 151. However, if no encryptor of the selected type is available (step 1029), the process is t~rmin~ted (step 1009).
When the training of encryptor 172 (step 1031), which follows the same 5 process as described above in conjunction with Fig. 5, is complete, a determin~tion is made in step 1033 as to whether, during the training interval, the other party (i.e., the party not involved in the step 1023 request for encryption) has signalled a request to initiate encryption of m~ss~ges sent over the rem~in(ler of the co--.--.~ ic~tion path. If not, the call placed on hold in step 1027 and the call from controller 152 to 20 encryptor 172, are bridged in step 1035. At this point, controller 152 may bedropped from the co..,.-.~-.-ication path by sending an a~ liate control signal to switch 151, which establishes a bridging connection intern~l to the switch. Notehowever, that because encryptor training was accomplished with controller 152 inthe co----------ication path, it is important that removal of controller 152 from the path 2s not disturb the ability of CPE 101 and 102 and encly~ol~ 172 and 174 to continue encrypted cc,lnlllullication. This can be arranged by assuring that controller 152 introduces only negligible delay and frequency distortion in the co-~ -..nic~tion path.
If the other party has signalled a request to initiate encryption, steps 1025 - 1031 are repeated with respect to that party's encryptor type. In this manner, 30 a secure-to-secure call is completed.
The hardware diagrams in Figs. 11-15 illustrate the process depicted in Fig. 10. Fig. 11 illustrates the arrangement of CPE 101 and 102, switch 151 and controller 152, after step 1019 is completed. Note that con~oller 152 is inserted in the clear co.-----ll,lication path that exists between calling and called parties.

- -In Fig. 12, the arrangement of the same hardware components is illustrated after step 1031 is completed. At this point in the process, encryptor 172 is training with the encryption module in CPE 101, and, con~;wlenlly, the called party at CPE 102 is on hold, typically receiving an announcement from VRU 153 in 5 controller 152 indicating that training is ongoing with the other party.
In Fig. 13, the process of Fig. 10 has been completed with respect to a secure-to-clear call. Note that the hal.lwal~e arrangement is similar to that shown in Fig. 3, with the exception of the fact that controller 152 is not in the co",.~ irati~ n path.
0 Fig. 14 illustrates the additional element~ involved in a secure-to-secure call, when the other party initiates encryption in step 1033. As shown, the encryption module in called party CPE 102 is training with a second encryptor, encryptor 174. When the training process is complete, the h~dwale arrangement isas illustrated in Fig. 15. Note that this arrangement is similar to that shown in Fig.
15 7, with the exception of the fact that controller 152 is not in the c~mmnnication path.
Various modifications may be made to the arrangement illustrated in the figures, without departing from the spirit and scope of the present invention. Several examples will illustrate:
To protect against fraud and other abuses, security node 150 may be 20 arranged to track the number of call ~ tlllp~S per calling party (as determined by monitoring ANI) to access that node. After a predetermined number of attempts within a predele~ ed time interval, the se-;wi~y node autom~tir~lly blocks any further attempts from that calling party (ANI) to gain access into the node. Secure addressing may also be provided. This permits securing the call from the calling2s STD or CPE to the security node prior to inputting the called number, so that an eavesdl~per cannot ascertain the called number and/or dialing patterns of the calling party.
The Secure Telephone Device While Fig. 8 contemplates CPE in which encryption/decryption 30 elements and related signal conversion is performed intern~l to a telephone station, in some arrangements, as stated previously, it may be preferable to attach an external device, known as a "secure telephone device" (STD) to an otherwise ordinary terminal, in order to give the tennin~l the same functionality as described above. In this arrangement, the STD is attached to the users telephone between the handset and 35 the telephone base. As would be readily apparent to one of ordinary skill in the art, the STD connects to the handset and base by means of standard 4-wire modular 212~3~7 telephone jacks and conventional handset cords and employs a telephone base interface (813) in place of the line interface 813 shown in Fig. 8. A separate AC
transformer supplies power to the STD.
Preferably, the STD is compatible with many types of electronic, 5 modular, touch tone business and resiclenti~l phones. If desired, a user may configure the STD through a display device and software defined switches on the STD. Such a display device provides the user with i(lentification of secure or clear mode and a visual signal to assure the user that an unauthorized person has not altered their co.. ~ ic~tion~. The STD can be small and light enough to be portable lo (e.g., an illustrative STD housing may be made of plastic (7"x4 1/2"xl 1/4")), such that it can be conveniently carried be~weell locations (i.e., office, home, travel).
When a calling and called party use STDs employing the same encryption/decryption algorithm~, a secure call may be established between such parties without operation of security node 150. Such secure calls may be established 15 as follows (see Figs. 1 and 8). A calling party employing a conventional telephone with an STD 191 initiates an ordinary (non-secure) call to a called party also having an STD 192. This is done in conventional fashion by dialing the called party's telephone number and allowing the switched teleco.--...~ ic~tions network 156 tocomplete the call. When the called party answers his telephone, the ordinary non-20 secure call is established. At this point, the calling and called party may converse inordinary non-secure fashion. Each party's STD 191, 192 acts as a simple conduit, receiving non-secure signals from a party's handset or base and passing such signals on to the base or handset, respectively (each STD 191, 192 may perform A/D and D/A con~,el sion, but no encryption/speech coding or decryption/speech decoding is 25 performed).
When the parties to the call decide they wish to employ secure coll...-ll.-ications, either party may initiate a switch to secure mode. To establish secure co~ --ic~tions, either party, e.g., the calling party, depresses the "secure button" 824 on his STD 191. This initiates training and key exchange sequences as 30 described above with reference to steps 401-407 of Fig. 4 (concerning the encryption unit within CPE 101 and encryptor 172 of node 150; in this case encryptor 172 isreplaced by the encryption unit 807 of the called party's STD 192; see Fig. 8). Both STDs involved in these sequences employ the same encryption algorithm, such as FIPS 140-1. As a result of these sequences, the parties can converse in a secure35 fashion. When they desire to converse in non-secure mode, either party may depress the "clear button" 825 on his STD (191 or 192) and the signalling sequence described above with reference to steps 411-417 of Fig. 4 is used to effect non-secure (or clear) mode.
Services The present invention may be used in conjunction with various services s that are already available, as well as many new services that are to be offered in the future. One such service is termed the "totally secure phone call." This service is similar to those discussed above with reference to node 150 except that sensitive information is com,llullicated while in secure mode, not in clear mode. For example, such sensitive information might include the telephone number of the called party.
0 This service may be understood with reference to Fig. 16.
According to this service, a user whose telephone includes an STD 191 dials a special telephone number with the keypad on, e.g., the user's telephone base.
The special number connects the user's (caller's) telephone 193 with security node 150 in the lllamler discussed above (step 1605). Controller 152 ~lump~ the caller 5 for a milliluulll amount of infolllla~ion needed to go into secure mode (step 1610).
For example, controller 152 may prompt the caller for "login" infolllla~ion as discussed above. Once in receipt of this "login" information (step 1615), controller 152 determines whether the caller is an authorized user (step 1620). If so, the caller's STD encryption algoli~ is determined such that a secure link may be established between the caller and the node 150 (step 1630). Such a determin~tion may be made by access to database 154 using the received login as an index. If the caller is not authorized, the call is termin~ted (step 1625).
Once the encryption algorithm is known, a secure link between node 150 and the calling party is established according to the procedures discussed above with reference to Fig. 2 (steps 211-221) and Fig. 4 (steps 401-407) (step 1635). In this case, secure mode may be instigated by controller 152 which sends a training message to the calling party's STD. A key exchange between the cryptographic system of the STD and an encryptor, e.g., encryptor 172, of node 150 follows as described above.
After a secure call is established between the calling party and the node 150, controller 152 may prompt the calling party to supply the sensitive information (step 1640). These ~lonl~s are encrypted by encryptor 172 and communicated to the calling party as discussed above. Here, however, the calling party's STD 191decrypts the prompt. Caller responses to plOlllpLs are similarly encrypted by the 35 caller's STD and are provided to encryptor 172 for conversion into clear text for subsequent use by controller 152 (1645).

-23- 212331~

Caller responses to requests may be entered through use of the keypad 822 on the STD 191 as shown in Fig. 8. This keypad may appear like an ordinary DTMF generator pad, but it need not necessarily generate DTMF tones. All that isrequired is that it gencrale a digital code identifying a given button when depressed.
s Should digital codes be generated rat'ner than DTMF tones, a special flag should be co,~ ted idellliryillg the information as a code (rather than a tone). In this way, node 150 will be able to interpret the coll~ ted information as a code rather than as an audible tone or speech. Digital codes generated in this fashion are provided via interface 820 and CPU 830 to crypto system 807. Crypto system 807 0 encrypts these digital codes to provide the desired security for response data. When CPU 930 of receiving encryptor 172 (Fig. 9) detects the special flag indicating that an STD button has been depressed, CPU 930 directs crypto system 907 to output a digital signal representing an appropriate DTMF tone to speech codec 905. The output of speech codec 905 is therefore a DTMF tone representative of the button5 pushed on the STD. Thus, sensitive response inro",.Ation, such as a user's password or the number of the called party, may be m~int~ined in secure fashion.
Once the node 150 receives all needed information in secure mode from the calling party, the controller 152 of node 150 can establish a secure call to a called party (the decision to encrypt the call to the called party is implicit). To do this, 20 controller 152 first de~ ~ines the encryption algolilllll, of the called party (step 1650). The encryption algorithm of the called party is known (due to use of a CCSl~ 011 STD) or determined by access to database 154 (as above, database 154 incl~ldes inrollllalion on the encryption algolithllls of called parties; other embo lim.o,nt~ can employ a non-secure query to the called party for encryptor type).
25 Given the decrypted called party's telephone number, controller 152 generates the necessary control signals to dial the called party (who also has an STD) (step 1655).
Once the called party answers the telephone, VRU 153 of controller 152 informs the called party that a secure call is being made. Secure comm~1nic~tion with the called party is enabled in the manner discussed above with reference to Fig. 5 (step 1660).
30 At this point, the two calls may be bridged as discussed above. As a result, sensitive information may be used to establish a call without concern that such information will be col~ u,msed. Unlike as described above, the first and second links to this call (caller to node; node to called party) employ the same encryption algorithm.
In light of this discussion, it will be apparent that the "totally secure 35 phone call" service may be provided using the techniques and equipment (including STDs) discussed generally above with reference to Figs. 1-7. A salient difference is that rather than all node prolll~ and party responses occurring in clear (i.e., non-secure) mode, one or more of such plolllp~ and responses occur after a secure link has been established.
Related to the "totally secure phone call" service is a method for 5 co.~ ic~ting "secure personal information." Often there is a need to provide sensitive p~,lsollal infollllation over the telephone to a receiving device or system, such as an infol~llation service system. For example, an automated information service system accessed by a calling party, such as automated banking-by-phone, may require the calling party to provide a personal identification number (PIN),0 social security number, or the like, as part of, for example, a sign-on procedure. An STD (or other CPE) including a keypad of the type presented in Fig. 8 and discussed above may be used in combination with an automated information service system toprovide the desired security. Fig. 17 presents an illustrative schem~tic represent~tion of such a combination.
As shown in the Figure, the combination comprises calling party telephone/STD eqniI)ment 1705-1720 of the type discussed above and an ~lltom~tedinformation service 1760. The ~I~tom~ted information service (AIS) 1760 comprises CPE 1740 and an AIS platform 1750. CPE 1740 is similar to the STD discussed above with reference to Fig. 8. However, CPE 1740 is controlled by application of 20 control signals from the AIS platform. These control signals replace the "secure"
and "clear" button user intP.rf~re discussed above. The control signals are applied via coupling 1745 to panel interf~e 820 of CPE 1740. AIS platform 1750 r~l~,sent~ any of the possible information services ~ccessihle by telephone, such as banking-by-phone. The illustrative AIS platform 1750 includes a voice response 25 unit (VRU) 1755 and database 1757 and may be a Conversant~ system available from AT&T. The fl~t~ba~e 1757 includes, among other things, voice scripts for playing to a user with use of the VRU 1755.
At the outset of AIS 1760 operation, the AIS platform 1750 m~int~in~
CPE 1740 in clear mode via a "clear" control signal co.. ~ t~l over coupling 30 1745. In clear mode, AIS 1760 can receive telephone calls from service users in conventional fashion. CPE 1740 acts as a conduit for incoming calls, passing such calls on to AIS platform 1750 via coupling 1747. When an AIS service user dials the AIS service 1760, the VRU 1755 ~nulllpls the user for information in accordance with a stored script in local service database 1757. Such ~lulllpl~d information may 35 comprise a "login" and information reflecting whether the user has an STD 1710. If a user has an STD 1710, the VRU 1755 may prompt the user to initiate secure 212~307 co..~ ic?tions by, e.g.1 depressing the "secure button" on the user's STD 1710.
(Alternatively, the AIS platform 1750 may determine for itself that the user hassecure comml-nic~tion~ capability and signal its own CPE 1740 via coupling 1745 to initiate secure mode). As a result of initi~ting secure c~mmllnic~tinns~ training and 5 key e~ch~nge occur as discussed above between STD 1710 and service CPE 1740.
At this point, the link belween the calling party and the service 1760 is secure. As such, the user may access the i~lfo~ ation service is conventional fashion. All further voice inf(~ alion provided by the service 1760 is passed through the CPE1740 for encryption prior to being sent to the calling party. Moreover, all calling 0 party information is encrypted by STD 1710 prior to being co~ tçd to the service 1760. Such infollllation may include, for example, PINs or social security numbers entered via the STD keypad as discussed above. At any point during the secure call, either the user or the information service may command a return to non-secure mode. The user may do this by pressing the "clear button" on his STD. The5 service may do this by the platform 1760 sending a "clear" control signal to the CPE
1740 via coupIing 1745. Either way, a switch to the clear mode may be effected as discussed above.
It should be understood that method for secure personal information may be combined with the "totally secure phone call" service discussed above.
20 According to this combination, coupling 1730 (between the user's telephone base 1720 and the service 1760) compri~es node 150 and other aspects of the switched network 156 (as described above with reference to the secure service). With thiscombination, a user dials the number ~ccessing node 150 in clear mode. A secure connection is established between the user and node as discussed above. Finally,2s node 150 dials the irlfo~ ation service and establishes a secure link between itself and the service platform. In this way, all information related to the user's access to the service is maintained in secure fashion.
The concept of communicating in secure fashion with an information service is further illustrated with reference to voice messaging systems, such as the 30 AUDIX~9 system available from AT&T. Specifically, a user of a voice m~oss~qging system may wish to leave a secure voice message for a recipient. As a general matter, this may be done by equipping users and the voice mçssaging system with STD/CPE equipment to allow secure access to stored messages. Secure voice messaging may be understood with reference to Figure 18.

Figure 18 presents a secure voice m~ss~gng system 1821 coupled to two secure user telephone stations 1801 and 1859. The secure voice m~ss~ging system 1821 comprises a switch 1825, CPE 1835, a voice m~s~ging platform 1850 and a database 1855 on which to store received ml-ss~ges and other data. The switch s 1825 may be the Definity~M digital PBX available from AT&T. CPE 1835 is as described above with reference to Fig. 17. The voice mtoss~ging platform and database 1850 and 1855 may be the AUDIX~9 system available from AT&T. The platform comprises a VRU 1851 and script database 1853. In this case, the voice messaging platform 1850 is adapted to provide CPE control signals as discussed 0 above. Each user station 1801, 1859 comprises a h~n~l~et 1805, 1860, an STD 1810, 1865, and a telephone base 1815 and 1870, respectively.
In operation, a user at station 1801 (the "caller") dials the number of another user at station 1859. If the user at station 1859 fails to answer, the switch 1825 connects the caller with the platform 1850 via CPE 1835. ~ltern~ively, the 5 caller may dial a special extension to access the platform (via CPE 1835) directly. In either event, CPE 1835 is operating in clear mode at this point in time. That is, it is acting as a conduit passing speech and DTMF signals from the caller's station 1801 to the voice m--ss~gng platform 1850. The voice messaging platform 1850 p~ pls the caller for information as is conventional (with use of VRU 1851 and database20 1853). The caller responds to such pro~ with DTMF tones in conventional fashion. In addition, the platform 1850 may prompt the caller to use secure mode if the caller so desires. In response to a prompt from platform 1850 to use secure mode, the caller may depress the "secure button" on the caller's STD 1810. As a result, training and key exchange sequences are p~,lfo~ ed by STD 1810 and CPE
25 1835 as described above. Once in secure mode, the caller may record a message for the recipient for later retrieval. Such a message is encrypted by STD 1810 and decrypted by CPE 1835. Once decrypted by CPE 1835, the message is stored as clear text on database 1855. Any comm~n(l~ required to be given to the voice m-oss~ging platform 1850 by the caller are provided with use of the keypad on the 30 STD 1810. As discussed above, these comm~n-ls may include DTMF tones or suitable identified codes corresponding to keypad buttons. If codes are used, the CPU and crypto system of CPE 1835 recognize and replace these codes with digitalsignals for DTMF tones as discussed above.
When retrieving voice messages, the message recipient at station 1859 35 dials the messaging access number and is connected to the messaging system inconventional fashion via switch 1825 and CPE 1835. The recipient responds to voice pro~ via the telephone base 1870 keypad is as conventional. The recipient may also go into secure mode in the manner discussed above by depressing the "secure button" on the recipients STD 1865. Once in secure mode, the recipient may retrieve stored m~ss~ges securely. These m~s~ges are retrieved by comm~nds to the s m-osS~ging system issued with use of the keypad on the STD 1865.
Secure voice and fax storage and retrieval may be provided by the arrangement of Figure 18 to allow an incoming meSs~ge (on ring no-answer or busy) to be folw~ded to a secure mailbox (i.e., d~t~b~e) where the message will be stored in encrypted format for subsequent access by the called party. This protects the0 encrypted m-oss~e in a secure location until it can be retrieved by an authorized party. The calling party can be assured that the information is safe until it gets to the intended recipient.
In storing messages in secure fashion for later retrieval, CPE 1835 does not decrypt received mtoss~ges Rather, CPE 1835 passes encrypted m~ss~ges in 15 digital form to database 1855 via platform 1850. Naturally, CPE 1835 does notperform speech decoding on the received m~ss~ge. Stored along with the encryptedmessage is the encryption key obtained during the key exchange referenced above.In retrieving an encrypted message from the database 1855, CPE 1835 initi~tes training and key exchange sequences with STD 1810. The key used will be the key 20 stored with the message. Tniti~tion of such sequences is made under the control of platform 1850. Platform 1850 initi~tes secure co,.""~ ir~tirns by comm~nd to CPE1835 via coupling 1845. Once secure co"~ -ic~tions is established, encrypted message data stored in database 1855 is co~ ic~ted to the user at station 1859 via CPE 1835, switch 1830 and channel 1875. Processing by STD 1865 to decrypt and 25 decode the received message is as discussed above.
Removable Interface Module for the STD
As discussed above, an STD may be configured to be compatible with many types of telephones through use of software defined switches on the STD.
However, STD telephone compatibility, as well as STD portability, may also be 30 f~cilit~t~ by use of removable/replaceable telephone handset and base interfaces.
An illustrative STD adapted to include such interfaces comprises a set of core components (which need not be changed) and handset and base interfaces associated together in a removable interface module. This removable module may be changed to suit the STD operation en~ir~ llellt (i.e., the telephone with which the STD must 35 function). The removable module may be realized, for example, as a cartridge containing interface cil~;uilly which slides into an opening or channel in the STD

-28- 21~3~~

housing and connects to electrical contacts within the STD. An STD configurationwith a removable interface module is illustratively presented in Figures 19, 20 and 21.
As shown in Figure 19, the illustrative STD is similar to that presented s in Figure 8 except that the base and handset interf~ces are associated together in a removable module (or cartridge) 1910. The coupling of module 1910 to STD core components (collectively identified as 1920) is made by a conventional plug-typeconnector well known in the art (any connector suitable for plug-in module-type coupling may be used). Core components shown in Fig. 19 which are iclentic~l to 10 components illustrated in Figure 8 have been numbered in the same fashion. Base and handset interfaces 1912 and 1914, respectively, perform the same functions as their counterparts in Fig. 8 (813 and 801), but are physically coupled together in module 1910.
The configuration of Fig. 19 f~cilit~tPs STD compatihility and 5 portability because the module 1910 functions to adapt the STD to the electrical requu~;mell~s of the telephone set to which it is connected. Should a user wish to use his or her STD with telephone sets having differing electrical interface re~uire~ n~
(such differing requirements due to, e.g., a dirrt;~ ce in handset microphone types), all that is required is the replacement of module 1910 with an a~plo~,liate module 20 adapted to interface with the given telephone set. As is well understood in the art, many telephones have substantially similar interface requirements. Consequently, a single plug-in module may be sufficient for more than one telephone. Because of the ability to adapt an STD to various telephones, a user may take his or her STD tovarious locations and use the STD to turn a conventional telephone set at a given 2s location into one having secure voice capability.
Figure 20 presents a further detailed view of the handset interface 1914 of plug-in module 1910. Connector 2005 couples a handset (not shown) to the handset interface of module 1910. As shown, this coupling comprises four coupling pins (1-4). Pin 4 couples the handset to a five volt power supply. Pin 2 couples the 30 handset to ground. Pin 3 couples the handset receiver (loudspeaker) to its driving signal provided by the STD (i.e., provided by core components 1920 through amplifiers 2025 and 2030). Pin 1 couples the handset transmitter (microphone) tothe STD (i.e., to amplifiers 2015 and 2020 and core components 1920).
The interface shown facilitates the operation of core components 1920 35 with many standard AT&T handsets, such as "K" type handsets. Other handset types may be accommodated by varying interface component values and pin assignments.

2128~07 For example, some handsets require handset connecting pin 3 to ground and pin 2 to amplifier 2025; and connecting pin 1 to the power supply and pin 4 to amplifier 2015. Also, some handsets may require different transmitter load impedance. Thismay be accomplished by varying the value of resister 2010 (illustrative component s value v~ri~tion~ are pl~,s~ ed in parentheses). Resistors R2 andR3 are provided to match handset speaker impe~nce. Values for these resistors may be changed to suit handset speaker re~luilc~lellt~7. Finally, the value of the gain of amplifiers 2015 and 2025 may be adjusted to suit transmit/receive voltage re~ui~lllents between a given handset and the core components 1920 of the TSD. Amplifiers 2020 and 2030 are 0 convell~ional buffer amplifiers. ResistorR3 provides a conventional "side tone"
signal allowing a speaker to hear himself (or herself~ in his (her) handset ear piece.
Figure 21 presents a further detailed view of the illustrative base interface 1912 of plug-in module 1910. Connector 2105 couples a telephone base (not shown) to the base interface of module 1910. As with h~ndset connector 2005, 5 connector 2105 co~,ises four coupling pins (1-4). Pin 4 is left as an open circuit since it carries a power supply voltage from the telephone base. Pin 3 provides a receiver signal intçnde l for the handset receiver. Pin 2 provides a common ground.
Pin 1 provides a tr~nsmittt~r signal from the handset microphone to the base.
Transformers 2110 and 2115 provide d c. isolation between the base and the TSD
20 and make the base interface polarity in~en~itive.
As shown, base interface 1910 will operate with many AT&T phone bases. However, the configuration of Fig. 21 may be adapted to conform to the requirements of other phone bases. For example, some bases provide a handset power supply voltage on pin 1 and expect transmit output signals on pin 4. Thus, the 25 couplings of these pins may be exchanged. In such a case, pin 1 would be an open circuit and pin 4 would provide the tr~nsmitter output. Under the circumstances where pin 1 is an open circuit, pin 2 cannot be a common ground. As such, pin 3 serves as the common ground instead and pin 2 provides the receiver signal to the handset. Other bases do not provide for a common ground or a supply voltage. In 30 such a case, e.g., pins 1 and 4 may be used to carry the signal voltage across the 27K
ohm resistor and pins 2 and 3 may be used to carry the signal voltage across transformer 2110. The gains of amplifiers 2125 and 2135 are varyed by adjusting resistors R 5 and R 3, respectively. These amplifiers adjust the level of signals coming to and from the base. Amplifiers 2130 and 2140 are conventional buffers.
3s (All amplifiers shown in Figures 20 and 21 may be provided with conventional operational amplifier circuitry.) It will be readily app~Gnt to those of ordinary skill in the art that the handset interface of module 1910 may be replaced by other interfaces suitable for coupling the core components 1920 with other devices, such as speaker phones, cellular phones, fax machines, cc~myul~ etc. Also, separate plug-in modules could 5 be provided for the handset and base interf~ces. Buffer amplifiers 2020, 2030, 2130, 2140 illustrated in Figures 20 and 21 may be located with cone components 1920, rather than in module 1920.
An STD may be used as an interface for coupling any of various collullunications devices (which ordinarily require a 2-wire telephone "line"
0 coupling, such as fax machines, com~u~ , etc.) to a 4-wire telephone base jack. In this case, the STD would include a 4-wire interface as discussed above for coupling the STD to the handset jack of the telephone base and a conventional 2-to-4 wireint~ ce for coupling such a co"""lll-ications device to the STD. Assuming the co"""ll.-ications device sends and receives modulated non-voice signals, modem 5 809 and speech codec 805 are removed from the STD signal path (either literally or logically). Thus, the STD may be advantageously employed to couple a conventional co,, ,,~ tions device having analog output signalling over two wires to digital subscriber loops (to which the telephone base is connected).
The STDs of Figures 8 and 19 employ digital encryption of a 20 co~ ssed digital speech signal. ~ltern~tively, the STD could be realized with an analog scrarnbler. In such a realization, digitaVanalog converters 811, 803, modem 809, cryptographic system 807, and speech codec 807 would be replaced by a single analog scrambler device, such as the EPU (Embeddable Privacy Unit) analog scrambler available from DATOTEK Corp. An STD with an analog scrambler 25 would include a base interface 1912/813 and a handset interface 801/1914. Each of these interfaces is adapted to the electrical characteristics of the handset and base, as well as the scrambler, in a fashion similar to that discussed above. Naturally, these interfaces may be removable, as discussed above.
The interface features of the STD provide useful functionality in 30 addition to their use as part of a security device. Specifically, the STD interface cihcuilly may be used to interface various communication devices to a telephone base even if encryption is not provided. As stated above, the interface CilCuitly may be removable. In the capacity of an interface, the STD need include no other special circui~ly since electrical compatibility is the feature to be provided. Illustratively, 35 such an embodiment would include conventional jacks to couple the STD betweenthe devices/systems to be interfaced, an internal coupling connecting these jacks to a -31- 21 283 ~ 7 removable interface connector, and interface CilCUitly coupled to the connector. In this way, such devices/~ysLt;ms are coupled through the removable interface of the STD. It will be understood that the STD may include other components (such as, e.g., a cryptographic system), but that in this interf~ce capacity, such other s components need not be operative.
While portions of the foregoing description mentioned voice calls, it is to be clearly understood that the present invention can be utilized as well in connection with the co,.~ tion of all types of secure data. (As would be clear to those of ordinary skill in the art, in such configurations where speech is not lo co--..-~ -ie~ted, the speech coder/decoder of the STD may be removed). For example, the invention is ideal for protecting tr~nsmi~ions between PCs and between PCs and mainframe colllpulel~. This application requires only that the STD
interfaces between the comml-nications device and the telephone equipment, be ap~ropliately modified, which is easily accomplished by persons of ordinary skill.
5 (Note that such modified interfaces may be removable, as discussed above.) In the same vein, secure fax may be used to protect tran~mi~sions between fax m~chines and fax store and forward services. A~lth~nti--~tion of receipt of the fax (to whom was fax the delivered) can also be provided. Thus, an STD may be used to convert a colllp~llel, fax, etc., to a secure commllnications device.
With respect to call billing, various arrangements are possible. For example, security node 150 may be arranged to capture origin~ting and termin~ting ANI, and call duration infol.llation associated with each User I.D. #. This inro....~tion, along with the main billing number are then passed to bill rating and form~tting system 187, for processing based on the subscribers outbound calling 25 plan and inclusion into the customer's bill. The call is rated based on the call flow between the originating and termination locations, not between originating location to security node to tçnnin~ting location. Thus, the cost of delivering the call to and from secllrity node 150 will typically be part of the encrypting/decrypting feature charge, and will not appear as an item on the subscribers billing st~t~om~-nt. Billing 30 will begin when answer supervision is provided from the called end to security node 150. Dirr~.ellt billing arrangement may be used for subscriber ini~i~ted calls (i.e., secure-to-clear, secure-to-secure), in which the cost of the call can be applied to the calling subscriber's bill, as compared to clear-to-secure calls, for which the called subscriber will assume responsibility for the cost of the call (as if it were a collect 3s call).

-32- 21 283 0 ~

Finally, while the preceding description illustrates switch 151 and controller 152 as separate app~us, it is envisioned that a single "intelligent switch"
capable of monilo. illg calls, issuing voice prolllpl~ and collecting responses, storing information, making connections under the control of stored programs, and s pelrolllling various associated functions, can be disposed within the telecc,-""~ ic~tions network and used instead.

Claims (48)

1. An apparatus for providing secure communication of information signals over a communications network, the apparatus for coupling between a telephone base and an information signal generator, the telephone base coupled to the communications network, the apparatus comprising a signal encryptor for coupling to the information signal generator and the telephone base, the signal encryptor for generating encrypted signals reflecting signals formed by the generator, the telephone base for transmitting over the network signals reflecting the generated encrypted signals.

2. The apparatus of claim 1 further comprising a speech coder for coupling to the information signal generator and coupled to the signal encryptor, the speech coder for generating coded speech signals reflecting speech signals formed by the generator, such that the signal encryptor generates encrypted signals which reflect the coded speech signals.

3. The apparatus of claim 1 further comprising a modulator coupled to the signal encryptor and for coupling to the telephone base, the modulator for generating modulated signals reflecting encrypted signals generated by the signal encryptor, wherein the signals transmitter by the telephone base reflect the modulated signals.

4. The apparatus of claim 1 further comprising a telephone base interface coupled to the signal encryptor and for coupling to the telephone base, the telephone base interface for adapting the apparatus for operation with the telephone base.

5. The apparatus of claim 1 further comprising an information signal generator interface coupled to the signal encryptor and for coupling to the information signal generator, the information signal generator interface for adapting the apparatus for operation with the information signal generator.

6. The apparatus of claim 1 wherein the information signal generator is a microphone.

7. The apparatus of claim 1 wherein the information signal generator is a fax machine.

8. The apparatus of claim 1 wherein the information signal generator is a computer.

9. The apparatus of claim 1 further for coupling between a telephone base and a decrypted signal utilization device and further comprising a signal decryptor for coupling to the utilization device and the telephone base, the signal decryptor for generating decrypted signals to be provided to the utilization device, the decrypted signals reflecting encrypted signals provided by the telephone base.

10. The apparatus of claim 9 further comprising a speech decoder coupled to the signal decryptor and for coupling to the utilization device, the speech decoder for generating uncoded speech signals reflecting decrypted signals generated by the signal decryptor, wherein the uncoded speech signals are decrypted signals for use by the utilization device.

11. The apparatus of claim 9 further comprising a demodulator coupled to the signal decryptor and for coupling to the telephone base, the demodulator for generating demodulated signals reflecting signals provided by the telephone base, wherein the decryptor generates decrypted signals which reflect the demodulated signals.

12. The apparatus of claim 9 wherein the signal utilization device comprises a speaker.

13. The apparatus of claim 9 further comprising a utilization device interface coupled to the signal decryptor and for coupling to the utilization device, the interface for adapting the apparatus for operation with the utilization device.

14. The apparatus of claim 1 wherein the signal encryptor comprises a scrambler circuit.

15. An apparatus for providing secure communication of information signals over a communications network, the apparatus for coupling between a telephone base and an information signal utilization device, the telephone base coupled to the communications network and for receiving information signals therefrom, the apparatus comprising a signal decryptor, for coupling to the telephone base and the utilization device, the signal decryptor for generating decrypted signals for use by the utilization device, the decrypted signals reflecting encrypted signals provided by the telephone base.

16. An apparatus for providing secure telephone communication, the apparatus for coupling between a telephone base and a telephone microphone, the telephone base coupled to a communications network, the telephone microphone forgenerating first signals reflecting speech, the apparatus comprising:
a speech coder for coupling to the telephone microphone, the speech coder for generating coded signals reflecting the first signals; and a signal encryptor coupled to the speech coder and for coupling to the telephone base, the signal encryptor for generating encrypted signals reflecting the coded signals;
the telephone base for transmitting over the network signals reflecting the encrypted signals.

17. The apparatus of claim 16 wherein the speech coder comprises a CELP coder.

18. The apparatus of claim 16 wherein the signal encryptor conforms to the Federal Information Processing Standard 140-1.

19. The apparatus of claim 16 further comprising a modulator coupled to the signal encryptor and for coupling to the telephone base, the modulator for generating modulated signals reflecting the encrypted signals.

20. The apparatus of claim 19 further comprising a telephone base interface coupled to the modulator and for coupling to the telephone base, the telephone base interface for adapting the apparatus for operation with the telephone base.

21. The apparatus of claim 20 wherein the modulated signals are digital signals and further comprising means, coupled between the telephone base interface and the modulator, for generating analog signals which reflect the digital signals generated by the modulator.

22. The apparatus of claim 16 wherein the telephone microphone comprises a telephone handset microphone.

23. The apparatus of claim 22 further comprising a handset interface coupled to the speech coder and for coupling to the handset microphone, the handset interface for adapting the apparatus for operation with the handset.

24. The apparatus of claim 23 wherein the handset interface provides analog signals and further comprising means, coupled between the handset interface and the speech coder, for generating digital signals which reflect the analog signals provided by the handset interface.

25. The apparatus of claim 16 further comprising a user interface for controlling apparatus operation.

26. The apparatus of claim 25 wherein the user interface comprises a keypad.

27. The apparatus of claim 26 wherein the keypad comprises one or more DTMF signal generators.

28. The apparatus of claim 25 wherein the user interface comprises a display.

29. The apparatus of claim 28 wherein the display comprises a liquid crystal display.

30. The apparatus of claim 25 wherein the user interface comprises means for initiating secure communications.

31. The apparatus of claim 25 wherein the user interface comprises means for initiating clear communications.

32. The apparatus of claim 25 further comprising a control processor coupled to the user interface and the signal encryptor, the control processor for controlling the operation of the signal encryptor in response to signals from the user interface.

33. The apparatus of claim 16 further comprising a removable interface module, coupled to the speech coder and for coupling to the telephone microphone, the removable interface module comprising a microphone interface.

34. The apparatus of 16 further comprising a removable interface module, the removable interface module comprising a telephone base interface coupled to the signal encryptor and for coupling to the telephone base.

35. The apparatus of claim 16, wherein the telephone base provides second signals reflecting encrypted speech signals received from the communications network, the apparatus for further coupling between the telephonebase and a telephone speaker, the apparatus further comprising:
a signal decryptor for coupling to the telephone base, the signal decryptor for generating decrypted signals reflecting the second signals, and a speech decoder coupled to the signal decryptor and for coupling to the telephone speaker, the speech decoder for generating decoded speech signals reflecting the decrypted signals;
the speaker for generating audible signals reflecting the decoded speech signals.

36. The apparatus of claim 35 further comprising a demodulator coupled to the signal decryptor and for coupling to the telephone base, the demodulator for generating demodulated signals reflecting the second signals.

37. The apparatus of claim 36 further comprising a telephone base interface coupled to the demodulator and for coupling to the telephone base.

38. The apparatus of claim 37 wherein the second signals provided to the telephone base interface are analog signals and further comprising means, coupled between the telephone base interface and the demodulator, for generating digitalsignals which reflect analog signals provided by the telephone base interface.

39. The apparatus of claim 35 wherein the telephone speaker comprises a telephone handset speaker.

40. The apparatus of claim 39 further comprising a handset interface coupled to the speech decoder and for coupling to the telephone handset speaker.

41. The apparatus of claim 40 wherein the decoded speech signals are digital signals and further comprising means, coupled between the handset interface and the speech decoder, for generating analog signals which reflect the digital signals generated by the speech decoder.

42. The apparatus of claim 35 further comprising a removable interface module, the removable interface module comprising a telephone speaker interface coupled to the speech decoder and for coupling to the telephone speaker.

43. The apparatus of claim 35 further comprising a removable interface module, the removable interface module comprising a telephone base interface coupled to the signal decryptor and for coupling to the telephone base.

44. An apparatus for providing secure telephone communication, the apparatus for coupling between a telephone base and a telephone speaker, the telephone base coupled to a communications network and for providing first signals reflecting encrypted signals received from the communications network, the apparatus comprising:
a signal decryptor for coupling to the telephone base, the signal decryptor for generating decrypted signals reflecting the first signals, and a speech decoder coupled to the signal decryptor and for coupling to the telephone speaker, the speech decoder for generating decoded speech signals reflecting the decrypted signals;
the speaker for generating audible signals reflecting the decoded speech signals.

45. An apparatus for providing secure telephone communication, the apparatus for coupling between a telephone handset and a telephone base, the telephone handset including speaker and a microphone for generating first signals reflecting speech, the telephone base coupled to a communications network and for producing second signals reflecting encrypted speech signals received from the network, the apparatus comprising:
(a) a speech coder for coupling to the handset microphone, the speech coder for generating coded signals reflecting the first signals;
(b) a signal encryptor coupled to the speech coder, the signal encryptor for generating encrypted signals reflecting the coded signals;
(c) a modulator coupled to the signal encryptor and for coupling to the telephone base, the modulator for generating modulated signals reflecting the encrypted signals, the telephone base for transmitting over the network signals reflectingthe modulated signals;
(d) a demodulator for coupling to the telephone base, the demodulator for generating demodulated signals reflecting the second signals;
(e) a signal decryptor coupled to the demodulator, the signal decryptor for generating decrypted signals reflecting the demodulated signals; and (f) a speech decoder coupled to the signal decryptor and for coupling to the telephone speaker, the speech decoder for generating decoded speech signals reflecting the decrypted signals; the telephone speaker for generating audible signals reflecting the decoded speech signals.

46. The apparatus of claim 45 further comprising:
a user interface for controlling the operation of the apparatus; and a control processor, coupled to the user interface and the signal encryptor and signal decryptor, the control processor for controlling the operation of the encryptor and decryptor responsive to signals from the user interface.

47. The apparatus of claim 46 wherein the user interface comprises:
means, coupled to the control processor, for initiating secure communications;
means, coupled to the control processor, for initiating clear communications;
and a display, coupled to the control processor, for indicating operation status.

48. The apparatus of claim 45 further comprising a removable interface module, the removable interface module including a telephone base interface and a telephone handset interface, (i) the telephone base interface for coupling to the telephone base, the modulator, and the demodulator, the telephone base interface for adapting the apparatus for operation with the telephone base, (ii) the telephone handset interface for coupling to the telephone handset, the speech encoder, and the speech decoder, the telephone handset interface for adapting the apparatus for operation with the telephone handset.