Patent Publication Number: US-7219225-B2

Title: Network arrangement for communication

Description:
This application is a continuation of international application Ser. No. PCT/GB00/00602, filed 18 Feb. 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a secure method and network arrangement for communication. 
     BACKGROUND TO THE INVENTION 
     Subscribers of communication services on fixed or mobile networks register terminals for use within a given network with the operator of that network. The network operator can thus deliver relevant subscriber services and support call origination and delivery for that registered terminal. For example, following user registration, the network can perform connection set up, call routing and billing functions. Where a subscriber is mobile and visits another network, communication services may still be available by means of roaming agreements between the network operators. 
     Internet applications and particularly wireless Internet applications have been proposed which allow subscribers of secure local networks to choose between communication routes which are deemed relatively secure and alternative communication routes which are inherently less secure. The Internet is regarded as providing insecure communication routes, particularly when compared with traditional communication networks such as a fixed-cable telecommunication network or a mobile telecommunication network. Accordingly, if a terminal located in a first secure network wishes to communicate with a terminal located in a second secure network, the intermediate communication route can either be secure or insecure. For example an intermediate network such as the PLMN, PSTN or ISDN networks would be deemed relatively secure. However, an intermediate network incorporating the Internet would render the communication route insecure. 
     Where an insecure network is used the originating and terminating end terminals may use an encryption technique. Applications for implementing the chosen encryption technique need to be provided at both the originating and destination end terminals. In practice, situations arise where a plurality of end terminals in one network wish to communicate with a plurality of end terminals in another network and mutually compatible encryption applications must be provided to each of the plurality of end terminals. 
     Security services employed on fixed and mobile networks include encryption, certification and authentication. Encryption, for example, typically employs systems based on key pairs. That is, before transmission a subscriber protects the transmission by running an encryption application on the originating end terminal using a key. The transfer is made with the content of the message in an encrypted (protected) format. At the destination end terminal, the message is decrypted by running a mutually compatible decryption application also with a key. 
     One well known type of encryption application employs a “private/public key pair system”, where the originating subscriber protects his transmission using a private key and the message is then transferred via an intermediate network to an end terminal where it can be decrypted by the destination subscriber by means of a public key. This system requires that the originating subscriber makes the relevant public key available to the or each destination subscriber. Subscribers do not usually make private keys available. Options for making public keys available to destination subscribers include, for example, email or posting the key on web sites which are accessible to destination subscribers. Although the keys are available to the intended recipients, this system is inconvenient and vulnerable to those who are intent on obtaining public keys for deciphering messages not intended for them. Imitation (hoax) web sites have been used to manipulate such arrangements. 
     Another type of key system employed in encryption applications is the “shared secret key pair system”. This system requires that the originating subscriber projects his transmission using a secret key and the terminating subscriber uses the same key (shared secret key) to extract the message information. This system differs from the private/public key pair system in that it requires that each receiving subscriber has access to the senders secret key. This arrangement is only acceptable where there is a high degree of trust between originating and receiving subscribers and secure networks therebetween. 
     In general, encryption techniques require that both the communicating end terminals of the subscribers have access to the relevant encryption/decryption algorithms/keys etc. The communicating end terminals must also be provided with and be able to run a suitable application. Any changes or modifications to the encryption technique at the originating end must be provided to the relevant terminal at the receiving end. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention seek to address the problems outlined hereinbefore. 
     According to an aspect of the present invention there is provided a method for secure communication between a first end terminal located in a first secure network and a second end terminal located in a second secure network, said first and second networks being separated by a relatively insecure intermediate network, the method including the steps of: selectively routing a communication from the first end terminal to the second end terminal over said relatively insecure intermediate network by means of one or more network elements triggerable to selectively route said communication; and encrypting said selectively routed communication by means of an encryption engine before it traverses said intermediate network, wherein said one or more network elements and said encryption engine are located substantially within said first secure network. 
     Preferably the one or more triggerable network elements comprises a switch means provided with a control means, and a storage means. The storage means can store routing information and/or security information such as encryption/decryption information and electronic cash bit strings. The switch means can selectively route a predetermined type of communication according to routing information held in the storage means and the encryption engine can encrypt said selectively routed communication according to encryption information held in said storage means. 
     In a preferred embodiment, said predetermined types of communication are identified by means of one or more of the following triggers set up in the switch means: recognition of originating subscriber characteristics; recognition of destination subscriber characteristics; recognition of payload characteristics; or recognition of network service characteristics. 
     Preferably, the one or more network elements is operable to store encryption/decryption and is triggerable to distribute decryption information from said first node to one or more target nodes. Typically, the encryption/decryption information includes algorithms or keys. For example, the one or more network elements can use a private key to encrypt and can distribute a public key for use by the recipient in decryption messages. 
     Preferably, the encryption information held in the storage means defines a preferred algorithm or key for use with said predetermined types of communication. In addition, the information held in the storage means can identify one or more groups of users whose communications are to be routed and encrypted according to common preferences. 
     According to a second aspect of the present invention there is provided a secure network arrangement for communication between a first end terminal located in a first secure network and a second end terminal located in a second secure network, said first and second networks being separated by a relatively insecure intermediate network, the secure network arrangement including one or more network elements triggerable to selectively route a communication from the first end terminal to the second end terminal over said relatively insecure intermediate network and an encryption engine for encrypting said selectively routed communication before it traverses said intermediate network wherein said one or more network elements and said encryption engine are located substantially within said first secure network. 
     According to another aspect of the present invention there is provided a network arrangement for the distribution of security information between a first node in a first secure network and one or more nodes in a second secure network, said first and second networks being separated by a relatively insecure network, wherein communications from said first node to one or more of said second nodes via said relatively insecure network are encrypted, the network arrangement comprising one or more network elements operable to store security information and triggerable to distribute said security information in a secure manner from said first node to one or more target nodes in said second secure network. 
     A switch means can be operable to selectively distribute an algorithm and/or key in response to a predetermined type of communication. In preferred embodiments, said predetermined type of communication is identified by means of one or more of the following: recognition of originating subscriber characteristics, recognition of destination subscriber characteristics; recognition of payload characteristics or recognition of network service characteristics. 
     In other embodiments, distribution of the decryption information is triggered according to predetermined time schedules by an intelligent peripheral communicating with said network element. 
     Network arrangements according to the invention allow the distribution of decryption information to end terminals in the second network and/or to a node within the second network other than the destination end terminal for the communication in question. Preferred network elements may be located, for example, substantially within said first network or substantially within said second network, possibly at different levels of hierarchy. 
     According to another aspect of the present invention there is provided a method for the distribution of security information between a first node and one or more second nodes, including the step of providing one or more network elements operable to store security information and triggerable to distribute the security information from said first node to one or more of said second nodes. 
     Preferred embodiments have applications, for example, in distributing algorithms and/or keys between nodes in secure networks over a relatively insecure intermediate network but also in distributing algorithms and/or keys and/or secure numbers or bit strings etc. over different network arrangements. Examples of uses include in ECASH (electronic cash) applications. 
     According to another aspect of the present invention, there is provided a method for the distribution of security information between a first node and one or more second nodes, including the step of providing one or more network elements operable to store security information and triggerable to distribute the security information from said first node to one or more target nodes. 
     According to another aspect of the present invention, there is provided a network arrangement for the distribution of security information between a first node and one or more second nodes, including one or more network elements operable to store security information and triggerable to distribute the security information from said first node to one or more of said second nodes. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a better understanding of the present invention and to understand how the same may be brought into effect, reference will now be made by way of example only to the following Figures in which: 
         FIG. 1  schematically illustrates examples of alternative communication routes between a first end terminal in a first network and a second end terminal in a second network; 
         FIG. 2  schematically illustrates a preferred method for communication between first and second end terminals located in secure networks and separated by an insecure network; 
         FIG. 3  schematically illustrates the method of  FIG. 2  applied to communication to and from a roaming mobile terminal; 
         FIG. 4  schematically illustrates a preferred method for the distribution of security information; and 
         FIG. 5  schematically illustrates a second method for the distribution of security information; 
         FIG. 6  schematically illustrates another method for the distribution of security information. 
         FIG. 7  schematically illustrates another method for the distribution of security information. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     The term “encryption” used herein can refer either to direct encryption of the IP payload, possibly with addition of an encryption header, or tunnelled payloads (i.e. not only encrypting but adding a further network header to address the encrypted packets to a known tunnel end point). The term is also used in a broader sense to refer to general compression techniques. The term “key” can refer to encryption/decryption keys/algorithms and secure codes/numbers used, for example, in electronic cash applications. 
       FIG. 1  shows a first end terminal  10  wishing to communicate with a second end terminal  12 . The originating end terminal  10  is in a first network (A) controlled by a first network operator and the second end terminal  12  is located in a second network (B) controlled by a second network operator. The networks (A) and (B) may be fixed (e.g. PSTN) or mobile (e.g. PLMN) networks operated by trusted network operators and are thus deemed relatively secure. The networks (A) and (B) are separated by intermediate networks which can include, for example, a public land mobile network PLMN or a switched telephone network PSTN and the Internet  22 . Whereas the PLMN/PSTN  16  could be regarded as a relatively secure intermediate network for transfer between the end terminals  10  and  12 , the Internet  22  would be regarded as an insecure network. 
     Switch  14  represents a general service switching point, for example a mobile services switching centre (MSC) or any suitable telecommunications switch or routing element. In some embodiments a service switching point SSP is provided integrally with the MSC. However, in others the SSP is provided as a separate network element. Communications can occur between the first end terminal  10  and the second end terminal  12  via a secure intermediate route indicated by arrows  19 , shown here as via the PLMN/PSTN  16 . Alternatively, communication between the first and second end terminals  10  and  12  can occur via an insecure intermediate route indicated by arrows  20 , shown here as including the Internet  22 . 
     Referring now to  FIG. 2 , a first preferred method for communication provides a secure network arrangement including a network element which permits the construction of a tunnel through the insecure network between first and second end points within the secure networks of the originating and terminating end terminals, respectively. The effect is to create a virtual private network (VPN) for secure communication between the two terminals  10  and  12 . A group of logically associated intelligent network elements  30  are provided in a secure network between the first end terminal  10  and the terminating end terminal  12 . In this example, the intelligent network elements  30  are provided in the network (A) of the originating end terminal  10 . The intelligent network elements  30  can communicate with end terminal  10  and also communicate with an encryption engine  40  in the first network (A). 
     The intelligent network elements  30  include a service switching point (SSP)  32  which may or may not be provided integrally with the MSC, a service control point (SCP)  34  for providing an intelligent function, a service management point SMP  35  including service data base (SDB)  36  for storing subscriber profiles and an intelligent peripheral (IP)  38 . The intelligent peripheral IP is connected to the service control point SCP and/or to the service switching point SSP by means of SS 7  signalling. For example, one intelligent peripheral IP serve several service switching points SSPs and may be provided as a separate (external) network element. The service switching point  32  can transfer messages from and/or to the first end terminal  10  and one or more of the intermediate networks  16 ,  22 . The service switching point  32  is connected to the service control point  34  which has processor functionality and access to the service database  36  of the service management point SMP  35 . The intelligent peripheral  38  is connected to the service control point  34  and/or possibly directly to the SSP  32  as explained above. 
     To communicate with either of the intermediate networks, the service switching point  32  can transfer messages to and/or from either the PLMN/PSTN  16  or the encryption engine can be integrated to other  40  which defines a first end point of a tunnel  41  through the Internet  22 . The encryption engine  40  may be provided integrally with one or more of the remainder of the group of network elements  30 . Alternatively, the encryption engine  40  may be a separate (external) network element. A further switch  18  is provided in the second network (B). The switch  18  is connected to each of the intermediate networks, namely the PLMN/PSTN  16  and a second end point  42  of the Internet tunnel  41 , and with the second end terminal  12 . Note that the encryption engine  40  defining one end point of the tunnel  41  and the other end point  42  of the tunnel  41  are located in the first and second secure networks (A) and (B), respectively. The tunnel  41  is thus constructed as a secure passageway for transfer through the Internet  22 . 
     The intelligent network elements  30  enable the operator of the first network (A) to offer subscribers a secure communication route over a usually insecure network. This is achieved by intelligent management of route and encryption techniques in respect of specific subscribers or groups of subscribers. In a situation where the first end terminal  10  wishes to communicate with the second end terminal  12  via the Internet  22 , the first terminal  10  originates the communication and follows call access  50  and call set-up  52  procedures. Typically the end terminal  10  transmits both an identification number and a destination number on a control channel. The service switching point  32  receives the information from terminal  10  and can refer to the service control point  34  in response to a predetermined trigger. The type of trigger employed can vary but will generally be set-up such that the intelligent network elements  30  provide the subscriber of the end terminal  10  with his preferred network service. For example, the service switching point  32  can be set up to refer to the service control point  34  in response to a trigger being set, for example, on the network address of the originating  10  or terminating  12  end terminals, on flow ID which is an identity associated with a succession of packets and/or or on payload information. In this example, the trigger is set to respond to a characteristic of the destination number. In other embodiments, the service switching point  32  may recognise a range of numbers in the originating ID number, and/or destination number or may respond to prepaid only, voice only, data only messages, and be dependent on time-of-day etc. This list of possible triggers is obviously not exhaustive. 
     When a referral by the service switching point  32  to the service control point  34  has been triggered as described above, the service control point  34  accesses the relevant subscriber profile stored in the service database  36  of the service management point SMP  35 . The subscriber profile contains subscriber specific information including information regarding the network services paid for by each subscriber or group of subscribers. In this example, the subscriber profile contains subscriber specific routing and encryption information which is taken into account whenever a trigger is determined. The information stored in the service database  36  may include one or more preferred encryption algorithms (or compression algorithms etc.) and/or keys. Subscriber specific profile information is then returned to service switching point  32  via service control point  34  and the transfer is routed as appropriate. If the subscriber in question prefers communication between the first network (A) and the second network (B) to go via the PLMN/PSTN  16 , the profile information will indicate this and the service switching point  32  will direct the transfer accordingly. However, if the subscriber in question prefers communication between the first network (A) and the second network (B) to go via the Internet  22 , then the service switching point  32  will redirect the communication to the encryption engine  40  where the message content is automatically encrypted using an algorithm. In this example, the preferred algorithm is part of the subscriber specific information specified in the service database  36 . Once encrypted, the message content enters the Internet tunnel  41  where it remains in an encrypted format while it traverses the Internet, i.e. until it reaches the end point  42  located within the secure network (B). 
     The provision of triggered redirection and, where appropriate, automatic encryption permits a secure tunnel  41  to be constructed through the usually insecure Internet. From the end point  42  the message is routed on to switch  18  and thereafter to the destination end terminal  12 . Between the end terminals  10 ,  12  and their respective access switches (i.e. the service switching point  32  and the switch  18 ) in the access networks (e.g. GSM or GPRS) specific encryption or physical security is used and thereby provides inherent security within the first and second networks (A) and (B). 
     Any information held in the service database  36  of the service management point SMP  35  can be easily modified or changed without down-loading or up-loading to and from end terminals  10 ,  12 . For example modifications can effect updates of stored algorithms/keys or alter group lists to permit guest users of a subscriber to benefit from the service. The modifications may be made, for example, via an intelligent network service management access point (SMAP) which allows the operator or even the subscriber himself to change the database  36  records constituting the subscriber profile information as appropriate. 
     Preferred methods therefore provide a secure method of communication, wherein triggers set on say originating subscriber identity, destination subscriber number, IP address, flow ID or payload information can be mapped to intelligent network service logic available to the subscriber. Preferred arrangements in effect permit the creation of a virtual private network (VPN) for communication between the end terminals  10  and  12 . Preferred arrangements represent a triggered intelligent network service on an intermediate-system (i.e. on a switch/router within a network), rather than an application based system operating on end terminals. An advantage is that the same service can be triggered for any subscriber and, if desired, the algorithms or keys used in encryption can be proprietary to a subscriber. Paying subscribers can benefit from the advantages, whether they are in home or visitor networks provided the network operators of the relevant home and visited networks are party to a roaming agreement. 
     Individuals or commercial entities who are subscribers and have paid for specific services will be identified in the group lists held within the service data base and can benefit from a secure network service customised according to their own preferences. 
     Another advantage is that commercial entities or other group subscribers can define an algorithm to be used exclusively in connections between members of a specific group. That is, company A could define an algorithm to be used in transfers between employees of company A only; in which case when establishing a connection between company A employees, the service control point  34  would inform the service switching point  32  to forward an encryption algorithm specific to company A to the encryption engine  40 . 
     Another advantage is that because handling of encryption is in fact network based there is no need to store encryption or compression algorithms or the like at either of the respective end terminals  10 ,  12 . 
     Intelligent network elements  30  can cause encryption keys or even encryption algorithms themselves to be loaded and used at encryption end points associated with the service switching point  32 . The encryption engine  40  may, but does not need to-be, part of the intelligent network elements  30  served directly by the service switching point  32  which triggers the service. For example, the triggering service switching point  32  may simply redirect packets or flows of a specific subscriber to an encryption engine  40  on a separate network/sub-network, by re-routing to the relevant host in order to enter the encryption engine  40 . Of course, a decryption point would still need to be located at the end point  42  or at least within the secure network (B) 
     In one modified version the algorithm is run in a centralised encryption (or compression etc) network element (NE) separate from the service switching point  32  but still within the first network (A). In this case, the service control point  34  returns routing instructions (e.g. a tunnel to the NE) and any encryption parameters to be used in the encryption NE. Corresponding means may be provided within the second network (B) to effect decryption/de-compression of the message. In another modified version, the service is triggered in response to a specific message sent by the source terminal. That is, the service is specifically commanded by the end terminal in communication. 
     In another modified version, the service switching point  32  may refer to the service control point  34  as a matter of course. (i.e. without a trigger being recognised). The records in the service data base then being accessed by the service control point  34  to determine specific routing instructions and encryption/decryption information. 
     Where roaming agreements are in place between the operators of networks (A) and (B), corresponding secure network services can be provided on service switching points in the visited network. These service switching points may run algorithms set up in advance through agreement between the network operators or transferred dynamically, for example upon an end terminal attaching to a visited network. Alternatively, distribution of the necessary encryption/decryption information may be achieved via a secure virtual home environment (VHE) mechanism or by a distribution method/arrangement described hereinafter. 
       FIG. 3  shows how a roaming agreement set up between the operators of networks (A) and (B) may allow originating end terminal  10  to benefit from the advantages of the preferred method while visiting network (B). End terminal  10  in effect experiences a virtual home environment (VHE) facilitated by secure communications between the network operators party to the agreement. The virtual home environment enables terminal  10  to initiate the normal access  50  and connection set up  52  operations as if it was located in its home network. If the subscriber of end terminal  10  normally benefits from secure network communications provided by his home network operator, a trigger set up using intelligent network elements  60 , as mentioned above will be identified in the service switching point  62 . If no such trigger is identified the service switching point will route the call via the PLMN/PSTN  16  or via the Internet  22  non securely. Where a trigger is identified by the service switching point  62 , the service control point  64  accesses the service database  66  in which the subscriber profile contains encryption information. According to the profile information contained in service database  36 , in this example routing information, encryption information and group subscriber lists, etc., the service control point  64  controls the service switching point  62  to redirect the call in a secure manner via the Internet  22 . As before, the message would be then redirected to an encryption engine  80  where the message is encrypted before it enters a tunnel  41  for secure transfer through the Internet  22  to a secure end point  82  within the destination network (A). From this end point  82 , the call is routed via the switch  14  to the destination end terminal  12 . Triggers are available not only in the originating network on messages from the source terminal but also in the destination network on messages intended for the destination terminal. 
     The above type of secure service can be made available anywhere in the world provided subscribers are visiting areas covered by roaming agreements with their home network operator. These services can be run from any terminal because the manner of operation means they are actually effected on the network. All of the earlier mentioned advantages apply to such roaming methods. 
     In order for originating and terminating end points to decipher encrypted (or compressed) data, they must have access to the relevant decryption (or de-compression) algorithms and/or keys and be able to run them. In the cases of the methods of  FIGS. 2 and 3 , the encryption end points  40 ,  80  and  42 ,  82  need to be provided with the relevant encryption/decryption information. It is desired that only those for whom the message is intended can access the algorithms and/or keys which enable the message to be deciphered. Moreover, these keys should not be distributed over insecure networks. Where transmission of decryption information is unavoidable, it should be distributed over networks in a secure manner. 
     Two trusted network operators such as the operators of the first and second networks (A) and (B) would normally have access to corresponding encryption/decryption keys. Nevertheless, the subscriber may still prefer to pay extra for specific algorithm services which in effect function as an additional layer of encryption or represent a specific tunnel construction. In addition to the Internet  22 , insecure intermediate networks may include fixed and mobile networks over which the network operator cannot offer the standard of encryption required. Where this situation occurs, security beyond the basic ciphering provided in for example GSM networks (and future UMTS networks) may be required by network users. When such additional protection is required, the destination end point  42  and/or the destination end terminal  12  must have access to the necessary decryption information which is typically an algorithm or a key. The intelligent triggered method of  FIG. 4  works by querying a security server connected in an intelligent network as an intelligent peripheral as described below. 
       FIG. 4  schematically shows a preferred method for the distribution of encryption/decryption information. The illustrated network uses an algorithm/key distribution system managed by intelligent network elements  30 . The arrangement of  FIG. 4  is similar to that of  FIG. 2  and like reference numerals indicate like features. A first end terminal  10  wishes to communicate with a second end terminal  12  in a secure manner. The originating end terminal  10  is in a first network (A) controlled by a first network operator and the second end terminal  12  is located in a second network (B) controlled by a second network operator. The networks (A) and (B) may be fixed or mobile networks operated by trusted network operators and are thus deemed relatively secure. In order for the message content to traverse the Internet  22  in a secure manner it will need to be encrypted at or before the tunnel end point defined by encryption engine  40  and decrypted at or once it has passed end point  42 . Thus it is possible for encryption/decryption to occur at nodes within either of the networks (A) and (B) (e.g. encryption engine  40  or end point  42 ). Alternatively, it is possible for encryption/decryption to occur at the end terminals  10 ,  12 , respectively. 
     In operation, the end terminal  10  goes through the attach  50  and connection set up  52  procedures which inevitably depend on the type of network. Service switching point  32  handles the request for communication and, if present, a trigger causes the service switching point  32  to refer to the service control point  34 . Examples of the various types of trigger set-up available were mentioned earlier with reference to  FIGS. 2 and 3 . The SCP  34  provides an intelligent function and can refer to a subscriber profile in the service database  36  of the service management point SMP  35 . The subscriber profile provides subscriber specific encryption information and may also provide routing preferences. The service control point  34  then communicates with the service switching point  32  to route the transfer either through the PLMN/PSTN  16  or via the Internet  22 . Where the subscriber profile in service database  36  specifies encryption, the message is routed to the encryption engine  40  and onwards to switch  18  via the Internet  22 . There is a corresponding end point  42  where the message is decrypted within the secure network (B). It would of course be possible for the relevant decryption to be performed at the end terminal  12 . 
     An intelligent network service management access point (SMAP)  100  allows the operator to alter records in the database  36  and, therefore, specify, load and change the algorithms or keys to be stored and/or distributed. Accordingly, a given subscriber can manage his own key hierarchy by instructing the network operator to make, delete or alter relevant entries in the database  36 . 
     Note that the network (A) includes intelligent network elements  30  and the service database  36  containing security information managed by the operator of network (A). An intelligent peripheral could also hold security information for example, keys. The security information stored in service database  36  of the service management point SMP  35  might include encryption algorithms, compression algorithms, keys  39 , secure numbers or bit strings etc. for use in connection with electronic cash applications etc. As before, where this security information is held within or is associated with a given subscriber profile, it can be proprietary to a specific subscriber. A selection of different algorithms or keys may be held in association with a specific group of subscribers. More than one algorithm/key may be stored in the service database  36  with the various items being held in a hierarchy along with specific instructions for use thereof. 
     Preferred network arrangements can be set up to automatically communicate the particulars of encryption or indeed whether or not encryption is required at all. Preferred networks can be set up to ensure decryption algorithm/keys are received by the or each destination end terminal, either at the same time or at a different time to the message itself. That is, any one who was targeted as a recipient of a message can automatically receive the relevant decryption information. As before, the effect is to create a virtual private network between communicating end terminals. 
     Where a message is a broadcast message intended for a target group consisting of a number of end terminals  12 , a plurality of keys  39  can be distributed simultaneously for the plurality of target end terminals  12 . Since the second network (B) is deemed to be secure, it is not necessary for terminating end terminals  10 ,  12  to run decryption applications nor handle any type of algorithm/keys at all. Encryption or decryption can be performed at any secure points within, for example, networks (A) and (B) under the control of the intelligent functions as described with reference to  FIGS. 2 and 3 . Thus it is possible for preferred embodiments to distribute security information such as encryption/decryption information to a node within a secure network, rather than the destination end terminal for the communication in question (see also  FIG. 6 and 7 ). In such cases the receiving node in the secure network acts on behalf of the destination end terminal to proxy the relevant service, e.g. decryption. 
     However, in certain circumstances it may be that distribution of decryption information for example keys to end terminals is preferred and this is also possible provided the or each end terminal in question is provided with the means necessary to run the decryption application. The distribution of a key need not be triggered specifically by a message content associated with a call. The intelligent network may, for example, periodically distribute keys to selected end points or end terminals or in response to external events. Thus with a preferred network incorporating an intelligent network function for the distribution of encryption/decryption information, keys can be distributed for any party attached to any point in the network and the distribution process can be network initiated. That is network-initiated key up dates can be propagated to secure end points  42  within the destination network or directly to end terminals  12  of subscribers between sessions or calls. The network-initiated update may be to the or each user selectively or it may be to one or more of the operators and the distribution thereafter managed by the operator. Similarly, any modifications or changes to algorithms/keys or the key hierarchy can be specified and transmitted to destination nodes with great efficiency. 
     The timings of network-initiated key distributions can be selected to maximise security. For example, the keys may not be distributed simultaneously with the messages they may be distributed at different predetermined times which may be regular or irregular times. All of the above services would be available on a fixed network or on a mobile network and in the latter case switching on or moving, for example, may be used as triggers to push encryption information updates around the various networks. In one embodiment, the distribution is triggered when a mobile station initiates communication with a visited network. 
     In mobile networks where the originating and/or terminating end terminal is visiting another operator&#39;s network, the service may be offered in accordance with roaming agreements. Preferably, trusted communications between reputable network operators will permit a virtual home environment (VHE) to be provided to visiting mobile terminals and, therefore, a subscriber could have access to the service anywhere in the world provided the local network is party to such an agreement. A virtual home environment is facilitated when information concerning all aspects of the service possibly including encryption/decryption information, is shared between network operators in a secure manner. 
     Recipient end terminal users can specify that they wish to answer calls only according to certain circumstances. For example, they may choose not to answer any calls which are not accompanied by keys or for which they do not have access to keys. 
     Public keys can be securely distributed to target subscribers over usually insecure intermediate networks for use with a private key service held at a secure location within one of networks (A) or (B). Alternatively, private keys may be distributed specifically to the service subscriber for him to use exclusively in signing certificates or data. This service has obvious advantages over a system in which keys are distributed in a non-specific manner. 
     Signed certificate data can be verified by the public key distributed to other parties needing authentication of the sender. Where public keys are made available by general broadcast or held at specific sites it is desirable for the validity of the key to be certified by some authority. Network operators may authenticate signed data/keys that is, act as a Certification Authority and, where appropriate, charge for the service. 
     In cases of secure symmetric encryption, a shared (secret) key can be distributed for secure sessions between two or more end terminals  10 ,  12  wishing to form secure connections across one or more usually insecure networks. Secure encryption techniques are possible because the intelligent network elements  30  and particularly the tunnel entry  40  and tunnel exit  42  end points are located within networks owned by trusted network operators using network specific (e.g. GPRS or GMS) encryption. 
     The intelligent network function for the distribution of encryption information may be provided in originating network (A) or terminating network (B). In fact, one or more intelligent network elements may be provided in both ends of the communication chain.  FIG. 5  shows an arrangement in which intelligent network elements GO are provided at the destination end of the communication chain. In order to communicate a message, the end terminal  10  would go through the usual access  50  and connection set up  52  procedures, regardless of the type of switch  14  in network (A) which may be, for example, a fixed telecommunication switch, an MSC or an intelligent network element. Assume also that switch  14  is operable to direct the transfer via the Internet  22  in an encrypted form. The message would thus be routed to a first tunnel end point, in this case defined by encryption engine  40 . The exit to the tunnel  41  is defined by a second tunnel end point  42  from where the message is routed to intelligent network elements  60 . 
     When the message reaches the group of intelligent network elements  60  it is received by service switching point  62 . If a trigger has been set up and is identified, the service switching point  62  refers to the service control point  64 . SCP  64  provides an intelligent function and accesses the service database  66  of the SMP  35  to get information on the algorithm or key relevant to the message in question. Information in the service database  66  can be associated with the message by any suitable means, e.g. by the ID of the originating subscriber or the destination number. In fact, the trigger may operate in response to any address message, ID, IP address, flow ID or payload information etc. The relevant encryption information, in this case key  69 , is transmitted back to the service control point  64  and then on to the service switching point  62  for transfer directly to the destination end terminal  12 . 
     All advantages described in relation to the method of  FIG. 4  also apply here. For example, subscribers are able to control and manage their own key hierarchy in the same way as described with reference to  FIG. 4 . 
     Clearly, the or each group of intelligent network elements  30 ,  60  providing the triggering and distribution functions can be positioned at any convenient point in the communication chain, provided that the chosen location is approximate in terms of security. Further, the elements of the or each group of elements  30 ,  60  providing the trigger (recognition) and distribution functions, namely the service switching points  32 ,  62  and the service control points  34 ,  64  need not be in the same part of the distribution chain. That is, a first group of intelligent network elements  30  in network (A) can instruct a second group of intelligent network elements  60  in network (B) to distribute a key (or algorithm) to one or more destination end terminals  12 . 
     Where added encryption is required on usually secure networks (e.g. PLMN/PSTN  16 ), it is possible to provide an arrangement wherein the necessary encryption/decryption means  40 ,  42  are provided in the communication chain at either end of the PLMN/PSTN  16  network or on the end terminals  10 ,  12 . 
     Short message services (SMS) could be used to deliver keys. However, under short message service conditions nothing would be automatic, i.e. the key would not necessarily be received when the call is received in which case it would need to be requested subsequently. Short message service delivery may not always be possible if the receiving party is analogue mobile or fixed telephone. Preferred embodiments are therefore most effective when used with fixed or mobile terminals whereas GSM mobile has the additional option of SMS services. Alternatively, security information of the various types referred to herein can be distributed by means of USST in the form of unstructured supplementary data. 
     Under certain circumstances, it may be preferable for the security information such as keys to be delivered on control channels rather than on user channels. 
     A further embodiment is described with reference to  FIG. 6 . In order to proxy electronic-payment on behalf of an end-terminal  10 , storage in a network element such as a service control point or a service data base  36  or an intelligent peripheral  38  may be provided for electronic-cash bit strings. Alternatively, storage for electronic cash related information may be provided in a separate electronic payment network element. Electronic-cash held in the electronic-payment network element SCP  35  or SMP  35  or some dedicated electronic payment network element could transfer electronic-cash as electronic-cash bit strings over the networks  16 ,  12  in a secure manner to receiving end terminal  12  where payment is required. In other circumstances payment may be made to end terminal  13  within the same secure network in a similar manner. This electronic-payment service is available to those end-terminals that have subscribed to these services and are recognised by their subscriber identities known via the service switching point  32 . The subscriber on whose behalf the payment was made may then be billed by conventional means if necessary, that is by the network operators billing centre. 
     With reference to  FIG. 7 , a network element, such as an Intelligent Peripheral  38 , may be provided in the secure network (A) to sign messages or certificates originating from an end-terminal  10  in the secure network (A) and destined for other communicating parties which are either within the same secure network such as the end terminal  13 , or more likely to an end terminal  12  in another network such as the PLMN/PSTN  16  or Internet  22  connected to the secure network. The switch  18  is shown to illustrate that a receiving end-terminal  12  can be connected to the PLMN/PSTN  16  or the Internet  22  or both. Switch  18  need not be shown if a direct connection is made to the PLMN/PSTN  16  or the Internet  22 . 
     The operator of network (A) can distribute the security information to many end-terminals  10 ,  12 ,  13  in a group simultaneously as a multicast to the group or as multiple separate point-to-point communications. Group lists are maintained by the operator of network (A) in the service data base  36  and subscribers can be added/removed from the lists. This allows distribution to more than one end-terminal simultaneously on the occurrence of a single event such as a network trigger from a connection set up, a specific command from an end-terminal or a network-initiated distribution from a periodic trigger or external event, for instance in the knowledge that the old security information has been compromised. The network operator thus controls a secure network with many authenticated subscribers at many end-terminals. This permits the secure distribution of new/updated security information to many subscribers at the occurrence of a single network event. 
     It is also possible for preferred embodiments to distribute security information to a node within one or more of the first and second secure networks, rather than the destination end terminal for the communication in question. The receiving node in the secure network can act on behalf of the end terminal to proxy such services as encryption/decryption, electronic payment or signing messages/certificates. 
     The schematic illustrations of preferred embodiments are not intended to limit the invention to one or more of the specific arrangements disclosed herein. For example, the or each of the network elements for performing the invention may be provided in any suitable arrangements and one or more is likely be provided in different hierarchical layers of the relevant telecommunication network.