SE512440C2 - Method for secure telephony with mobility in a telephone and data communication system comprising an IP network - Google Patents

Abstract

The invention relates to a method for safe telephony with mobility in a tele and data communications system (1) which includes an IP-network (15), at which the telephony is executed with mobile units and at which the method for each mobile unit includes the steps: to create a unique identity code and store it in the unit; to, at the switching on of the unit, at least at switching it on in a home domain, transmit the identity code to a mobility manager (9); to, via the IP-network, establish contact between the mobility manager and an initiating database (13) for transmission of initiating information for Internet communication from the initiating data base to the mobility manager, which step includes to, by utilisation of the identity code, authenticate the mobility manager for access to the initiating data base, and to encrypt the initiating information at the transmission; and to, by means of the initiating information, start a proxy (11) which represents the unit towards the Internet.

Description

15 20 25 30 35 512 440 2 tiering service (AS) a so-called TGS ticket in return for the user proving that he is who he pretends to be.

The user identification takes place by the user initially a bunch of everyone registering manually and receiving a password from Kerberos®. The password is stored centrally. When the user then wants to use services in the network, he / she orders the TGS ticket with his / her user identity as identification. The TGS ticket includes, among other things, a TGS session key, the name of the service (ie TGS), a time stamp and validity period. In return from TGS, the user receives the TGS ticket encrypted with TGS password and a copy of the TGS session key encrypted with the user's password. Thus, only the genuine user can decrypt and use the information. In this way, the password is never sent freely over the net.

The TGS ticket is valid as access to a ticket issuing service (TGS). In the second step, the user therefore turns to TGS to get service tickets for other services. In this step, the user sends the TGS ticket encrypted with TGS password and the name of the service requested to TGS. TGS sends back a ticket to the service encrypted with the service's password and a copy of a service session key encrypted with the TGS session key.

For each new service that the user wants to use, he addresses the said TGS in the same way and sends with his TGS ticket.

This known method has several advantages. The user only needs to enter their password once each work session.

Only registered users can use the system as the user must authenticate with AT before receiving a ticket to a service. Services know that the sender is genuine and not someone who copied the correct message because only the genuine sender knows the session key and can decode the traffic. Likewise, the user knows that a service is genuine because the session key in the ticket is encrypted with the service key. Only the genuine service can thus decode the session key. In addition, the user is always waiting for an answer and can therefore be sure that the service is genuine.

However, the Kerberos® method is not directly applicable to IP telephony with mobility, such as a system with DECT telephones that have access to an IP network. There is therefore a need for a security solution for such telephony.

Summary of the invention The object of the invention is therefore to create a security solution for IP telephony with mobility. The object is achieved with a method for secure communication according to the invention as defined in claim 1 in the appended claims.

Brief Description of the Drawings In the following, embodiments of the method according to the invention will be described in more detail with reference to the accompanying drawings, in which: Fig. 1 schematically shows a telecommunication and data communication system in which an embodiment of the method is implemented; and Fig. 2 schematically shows a part of the system in Fig. 1 in detail.

Detailed Description of Embodiments Hereinafter, a preferred embodiment of the method according to the invention will be described, exemplifying it applied in a telecommunications and data communication system comprising cordless telephones in the form of DECT telephones and shown in Fig. 1. The method according to the invention is particularly suitable for such systems.

Each DECT telephone 3 stores an identity code (ID code), which is created in such a way that it becomes unique, preferably globally unique. When the DECT telephone 3 is in a home domain, i.e. a DECT domain, and is switched on: iiziziii: W 10 15 20 25 30 35 512 440 4 the ID code is sent to the domain base station 5. From there the ID code is forwarded to a mobility manager, here a so-called proxy manager 9, see Fig. 2, which is arranged in an IP management unit (IMU) 7. The proxy manager 9 starts for each DECT telephone 3 a proxy 11, ie a switch representative, which represents DECT phone 3 to the Internet, or any other IP network. However, the proxy manager 9 requires some initialization information to be able to start a proxy ll. The information is retrieved from a special initialization database 13, which is referred to here as the telephone directory.

The telephone directory is accessed via the IP network 15. In order for the information to be transmitted in a secure manner, the above-described, known method called Kerberos® is used, which is among other things implemented on a server 17, which handles the central distribution of keys. The information includes the IP address, the subscriber's username and a key for mobile IP.

In this situation, the proxy manager 9 is the user and the telephone directory 13 is the service to be used. In order for the proxy manager 9 to receive the information, it must thus authenticate itself to the AS 17 part of the server 17 in order to obtain a TGS ticket, and then use the identity code as the user identity, and then by sending the TGS ticket to the server 17 TGS part receive a service ticket to the telephone directory. The information is transmitted well encrypted from the telephone directory 13 to the proxy manager 9, as described above. The proxy manager 9 then starts a proxy 11 with the information as input.

Proxy 11 now has the function of a mobile node. If it were to be in a foreign network, it uses mobile IP to ensure that traffic intended for it is routed to the correct address. In mobile IP, authentication is of the utmost importance because unauthorized persons, in the absence of authentication, could move the traffic into the system at will or falsely pretend to be someone other than themselves. This authentication takes place by means of an encryption algorithm and a secret key, Au H 10 15 20 25 30 512 440 5 which is shared by the mobile node, i.e. the proxy 11, and the mobility manager in its home network. The secret key is the above-mentioned key for mobile IP that the proxy manager 9 receives from the database 13.

When the subscriber wants to use one of the services that the network operator offers, for example making a call, both the subscriber and the operator are interested in the billing for the use being correct. The proxy will then contact a debiting service to debit the correct account with the correct amount. This communication also takes place with the help of Kerberos® _ _ Proxyn 11 is preferably compatible with ITU-E standard H.323, which can be used as follows.

When communicating between two subscribers, the receiver retrieves a session key from Kerberos® and sets up a secure and authenticated channel. Then H.323 takes over. The number is thus transmitted encrypted so that it is not possible to listen through the authentication. At the same time, operators who are not authorized subscribers to the system are prevented from making free calls.

A preferred embodiment of the method according to the invention has been described above. This should only be seen as an example of how the invention can be practiced. Many modifications are possible within the scope of the invention as defined in the claims. Below are some examples of such modifications.

The method described above for IP telephony with DECT telephones has been described above. It is also applicable to other types of mobile IP telephony. An example is a computer that is moved between different access points.

The key distribution method Kerberos®> described above can be replaced by another equivalent method that involves equally good authentication and encryption. b

Claims (5)

| .. Mll 10 15 20 25 30 35 512 440 6 PATENTKRAV A method of secure telephony with mobility in a telecommunications and data communication system (1) comprising an IP network (15), the telephony being performed with mobile devices and wherein the method of each mobile device is characterized by the steps: -that create a unique identity code and store it in the unit; - when switching on the device, at least when switching on in a home domain, to transfer the identity code to a mobility manager (9): - to establish contact via the IP network between the mobility manager and an initialization database (13) for transmission of initialization information for Internet communication from the initialization database to the mobility manager, which step comprises using the identity code to authenticate the mobility manager for access to the initialization database and to encrypt the initialization information before the transfer; and - by means of the initialization information, starting a deputy (11), who represents the unit towards the Internet. Method according to claim 1, characterized in that said deputy for accessing services in the communication system initially authenticates via a data included in the initialization information for a server which centrally handles keys, wherein the deputy from a part of the server receives a TGS ticket and then, by providing the TGS ticket, via a TGS part of said server receives service tickets for different services, each service ticket comprising a session key specific to the service in question. A method according to claim 1 or 2, characterized by storing in the database initialization information which for each user includes the IP address and key for mobile IP. Method according to one of the preceding claims, characterized in that the step of transferring the identity code to a mobility manager when the device is switched on, at least when switching on, when the device is a DECT telephone, comprises sending the identity code from the telephone to a base station (5) in the home domain and to forward the identity code from the base station to the mobility manager. Method according to one of the preceding claims, characterized in that the deputy, when in a foreign network, uses a mobile IP to ensure that the traffic intended for it is routed to the correct address.