DE3402467A1 - Dialling method protected against fraudulent use, for the subscribers of a radio network, in particular a mobile radio network - Google Patents

Abstract

Before a call is set up in mobile radio networks, each calling vehicle subscriber notifies his identity to the central station in the form of an identification code. Since this identification code can be intercepted, there is the risk that eavesdroppers may make radiotelephone calls at the expense of an authorised subscriber. To prevent this, the destination dialling information transmitted by the calling vehicle subscriber is transmitted following encryption 3 along with a fixed key 4 which is uniquely allocated to this vehicle subscriber only. In the central station, the subscriber-specific fixed key 7 is selected by the identification code of the calling subscriber, which code was previously transmitted in unencrypted form from a fixed key file 6 containing all the inverse fixed keys and, with the aid of said fixed key, the destination dialling information is decrypted 8. Any international indicator digit of a destination dialling code is transmitted in unencrypted form. To prevent identification of the fixed key of an external subscriber, the module 4 containing the subscriber-specific fixed key and the encryption module 3 are disposed in a technically inseparable and inaccessible manner, and are interconnected, in each station (Fig. 4). <IMAGE>

Description

Deutsche Bundespost? 535 -h ~ Ί Λ Π? Λ R 7

Dialing procedure for the participants in a point network, in particular a cellular network.

The invention relates to a dialing method for the subscribers of one of the services, which is secured against stealth a central station controlled radio network, in particular a mobile radio network.

It is the aim of every imitation of a foreign participant's identification, to get a connection to a particular subscriber, with the incurred call charges due to the imitation of the identification of another subscriber station are charged.

The previously known methods for combating the unauthorized use of identifications from foreign subscriber stations of a radio network are based on securing the identification of a subscriber station against imitation.

Such a procedure is described in DT-AS 24 19 615. It is a fixed key for encrypting the participant identification (Identifier) specified. Procedures with a fixed key can be made by listening to the exchange of information be undermined on the radio path.

Other methods with e.g. Constantly changing key rules are at risk if the key information, i. the message as to which key is currently up-to-date must be transmitted over the radio path.

The invention takes a different approach. It is directed against the success of imitating someone else's identification. Any use of a counterfeit identification leads to a wrong choice ... '. Ultimately, a manipulator of the Refrain from imitation of third-party identifications, because the connection to the telephone subscriber chosen by him / her (Target selection) does not come about.

German Federal Post 2535

To solve the problem presented above, the invention proposes that

a) the destination dialing information outgoing from the calling subscriber is sent out encrypted with a plague key that is individually assigned to this participant only,

b) in the central station by the subscriber identification or identifier of the previously sent unencrypted calling subscriber from a plague key file containing all inverse plague keys the subscriber-specific Plague key is selected and with its help the destination dialing information is decrypted.

Pig. 1 shows the mode of operation of the invention on a Subscriber station. The identification assigned to the subscriber station is encoded in the memory 1. In the destination dialer 2 is the call number of the respective desired subscriber (destination dialing) from the keypad of the subscriber station coded. This target selection is by means of the Yerschlüsseiung 3 after the subscriber station with the Identification assigned plague key from the plague key memory 4 encrypted. This encrypted Target selection arrives at the point transmission system with the open (unencrypted) subscriber identification.

Pig. 2 shows the mode of operation of the invention at the central station. The Identification after decoding 5 to the plague key file 6. The plague key file 6 contains the inverse key to all existing assignments of fixed keys to identifications in the network 6 determined inverse key 7 is with the encrypted destination dial received from the radio transmission system entered into the decryption 8. The decryption 8 delivers the coded destination dialing to the telephone network. The identification decoded with 5 also extends to the telephone network to debit the participant's account.

In the case of manipulation of a subscriber station with counterfeit identification or unassigned fixed

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German Federal Post 2535

key, the decryption with the assigned inverse key of the remote station results in a wrong choice. A manipulator is thus excluded from the success of his manipulation.
5

An advantageous development of the invention can be seen in the fact that the keys are selected in such a way that that in the event of manipulation, the wrong dialing resulting from a domestic destination cannot reach the foreign country:

If a potential manipulator who (legally or even illegally) possesses a trained according to the invention Subscriber station is, for the purpose of fraudulent charges, the one individually assigned to a foreign subscriber station If you want to determine the fixed key and generate it instead of your own, it will first become your own fixed key subdivided according to general algorithm and individual part try to determine. Then the manipulator could generate a foreign fixed key on a trial basis, which has at least the correct algorithm. Only then the individual part of the fixed key actually assigned to the foreign participant would become accessible by comparing many target selection entries with those actually achieved due to the key divergence other goals.

In order to prevent such a determination of a foreign fixed key, are in a further development of the invention in each subscriber station the assembly for the subscriber-specific Fixed key 4 and the assembly for encryption 3 of the target selection are technically inseparable and arranged without access and connected to one another.

A corresponding housing is indicated in Fig. 1 by a frame shown in dashed lines.

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Claims (1)

Deutsche Bundespost 2535 3 4 02467 Dialing procedure for subscribers in a point network, in particular a cellular network, secured against stealth (3) Claims A dialing procedure for subscribers controlled by a central station, secured against stealth Radio network, in particular mobile radio network, characterized in that a) the destination dialing information outgoing from the calling subscriber is transmitted encrypted (3) with a fixed key (4) which is only individually assigned to this subscriber (Fig. 1),
b) that in the central station the subscriber-specific fixed key (7) is selected from a fixed key file (6) containing all inverse fixed keys and the destination dialing information is decrypted (8) with its help ( Fig. 2). .. Dialing method according to Claim 1, characterized in that a foreign elimination number of destination dialing information ' is transmitted unencrypted. .3 subscriber station for carrying out the method according to ^: claim 1, characterized in that the subassembly contained in it for the subscriber-specific fixed key (4) and that for the encryption (3) of the destination are technically inseparable and access-free and connected to one another. COPY