CH625650A5 - Radiotelephony method - Google Patents

Description

The invention relates to a radio telephony method for a larger number of subscribers, in which the messages are transmitted by an encryption or concealment device with a specific subscriber-specific key.

In such radio telephony systems, in which mainly mobile stations are used, for example in public mobile land radio (öbL) or non-public mobile land radio (NÖbL), message protection against eavesdropping should be achieved in some way, i.e. the signals that are transmitted over the radio path are to be encrypted or concealed in a suitable manner. The corresponding points usually have one or more identical keys, which are attached to the device as a setting variant and on which the message transmission can be carried out after consultation. For military and other special networks, it is known how such keys are distributed and stored, for example by means of electronic components or, for example, punch cards. In the case of subscribers to a public radio network, for example in the case of the land radio mentioned, such methods fail because, owing to the large number of subscribers, transmission secured against eavesdropping is not possible even in a relatively limited radio range of a gateway or if the keys of the gateway are set individually All key settings of the participants (personal keys), including those who work at all other transfer points in the entire network, should be known and thus also have to be saved. Since many thousands of subscribers normally have to be switched in a network with several radio gateways that are distributed locally, knowing the key setting would not only allow eavesdropping, but also a call to the wrong number, which would result in fee miscalculation.

The invention has for its object to provide the problem presented as simple a solution as possible, which avoids the disadvantages of the type described above.

This task is performed in a radio telephony method for a large number of subscribers, in which the messages are transmitted through an encryption or concealment device with a specific subscriber-specific key.

According to the invention, this is achieved in that in addition to the specific individual key setting for each subscriber, the subscriber number itself or additionally a special code character is stored and that between the subscriber number or the code sign and the individual key setting there is a functional connection known only to the higher-level switching center that this individual key is also calculated in the exchange and the encryption or obfuscation council is programmed and then the encrypted transmission to the exchange and from there the transmission of the messages is carried out.

It is advantageous if the key setting in the exchange is determined separately by a computer before the start of each message transmission and is deleted after the end of the call.

To secure the switching data, it is also advantageous if the transmission of the subscriber number or the code sign is carried out redundantly before each start of the call.

The invention is explained in more detail below with reference to two figures, for example.

FIG. 1 shows a subscriber Tnl, whose NF is converted into a digital plain text KT (A / D) and then is subjected to encryption to the secret text GT in a mixer M with the key text ST - controlled by a key generator SG. This ciphertext is then transmitted by a transceiver SIE. The reverse process takes place on the reception side. To establish a connection, the encryption device SG + M should first be switched off. At some point, the subscriber Tnl will establish a connection with the radio gateway that is assigned to him locally, that is to say the radio switching center V. The radio gateway asks him for his subscriber number and, if necessary, for his connection request. At this point, the encryption device could now be activated when the callback was made to ensure that the subscriber had registered at his correct telephone number.

The encryption itself is based on the following basic idea. Normally, all keys of all participants should be known to the exchange. However, since all such keys would have to be stored at each switching station in a larger network with several switching stations and possibly a large number of subscribers, and this would involve a high level of technical and organizational complexity, the following procedure is followed in the invention. There is a functional relationship between the subscriber number or a code assigned to each subscriber according to some mathematical function, which is however only known in a key determiner SC at the switching station. The subscriber number is communicated to this key investigator and, on the basis of this, the key determiner can determine the individual subscriber key of the calling subscriber in a very short time by means of a computing device and store it in a device S-Sp / V for the duration of the connection. The switching station now calls back to the subscribers in encrypted form and if the subscriber Tnl has now correctly reported, then after switching on his key generator SG, which receives the key from his key store S-Sp / F, all further message transmissions between the Participants and the radio gateway V be secured. In the other case, the subscriber will not receive a callback because he does not understand the call of the switching station V because of another key, and this makes it impossible to transmit messages via an incorrect number, that is to say with incorrect billing. The participant can also do this

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is not by manipulation of his key generator or bar, and now begins to artificially cause on the side of the called memory, namely namely the functional participant the same game with the connection for his subscriber Tn3 between his subscriber number, his assigned key. In the key coding device SC, special dialing and call codes and the key for the switching center are known at the latest at the time of the encryption device. This assignment is known as 5 real message transmission between subscriber Tn 1 and only the radio transfer points V and there the transcoding of the keys is carried out in a special Tn3, that is to say stored computer. The received messages from the two subscribers are decrypted when the subscriber Tnl requests a connection and are connected through at this level (plain text). Example after subscriber Tn3, the switching center is now possible. In this way it is possible to find a secure message to subscriber Tn3 (see FIG. 2) if he is to guarantee 10 transmission, since the individual keys are in his local network at all or are only known to the associated subscriber.

1 sheet of drawings

Claims (3)

625650 1. Radio telephony method for a large number of subscribers, in which the messages are transmitted through an encryption or concealment device with a specific subscriber-specific key, characterized in that in addition to the specific individual key setting, the subscriber number itself or additionally a special code character is stored for each subscriber and that between the subscriber number or the code character and the individual key setting there is a functional connection that is only known to the higher-level switching center, that this individual key is also calculated in the switching center and the encryption or concealment device is programmed and then the encrypted transmission to the switching center and from there from which the transmission of the messages is carried out. 2. Radio telephony method according to claim 1, characterized in that the key setting in the exchange is determined separately by a computer before the start of each message transmission and is deleted again after the end of the call. 2nd PATENT CLAIMS 3. Radio telephony method according to one of the preceding claims, characterized in that the transmission of the subscriber number or the code character takes place redundantly before each start of the call.