Cryptography – Communication system using cryptography – Wireless communication
Patent
1998-03-17
2000-04-04
Swann, Tod R.
Cryptography
Communication system using cryptography
Wireless communication
380258, 380259, 380273, 380 43, 455410, 455411, 455435, 455 542, H04M 166
Patent
active
060470704
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for a reliable interface between a telephone having a card with subscriber identity and the network when dialing specific preprogrammed telephone numbers in a telephone system. In this way, the user of a telephone is to be allowed only to dial specific preprogrammed telephone numbers.
In the GSM (Group Special Mobile) mobile radio system, this feature is designated by FDN (Fixed Dialing Number). The permitted numbers and the fact of whether the restriction is switched on or off is stored on a smart card. If the feature "restriction" is switched on, the telephone carries out a check when a number is entered to see whether the latter is enabled, and carries out a call setup in the event of a positive result. However, there is the problem here that the interface between the card and the telephone is freely accessible, in other words the presence of any desired number in the list of permitted numbers can very easily be simulated by intercepting the relevant commands, for example.
SUMMARY OF THE INVENTION
The invention is based on the object of specifying a simple method for a reliable interface between a telephone having a card and the network for dialing only preprogrammed telephone numbers.
This object is achieved according to the invention in that when there is a desire for access or connection, the telephone number is transmitted from the telephone to the card, which checks a possible enabling of the number and, in the event of a positive result, uses a secret algorithm to produce a signature from this number and a varying code which is predetermined by the network, and in that the signature is transmitted together with the number to the network and the enabling of the dialed number by the card is determined by the network by checking the signature.
In general terms the present invention is a method for a reliable interface between a telephone having a card with subscriber identity and a network. Specific preprogrammed telephone numbers are stored on the card and, when there is a desire for access or connection, the dialed telephone number is transmitted from the telephone to the card, which checks a possible enabling of the telephone number.
In the event of a positive result of the check, a secret algorithm is used to produce a signature from this telephone number and a varying code which is predetermined by the network or by an authentication center. The signature is transmitted together with the telephone number to the network. The enabling of the dialed telephone number by the card is determined by the network by checking the signature.
Advantageous developments of the present invention are as follows.
When there is a desire for access or connection, a setup with the telephone number is performed by the subscriber equipment. A random number is drawn in the network and both are transmitted to the authentication center, in which a result is calculated. The random number drawn by the network is simultaneously transmitted to the subscriber equipment and is transmitted, together with the telephone number, to the card. A result is calculated if the telephone number is a specific preprogrammed telephone number. The result of the card is subsequently compared with the result of the authentication center in the network.
If a key from a preceding authentication is known to the card and to an authentication center, this key is used instead of a random number to calculate the result. The telephone number is contained in the fixed dialing number memory, and the telephone number is transmitted from the subscriber equipment to the network and, from the latter, is transmitted together with the key to the authentication center, in which a result of the center is calculated and is compared with the result of the card.
Together with the dialed telephone number, the location number of this telephone number is also transmitted to the card together with the random number or the previously exchanged key. The card calculates the result only when the transmitted
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Callahan Paul E.
Siemens Aktiengesellschaft
Swann Tod R.
LandOfFree
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