RU2367099C1 - Method of controlling access to cdma network - Google Patents

Abstract

FIELD: physics; communication.

SUBSTANCE: invention relates to mobile radio systems. For a CDMA network, which comprises not less than one base station, a control device and i mobile stations, where i=1, 2, …, N, binary identifier sequences I_i are generated for i mobile stations, which are stored in the control device of the CDMA network and in the i-th mobile station. A binary call sequence is generated in the i-th mobile station from the binary identifier sequence I_i of the i-th mobile station and the number of the called subscriber. The binary call sequence of the i-th mobile station is sent to the base station. The received binary identifier sequence is separated in the base station from the received binary call sequence and the i-th mobile station is granted access to the CDMA network. Binary secret key sequences K_i , where i=1, 2, …, N, for mobile stations are generated for the sender and the recipient, and stored in the control device of the CDMA network and in the i-th mobile station. A function F₁ is generated for generation of a code sequence and a function F₂ for generation of a call key for the mobile station.

EFFECT: increased security from attack through access denial to a CDMA network by intruders - non-serviced mobile station.

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Description

The invention relates to a mobile radio communication system, and more specifically to a cellular communication network technology CDMA (multiple access code-division multiplexing) with protection against unauthorized actions unattended mobile stations. Unattended mobile stations are understood to mean such mobile stations that do not legally have access rights to network resources. Accordingly, the served mobile stations are understood to mean such mobile stations that legally have access rights to network resources.

The claimed method can be used to protect against attacks blocking access to the CDMA network implemented by unattended mobile stations. The attack of blocking access to the network consists in the deliberate actions of intruders who form false call sequences at one or more unattended mobile stations, which are perceived by the base station of the network as call sequences of registered mobile stations. Unattended mobile stations transmit to the attacked base station a significant number of false calling sequences, the reception of which causes the base station to overload and the inability to provide access to the CDMA network of the served mobile stations.

Known methods for controlling access to a cellular and trunking network based on checking binary sequences of identifiers of mobile stations. These methods are described, for example, in the book: Trunking radio communication systems. / Ed. V.M. Tamarkin. - M.: Russian NTOERES them. A.S. Popova, 1997, p. 5-11. In these methods, binary sequences of identifiers I _{i of} mobile stations, where i = 1, 2, ..., N, are preformed for a network including at least one base station and N served mobile stations, where the served mobile stations are registered for their service at the base station, why binary sequences of identifiers of the served mobile stations are stored in the memory device of the base station in the service area of which the calling mobile station is located. A binary calling sequence is formed at the i-th mobile station from the binary sequence of the identifier I _{i of} this mobile station and the number of the called subscriber and transmit it to the base station. Having received the binary calling sequence, the base station extracts from it the received binary identifier sequence and sequentially compares it with the binary identifier sequences of the served mobile stations recorded in the memory device of the base station. When a match is found, the received binary call sequence is considered the binary call sequence of the served mobile station and gives it access to the network; otherwise, the received binary call sequence is considered the binary call sequence of the served mobile station and does not provide access to it.

The disadvantages of these analogues are the relatively low protection against attempts to obtain illegal access to a network of unattended mobile stations, as well as from an attack blocking access to a network implemented by violators - unattended mobile stations.

Also known are methods for controlling access to a cellular network of the GSM standard based on checking binary sequences of identifiers and binary sequences of authentication keys of mobile stations. These methods are described, for example, in the book: Chekalin A.A., Zaryaev A.V., Skryl S.V., Vokhmintsev V.A. Information Security in Mobile Communication Systems: Textbook for High Schools. - M.: Hot line - Telecom, 2005, pp. 104-111. In these methods, binary sequences of identifiers I _i and binary sequences of authentication keys of mobile stations, where i = 1, 2, ..., N, are preformed for a network including at least one base station, network control device and N served mobile stations stations are registered for their service at the base station, for which binary sequences of identifiers of the served mobile stations are stored in the memory device of the base station, in the service area The second is the calling mobile station. A binary calling sequence is formed at the i-th mobile station from the binary sequence of the identifier I _{i of} this mobile station and the number of the called subscriber and transmit it to the base station. Having received the binary calling sequence, the base station extracts from it the received binary identifier sequence and compares it with the binary identifier sequence of the i-th mobile station recorded in the memory device of the base station. When a match is made, a request is sent from the base station to the network control device to generate a random binary sequence and a binary response sequence of the i-th mobile station. Upon receipt of the request, a random binary sequence is generated on the network manager and the network station is generated by the response function of the mobile station, the binary sequence of the authentication key of the i-th mobile station and the random binary sequence, the binary response sequence of the i-th mobile station. The generated binary response sequence of the i-th mobile station and a random binary sequence are transmitted from the network control device to the base station. Then, a random binary sequence is transmitted from the base station to the i-th mobile station.

The i-th mobile station is formed by the function of generating a response of the mobile station, the binary sequence of the authentication key of the i-th mobile station and a random binary sequence, the binary sequence of the response of the i-th mobile station. Then, a binary response sequence of the i-th mobile station is transmitted from the i-th mobile station to the base station. The base station compares the received binary response sequence of the i-th mobile station with the network received from the control device and, if they coincide, consider the received binary calling sequence as the binary calling sequence of the served mobile station and provide it with access to the network, otherwise the received binary calling sequence is considered the binary calling sequence of unattended mobile station and do not provide her access.

A disadvantage of the known methods of access control to a cellular communication network of the GSM standard based on checking binary sequences of identifiers and binary sequences of authentication keys of mobile stations is also the relatively low protection against an attack of blocking access to the network realized by intruders - unattended mobile stations.

The closest in technical essence to the claimed method of access control to a CDMA network is a method of access control to a CDMA network

by international application (PCT) WO 2003/049476 dated 06/12/2003 (IPC Н04Q 7/38). The prototype method for controlling access to a CDMA network consists in preliminarily generating for a CDMA network including at least one base station, a CDMA network control device and N served mobile stations binary sequences of identifiers I _{i of} mobile stations, where i = 1, 2, ..., N, which are stored in the control device of the CDMA network and in the i-th mobile station, form a binary calling sequence in the i-th mobile station, for which they form a binary sequence identifier I _{i of the} i-th mobile station, number The called subscriber and the service parameters have a binary calling sequence, the binary calling sequence of the i-th mobile station is transmitted to the base station, the received binary identifier sequence and the service parameters of the i-th mobile station are extracted from the received binary calling sequence in the base station. If the received binary identifier sequence coincides with one of the binary sequences of identifiers I _{i of the} mobile stations and it is possible for the base station to provide access in accordance with the service parameters of the i-th mobile station, they provide access to the CDMA network of the i-th mobile station, otherwise they do not provide her access.

The disadvantage of the prototype of the claimed method of access control to the CDMA network is the relatively low security against attacks blocking access to the CDMA network, implemented by intruders - unattended mobile stations.

The specified disadvantage of the prototype is due to the fact that the base station cannot immediately determine whether it is a binary calling sequence of the i-th mobile station or whether it is formed by one of the unattended mobile station using the received binary calling sequence. Mobile stations that are not serviced by the network are capable of generating false binary calling sequences indistinguishable from binary calling sequences of i-th mobile stations from the binary sequences of identifiers I _i i of the mobile stations known to them. The reason is the absence of the dependence of the binary calling sequence of the i-th mobile station on the call time and the changing call parameters, unknown to violators.

The aim of the invention of the claimed technical solution is to develop a method for controlling access to the CDMA network, which provides increased protection against attacks blocking access to the CDMA network, implemented by intruders - unattended mobile stations, by performing a set of actions to verify the authenticity of the received binary call sequence.

This goal is achieved by the fact that in the known method of access control to a CDMA network, which consists in the fact that for a CDMA network including at least one base station, a CDMA network control device and i-th mobile stations, where i = 1, 2, ... , N, pre-generate binary sequences of identifiers I _{i of the} i-th mobile stations, which are stored in the control device of the CDMA network and in the i-th mobile station, form in the i-th mobile station a binary calling sequence from the binary sequence of the identifier I _i i-th my the mobile station and the called party numbers, transmit the binary calling sequence of the i-th mobile station to the base station, extract the received binary identifier sequence from the received binary calling sequence in the base station and provide access to the CDMA network of the i-th mobile station, additionally preliminarily for the sender and the receiver generates for the CDMA network binary sequences of secret keys K _{i of the} mobile stations, where i = 1, 2, ..., N, which are stored in the control device of the CDMA network and in i- of the mobile station, and form the function F ₁ generating the code sequence and the function F _{2 the} formation of the call key of the mobile station.

,The minimum allowable number M of matching bits of the received binary identifier sequence with the binary identifier sequence I _{i of the} i-th mobile station is pre-set. The minimum allowable number M of matching bits of the received binary identifier sequence with the binary identifier sequence I _{i of the} i-th mobile station is determined from the condition

,

- число сочетаний из

по µ,where P _add - predefined acceptable probability of erroneous recognition of the binary calling sequence of the unattended mobile station as a binary calling sequence of the i-th mobile station,

- the number of combinations of

by µ,

and M _o > M is the length in bits of the binary call sequence of the i-th mobile station.

A registration request is transmitted from the i-th mobile station to the base station, including the binary sequence of the identifier I _{i of the} i-th mobile station. After receiving a request from the base station, a request is transmitted to the control device of the CDMA network to generate a random binary sequence R and a binary sequence of the call key K _{Bi of the} i-th mobile station,

Formed in the CDMA network control device R. random binary sequence is then formed in the control device of the CDMA network function F ₂ generating a key of the mobile station call binary sequence a private key K _{i i-th} mobile station and a random binary sequence of R binary sequence call key K _Bi i-th mobile station. The generated binary sequence of the call key K _{Bi of the} i-th mobile station and the random binary sequence R are transmitted from the control unit of the CDMA network to the base station.

A random binary sequence R and a binary sequence of the current time value T are transmitted from the base station to the i-th mobile station.

Formed in the i-th mobile station by the function F ₂ generating a key of the mobile station call binary sequence a private key K _{i i-th} mobile station and a random binary sequence of R binary sequence call key K _Bi i-th mobile station. Then, the i-th mobile station is formed according to the code sequence generating function F ₁ , the binary key sequence of the call key K _{Bi of the} i-th mobile station, the random binary sequence R and the binary sequence of the current time value T is the binary code sequence of the call.

A binary calling sequence is generated in the i-th mobile station, for which a binary sequence is formed from the binary sequence of the identifier I _{i of the} i-th mobile station and the binary sequence of the called number, the binary sequence is expanded by repeating each of its bits n times, summing bitwise modulo 2 extended binary sequence with binary call code sequence. Then transmit the binary calling sequence of the i-th mobile station to the base station.

The authenticity of the received binary calling sequence is checked at the base station, for which purpose the code sequence generation function F ₁ , the binary key sequence of the call key K _{Bi of the} i-th mobile station, the random binary sequence R and the binary sequence of the current time value T are generated in the base station T binary code sequence call verification. Then, the received binary calling sequence with the binary call verification code sequence is bitwise modulo 2 summarized and each successive n bits of the summed binary sequence are decoded according to the majority decoding rule into successive bits of the decoded binary sequence. The received binary identifier sequence is extracted from the decoded binary sequence, the bitwise received binary identifier sequence is compared with the binary identifier sequence I _{i of the} i-th mobile station, and the number K _{from the} matched bits is calculated. The received binary calling sequence is considered the binary calling sequence of the i-th mobile station when K _c ≥M is executed and access is provided to the CDMA network of the i-th mobile station, otherwise the received binary calling sequence is considered the binary calling sequence of the unattended mobile station and does not provide access .

The specified new set of actions due to unpredictable for violators - unattended mobile stations, the dependence of the binary calling sequence formed in the i-th mobile station on the binary sequence of the secret key K _{i of the} i-th mobile station, the binary sequence of the current time value T and the random binary sequence R provides Increased security against an attack blocking access to the network, implemented by intruders. The repeated use by intruders of binary calling sequences of the i-th mobile stations as false binary calling sequences accepted by the base station as genuine is excluded. In the base station, in the process of receiving and verifying the authenticity of the received binary calling sequence at the base station without further checks, it is immediately established whether it is the binary calling sequence of the i-th mobile station or the binary calling sequence of the unattended mobile station. Therefore, the specified new set of actions allows to increase security against an attack blocking access to the CDMA network, implemented by intruders - unattended mobile stations.

The claimed method is illustrated by drawings, which show:

- figure 1 is an example of a structure of a CDMA network;

- figure 2 is a registration algorithm in the base station of the i-th mobile station;

- figure 3 - call algorithm of the i-th mobile station of the base station;

- figure 4 is a timing diagram of the formation of a binary call sequence;

- figure 5 is an algorithm for verifying the authenticity of a received binary calling sequence by a base station;

- figure 6 is a timing diagram of the verification by the base station of the authenticity of the received binary call sequence;

- Fig.7 is a graph showing the effect of the proposed method.

Consider the implementation of the method on the example of a CDMA network including at least one base station 1, as well as a control device of the CDMA network 2 and N≥1 of the mobile stations 3 ₁ , ..., 3 _N (Fig. 1). The control device of the CDMA 2 network includes a shaper of binary sequences of secret keys K _i and binary sequences of identifiers I _{i of the} i-th mobile stations 2.1, where i = 1, 2, ..., N. Using this shaper in the control device of the CDMA 2 network form for each i-th mobile station a binary sequence of the secret key K _i and a binary sequence of identifier I _{i of the} i-th mobile station, which are stored in the control device of the CDMA 2 network and in the memory card 3.1 of the i-th mobile station Nation 3 _i . Then, the i-th mobile station 3 _i , using the registration unit 3.2, transmits to the base station 1 a registration request including a binary sequence of the identifier I _{i of the} i-th mobile station. After receiving a registration request, the base station 1 transmits to the CDMA 2 network controller a request for generating a random binary sequence R and a binary sequence of the call key K _{Bi of the} i-th mobile station. In the control device of the CDMA 2 network, a random binary sequence R is generated using a random binary sequence generator R 2.2 and a binary sequence of a call key K _{Bi of the} i-th mobile station is generated using the call key generator of the mobile station 2.3. The generated sequences are transmitted from the control unit of the CDMA 2 network to the base station 1. After that, a random binary sequence R and a binary sequence of the current time value T. generated by the timing device of the base station 1.1 are transmitted from the base station to the i-th mobile station. Then, in i- of the mobile station using the call key generator of the mobile station 3.4, a binary sequence of the call key K _{Bi of the} i-th mobile station is generated. Next, in the i-th mobile station using a code sequence generator 3.5 form a binary call code sequence.

In the i-th mobile station, from the binary sequence of the identifier I _{i of the} i-th mobile station and the binary sequence of the called subscriber’s number, a binary calling sequence is formed using the address binary sequence generator 3.3, which is expanded in the repeater 3.6 into an extended address binary sequence. Then, using the adder 3.7, the extended binary sequence is added modulo 2 bitwise with the binary call code sequence and the binary call sequence of the ith mobile station is transmitted to the base station.

Having received the binary call sequence, in the base station 1 check its authenticity. To do this, using the call verification binary code sequence generator 1.2, the call verification binary code sequence is generated and, in adder 1.3, it is summed bitwise modulo 2 with the received binary calling sequence. Then, every next n bits of the summed binary sequence in the majority decoder 1.4 are decoded according to the majority decoding rule into the next bits of the decoded binary sequence, and the received binary identifier sequence is extracted from it in the extractor of the received binary sequence of identifier 1.5. In comparator 1.6, the received binary identifier sequence is compared with the binary sequence of the identifier I _{i of the} i-th mobile station and, with a sufficient degree of coincidence, the received binary call sequence is considered the binary call sequence of the i-th mobile station, the communication signal is transmitted to the communication unit 3.8 i- mobile station 3 and provide it access to the CDMA network; otherwise, the received binary calling sequence is considered a binary calling sequence Stu mobile station unattended and do not give her access. Unattended mobile stations 4 form false calling sequences and transmit them to the input of adder 1.3 of base station 1.

The implementation of the claimed method is as follows.

The binary sequence of the secret key K _i and the binary sequence of the identifier I _{i of the} i-th mobile station are shown in FIGS. 4 (a) and 4 (b), respectively. Single bit values in the figures are shown in the form of shaded pulses, zero bit values in the form of unshaded pulses. The binary sequence of the secret key K _{i of the} i-th mobile station is presented with the requirement of impossibility of its calculation by intruders who can be aware of a significant number of binary calling sequences of the i-th mobile station generated using it. The binary sequences of the secret key K _{i of the} i-th mobile stations are generated using a random pulse generator that generates random equally probable pulses that are independent of each other, as described, for example, in the book: D. Knut, "The Art of Computer Programming." - M .: Mir, 1977, v. 2, p. 22. The length of the binary sequence of the secret key K _i must be at least 64 bits, which is described, for example, in the book by M. D. Smid, D. K. Bransted, “Data Encryption Standard: Past and Future”. TIIER, 1988, v. 76, No. 5, p. 45.

The binary sequences of identifiers of I _i i-th mobile stations are formed using a random pulse generator that generates random equally probable pulses independent of each other, which is described, for example, in the book: D. Knut, "The Art of Computer Programming." - M .: Mir, 1977, v. 2, p. 22. The length of the binary sequence of the identifier I _{i of the} i-th mobile station should be at least 30-40 bits so that the identifiers of different mobile stations of the same network are not repeated when the number N of mobile stations of the CDMA network is of the order of N = 10 ⁶ ... 10 ⁸ .

Known methods for storing the binary sequence of the secret key K _i and the binary sequence of the identifier I _{i of the} i-th mobile station in the CDMA network control device and in the i-th mobile station are described, for example, in the book: B. A. Kalabekov "Microprocessors and their use in signal transmission and processing systems. " - M .: Radio and communications, 1988, p. 71.

The code sequence generation function F ₁ and the mobile station call key generation function F ₂ are preliminarily formed.

Preliminary formation of the function F _{1 the} formation of the code sequence is as follows. Known methods for generating a code sequence generating function F _{1 are} described, for example, in the book by M. D. Smid, D. K. Bransted, “Data Encryption Standard: Past and Future”. TIIER, 1988, v. 76, No. 5, p. 49. They consist in the formation _of a code sequence generating function F ₁ in the form of a DES data encryption algorithm in ciphertext feedback mode or in output feedback mode. In this case, the binary key sequence of the call key K _{Bi of the} i-th mobile station is used as the encryption key of the DES data encryption algorithm, and random binary sequences R and the binary sequences of the current time value T are repeated as required encrypted data. The total length of the repeated random binary sequences R and binary sequences of the current time value T must be at least the length of the binary calling sequence of the i-th mobile station. The output value of the function F ₁ is the binary call code sequence generated at the i-th mobile station and the binary call verification code sequence generated at the base station.

The following requirements are imposed _{on the} function F _{1 of} forming a code sequence:

1) the computational impossibility of violators to determine the binary code sequence of a call or, respectively, the binary code sequence of a call test with a known random binary sequence R and a binary sequence of the current time value T;

2) the dependence of each bit of the binary call code sequence (call verification) on each bit of the binary sequence of the call key K _{Bi of the} i-th mobile station, on each bit of the random binary sequence R and on each bit of the binary sequence of the current time value T.

These requirements are met when using as a function F _{1 the} formation of a code sequence of known data encryption algorithms, which is described, for example, in the book: GOST RF 28147-89. Information processing systems. Cryptographic protection. Cryptographic conversion algorithm. - M.: Gosstandart of the USSR, 1989.

Known methods for generating the mobile station call key function F ₂ are described, for example, in the book: Asoskov A.V., Ivanov M.A., Mirsky A.A., Ruzin A.V., Slanin A.V., Tyutvin A .AND. Stream ciphers. - M.: KUDITS-IMAGE, 2003, p. 169. They consist in generating the function _of generating the call key of the mobile station in the form of a hash function, to the input of which the combined binary sequence of the secret key K _{i of the} i-th mobile station and the random binary sequence R are received. The hash of these sequences is the binary sequence of the call key K _Bi i-th mobile station. For example, the function F _{2 of} generating a call key of a mobile station in a GSM cellular communication system is constructed as a hash function COMR128, which is described, for example, in the book: Asoskov A.V., Ivanov M.A., Mirsky A.A., Ruzin A.V., Slanin A.V., Tyutvin A.N. Stream ciphers. - M.: KUDITS-IMAGE, 2003.p.169.

The function F _{2 of} generating a call key of a mobile station has the following requirements:

1) the computational impossibility of violators identifying the binary sequence of the secret key K _{Bi of the} i-th mobile station with known random binary sequence R and the binary sequence of the call key K _{Bi of the} i-th mobile station;

2) the dependence of each bit of the binary sequence of the call key K _{Bi of the} i-th mobile station on each bit of the binary sequence of the secret key K _{i of the} i-th mobile station and on each bit of the random binary sequence R;

3) the non-repeatability of the generated binary sequences of the call key K _{Bi of the} i-th mobile station with non-repeating random binary sequences R.

These requirements are met when using the known cryptographic hashing functions as a call key of the mobile station as a function of F ₂ , which is described, for example, in the book: GOST R 34.11-94. Information technology. Cryptographic information security. Hash function. - M.: Gosstandart of the Russian Federation, 1994.

,The preliminary establishment of the minimum allowable number M of matching bits of the received binary identifier sequence with the binary identifier sequence I _{i of the} i-th mobile station is as follows. The minimum allowable number M of matching bits of the received binary sequence of the identifier of the mobile station with the binary sequence of the identifier I _{i of the} i-th mobile station is determined from the condition

,

- число сочетаний из M_o по µ, а M_o>М - длина в битах двоичной вызывной последовательности i-ой мобильной станции.where P _add - predefined acceptable probability of erroneous recognition of the binary calling sequence of the unattended mobile station as a binary calling sequence of the i-th mobile station,

is the number of combinations of M _o in μ, and M _o > M is the length in bits of the binary calling sequence of the i-th mobile station.

For example, the value of the admissible probability of erroneous recognition of a binary call sequence of an unattended mobile station as a binary call sequence of the i-th mobile station is set to

P _add = 10 ^-9 , which is recommended, for example, in state standard 28147-89. Information processing systems. Cryptographic protection. Cryptographic conversion algorithm. - M.: Gosstandart of the USSR. 1989. Accordingly, by setting, for example, the magnitude M _o = 100, which is recommended in the book Shackle IN Authentication of voice messages and images in communication channels. / Ed. prof. V.F.Komarovich. - Publishing house of the St. Petersburg Polytechnic University, 2006, p.198, it is advisable to establish the value of M not less than 82.

Known methods for transmitting a registration request from the i-th mobile station to the base station, including the binary sequence of the identifier I _{i of the} i-th mobile station, are described, for example, in the book: Sklyar B. Digital communication. Theoretical foundations and practical application. - M.: Williams Publishing House, 2003, p. 803. Known methods for transmitting a registration request from the i-th mobile station to the base station, for example, use the code extension methods of the registration request. Figure 2 presents the actions of the registration algorithm in the base station of the i-th mobile station.

Known methods for transmitting, after receiving a request from a base station to a CDMA network controller, a request for generating a random binary sequence R and a binary sequence of a call key K _{Bi of the} i-th mobile station, are known and described, for example, in the book: A.G. Zyuko, D .D. Klovsky, M.V. Nazarov, L.M. Fink "Theory of signal transmission." - M .: Radio and communications, 1986, p. 11.

The formation of a random binary sequence R in the control device of the CDMA network is as follows. A random binary sequence R is formed using a random pulse generator that generates random equally probable pulses that are independent of each other, as described, for example, in the book: D. Knut, "The Art of Computer Programming." - M .: Mir, 1977, v. 2, p. 22. To ensure the practical exclusion of cases of repetition of random binary sequences, the length of a random binary sequence R must be at least 30-40 bits, which is described, for example, in the book “The Art of Computer Programming” by D. Knut. - M .: Mir, 1977, v. 2, p. 22. A random binary sequence R is shown in FIG. 4 (c).

The formation in the control device of the CDMA network according to the function F _{2 the} generation of the call key of the mobile station, the binary sequence of the secret key K _{i of the} i-th mobile station and the random binary sequence R of the binary sequence of the call key K _{Bi of the} i-th mobile station is as follows. An input binary sequence is formed, consisting of the combined binary sequence of the secret key K _{i of the} i-th mobile station and a random binary sequence R. The input binary sequence is converted by hashing into the output binary sequence, which is further used as the binary sequence of the call key K _{Bi of the} i-th mobile station . For example, the formation on the control device of the CDMA network according to the F ₂ function _of generating the call key of the mobile station, the binary sequence of the secret key K _{i of the} i-th mobile station and the random binary sequence R of the binary sequence of the call key K _{Bi of the} i-th mobile station can be performed by the function СОМР128 hashing, as described, for example, in the book: Asoskov A.V., Ivanov M.A., Mirsky A.A., Ruzin A.V., Slanin A.V., Tyutvin A.N. Stream ciphers. - M.: KUDITS-IMAGE, 2003, p. 169.

A view of the binary sequence of the call key K _{Bi of the} i-th mobile station generated in the control device of the CDMA network is shown in Fig. 4 (d).

Known methods for transmitting the generated binary sequence of the call key K _{Bi of the} i-th mobile station and the random binary sequence R from the control device of the CDMA network to the base station are known and described, for example, in the book: A.G. Zyuko, D.D. Klovsky, M .V. Nazarov, L. M. Fink "Theory of signal transmission." - M .: Radio and communications, 1986, p. 11.

Known methods for transmitting from the base station to the i-th mobile station a random binary sequence R and a binary sequence of the current time value T are described, for example, in the book: Sklyar B. Digital communication. Theoretical foundations and practical application. - M.: Williams Publishing House, 2003, p. 798. Known methods for transmitting from the base station to the ith mobile station a random binary sequence R and a binary sequence of the current time value T use, for example, code extension methods of the transmitted sequences.

A binary sequence view of the current time value T is shown in FIG. 4 (e). The binary sequence of the current value of time T is formed by the timing device of the base station. In the base stations of the CDMA network, the next binary sequence of the current time value T is formed every 3 microseconds, which is described, for example, in the book: Sklyar B. Digital communication. Theoretical foundations and practical application. - M.: Williams Publishing House, 2003, p. 810.

Figure 3 presents the actions of the call algorithm of the i-th mobile station of the base station.

Known methods for the formation of a i-th mobile station by the function F ₂ generating a key of the mobile station call binary sequence a private key K _{i i-th} mobile station and a random binary sequence of R binary sequence key call K _Bi mobile station i-th described e.g. in the book: Asoskov A.V., Ivanov M.A., Mirsky A.A., Ruzin A.V., Slanin A.V., Tyutvin A.N. Stream ciphers. - M.: KUDITS-IMAGE, 2003, p. 169. They consist in hashing the combined binary sequence of the secret key K _{i of the} i-th mobile station and the random binary sequence R. The hash result is the binary sequence of the call key K _{Bi of the} i-th mobile station.

A view of the binary sequence of the call key K _{Bi of the} i-th mobile station generated in the i-th mobile station is shown in Fig. 4 (d). Formed in the i-th mobile station binary sequence call key K _Bi i-th mobile station, and formed in the control unit binary sequence CDMA network call key K _Bi i-th mobile station are identical.

The formation in the i-th mobile station by the function F _{1 of the} formation of the code sequence, the binary sequence of the call key K _{Bi of the} i-th mobile station, the random binary sequence R and the binary sequence of the current time value T of the binary code sequence of the call is as follows. The random binary sequence R and the binary sequence of the current time value T are repeated as many times as necessary so that the total length of the repeating binary sequences of the current time value T and random binary sequences R should be at least the length of the binary calling sequence of the i-th mobile station. Repeating binary sequences of the current time value T and random binary sequences R are encrypted, for example, using the DES data encryption algorithm in ciphertext feedback mode or in output feedback mode. Moreover, the binary sequence of the call key K _{Bi of the} i-th mobile station is used as the encryption key of the DES data encryption algorithm. A view of the binary call code sequence is shown in FIG. 4 (e).

The formation in the i-th mobile station of a binary calling sequence is as follows. First, an address binary sequence is formed from the binary sequence of the identifier I _{i of the} i-th mobile station and the binary sequence of the called party number. The address binary sequence is formed by reading into it the binary sequence of the identifier I _{i of the} i-th mobile station and the binary sequence of the called number. Known methods for reading the binary sequence of the binary sequence identifier I _{i of the} i-th mobile station and the binary sequence of the called number are described, for example, in the book: Sikarev A.A., Lebedev O.N. Microelectronic devices for the formation and processing of complex signals. - M.: Radio and Communications, 1983, p. 121.

The address binary sequence is shown in FIG. 4 (g).

The extension of the address binary sequence by repeating each of its bits n times is as follows. Each bit of the address binary sequence is written n times, forming an extended n times extended binary sequence. The extended binary sequence for n = 3 is shown in FIG. 4 (h).

Next, an extended binary sequence with a binary call code sequence is summed modulo 2 bitwise, forming a binary calling sequence of the i-th mobile station. The length of the extended binary sequence and the length of the binary call code sequence are the same. Known methods of summing modulo 2 bitwise extended binary sequences with a binary call code sequence are described, for example, in the book of B. A. Kalabekov "Microprocessors and their use in signal transmission and processing systems." - M.: Radio and Communications, 1988, p. 10. The binary call sequence of the i-th mobile station is shown in FIG. 4 (s).

Known methods for transmitting to the base station a binary calling sequence of the i-th mobile station are described, for example, in the book: Sklyar B. Digital communication. Theoretical foundations and practical application. - M.: Williams Publishing House, 2003, p. 803. Known methods for transmitting to the base station a binary calling sequence of the i-th mobile station use, for example, code extension methods of the transmitted sequence.

Figure 5 presents the actions of the algorithm for checking the authenticity of the received binary call sequence by the base station.

The verification at the base station of the authenticity of the received binary call sequence is as follows. First, a code sequence generation function, a binary sequence of a call key K _{Bi of the} i-th mobile station, a random binary sequence R and a binary sequence of the current time value T are formed in the base station according to a function F _{1 of} generating a code sequence. This action is identical to generating in the i-th mobile station according to the code sequence generating function F ₁ , the binary key sequence of the call key K _{Bi of the} i-th mobile station, the random binary sequence R and the binary sequence of the current time value T of the binary code sequence of the base station call. Accordingly, the type of the call verification binary code sequence shown in FIG. 6 (a) is the same as the base station call code binary sequence shown in FIG. 4 (e).

The binary calling sequence received by the base station may be different from the transmitted binary calling sequence of the ith mobile station due to transmission errors. An exemplary view of the received binary calling sequence is shown in FIG. 6 (b), which binary elements of the transmitted binary calling sequence of the i-th mobile station turned out to be distorted by transmission errors. For example, the second binary element of the first bit of the transmitted binary calling sequence of the i-th mobile station is inverted by an error, the second and third binary elements of the second bit (the fifth and sixth binary elements, counting from the beginning of the sequence) are inverted by errors, etc.

Known methods for summing modulo 2 bitwise received binary calling sequence with a binary code sequence of call verification are described, for example, in the book of B. A. Kalabekov "Microprocessors and their use in signal transmission and processing systems". - M.: Radio and Communications, 1988, p. 10. The summed binary sequence is shown in FIG. 6 (c).

Decoding according to the rule of majority decoding every next n bits of the summed binary sequence into the next bits of the decoded binary sequence is as follows. The number of unit values and the number of zero values among the next n bits of the summed binary sequence are calculated. If the number of zero values turned out to be more than the number of unit values, then the next bit of the decoded binary sequence has a value of zero, and accordingly, if the number of unit values turned out to be more than the number of zero values, the next bit of the decoded binary sequence has a unit value.

For example, when decoding the first bit of a summed binary sequence, two unit values and one zero value are accepted, which, according to the majority decoding rule, gives a unit value of the first bit of the decoded binary sequence (Fig. 6 (d)). Note that by using the expansion of the binary sequence in transmission by n times and decoding according to the rule of majority decoding in reception, one transmission error in each bit of the decoded binary sequence is corrected for n = 3. When transmitting in the second group of the next n = 3 bits of the summed binary sequence, two errors occurred, so the second bit of the decoded binary sequence was decoded at the reception with an error. A view of the decoded binary sequence is shown in FIG. 6 (g).

Known methods for extracting from the decoded binary sequence of the received binary sequence of the identifier are as follows. From the decoded binary sequence, starting with its first bit, a predetermined number of bits is read as the received binary identifier sequence. Known methods of reading from a decoded binary sequence, starting with its first bit, as a received binary sequence identifier of a given number of bits are described, for example, in the book: Sikarev A.A., Lebedev O.N. Microelectronic devices for the formation and processing of complex signals. - M.: Radio and Communications, 1983, p. 121. A view of the received binary identifier sequence is shown in FIG. B (e).

Known methods for comparing the bitwise received binary sequence of the identifier with the binary sequence of the identifier I _{i of the} i-th mobile station are described, for example, in the book: Sikarev A.A., Lebedev O.I. Microelectronic devices for the formation and processing of complex signals. - M.: Radio and Communications, 1983, p. 108. Bit-by-bit comparisons may result in coincidence or mismatch. For example, in the received binary identifier sequence shown in FIG. 6 (e) and in the binary identifier sequence I _{i of the} i-th mobile station shown in FIG. 4 (b), the first, penultimate and last bits match, and the second bit - did not match.

Known methods for calculating the number K _from matched bits consist in summing the number of matches, which is described, for example, in the book: Sikarev A.A., Lebedev O.I. Microelectronic devices for the formation and processing of complex signals. - M.: Radio and Communications, 1983, p. 125.

The received binary calling sequence is considered the binary calling sequence of the i-th mobile station when performing K _with ≥M and providing access to the CDMA network of the i-th mobile station, otherwise the received binary calling sequence is considered the binary calling sequence of the unattended mobile station and does not provide access . Known methods for establishing the fulfillment of condition K _with ≥M are described, for example, in the book: Sikarev A.A., Lebedev O.I. Microelectronic devices for the formation and processing of complex signals. - M.: Radio and Communications, 1983, p. 108.

Known methods for providing access to the CDMA network of the i-th mobile station are described, for example, in the book: Chekalin A.A., Zaryaev A.V., Skryl S.V., Vokhmintsev V.A. Information Security in Mobile Communication Systems: Textbook for High Schools. - M .: Hot line - Telecom, 2005, p. 121.

Verification of the theoretical background of the claimed method of access control to the CDMA network was verified by its analytical studies.

целесообразно установить минимально допустимое число М совпавших битов принятой двоичной последовательности идентификатора с двоичной последовательностью идентификатора I_i i-ой мобильной станции не менее 82. Для данных значений на фиг.7 представлена зависимость Р_пд от интенсивности передачи двоичных вызывных последовательностей необслуживаемых мобильных станций α, определяемой в числе передаваемых двоичных вызывных последовательностей необслуживаемых мобильных станций в час. Ожидаемое число i-ых мобильных станций, зарегистрированных на базовой станции, составляет N=100, что определено, например, в книге: Чекалин А.А., Заряев А.В., Скрыль С.В., Вохминцев В.А. Защита информации в системах мобильной связи: Учебное пособие для вузов. - М.: Горячая линия - Телеком, 2005, стр.120. При данных условиях в сети CDMA стандарта IS-95 при интенсивности передачи двоичных вызывных последовательностей необслуживаемых мобильных станций λ=3600 вызовов в час вероятность предоставления доступа к сети CDMA i-ой мобильной станции при атаке блокирования доступа к сети CDMA нарушителями - необслуживаемыми мобильными станциями составляет Р_пд=0,26, что является недопустимо низкой для известных сетей CDMA. Данная защищенность каналов доступа к сети CDMA стандарта IS-95 характерна для использованного прототипа заявленного способа управления доступом к сети CDMA.The probability of providing access to the CDMA network of the i-th mobile station in an attack of blocking access to the CDMA network by violators - unattended mobile stations is denoted by R _PD . The predefined acceptable probability of erroneous recognition of the received binary calling sequence as the binary calling sequence of the i-th mobile station is set to P = 10 ^-9 , which is recommended, for example, in state standard 28147-89. Information processing systems. Cryptographic protection. Cryptographic conversion algorithm. - M.: Gosstandart of the USSR. 1989. By setting, for example, the bit length of the binary calling sequence of the i-th mobile station M _o = 100, which is recommended in the book by I. Okov. Authentication of voice messages and images in communication channels. / Ed. prof. V.F.Komarovich. - Publishing house of the St. Petersburg Polytechnic University, 2006, p.198, from the condition

it is advisable to set the minimum permissible number M of matching bits of the received binary identifier sequence with the binary sequence of the identifier I _{i of the} i-th mobile station of at least 82. For these values, Fig. 7 shows the dependence of P _PD on the transmission intensity of binary calling sequences of unattended mobile stations α, determined among the transmitted binary calling sequences of unattended mobile stations per hour. The expected number of i-th mobile stations registered at the base station is N = 100, which is determined, for example, in the book: Chekalin A.A., Zaryaev A.V., Skryl S.V., Vokhmintsev V.A. Information Security in Mobile Communication Systems: Textbook for High Schools. - M .: Hot line - Telecom, 2005, p. 120. Under these conditions, the IS-95 standard CDMA network with the transmission intensity of binary calling sequences of unattended mobile stations λ = 3600 calls per hour, the probability of granting access to the CDMA network of the ith mobile station in an attack of blocking access to the CDMA network by intruders - unattended mobile stations is P _PD = 0.26, which is unacceptably low for known CDMA networks. This security of access channels to the CDMA network of the IS-95 standard is typical for the used prototype of the claimed method of access control to the CDMA network.

When using the claimed method for controlling access to the CDMA network under the same conditions, the probability of providing access to the CDMA network of the i-th mobile station in an attack of blocking access to the CDMA network by intruders — unattended mobile stations remains at least P _PD = 0.95, as shown in FIG. .7.

The studies confirm that when using the claimed method of controlling access to the CDMA network, it provides increased security against an attack blocking access to the CDMA network, implemented by intruders - unattended mobile stations.

Claims (2)

1. The method of access control to a CDMA network, which consists in the fact that for a CDMA network including at least one base station, the control device of the CDMA network and i-mobile stations, where i = 1, 2, ..., N, is pre-formed binary sequences of identifiers I _{i of the} i-th mobile stations, which are stored in the control device of the CDMA network and in the i-th mobile station, form a binary calling sequence in the i-th mobile station from the binary sequence of the identifier I _{i of the} i-th mobile station and the number of the called subscriber per the binary calling sequence of the ith mobile station is delivered to the base station, the received binary identifier sequence is extracted from the received binary calling sequence in the base station and the CDMA network of the ith mobile station is provided, characterized in that they additionally form binary sequences for the CDMA network private keys K _{i of} mobile stations, where i = 1, 2, ..., N, which are stored in the control device of the CDMA network and in the i-th mobile station, the code sequence generation function F ₁ and the function F _{2 of} generating the call key of the mobile station and, in addition, the minimum acceptable number M of matching bits of the received binary identifier sequence with the binary identifier sequence I _i of the 1st mobile station is pre-set, a request is transmitted from the i-th mobile station to the base station registration comprising binary sequence identifier i _{i i-th} mobile station is transmitted after receiving the request from the base station to the CDMA network control device a request to form tion random binary sequence R and the binary sequence call key K _Bi i-th mobile station, is formed in the control CDMA network device random binary sequence R is formed in the control CDMA network device from the function F ₂ generating a key of the mobile station call, the binary sequence of the secret key K _{i i-th} mobile station and a random binary sequence of R binary sequence call key K _Bi i-th mobile station, transmitting the generated binary sequence key Call K _Bi i-th mobile station and a random binary sequence R by controlling CDMA network device to the base station transmitted from the base station to the i-th mobile station random binary sequence R and the binary sequence current value of time T, is formed in the i-th mobile station functions F ₂ generating a key calling mobile station binary sequence a private key K _i of the mobile station and a random binary sequence of R binary sequence call key K _Bi i-th mobile with Antium is formed in i-th mobile station by the function F ₁ forming the code sequence, the binary sequence key call K _Bi i-th mobile station, a random binary sequence R and the binary sequence current time value T binary code calling sequence is formed in the i-th takeout mobile station binary sequence, which is formed from a binary sequence identifier i-th mobile station, and the binary sequence identifier i _{i i-th} mobile station and FEB call sequence of the called subscriber’s number, the address binary sequence is expanded, the address binary sequence is expanded by repeating each of its bits n times, the extended binary sequence with the binary code sequence of the call is added, modulo 2 bitwise, the binary calling sequence of the ith mobile station is transmitted to the base station, checked in the base station authenticity of the received binary calling sequence, for which form in the base station according to the function F ₁ formation of each sequence, the binary sequence of the call key K _{Bi of the} i-th mobile station, the random binary sequence R and the binary sequence of the current time value T is the binary code sequence of the call test, the received binary call sequence with the binary code sequence of the call test is added modulo 2, decoded by to the majority decoding rule, each successive n bits of a summed binary sequence into successive bits of a decoded binary -th sequence, extract the received binary identifier sequence from the decoded binary sequence, compare the bitwise received binary identifier sequence with the binary identifier sequence I _{i of the} i-th mobile station and calculate the number K _{from the} matched bits, consider the received binary calling sequence as the binary calling sequence of the i-th mobile stations when performing K _c ≥M and provide access to the CDMA network of the i-th mobile station, otherwise the received binary The calling sequence is considered the binary calling sequence of the unattended mobile station and does not provide access to it. 2. The method according to claim 1, characterized in that the minimum allowable number M of matching bits of the received binary identifier sequence with the binary identifier sequence I _{i of the} i-th mobile station is determined from the condition

where P _add - predefined acceptable probability of erroneous recognition of the binary calling sequence of the unattended mobile station as a binary calling sequence of the i-th mobile station,

- the number of combinations of M in µ,
and M _o <M is the bit length of the binary calling sequence of the i-th mobile station.

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