JP2012204919A - Backup communication circuit sharing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure that, when either side of two communication systems sharing one backup communication circuit is using the backup communication circuit, a communication system on the other side is disabled from knowing it.SOLUTION: On a transmitting side of a communication system 1 which has detected a communication circuit failure the data to be transferred is encrypted, while fixed value data is encrypted in a communication system 2 before being respectively output to a backup communication circuit. On a receiving side of the communication system 1, an encryption key of the communication system 2 is acquired, and the encrypted data received from the backup communication circuit is decoded using the encryption key of the local communication system and that acquired from the communication system 2, whereby the data to be transferred is obtained. Further, when acquiring the encryption key of the communication system 2, the communication system 1 uses a Secure Multiparty Computation protocol to ensure that the fact that it has used the backup communication circuit is not known to the communication system 2.

Description

  The present invention relates to a communication system that can share a line without knowing whether the other party is communicating.

  When a telecommunications carrier provides a communication service between two remote points, it is a common practice to prepare a backup communication line in advance and improve reliability in preparation for a communication line failure. However, for example, when a large-capacity communication service is provided by one line, it is necessary to prepare a communication line having the same capacity, and because of a line failure with a very low probability, a large cost is required for the backup communication line. There is a problem of having to pay (the problem of an increase in the number of lines).

  Therefore, a method in which a plurality of communication carriers share one backup communication line between two points can be considered. For example, when two carriers A and B provide services in the same region, carrier A prepares a backup communication line and when carrier B needs it (the line of carrier B is faulty) It is conceivable that the communication traffic is relayed to the backup communication line of carrier A. At this time, if each communication carrier shares and bears the cost of the backup communication line of the communication carrier A, the cost for the backup communication line can be reduced. In such a backup method, the main lines of the carriers A and B have a very low probability of causing a failure at the same time and can be ignored in practice, and the lines connecting the communication devices of the carriers A and B at each point are the main lines. It is effective when it is extremely short compared to the line and its cost is relatively negligible.

  However, the above prior art has a problem that the carrier A can obtain the channel quality information of the carrier B. Since the backup communication line is provided by carrier A, detailed line quality information indicating when and how long a failure occurred on carrier B's main line is provided by the operator. A knows (problem of disclosure of backup usage status). Since the frequency of communication facility failures is directly related to the quality of communication services, such information is useful information that affects competition among telecommunications carriers, and should be disclosed to other telecommunications carriers that are competitors. Is not desirable. For this reason, there is a need for a technique for using the backup communication line without sharing the presence / absence of communication with other communication carriers having the line while sharing the backup communication line.

  Conventionally, an encryption technique has been used as a technique for transmitting communication data to the other party without knowing the contents of communication or the presence or absence of communication by others. There is a symmetric encryption method as a basic encryption technique. In the symmetric encryption method, the sender and the receiver share a key (shared key) in advance, the sender encrypts the transmission data with the shared key, and the receiver decrypts with the same shared key, and communicates with a third party. This is a method of concealing the contents of. Representative examples include DES, RC4, AES, and the like.

  As a method of calculating an arbitrary function f while keeping the input given by each person and the output received by each person concealed by a plurality of persons communicating with each other, the Secure Multiparty Computation (SMC) protocol is known (for example, (See Non-Patent Document 1 and Non-Patent Document 2). For example, consider a problem in which two people A and B calculate a 2-input / 2-output function (Ya, Yb) = f (Xa, Xb). Assume that A gives an input Xa and receives an output Ya, and B gives an input Xb and receives an output Yb. Using the SMC protocol, this function f can be calculated without disclosing any other information to each person (ie, A does not know Xb and Yb, and B does not know Xa and Ya). it can.

Goldreich, O.M. Foundation of Cryptography, volume 2, Basic Applications, Cambridge University Press, 2004. Goldreich, O.M. Micali, S .; , And Wigderson, A .; How to play annual game. In Proceedings of the Nineteenth Annual ACM Symposium on Theory of Computing (1987), ACM, pp. 199 218-229. Tatsuaki Okamoto, Hiroshi Yamamoto, “Modern cryptography”, p. 227-236, Industrial Books (1997/07)

  According to the present invention, two different communication systems share one backup communication line to reduce the cost, and that the other communication system uses the backup communication line. To provide a backup communication line sharing system that cannot be known.

  In the present invention, when two different communication systems each having a communication line share one other communication line as a backup communication line, the fact that one communication system used the backup communication line In order to prevent the communication system from knowing, the transmission side of any one communication system that has detected that the communication line used during normal operation has failed encrypts the data to be transferred, and the other communication system transfers the data. Encrypt fixed value data as data to be encrypted, encrypt the two encrypted data with one as plain text and the other as the encryption key, and output to the backup communication line. On the receiving side of the communication system that detects this, the encryption key of the other communication system is obtained, and the encryption key obtained from the backup communication line is acquired. Decoded by to obtain data to be transferred by the encrypted data to the own communication system encryption key and the encryption key of the other communication system available.

Further, in the above configuration, when obtaining the encryption key of the other communication system on the receiving side of the communication system that detects the failure of the communication line, the encryption key of the other communication system is obtained by using the Secure Multiparty Computation (SMC) protocol. By obtaining, it is possible to ensure that the other communication system does not know that the encryption key has been obtained.

In addition, the random number generation unit that generates the encryption key includes a secret key generation unit that is a bit string smaller than the transmission information, and a random number generation unit that generates a random number having the same length as the transmission information using the generated secret key as a parameter. By doing so, the length of the encryption key passed between the communication systems can be shortened, and the delay due to the SMC protocol can be reduced.

According to the present invention, when two communication systems share a backup communication line, the signal flowing through the backup communication line is always encrypted with the encryption key of the own system. A communication system that is not used does not know whether transmission information of another communication system is included in a signal flowing through the backup communication line. Therefore, the problem of increase in the number of lines can be solved by sharing the backup communication line while solving the problem of disclosure of the backup usage status.

It is the 1st system configuration example explaining the present invention. It is an example of a structure of the encryption part of this invention. It is an example of a structure of the decoding part of this invention. This is an example in which an encryptor and a decryptor are exclusive ORed. It is explanatory drawing of the input / output signal of an encryption key exchange part. It is explanatory drawing of the logic operation | movement of an encryption key exchange part. It is an example of a structure of an encryption key exchange part. It is an example of the division | segmentation method of an input signal. It is a flow (procedure 1) figure of the division | segmentation method shown in FIG. It is a NOT calculation process flow (procedure 2). It is an AND operation processing flow (procedure 3). It is an output processing flow (procedure 4) figure. It is an example of a structure of the encryption key exchange part which implement | achieves a SMC protocol. 6 is a second system configuration example according to the present invention when a backup communication line is included in the communication system 1. It is a 3rd system configuration example by this invention at the time of comprising an encryption part with a random number generator and an encryption device. It is a 4th system configuration example by this invention in the case of initializing a random number generator with an encryption key. It is a figure which shows the structural example of LFSR which produces | generates a random number sequence by using an encryption key as an initial value. It is a figure which shows the structural example of the nonlinear feedback shift register which produces | generates a random number sequence by making an encryption key into an initial value. It is a figure explaining the operation | movement timing in the case of producing | generating a random number sequence by using an encryption key as an initial value.

Examples of the present invention will be described below.

FIG. 1 shows a configuration example of a backup communication line sharing system in which the communication system 1 and the communication system 2 share a backup communication line according to the present invention.

The communication system n (1, 2) (n = 1, 2) is composed of a transmission device n (11, 21), a reception device n (12, 22), and a communication line n (13, 23).

The transmission device n outputs the input signal Mn (14, 24) to the communication line n or the encryption unit n (113, 213) based on the signal from the line failure detection unit n (111, 212). n (111, 211), a line failure detection unit n that detects a failure in communication line n and outputs the result to communication path switching unit n, and an encryption unit that encrypts the output from communication path switching unit n n (113, 213).

The receiving apparatus n detects a line failure of the communication line n and outputs it to the communication path switching unit n-1 (121, 221) and the encryption key exchange unit n (125, 225). , 222) and the signal from the communication line n based on the signal from the line failure detection unit n-1, and the decoding unit n (123, 223) and the decoding unit n-1 (124, 224) The line path switching unit n-1 for selecting a signal from the backup communication line unit (3), and the decryption for decrypting the signal encrypted by the encryption unit n by inputting the signal from the backup communication line unit Unit n, a decryption unit n-1 that decrypts the output signal of decryption unit n with the encryption key obtained from encryption key exchange unit n, receives an encryption key from another communication system in the event of a line failure, It consists of an encryption key exchange unit n output to the decryption unit n-1. That.

The backup communication line unit receives an encrypted signal from the encryption unit 1 of the communication system 1 and the encryption unit 2 of the communication system 2, and encrypts one as plain text and the other as an encryption key. 3 (31), a common backup communication line (33), and a distribution unit (32) for distributing the backup communication line signals to the communication system 1 and the communication system 2.

As shown in FIG. 2, the encryption unit n (n = 1, 2) includes a random number generator n (1132) and an encryptor n (1131). Further, as shown in FIG. 3, the decryption unit n includes a random number generator n (1232) and a decryptor n (1231). The random number generator n of the encryption unit n and the random number generator n of the decryption unit n generate the same random number in synchronization. Various synchronization methods are known. For example, there are a method in which the transmission device and the reception device share and synchronize the absolute time with GPS, a method in which the absolute time and the system clock synchronize, a method in which each slot synchronizes, and the like. . The output random numbers of the random number generator 1 of the communication system 1 and the random number generator 2 of the communication system 2 are different because they are individually defined in each system. Also, the communication system 1 and the communication system 2 must protect each random number from being known to each other.

The encryptor n in FIG. 2 encrypts (scrambles) input data with a random number. The simplest calculation method of the scramble method is a method using exclusive OR (EXOR) (FIG. 4), but any calculation is possible as long as the decoder n of FIG. In general, if signals a and b are encoded on a set that forms an algebraic group, synthesis is performed with the operation a + b of the group, and separation is performed with a combination operation (a + b) with the inverse element -b of the signal b to be separated. ) + (− B) = a.

Encryption keys for decryption are input from the encryption key exchange unit 1 and the encryption key exchange unit 2 to the decryption unit 1-1 and the decryption unit 2-1, respectively. Since the decoding operation is the same as that of the decoding unit, description thereof is omitted.

The encryption key exchange unit 1 acquires the random number of the random number generator 2 (FIG. 3) of the decryption unit 2 through the encryption key exchange unit 2 of the communication system 2 when the communication line 1 of the communication system 1 fails. The data is delivered to the decryption unit 1-1. When the communication line 2 of the communication system 2 is out of order, the encryption key exchange unit 2 acquires the random number of the random number generator 1 (FIG. 3) of the decryption unit 1 through the encryption key exchange unit 1 of the communication system 1, The data is delivered to the decryption unit 2-1.

Ｆｎ（ｎ＝１，２）は、回線障害検出部ｎ−１の出力信号であり、通信システムｎの通信回線ｎが故障した場合、すなわち、通信システム１がバックアップ用通信回線を使用する場合は「１」、故障していない場合は「０」である。Ｒｎは通信システムｎの復号化部ｎの乱数生成器ｎ（図３）の出力信号、出力値Ｐｎは復号化器ｎ−１へ復号鍵として出力される信号である。 The operations of the encryption key exchange unit 1 and the encryption key exchange unit 2 are defined by the function f shown below.

Fn (n = 1, 2) is an output signal of the line failure detection unit n-1, and when the communication line n of the communication system n fails, that is, when the communication system 1 uses a backup communication line. “1”, “0” when there is no failure. Rn is an output signal of the random number generator n (FIG. 3) of the decryption unit n of the communication system n, and an output value Pn is a signal output as a decryption key to the decryptor n-1.

FIG. 5 shows input / output signals of the encryption key exchange unit 1 and the encryption key exchange unit 2, FIG. 6 shows a logical value table defining input / output operations, and FIG. 7 shows an example of a logic circuit configuration.

In FIG. 5, F1 and R1 are input to the encryption key exchange unit 1 (125), and P1 is output. F2 and R2 are input to the encryption key exchange unit 2 (225), and P2 is output.

In FIG. 6, when Fn = 1, the other party's encryption key (R1 or R2) is output to the output Pn. However, when both Fn are 0 or 1, the encryption key is not output. Here, the signal value in the case other than the case where the encryption keys R1 and R2 are output to Pn is “0” in FIG. 6, but may be “1”.

In FIG. 7, logic elements (1251, 251, 1252, and 2252) that output v1, v2, w1, and w2 represent AND gates, and logic elements (1253 and 2253) that output u1 and u2 represent NOT gates. Represents.

The operation of the backup communication line sharing system according to the present invention will be described with reference to FIGS. The failure probability of the communication line 1 of the communication system 1 and the communication line 2 of the communication system 2 is very small, and the probability of failure at the same time is negligibly small. In addition, each communication system uses a backup communication line in slot units in which time is discretely divided.

(1) When the communication line 1 and the communication system 2 of the communication system 1 are normal, respectively. In this case, the transmission device 1 of the communication system 1 and the transmission device 2 of the communication system 2 input to the backup communication line. The data M1 and M2 are not transmitted, and fixed value data is output from the communication path switching unit 1 to the encryption unit 1 and to the encryption unit 2 of the communication path switching unit 2, respectively. The communication system 1 and the communication system 2 know in advance what kind of fixed value data is output. The fixed value data may be changed according to the date and time. The fixed value data is, for example, 0 or 1 (here, the fixed value data “0” is output).

In FIG. 2, the encryption unit 1 (n = 1) outputs a random number R1 to the encryptor 1, and the encryption unit 2 (n = 2) outputs a random number R2 to the encryptor 2. Various schemes are known for the encryptor. Here, when exclusive OR (EXOR) is applied as shown in FIG. 4, the outputs of the encryption unit 1 and the encryption unit 2 are as follows. Since the random number R1 and the random number R2 are exclusive ORed with the fixed value data “0”, R1 and R2 are output as they are. The outputs of the encryption unit 1 and the encryption unit 2 are input to the encryption unit 3 of the backup communication line unit, and one is encrypted as a plaintext and the other as an encryption key (random number) (here, exclusive OR). . When the exclusive OR operation is represented by “+”, the output of the encryption unit 3 is represented by (R1 + R2). Hereinafter, “+” represents all exclusive OR operations.

The output of the encryption unit 3 is input to the communication system 1, the decryption unit 1 of the communication system 2, and the decryption unit 2 by the distribution unit through the common backup communication line. The random number output from the random number generator 1 (FIG. 3) of the decryption unit 1 and the random number output from the random number generator 2 (FIG. 3) of the decryption unit 2 are the encryption unit 1 and the encryption unit 2 on the transmission device side. The random numbers R1 and R2 (FIG. 2) are the same and synchronized. At this time, the output of the decoding unit 1 of the communication system 1 is an exclusive OR of the input signal and R1,
R2 = (R1 + R2) + R1
The output of the decoding unit 2 of the communication system 2 is an exclusive OR of the input signal and R2,
R1 = (R1 + R2) + R2
Are obtained respectively.

A random number R1 is input from the decryption unit 1 to the encryption key exchange unit 1 and a random number R2 is input from the decryption unit 2 to the encryption key exchange unit 2. As shown in FIG. 6, when the communication line 1 of the communication system 1 and the communication line 2 of the communication system 2 are not faulty, the encryption key exchange unit 1 and the encryption key exchange unit 2, as shown in FIG. Are “0”, fixed value data (fixed value data “0” in FIG. 6) is output to the decoding unit 1-1 and the decoding unit 2-1.

Since the decryption unit 1-1 performs an exclusive OR of the output value “0” from the encryption key exchange unit 1 and the output value R2 of the decryption unit 1, R2 is input to the communication path switching unit 1-1. Is done. Further, since the decryption unit 2-1 performs exclusive OR of the output value “0” from the encryption key exchange unit 2 and the output value R1 of the decryption unit 2, R1 is the communication path switching unit 2-1. Is input. In the line route switching unit 1-1 and the line route switching unit 2-1, since there is no failure in the communication line 1 and the communication line 2, the input signal from the backup communication line is discarded.

On the receiving side of the communication system 1 and the communication system 2, since the random numbers R1 and R2 on the other side are acquired through the backup communication line, information on whether the other party is using the backup communication line is used for backup. It cannot be obtained from information from the communication line.

(2) When the communication line 1 of the communication system 1 is faulty and the communication line 2 of the communication system 2 is normal In this case, the communication system 1 switches the input signal M1 in the slot at the time of the fault switching. The transmission device 2 of the communication system 2 does not transmit the input signal M2 from the communication path switching unit 2 to the backup communication line and outputs fixed value data. The communication system 1 knows in advance what fixed value data is output from the communication system 2. The fixed value data may be changed according to the date and time. The fixed value data is, for example, “0” or “1” (here, the fixed value data “0” is output).

The encryption unit 1 of the communication system 1 outputs an exclusive OR (R1 + M1) of the random number R1 and the input signal M1. On the other hand, the random number R2 is output as it is from the encryption unit 2 of the communication system 2. The outputs of the encryption unit 1 and the encryption unit 2 are input to the encryption unit 3 of the backup communication line unit, one of which is encrypted as plaintext and the other as an encryption key (random number) (here, exclusive OR). (R1 + R2 + M1).

The output of the encryption unit 3 is input from the distribution unit to the decryption unit 1 and the decryption unit 2 through the shared backup communication line. The decoding unit 1 and the decoding unit 2 decode the input signal (R1 + R2 + M1). Since the output of the decoding unit 1 is an exclusive OR of the input signal and R1,
R2 + M1 = (R1 + R2 + M1) + R1
And the output of the decoding unit 2 is
R1 + M1 = (R1 + R2 + M1) + R2
It becomes.

The encryption key exchange unit 1 receives the random number R1 from the decryption unit 1 and the encryption key exchange unit 2 receives the random number R2 from the decryption unit 2. As shown in FIG. 6, when the communication line 1 of the communication system 1 has a failure and the communication line 2 of the communication system 2 has no failure, the encryption key exchange unit 1 outputs “ 1 ”and the line failure detection unit 2 output F2 is“ 0 ”, so the output from the encryption key exchange unit 1 to the decryption unit 1-1 is“ R2 ”, and the encryption key exchange unit 2 to the decryption unit 2-1 The output to is fixed value data “0”.

Since the inputs of the decryption unit 1-1 are the random numbers R2 and (R2 + M1), M1 is obtained by taking the exclusive OR. Since the inputs of the decoding unit 2-1 are the fixed value data “0” and (R1 + M1), the output (R1 + M1) is obtained by taking the exclusive OR.

Since the communication path 1 is faulty in the line path switching unit 1-1 of the communication system 1, the output M1 of the decoding unit 1-1 is selected, and the line path switching unit 2-1 of the communication system 2 selects the backup communication line. The input signal (R1 + M1) from is discarded.

In the receiving device 2 of the communication system 2, since (R1 + M1) is a random number, information on whether or not the communication system 1 uses a backup communication line can be obtained from information from the backup communication line. Can not.

(3) When the communication line 2 of the communication system 2 is faulty and the communication line 1 of the communication system 1 is normal In this case, the communication system 1 and the communication system 2 are replaced by the operation (2). Therefore, although detailed explanation is omitted, the input data M2 of the transmission apparatus 2 of the communication system 2 is encrypted and becomes (R1 + R2 + M2) and is input to the backup communication line. The output of the decoding unit 1-1 of the receiving device 2 of the communication system 1 is (R1 + M2), and the output of the decoding unit 2-1 of the receiving device 2 of the communication system 2 is M2. The communication path switching unit 1-1 of the receiving device 1 of the communication system 1 outputs a signal from the communication line 1, and the signal (R1 + M2) from the backup communication line is discarded. The communication path switching unit 2-1 of the receiving device 2 of the communication system 2 outputs a signal M2 from the backup communication line. Also in this case, since the signal obtained from the backup communication line is a random number (R1 + M2) in the communication system 1, information on whether or not the communication system 2 uses the backup communication line is obtained from the backup communication line. It cannot be obtained from the information.

Next, the encryption key exchange unit illustrated in FIGS. As can be seen from the logic circuit shown in FIG. 7, the encryption key exchanging unit 1 of the communication system 1 receives the information of F2 and R2 from the encryption key exchanging unit 2 of the communication system 2, and the encryption key exchanging unit 2 of the communication system 2 Since F1 and R1 are received from the encryption key exchange unit 1 of the communication system 1, the communication system 1 can obtain failure information of the communication system 2 from F2 and random number information of the communication system 2 from R2. For this reason, it is possible for the administrator of the communication system 1 or the communication system 2 to acquire and use these pieces of information maliciously. Therefore, the Secure Multiparty Computation (SMC) protocol is applied to the encryption key exchange unit. As a result, it is possible to make it impossible to acquire information on the other system.

Details of the SMC protocol are described in Non-Patent Document 3. According to this, the functions (Y1, Y2) = f (X1, X2) while the communication system 1 and the communication system 2 conceal each other's input / output.
The procedure for calculating is as follows. First, the input signal is divided according to the procedure 1. Next, for each logic gate in the logic circuit representing the function f, the procedure 2 is performed for the NOT operation, the procedure 3 is performed for the AND operation, and the procedure is performed for all logic gates 2. After executing step 3, execute step 4 to obtain an output value. Since all the logic circuits can be converted into NOT gates and AND gates, any logic circuit can be calculated as long as NOT and AND can be calculated.

(Procedure 1) FIGS. 8 and 9 show an input signal division processing circuit and a processing flow.
The encryption key exchange unit of each communication system divides each bit x of the input Xn of each communication system into two bits satisfying x = x1 + x2 (+ is an exclusive OR of bits), and x1 is held by itself. , X2 are sent to the encryption key exchange unit of the other communication system. FIG. 8 shows an embodiment when x1 and x2 are obtained by the following calculation.
x1 = x + s01, x2 = s01
Here, s01 represents each bit of an arbitrary random number sequence S01.

FIG. 9 is a flowchart of the arithmetic processing in FIG.

(1) An arbitrary random number s01 is acquired from a random number generator (S601).

(2) Calculate x1 = x + s01 and hold it by itself (S602).

(3) Send x2 = s01 to another encryption key exchange unit (S603, S604).

(Procedure 2) FIG. 10 shows a processing flow of NOT calculation.
For a NOT gate with input bit p (= p1 + p2) and output bit r = ¬p (= r1 + r2), the encryption key exchange unit 1 sets r1 as p1 + p2 = ¬ (r1 + r2), The encryption key exchange unit 2 is obtained.

(1) Since the encryption key exchange unit 1 has p1 (S701), r1 = p1 is set (S702).

(2) Since the encryption key exchange unit 2 has p2 (S703), r2 = p2 is set (S704).

(Procedure 3) FIG. 11 shows a processing flow.
For an AND gate having input bits p (= p1 + p2), q (= q1 + q2) and output bits r = p∧q (= r1 + r2), r1 + r2 = (p1 + p2) ∧ (q1 + q2) is obtained by the following procedure. , R2 are obtained by the encryption key exchange unit 1 and the encryption key exchange unit 2.

(1) The encryption key exchange unit 1 has p1 and q1 (S801).

(2) A random bit s1 is generated (S802), and r1 = (p1∧q1) + s1 is set (S803).

(3) The encryption key exchange unit 1 generates four public key private key pairs, and sends four public keys kij (k00, k01, k10, k11) to the encryption key exchange unit 2 (S804).

(4) The encryption key exchange unit 2 has p2 and q2 (S807).

で暗号化した信号を、

と表記する。 (5) The encryption key exchange unit 2 generates one public key private key pair (S808), encrypts the public key k ′ with one of the public keys received from the encryption key exchange unit 1, and encrypts the encryption key. The data is sent to the exchange unit 1 (S810). k '

The signal encrypted with

Is written.

(6) The encryption key exchange unit 1 decrypts the received (Equation 3) with its four secret keys (S805), and each of the keys k′ij (k′00, k′01, k′10, k ′). 11) (one of which is correctly decrypted into the public key k ′ of the encryption key exchange unit 2 and the remaining three are decrypted into meaningless random numbers because the keys do not match, but the encryption key exchange Part 1 doesn't know which k '). The encryption key exchange unit 1 encrypts four u (i, j) = s1 + (p1∧i) + (q1∧j) (where i, j∈ {0,1}) with k′ij 4 Two ciphertexts are sent to the encryption key exchange unit 2 (S806).

(7) The encryption key exchange unit 2 decrypts u (i, j) with its own secret key (S811), and sets r2 = (p2∧q2) + u (p2, q2) (S812).

(Procedure 4) FIG. 12 shows a processing flow.
After performing steps 1 to 3 for all the logic gates, the encryption key exchange unit n (n = 1, 2) obtains an output Yn by the following procedure.

Ｙ２出力を

とし、通信システムｎの暗号鍵交換部ｎがＹ１出力、Ｙ２出力についてそれぞれ、

を保有しているものとすれば、

が成り立っている。 (1) The entire output of the logic circuit Y = (Y1, Y2), where k and l are the number of outputs,
Y1 output

Y2 output

And the encryption key exchange unit n of the communication system n has Y1 output and Y2 output respectively.

If you have

Is true.

について、自分の持つ

を他通信システムの暗号鍵交換部に送る（Ｓ９０１，Ｓ９０４）。 (2) The encryption key exchange unit n is each bit of the output Yn to be obtained by the encryption key exchange unit of another communication system

About my own

Is sent to the encryption key exchange unit of the other communication system (S901, S904).

について、自身が持っている

をロードし（Ｓ９０２）、暗号鍵交換部２から受け取った

により、

を復元する（Ｓ９０３）。暗号鍵交換部２は自身の得るべき出力Ｙ２の各ビット

について、自身が持っている

をロードし（Ｓ９０５）、暗号鍵交換部１から受け取った

により、

を復元する（Ｓ９０６）。 The encryption key exchange unit 1 receives each bit of the output Y1 to be obtained by itself.

About what I have

(S902) and received from the encryption key exchange unit 2

By

Is restored (S903). The encryption key exchange unit 2 receives each bit of the output Y2 to be obtained.

About what I have

(S905) and received from the encryption key exchange unit 1

By

Is restored (S906).

FIG. 13 shows an embodiment of an encryption key exchange unit that implements the SMC protocol. The encryption key exchange unit includes an input I / F unit (12500) that is an interface with input signals Fn and Rn (n = 1, 2), an output I / F unit (12501) that outputs a signal Pn to the outside, Encryption key exchange unit I / F unit (12502) for exchanging data between the communication system 1 and the encryption key exchange unit of the communication system 2, an encryption key (public key, secret key), and an encryption key for generating random numbers A random number generation unit (12503), an encryption / decryption unit (12504) that performs encryption / decryption with an encryption / decryption key acquired from the outside or acquired from the encryption key random number generation unit, and an SMC protocol program A memory (12505) that stores information temporarily or permanently, and a control unit (1255) that reads a program from the memory, controls each unit based on the input data, and performs a predetermined operation 6), and a bus line (12507) for the exchange of data between their respective sections.

A case where the operation of the encryption key exchange unit of FIG. 13 is applied to the logic circuit of FIG. 7 will be described.

(1) Input signal division processing (procedure 1)
A set of data obtained by dividing the bits f1, r1, f2, r2 of the input signals F1, R1, F2, R2 according to FIG.
F1: (f11, f12), f1 = f11 + f12
R1: (r11, r12), r1 = r11 + r12
F2: (f21, f22), f2 = f21 + f22
R2: (r21, r22), r2 = r21 + r22
Each element of is represented by the following equation.
f11 = f1 + s11, f12 = s11, r11 = r1 + s12, r12 = s12
f22 = f2 + s21, f21 = s21, r22 = r2 + s22, r21 = s22
Here, s11, s12, s21, and s22 are arbitrary random numbers.

The above calculation is performed as follows in the circuit shown in FIG. First, the control unit of the encryption key exchange unit 1 acquires the input data f1 and r1 from the input I / F unit, and acquires the random numbers s11 and s12 from the encryption key random number generation unit. Thereafter, the control unit calculates f11 and r11 by taking the exclusive OR operation of f1 and r1 and s11 and s12, respectively, and stores it in the memory. Also, s11 is set to f12 and s12 is set to r12, and sent to the encryption key exchange unit I / F. The encryption key exchange unit I / F of the encryption key exchange unit 2 notifies the control unit that the input signal has been received, and the control unit of the encryption key exchange unit 2 stores f12 and r12 in the memory.
Similarly, f21 and r21 are sent from the encryption key exchange unit 2 to the encryption key exchange unit 1, and the control unit of the encryption key exchange unit 1 stores f21 and r21 in the memory.

(2) Processing of NOT gate (1253, 2253 in FIG. 7) (Procedure 2)
Since the signal F1 is input to the NOT gate 1253 by f11 in the encryption key exchange unit 1 and f12 in the encryption key exchange unit 2, if the procedure 2 is applied,
Calculation result of NOT gate 1253: u11 = ¬f11 (encryption key exchange unit 1), u12 = f12 (encryption key exchange unit 2)
Is obtained. Similarly,
Calculation result of the NOT gate 2253: u21 = f21 (encryption key exchange unit 1), u22 = ¬f22 (encryption key exchange unit 2)
Is obtained. Here, u1 = u11 + u12 and u2 = u21 + u22.

The above calculation is performed in the circuit shown in FIG. 13 as follows.
Since the signal F1 is input to the NOT gate, the control unit of the encryption key exchange unit 1 executes the procedure 2 as the operation of the NOT gate 1253. In procedure 2, since the input data f11 is input to the encryption key exchange unit 1, the control unit reads from the memory and performs NOT processing.
u11 = ¬f11
Is stored in memory.

Further, since the signal F2 is input to the NOT gate 2253, the control unit of the encryption key exchange unit 1 executes the procedure 2 as the operation of the NOT gate 2253, and the input data f21 is transmitted from the encryption key exchange unit 2. Read from memory as input,
u21 = f21
Is stored in memory.

Similarly for the control unit of the encryption key exchange unit 2
u12 = f12
u22 = ¬f22
Is stored in memory.

(3) Processing of AND gate 1251 (procedure 3)
The control unit of the encryption key exchange unit 1 inputs f11 and u21 to the AND gate 1251, and the control unit of the encryption key exchange unit 2 inputs f12 and u22 to the AND gate 1251.

As a result, the output v11 on the encryption key exchange unit 1 side and the output v12 on the encryption key exchange unit 2 side of the AND gate 1251 are
v1 = v11 + v12
v11 = (f11∧u21) + s13
v12 = (f12∧u22) + ua (f12, u22)
here,
s13 is an arbitrary random number, and ua (f12, u22) = s13 + (f11ｆf12) + (u21∧u22) is a value delivered from the encryption key exchange unit 1 to the encryption key exchange unit 2 according to the procedure 3.

The above calculation is performed as follows in the circuit shown in FIG. Since the signal F1 and the NOT gate 2253 output are input to the AND gate 1251, the control unit of the encryption key exchange unit 1 executes the procedure 3 (FIG. 11) as an AND gate operation.

In procedure 3, the control unit of the encryption key exchange unit 1 reads f11 and u21 from the memory (S801). Next, the random number s13 is acquired from the encryption key random number generator (S802),
v11 = (f11∧u21) + s13
Is calculated and stored in the memory (S803).

Further, the control unit of the encryption key exchange unit 1 acquires four public key private key pairs from the encryption key random number generation unit, and uses the four public keys kij (k00, k01, k10, k11) as the encryption key exchange unit. The data is sent to the encryption key exchange unit I / F of the encryption key exchange unit 2 through the I / F (S804).

The control unit of the encryption key exchange unit 2 reads f12 and u22 from the memory (S807). Also, a pair of encryption key private key pair (public key k ′) is acquired from the encryption key random number generation unit (S808).

と、前記取得したｋ’を暗号化復号化部に引き渡し、ｋ’を上記（数式１８）で表された公開鍵で暗号化する。暗号化したｋ’を次のように表記する。

制御部は上記（数式１９）で表されたデータを暗号鍵交換部Ｉ／Ｆに送出する（Ｓ８１０）。 The control unit that has received notification from the encryption key exchange unit I / F of the encryption key exchange unit 2 that there is a signal input from the encryption key exchange unit 1 receives four public keys from the encryption key exchange unit I / F. get. From the acquired four public keys, it is one of them.

Then, the obtained k ′ is delivered to the encryption / decryption unit, and k ′ is encrypted with the public key expressed by the above (Equation 18). The encrypted k ′ is expressed as follows.

The control unit sends the data represented by (Equation 19) to the encryption key exchange unit I / F (S810).

The control unit that has received notification from the encryption key exchange unit I / F of the encryption key exchange unit 1 that there has been a signal input from the encryption key exchange unit 2 changes the above (Equation 19) to the encryption key exchange unit I / F. Obtained from, transferred to the encryption / decryption unit, decrypted with the secret keys corresponding to the four public keys kij, and k′ij (k′00, k′01, k′10, k ′) that are candidates for k ′. 11) is obtained (S805).

The control unit of the encryption key exchange unit 1 delivers the following four data encrypted by passing the following ua (i, j) and k′ij to the encryption / decryption unit to the encryption key exchange unit I / F. The data is sent to the exchange unit 2 (S806).
ua (i, j) = s13 + (f11∧i) + (u21∧j) (where i, jε {0,1})

The control unit of the encryption key exchange unit 2 obtains the encrypted ua (i, j) from the encryption key exchange unit I / F, and delivers the encrypted ua (f12, u22) to the encryption / decryption unit. By decrypting with the private key corresponding to the public key k ′, ua (f12, u22) is obtained (S811),
v12 = (f12∧u22) + ua (f12, u22)
Is calculated and stored in the memory (S812).

(4) Processing of AND gate 2251 (procedure 3)
Similarly, since f2 and u1 are calculated for the AND gate 2251, the following outputs v21 and v22 can be obtained by applying the procedure 3 (FIG. 11).
v2 = v21 + v22
v22 = (f22∧u12) + s24
v21 = (f21∧u11) + ub (f21, u11)
Here, ub (f21, u11) = s24 + (f22∧f21) + (u12∧u11)
The operation in FIG. 13 is the same as that in (3) above, and a description thereof will be omitted.

(5) Processing of AND gate 1252 (procedure 3)
Since the inputs v1: (v11, v12) and R2: (r21, r22) are obtained for the AND gate 1252, the following outputs can be obtained by applying the procedure 3.
w1 = w11 + w21
w11 = (v11∧r21) + s14
w21 = (v12∧r22) + uc (v12, r22)
here,
uc (v12, r22) = s14 + (v11∧v12) + (r21∧r22)

The operation when the above calculation is performed by the circuit shown in FIG. 13 is the same as (3) above, and thus the description thereof is omitted.

(6) Processing of AND gate 2252 (procedure 3)
With respect to the AND gate 2252, since inputs v2: (v21, v22) and R1: (r11, r12) are obtained, the following outputs can be obtained by applying the procedure 3.
w2 = w22 + w12
w22 = (v22∧r12) + s25
w12 = (v21∧r11) + ud (v21, r11)
here,
ud (v21, r11) = s25 + (v22∧v21) + (r12∧r11)

The operation when the above calculation is performed by the circuit shown in FIG. 13 is the same as (3) above, and thus the description thereof is omitted.

(7) Output process (Procedure 4)
In FIG. 7, an output signal P1 is a signal to be obtained by the encryption key exchange unit 1, and an output signal P2 is a signal to be obtained by the encryption key exchange unit 2. The encryption key exchange unit 1 has w11 and w12 for the output data w1 and w2 corresponding to the output signals P1 and P2, respectively. The encryption key exchange unit 2 has w21 and w22 for the output data w1 and w2, respectively. Thereby, each encryption key exchange part can calculate the next output.
P1 (encryption key exchange unit 1): w1 = w11 + w21
P2 (encryption key exchange unit 2): w2 = w12 + w22

The above calculation is performed as follows in the circuit shown in FIG.
The control unit of the encryption key exchange unit 1 takes out w12 from the memory, delivers it to the encryption key exchange unit I / F, and sends it to the encryption key exchange unit 2 (S901). Similarly, the control unit of the encryption key exchange unit 2 takes out w21 from the memory, delivers it to the encryption key exchange unit I / F, and sends it to the encryption key exchange unit 1 (S904).

The control unit of the encryption key exchange unit 1 receives w11 from the memory (S902) and w21 from the encryption key I / F, and obtains w1 = w11 + w21 (S903).

Similarly, the control unit of the encryption key exchange unit 2 receives w22 from the memory (S905) and w12 from the encryption key I / F, and obtains w2 = w12 + w22 (S906).

FIG. 14 shows an embodiment of the invention according to claim 2 in which a common backup communication line is included in the communication system 1, and FIG. 15 shows an embodiment of the invention according to claim 4. Since the operation of the system is the same as that of the embodiment of FIG.

FIG. 16 shows an embodiment of the fifth aspect of the present invention. The only difference from the embodiment of FIG. 1 is the configuration of the random number generator and the encryption key delivered between the encryption key exchange unit 1 and the encryption key exchange unit 2. Since the random number generator described in the embodiment of FIG. 1 generates the same random number sequence by synchronizing the random number generators of the transmitting device and the receiving device with absolute time, and each of them generates free-running random numbers, When it occurs, the encryption key exchange unit must obtain an encryption key of a random number sequence having the same length as the transmission information from the other party. On the other hand, the random number generator shown in FIG. 16 generates a random number by setting the key information from the key generator as an initial value for each slot while the line failure continues. With this configuration, the data length of the encryption key exchanged by the encryption key exchange unit can be shortened, and the processing time of the encryption key exchange unit can be shortened.

As a method for generating random numbers using key information as an initial parameter, a linear feedback shift register (LFSR), a nonlinear feedback shift register, and the like are known. A specific configuration example of the random number generator is shown in FIG. In the figure, the key generator (700) is composed of an n-bit register, and the random number generator (701) is composed of an n-bit shift register (702) and an exclusive OR (EXOR) calculator (703 to 705). The key generator (700) generates an encryption key for each slot and may itself be a random number generator. The random number generator 701 is an LFSR, and the n-bit shift register (702) moves data to the right every clock. Further, taps are extracted from some registers, and exclusive OR is performed with tap outputs, shift registers (rn), or EXOR outputs of the previous stage. The tap position at which the random number period is determined by the tap position and the random number having the longest period is obtained when n = 16 is, for example, the 11th, 13th, and 14th registers.

FIG. 18 shows a configuration example of the nonlinear feedback shift register. The nonlinear function calculation unit feeds back y calculated by the nonlinear function y = f (r1,..., Rn) to the first bit (r1) of the shift register. Since these techniques are well-known techniques, detailed description thereof is omitted.

FIG. 19 shows the operation timing of the key generator and the random number generator when a line failure occurs. When a failure occurs in the communication line, the key generator generates an encryption key K1 and sets K1 to the initial value of the random number generator immediately before the start timing of slot 1. The random number generator starts generation of random numbers at the start timing of the next slot (start timing of slot 1). In the next slot, the key generator generates the encryption key K2, sets K2 as an initial value in the register of the random number generator immediately before the start timing of slot 2, and starts generating random numbers at the start time of slot 2, Takes the same action.

In FIG. 16, a case where a failure occurs in the communication line 1 (55) of the communication system 1 (5) will be described.

The key generator 11 (516) and the key generator 12 (527) generate the same key K11. The random number generator 11 (514) and the random number generator 12 (525) use the same key K11 as an initial value for each slot. Generate the same random number sequence. The key generator 21 (615) and the key generator 22 (627) generate the same key K21, and the random number generator 21 (614) and the random number generator 22 (626) use the same key K21 as an initial value for each slot. Generate the same random number sequence.

The encryption operation by the encryptor 11 (513) and the encryptor 21 (613) and the decryption operation by the decryptor 12 (525) and the decryptor 22 (625) are the same as the operations in FIG. Therefore, explanation is omitted.

1 and 3, when there is a failure in the communication line 1 (13) of the communication system 1 (1), since the communication system 1 uses the backup communication line, the encryption key exchange unit 1 (125) To the decryption unit 1-1 (124) is a random number sequence R2 (FIG. 3) from the random number generator 2 of the decryption unit 2 of the communication system 2 (2). On the other hand, in FIG. 16, the output key K22 of the key generator 22 (627) of the communication system 2 (6) is output from the encryption key exchange unit 1 to the random number generator 13 and set to the initial value immediately before the start of the slot. The random number is generated and output to the decoder 13 (524). The random number sequence R2 is a random number having the same length as the data to be transmitted, but the key K22 is an initial parameter for generating a random number and is much shorter than the data to be transmitted. For this reason, the processing time of the encryption key exchange part 1 and the encryption key exchange part 2 can be shortened.

1, 5 Communication system 1
2, 6 Communication system 2
3 Backup communication line unit 11, 21, 51, 61 Transmitting device 12, 22, 52, 62 Receiving device 13, 23, 55, 57, 58, 65, 66 Communication line 33, 56 Backup communication line 14, 24, 53, 63 Transmission user data 15, 25, 54, 64 Reception user data 111, 211, 121, 221, 511, 521, 611, 621 Communication path switching unit 112, 212, 122, 222, 512, 522, 612, 622 Line failure detection unit 31, 113, 213, 311 Encryption unit 123, 124, 223, 224 Decryption unit 125, 225, 523, 623 Encryption key exchange unit 32, 312, 527 Distribution unit 513, 515, 613, 1131 Encryption 524, 525, 624, 625, 1231 Decoders 516, 615, 527, 62 7,700 Key generators 514, 614, 526, 626, 628, 701, 1132, 1232, 10032, 12511 Random number generators 703, 704, 705, 10031, 12510 Exclusive OR (EXOR)
702 Shift register 706 Non-linear function calculation unit 1253, 2253 NOT element 1251, 1252, 2251, 2252 AND element 12500 Input interface 12501 Output interface 12502 Encryption key exchange unit interface 12503 Encryption key / random number generation unit 12504 Encryption / decryption unit 12505 Memory 12506 Control unit 12507 Common signal transmission path (bus)

Claims (7)

When two communication systems each having a communication line share a backup communication line,
On the sending side,
Any one communication system that detects that the communication line used during normal operation has failed encrypts the data to be transferred with its own encryption key,
The other communication system encrypts fixed value data with its own encryption key,
The encrypted two data are encrypted using one as plain text and the other as an encryption key and output to the backup communication line,
On the receiving side,
The communication system that has detected that the communication line has failed acquires the encryption key of the other communication system, and obtains the encrypted data obtained from the backup communication line and the encryption key of the own communication system and the other A backup communication line sharing system, wherein decryption is performed using an encryption key of a communication system.   2. The backup communication line sharing system according to claim 1, wherein the encryption and decryption are exclusive OR operations. 3. The backup communication line sharing system according to claim 1, wherein the backup communication line is incorporated in any one of the communication systems. A failure occurs in the first transmission means and the first reception means for transmitting and receiving data, and the first communication line and the first communication line that transmit data from the first transmission means to the first reception means. A first communication system comprising a backup communication line for transmitting data in place of the first communication line,
A second communication system comprising second transmission means and second reception means for transmitting and receiving data, and a second communication line for transmitting data from the second transmission means to the second reception means When,
A third communication line for transmitting data from the second transmission means to the first transmission means;
A fourth communication line for transmitting data from the first receiving means to the second receiving means;
A fifth communication line for transmitting encryption key data and line failure information between the first receiving means and the second receiving means;
In a communication system composed of:
The first transmission means is
First communication that outputs input data to the first communication line when the first communication line functions normally and outputs to the following first encryption means when a failure occurs in the first communication line Route switching means;
First random number generating means for generating a first random number;
A first encryption means for encrypting an output signal of the first communication path switching means by the first random number;
The first encryption means output is encrypted by the following third encryption means output, or the following third encryption means output is encrypted by the first encryption means output and output to the backup communication line. Two encryption means;
Consisting of
The first receiving means is
When the first communication line functions normally, it takes in the signal from the first communication line and outputs it to the outside of the first communication system. If a failure occurs in the first communication line, the second decoding below Second communication path switching means for capturing a signal from the means and outputting the signal to the outside of the first communication system;
First line failure detection means for detecting a line failure in the first communication line;
Second random number generation means for generating a second random number that is identical and synchronized with the first random number;
First decryption means for decrypting data obtained from the backup communication line with the second random number;
Second decryption means for decrypting the following first decryption means output with the output signal of the following first encryption key exchange means;
Input the second random number, the output of the first line failure detection means, and the information obtained through the fifth communication line from the second encryption key exchange means described below, and the first communication line functions normally. In the case, the fixed value data is output to the second decryption means, and when the first communication line fails, the following fifth random number is output to the second decryption means. A first encryption key exchange means for outputting a random number and the first line failure detection means output to a second encryption key exchange means through a fifth communication line;
Consisting of
The second transmission means is
Third communication that outputs input data to the second communication line when the second communication line functions normally and outputs to the third encryption means below when a failure occurs in the second communication line Route switching means;
A fourth random number generating means for generating a fourth random number;
Third encryption means for encrypting the third communication path switching means output by the fourth random number;
Consisting of
The second receiving means is
When the second communication line functions normally, a signal is fetched from the second communication line and output to the outside of the second communication system. If a failure occurs in the second communication line, the fourth decoding means is used. A fourth communication path switching means for capturing a signal from the second communication system and outputting the signal to the outside of the second communication system;
Second line failure detection means for detecting a line failure in the second communication line;
Fifth random number generating means for generating a fifth random number that is the same and synchronized with the fourth random number;
Third decryption means for decrypting data from the backup communication line obtained through the fourth communication line with the fifth random number;
A fourth decryption means for decrypting the third decryption means output with the following second encryption key exchange means output signal and outputting to the fourth communication path switching means;
Input the fifth random number, the second line failure detection means output, the information obtained from the first encryption key exchange means through the fifth communication line, and
When the second communication line functions normally, the fixed value data is output to the fourth decryption unit, and when the second communication line fails, the second random number is output to the fourth decryption unit, A second encryption key exchange means for outputting the fifth random number and the second line failure detection means output to the first encryption key exchange means through the fifth communication line;
A communication line sharing system for backup consisting of A failure occurs in the first transmission means and the first reception means for transmitting and receiving data, and the first communication line and the first communication line that transmit data from the first transmission means to the first reception means. A first communication system comprising a backup communication line for transmitting data in place of the first communication line,
A second communication system comprising second transmission means and second reception means for transmitting and receiving data, and a second communication line for transmitting data from the second transmission means to the second reception means When,
A third communication line for transmitting data from the second transmission means to the first transmission means;
A fourth communication line for transmitting data from the first receiving means to the second receiving means;
A fifth communication line for transmitting encryption key data and line failure information between the first receiving means and the second receiving means;
In a communication system composed of:
The first transmission means is
First communication that outputs input data to the first communication line when the first communication line functions normally and outputs to the following first encryption means when a failure occurs in the first communication line Route switching means;
First random number generating means for generating a first random number;
First key generation means for generating a first encryption key that is a parameter when the first random number generation means generates a random number;
First encryption means for encrypting the first communication path switching means output with the first random number;
The second encryption means output is encrypted by the following third encryption means output, or the following third encryption means output is encrypted by the first encryption means output, and is output to the backup communication line. Encryption means,
Consisting of
The first receiving means is
When the first communication line functions normally, it takes in the signal from the first communication line and outputs it to the outside of the first communication system. If a failure occurs in the first communication line, the second decoding below Second communication path switching means for capturing a signal from the means and outputting the signal to the outside of the first communication system;
First line failure detection means for detecting a line failure in the first communication line;
A second random number generating means for generating a second random number that is the same as and synchronized with the first random number generated by the first random number generating means;
A key generator for generating a second encryption key that is a parameter when the second random number generation means generates a random number, wherein the second random number generation means generates an encryption key that is identical and synchronized with the first key generation means. A second key generation means;
A third random number generating means for generating a third random number that is the same as and synchronized with the fourth random number when the parameter for generating the random number is the following fourth encryption key;
First decryption means for decrypting data obtained from the backup communication line with the second random number;
A second decryption means for decrypting the first decryption means output with the third random number and outputting to the second communication path switching means;
Input the second encryption key, the first line failure detection means output, the information obtained through the fifth communication line from the following second encryption key exchange means, and
Fixed value data is output when the first communication line functions normally, and the following fourth encryption key is used as a third random number as a parameter when generating a random number when a failure occurs in the first communication line. First encryption key exchange means for outputting to the generation means, and further outputting the second encryption key and the first line failure detection means output to the second encryption key exchange means through the fifth communication line;
Consisting of
The second transmission means is
When the second communication line functions normally, the input data is output to the second communication line. When a failure occurs in the second communication line, the input data is output to the third encryption means described below. Communication path switching means;
Third encryption key generation means for generating a third encryption key;
Fourth random number generation means for generating a fourth random number using the third encryption key as a parameter;
A third encryption means for encrypting a third communication path switching means output by the fourth random number and outputting it to a third communication line;
Consisting of
The second receiving means is
When the second communication line functions normally, it takes in the signal from the second communication line and outputs it to the outside of the second communication system. If a failure occurs in the second communication line, the fourth decoding below Fourth communication path switching means for capturing a signal from the means and outputting the signal to the outside of the second communication system;
Second line failure detection means for detecting a line failure in the second communication line;
Fifth random number generating means for generating a fifth random number that is the same and synchronized with the fourth random number;
A key generator for generating a fourth encryption key, which is a parameter when the fifth random number generation means generates a random number, and generates a same encryption key in synchronization with the third key generation means. Key generation means,
A sixth random number generating means for generating a sixth random number that is identical to and synchronized with the first random number when the parameter for generating the random number is the second encryption key;
Third decryption means for decrypting data from the backup communication line obtained through the fourth communication line with the fifth random number;
A fourth decryption means for decrypting the third decryption means output by the sixth random number and outputting to the fourth communication path switching means;
Input the fourth encryption key, the second line failure detection means output, the information obtained through the fifth communication line from the first encryption key exchange means, and
Outputs fixed value data when the second communication line is normal, and outputs the second encryption key to the sixth random number generation means as a parameter for generating a random number when a failure occurs in the second communication line And a second encryption key exchange means for outputting the fourth encryption key and the second line failure detection means output to the first encryption key exchange means through the fifth communication line,
A communication line sharing system for backup consisting of 6. The backup communication line sharing system according to claim 4, wherein the encryption means and the decryption means are exclusive OR operations. The backup according to claim 1, 2, 3, 4, 5, or 6, wherein the secure multi-computation (SMC) protocol is used for exchanging encryption key and line failure information. Communication line sharing system.

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