JP2005045699A - Digital information transmission system and digital information transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that a common key should be sufficiently taken into account to be hardly analyzed in a conventional system wherein entities own the same key, and that data can not be exchanged without notice on the assumption that the key is shared in a conventional system dependent upon a key exchange scheme like Diffie-Hellman key sharing. <P>SOLUTION: An encryption means 15 encrypts digital data 16 to be transmitted repeatedly (n) times with (m) common keys 14 selected at random out of a common key bundle 11 by a key selection means 13 on the basis of key selection information B from a random number generator 12 and transmits encrypted data A. A key selection means 22 selects the same (n) common keys 23 as a transmission side out of the same key bundle 21 as the common key bundle 11 on the basis of the received key selection information B. A decryption means 24 decrypts the received encrypted data A (n) times using the common key 23 and decrypts original digital data 25. Thus, digital information can be delivered without requiring a negotiation beforehand. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital information transmission system and a digital information transmission method, and more particularly to a digital information transmission system and a digital information transmission method for exchanging digital information between computer networks and apparatuses that use and process digital data.

  In a digital information transmission system in which digital information is transmitted from a transmission device to a desired reception device via a transmission line such as a computer network, the digital information being transmitted is intercepted by an unspecified number of third parties, or the contents of the information are Since there is a risk of falsification, digital information is conventionally encrypted and transmitted in order to ensure the security of information transmission.

  In this case, the transmission device side encrypts the digital information with the encryption key, and the reception device side uses the same encryption key as the transmission device side to decrypt (decrypt) and restore the original digital information. The method is known. This common key encryption method is based on the premise that the same encryption key (digital key) is shared in advance between the transmission device and the reception device (between a plurality of entities).

  As another encryption method, a public key encryption method based on Diffie-Hellman key sharing, which was created by Diffie and Hellman, is widely known (for example, see Non-Patent Document 1). . In this public key encryption method, the transmitting entity generates an encryption key from its own private key and the receiving entity's public key, encrypts and transmits the digital information, and the receiving entity transmits its private key and A decryption key for decryption is generated from the public key of the transmitting entity, and the received encrypted digital information is decrypted. Therefore, in this encryption method, a part of key information is mutually exchanged between a plurality of entities, and as a result, sharing of the same key is realized. There is also a method of recording a common key in all entities in advance.

  Further, a digital information transmission system that includes an initial key selection unit that selects one of the initial keys from the key ring and performs encryption using the initial key selected by the initial key selection unit has been conventionally known (for example, Patent Documents). 1).

Douglas R. Stinson, translated by Koichi Sakurai, "Basics of Cryptography", Kyoritsu Publishing Co., Ltd. JP-A-11-220462

  However, in order to share the above-described conventional digital key among a plurality of entities, in the digital information transmission system based on the common key encryption method in which each entity holds the same key in advance, the common key is fixed. If the data is parsed from the data when the data encrypted with the common key is transferred, the common key of all entities will be known, and as a result, the reliability of the entire system is impaired. Care must be taken to ensure that the common key is difficult to analyze.

  In addition, in a conventional digital information transmission system using a key exchange method such as Diffie-Hellman key sharing, it is necessary for each entity to exchange a part of the key in advance, and suddenly it is assumed that the key is shared. Data cannot be passed.

  Furthermore, the conventional digital information transmission system described in Patent Document 1 has a problem that the analogy of the key selected from the encryption result is relatively easy, and the encryption strength deteriorates when the encryption is repeated.

  The present invention has been made in view of the above points, and in order to establish an encrypted secure communication path by exchanging encryption keys for digital data encryption communication, the encryption key can be used safely and with fewer procedures. It is an object of the present invention to provide a digital information transmission system and a digital information transmission method for exchanging digital information.

  In order to achieve the above object, a digital information transmission system according to a first aspect of the present invention encrypts and transmits digital information to be transmitted by a digital data transmitting apparatus, and receives the encrypted digital information by a digital data receiving apparatus. In the digital information transmission system for decrypting and decrypting the original digital information, the digital data transmitting apparatus includes a first common key bundle that holds in advance m (m is an integer of 2 or more) different common keys. , Based on the key selection information, key selection information generating means for generating key selection information for randomly selecting n (n is a positive integer less than or equal to m) common keys from the first common key ring, Digital information to be transmitted by a first key selection means for randomly selecting n common keys from one common key ring and n common keys selected by the first key selection means. A digital data receiving apparatus, comprising: an encryption means for repeatedly encrypting n times repeatedly; and a transmission means for transmitting encrypted digital information finally obtained by repeated encryption by the encryption means together with key selection information. Received by the receiving means, the receiving means for receiving the encrypted digital information and the key selection information, the second common key ring having m common keys identical to the first common key ring, and the receiving means. The second key selecting means for selecting n common keys from the second common key bundle based on the selected key selection information, and the receiving means with the n common keys selected by the second key selecting means. And decrypting means for repeatedly decrypting the encrypted digital information received n times and finally decrypting the original digital information.

  In this invention, the same common key ring is shared between the digital data transmitting apparatus and the digital data receiving apparatus which are different entities, and the digital data transmitting apparatus selects one piece of digital information to be transmitted at random from the common key ring. Encrypting with one common key, and further encrypting the obtained cryptographic processing result with another common key randomly selected from the common key bundle, is repeated n times in total. The encrypted digital information obtained by the encryption of n and the selection key information of n common keys are transmitted, and the digital data receiving apparatus obtains n common keys from the common key bundle based on the received selection key information. By using these selected common keys, the decryption process, which is the reverse process of the encryption process, is repeatedly performed n times on the received encrypted digital information. Realized to share any digital information between entities. Thereby, in this invention, the difficulty of estimating the key selected from the encryption result can further be improved by selecting a some common key from a common key ring and repeating encryption several times.

  In order to achieve the above object, the digital information transmission system of the second invention inputs the encryption means of the first invention with each of the n common keys selected by the first key selection means. N pieces of cascade-connected encryption processing units for encrypting the received information, supplying digital information to be transmitted to the first encryption processing unit of the n encryption processing units, Means for outputting the encrypted digital information from the stage encryption processing unit, and the decryption means is selected by each of the n common keys selected in the reverse order from the first key selection means by the second key selection means. It consists of n cascade-connected decryption processing units that decrypt input information, and supplies the received encrypted digital information to the first decryption processing unit of the n decryption processing units. Deciphered and decrypted from the final stage decryption processor Characterized in that the means for outputting information.

  In order to achieve the above object, a digital information transmission system according to a third aspect of the invention provides a key selection information generation means according to the first aspect, wherein the key selection means obtains n common keys from the first common key bundle. At the time of selection, it is characterized in that key selection information for prohibiting selection of at least one of the duplicate selection of the same common key and the selection of the common key of the combination serving as the comparison key is generated. According to the present invention, it is possible to prevent occurrence of bias in the encryption processing result.

  In order to achieve the above object, the digital information transmission system according to the fourth invention is characterized in that the key selection information generating means according to the first or third invention includes a revocation list in which a selection-prohibited common key is stored, a key And random number generating means for generating key selection information for selecting a total of n common keys not stored in the revocation list from the first common key ring by the selecting means. In the present invention, the selection-prohibited common key stored in the revocation list is not selected by the key selection means, and cannot be used for the encryption process.

  In order to achieve the above object, a digital information transmission method according to a fifth aspect of the present invention encrypts and transmits digital information to be transmitted, receives the encrypted digital information, decrypts it, and transmits the original digital information. In a digital information transmission method for decoding information, n randomly (n is a positive integer less than or equal to m) from a first common key bundle composed of m different (m is an integer greater than or equal to 2) common keys A first step of selecting a common key, a second step of repeatedly encrypting digital information to be transmitted n times with the n common keys selected in the first step, and a second step A third step of transmitting encrypted digital information finally obtained by repetitive encryption together with key selection information for selecting a common key from the first common key ring in the first step; Received by the fourth step from the fourth step of receiving the encrypted digital information and the key selection information and the second common key ring comprising the m common keys identical to the first common key ring. The fifth step of selecting n common keys based on the selected key information, and the encrypted digital information received in the fourth step with the n common keys selected in the fifth step. a sixth step of repeatedly decoding n times and finally decoding the original digital information.

  In the present invention, the digital information to be transmitted is encrypted with one common key randomly selected from the common key ring, and the obtained cryptographic processing result is further encrypted with another random key selected from the common key ring. Encryption with one common key is repeated n times in total, and the encrypted digital information obtained by the nth encryption and the selection key information of n common keys are transmitted to receive digital data. On the side, n common keys are selected from the common key bundle based on the received selection key information, and using these selected common keys, the received encrypted digital information is subjected to reverse processing of encryption processing. Since a certain decryption process is repeated n times, a plurality of common keys are selected from the common key bundle, and the encryption is repeated a plurality of times, thereby making it difficult to infer the selected key from the encryption result. Can further improve .

  In order to achieve the above object, in the digital information transmission method of the sixth invention, the second step in the third invention should be transmitted with the common key first selected from the first common key ring. Encrypt the digital information, encrypt the encryption result with the second common key selected from the first common key ring, and encrypt the encryption result with the next common key selected from the first common key ring And the process of outputting the encrypted digital information by the n-th encryption is performed, and the sixth step is changed from the second common key ring in the reverse order to the first step by the fifth step. The information input by each of the selected n common keys is sequentially decrypted, and the digital information decrypted by the n-th decryption is output.

  In order to achieve the above object, a digital information transmission method according to a seventh aspect of the present invention is characterized in that at least the first step of the fifth aspect selects at least n common keys from the first common key bundle. Selection of either one of duplicate selection of the same common key and selection of a common key of a combination serving as a control key is prohibited. According to the present invention, it is possible to prevent occurrence of bias in the encryption processing result.

  Furthermore, in order to achieve the above object, in the digital information transmission method of the eighth invention, the first step of the fifth invention or the seventh invention obtains n common keys from the first common key ring. When selecting, a common key that is not stored in the revocation list is selected. The selection-prohibited common key stored in the revocation list is not selected by the key selection means, and cannot be used for the encryption process.

  According to the present invention, by selecting a plurality of common keys from the common key ring and repeating the encryption a plurality of times, it becomes more difficult to infer the selected key from the encryption result, so that the security of the transmission system is increased. Can be increased. Further, according to the present invention, digital information can be delivered without requiring negotiation in advance, so that digital information can be safely delivered via a package medium.

  Furthermore, according to the present invention, when a plurality of common keys are selected from a common key bundle, at least one of duplicate selection of the same common key and selection of a common key of a combination to be a control key is prohibited. As a result, the occurrence of bias in the encryption processing result is prevented, so that it is possible to prevent the deterioration of the encryption strength due to repeated encryption.

  Further, according to the present invention, the selected prohibited common key stored in the revocation list is not selected by the key selection means and cannot be used for the encryption process. Even when some of the encryption keys are known to a third party, only the encryption key can be revoked.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of a digital information transmission system according to the present invention. In the figure, a digital information transmission system includes a digital data transmitting apparatus (entity) 10 that transmits encrypted data A obtained by encrypting data 16 together with key selection information B to a predetermined transmission path, and the above-described encryption. It comprises a digital data receiving device (entity) 20 that receives encrypted data A and key selection information B via a predetermined transmission path and decrypts encrypted data A.

  The digital data transmitting apparatus 10 includes a common key bundle 11 composed of m different (m is an integer of 2 or more) common keys Kc (0, 1,..., M−1) and an arbitrary positive number less than m. , An integer (n) and index (0), index (1), index (1),..., Index (n−1), and n (n is less than or equal to m) from the common key bundle 11 A key selection means 13 for selecting a common key 14 of a positive integer), and encryption for repeatedly encrypting digital data 16 to be transmitted with the selected n common keys 14 n times and outputting encrypted data A Means 15 includes a control device 17 and a revocation list 18.

  On the other hand, the digital data receiving apparatus 20 has a common key composed of m different (m is an integer of 2 or more) common keys Kc (0, 1,..., M−1) that are the same as the common key bundle 11. In accordance with the bundle 21 and the received common key selection information B, the key selection means 22 for selecting n (n is a positive integer less than or equal to m) common keys 23 from the common key bundle 21, and the n common items selected Decryption means 24 for obtaining the decrypted digital data 25 by repeatedly decrypting the received encrypted data A n times with the key 23.

  Next, the operation of transmitting the digital data 16 held by the digital data transmitting apparatus 10 to the digital data receiving apparatus 20 will be described with reference to the block diagram of FIG. 1 and the flowchart of FIG. First, the digital data transmitting apparatus 10 uses an arbitrary integer n and n random numbers index (0), index (1), index (2), ..., index (n-1) as keys from the random number generator 12. It is generated as information (steps S1 and S2 in FIG. 2).

  At this time, the control device 17 causes the random number generator 12 to generate the same key information as the generated key information or the control key in order to avoid that the encryption processing result is biased and the key analysis becomes easy. Is controlled so as not to include the combination of the key and the key information included in the revocation list 18 is not included. The key information selected here is output as key selection information B.

  The revocation list 18 is a list of revoked keys, and the key selection means 13 generates key information (key selection information) from the random number generator 12 so as not to select a common key included in the revocation list 18. Even when a part of the common key of the common key ring 11 is known to a third party, only the common key can be revoked. It should be noted that the generation control of the key selection information for prohibiting the duplicate selection of the same common key, prohibiting the selection of the common key of the combination serving as the control key, and prohibiting the selection of the common key included in the revocation list 18 is as follows. , At least one of them may be included.

  Next, in the key selection means 13, n keys Kc (index (0)), Kc (index (1)), Kc (index (2)),..., Kc (index (n− 1)) is selected as the common key 14 (step S3 in FIG. 2). That is, a large number of keys are stored in the key ring 11 in advance, and the key selection unit 13 selects keys in the order corresponding to the value of the key information indicated by the key selection information B. For example, if the value of the key information is index (0), the key Kc (index (0)) in that order from the key bundle 11 is selected as one of the common keys 14.

  Next, the original digital data 16 is stored in the storage area data (0) in the encryption means 15 (step S4 in FIG. 2), the variable i is initialized to 0 (step S5 in FIG. 2), and then the storage area The digital data 16 stored in the data (0) is encrypted with the first key Kc (index0) of the common key 14 input from the key selection means 13, and the encrypted data is stored in the next storage area data ( The encryption process stored in 1) is performed (step S6 in FIG. 2).

Next, the variable i is incremented by 1 (step S7 in FIG. 2), and whether or not the incremented variable i is smaller than the integer n is compared (step S8 in FIG. 2). If i is smaller than n, the step is again performed. The encryption process of S6 is performed. In this way, the encryption process of step S6 is repeated n times while increasing the value of n by 1 and updating the common key until i becomes equal to n. The encryption process in step S6 is expressed by an equation:
data (i + 1) = E (Kc (indexi), data (i))
It becomes. In this way, the encrypting means 15 encrypts the data 16 n times, and outputs the encrypted data data (n−1) obtained by the n-th encryption as the encrypted data A ( Step S9 in FIG. The encrypted data A and the common key selection information B obtained by branching the random number supplied from the random number generator 12 to the key selection means 13 are transmitted to the digital data receiving device 20 of the communication partner.

  Next, the key encryption process will be described in more detail. FIG. 3 shows a block diagram of an example of the encryption means. In the figure, the same components as those in FIG. In FIG. 3, the encryption unit 15 includes five encryption processing units 151 to 155 connected in cascade, and five different keys are supplied from the key selection unit 13 to the respective encryption processing units 151 to 155. Thus, the encryption is performed 5 (= n) times. In addition, it is assumed that the common key bundle 11 stores 10,000 common keys in total of the keys K0 to K9999.

  At the time of encryption, first, five common keys are selected by the key selection means 13. Here, the key selection means 13 has five key numbers recorded in the key selection information B input from the random number generator 12, and in accordance with the key numbers, all in the order of K45, K184, K3, K9218, and K75. Assume that five common keys are selected. The first selected common key K45 is supplied to the first encryption processing unit 151, the second selected common key K184 is supplied to the encryption processing unit 152, and the third selected common key K3 is the encryption key. The fourth common key K9218 selected by the encryption processing unit 153 is supplied to the encryption processing unit 154, and the fifth common key K75 selected is supplied to the last encryption processing unit 155.

  On the other hand, the data 16 to be transmitted is input to the first-stage encryption processing unit 151, encrypted here with the common key K45, and then input to the second-stage encryption processing unit 152. The encryption processing unit 152 encrypts the input encrypted data with the common key K184, and supplies the obtained encrypted data to the encryption processing unit 153 at the next stage.

  Hereinafter, similarly, the encrypted data input to the encryption processing unit 153 is encrypted here with the common key K3, and further, the encryption result is input to the encryption processing unit 154 at the next stage and the common key K9218. The encrypted result is input to the last-stage encryption processing unit 155 and encrypted with the common key K75, and the obtained encrypted data is transmitted as encrypted data A. A random number indicating the common key selected by the key selection unit 13 is transmitted from the random number generator 12 as key selection information B for identification by the digital data receiving device 20.

  Next, the receiving operation of the digital data receiving apparatus 20 will be described with reference to the block diagram of FIG. 1 and the flowchart of FIG. First, the key selection means 22 of the digital data receiving apparatus 20 receives the key selection information B transmitted by the digital data transmission apparatus 10 and, based on the key selection information B, n common keys 23 from the common key bundle 21. (Kc (index (0)),..., Kc (index (n−1))) is selected (step S11 in FIG. 4).

  Next, the received encrypted data A is stored in the storage area data (0) in the digital data receiving apparatus 20 (step S12 in FIG. 4). Subsequently, after storing the initial value 0 in the variable i (step S13 in FIG. 4), the decryption means 24 uses the first common key Kc (index0) of the common keys 23 input from the key selection means 22. Decryption processing is performed to decrypt the encrypted data in the storage area data (0) and store the decrypted data in the next storage area data (1) (step S14 in FIG. 4).

Subsequently, the variable i is incremented by 1 (step S15 in FIG. 4), and it is compared whether or not the variable i after the increment is equal to the integer n (step S16 in FIG. 4). If i is smaller than n, step S14 is performed again. Is decrypted. In this way, the decryption process of step S14 is repeated n times while increasing the value of n by 1 and updating the common key until i becomes equal to n. The decryption process in step S14 is expressed by an equation:
data (i + 1) = D (Kc (indexi), data (i))
It becomes. In this way, the decryption means 24 decrypts the encrypted data A n times, and the decrypted data data (n−1) obtained by the n-th decryption is converted into the decrypted data 25. Output (step S17 in FIG. 4). This data 25 is the original data 16.

  Next, the key decryption process will be described in more detail. FIG. 5 shows a block diagram of an example of the decoding means. In the figure, the same components as those in FIG. In FIG. 5, the decryption means 24 includes five decryption processing units 241 to 245 connected in cascade, and five common keys are selected from the key selection means 22 based on the received key selection information B, and each decryption is performed. By being supplied to the processing units 241 to 245, the decoding is performed 5 (= n) times. In addition, it is assumed that the common key ring 21 stores 10,000 common keys in total, which are the same keys K0 to K9999 as the common key ring 11.

  At the time of decryption, first, five common keys are selected by the key selection means 22. Here, the key selection means 22 follows all the key numbers recorded in the reception key selection information B in the order of K75, K9218, K3, K184, K45 (that is, the reverse order of the common key selection on the transmission side). Select 5 common keys.

  The first-selected common key K75 is supplied to the first-stage decryption processing unit 241, and the second-selected common key K9218 is supplied to the second-stage decryption processing unit 242, and the third-selected common key is selected. The key K3 is supplied to the third-stage decryption processing unit 243, the fourth selected common key K184 is supplied to the fourth-stage decryption processing unit 244, and the fifth selected common key K45 is the final one. Is supplied to the stage decoding processing unit 245.

  On the other hand, the received encrypted data A is input to the first-stage decryption processing unit 241, where it is decrypted with the common key K75 and then input to the second-stage decryption processing unit 242. The decryption processing unit 242 decrypts the input decrypted data with the common key K 9218 and supplies the obtained decrypted data to the decryption processing unit 243 at the next stage.

  Hereinafter, similarly, the decrypted data input to the decryption processing unit 243 is decrypted here with the common key K3, and the decryption result is further input to the decryption processing unit 244 at the next stage to obtain the common key K184. The decryption result is input to the decryption processing unit 245 at the final stage, decrypted with the common key K45, and the obtained decrypted data is decrypted as the original data 25.

  Thus, according to the present embodiment, encrypted digital data can be delivered without requiring negotiation in advance, so that digital data can be safely delivered via the package medium. Also, since encryption is repeated n times using a common key, it is possible to improve the difficulty of analyzing the encryption key from the encryption result.

  INDUSTRIAL APPLICABILITY The present invention can be used to establish an encrypted secure communication path by exchanging encryption keys for encryption communication of digital data between computer networks and apparatuses that use and process digital data.

It is a block diagram of one embodiment of the present invention. 3 is a flowchart for explaining the operation of the digital data transmitting apparatus according to the present invention. It is a block diagram which shows an example of a structure of the encryption means of the principal part of FIG. 3 is a flowchart for explaining the operation of the digital data receiving apparatus according to the present invention. It is a block diagram which shows an example of a structure of the decoding means of the principal part of FIG.

Explanation of symbols

10 Digital data transmitter (entity)
DESCRIPTION OF SYMBOLS 11, 21 Common key ring 12 Random number generator 13, 22 Key selection means 14, 23 Selected common key 15 Encryption means 16 Digital data to be transmitted 17 Controller 18 Revocation list 20 Digital data receiver (entity)
24 Decryption means 25 Decrypted digital data A Encrypted data B Common key selection information

Claims (8)

In a digital information transmission system for encrypting and transmitting digital information to be transmitted by a digital data transmitting device, receiving and decrypting the digital information encrypted by the digital data receiving device, and decrypting the original digital information,
The digital data transmitting device is:
A first common key bundle preliminarily holding m different (m is an integer of 2 or more) common keys;
Key selection information generating means for generating key selection information for randomly selecting n (n is a positive integer less than or equal to m) common keys from the first common key ring;
First key selecting means for randomly selecting the n common keys from the first common key ring based on the key selection information;
Encryption means for repeatedly encrypting the digital information to be transmitted n times with the n common keys selected by the first key selection means;
Transmission means for transmitting encrypted digital information finally obtained by repeated encryption by the encryption means together with the key selection information,
The digital data receiver is
Receiving means for receiving the encrypted digital information and the key selection information;
A second common key ring that holds in advance m common keys identical to the first common key ring;
Second key selecting means for selecting the n common keys from the second common key ring based on the key selection information received by the receiving means;
Decryption that repeatedly decrypts the encrypted digital information received by the receiving means n times with the n common keys selected by the second key selecting means, and finally decrypts the original digital information And a digital information transmission system.   The encryption means includes n encryption processing units connected in cascade to encrypt information input with each of the n common keys selected by the first key selection means, means for supplying and encrypting the digital information to be transmitted to the first encryption processing unit of the n encryption processing units, and outputting the encrypted digital information from the last encryption processing unit; And n means for decrypting the information inputted by each of the n common keys selected by the second key selection means in the reverse order to the first key selection means. Of the n decryption processing units, the received encrypted digital information is supplied to the first decryption processing unit and decrypted, and then decrypted from the final decryption processing unit. It is a means for outputting digital information. Digital information transmission system according to claim 1, wherein.   The key selection information generation means is configured to select at least the same common key as a duplicate key and a comparison key when the first key selection means selects the n common keys from the first common key bundle. 2. The digital information transmission system according to claim 1, wherein key selection information for prohibiting selection of any one of the common keys is generated.   The key selection information generation means includes a revocation list in which a selection-prohibited common key is stored and a common key that is not stored in the revocation list from the first common key bundle by the first key selection means. 4. The digital information transmission system according to claim 1, further comprising random number generating means for generating key selection information for selecting the n items. In a digital information transmission method for encrypting and transmitting digital information to be transmitted, receiving and decrypting the encrypted digital information, and decrypting the original digital information,
A first step of randomly selecting n (n is a positive integer less than or equal to m) common keys from a first common key bundle composed of m different (m is an integer greater than or equal to 2) common keys When,
A second step of repeatedly encrypting the digital information to be transmitted n times with the n common keys selected in the first step;
The encrypted digital information finally obtained by repetitive encryption in the second step is transmitted together with key selection information for selecting the common key from the first common key bundle in the first step. A third step;
A fourth step of receiving the encrypted digital information and the key selection information;
Based on the key selection information received in the fourth step, the n common keys are selected from the second common key bundle consisting of m common keys identical to the first common key ring. A fifth step of selecting
The encrypted digital information received in the fourth step is repeatedly decrypted n times with the n common keys selected in the fifth step, and finally the original digital information is decrypted. 6. A digital information transmission method comprising: 6 steps.   The second step encrypts the digital information to be transmitted with a common key first selected from the first common key ring, and the encryption result is selected second from the first common key ring. Encrypting with the common key, repeatedly encrypting the encrypted result with the next common key selected from the first common key bundle, and outputting the encrypted digital information by n-th encryption And the sixth step sequentially inputs the information input by each of the n common keys selected from the second common key ring in the reverse order of the first step by the fifth step. 6. The digital information transmission method according to claim 5, wherein a process of decoding and outputting the decoded digital information by n-th decoding is performed.   In the first step, when selecting the n number of common keys from the first common key bundle, at least one of the same common key duplication selection and the selection of the combination common key serving as the control key 6. The digital information transmission method according to claim 5, wherein one of the selections is prohibited. The said 1st step selects the common key which is not memorize | stored in the revocation list | wrist, when selecting the said n common key from the said 1st common key ring, The Claim 5 or 7 characterized by the above-mentioned. Digital information transmission method.

Images