JP5100497B2 - Decoding device - Google Patents

Description

  The present invention relates to a decryption device that decrypts encrypted ciphertext data and extracts plaintext data.

Encryption schemes using a common key are broadly divided into block ciphers that are encrypted in fixed block units and bit stream ciphers.
In contrast to these encryption methods, a block cipher is often used as a method for encrypting a packet on a network by a relay device such as a router. For example, a packet is transmitted at high speed by IPsec (IP security) using the block cipher. There is a technique described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-180234) as a method for encrypting the password.

On the other hand, stream ciphers can generate random numbers with high throughput once initialization such as common key and IV (Initialization Vector) settings is performed, and transmission efficiency is high because padding to match block sizes is unnecessary There is an advantage, and it may be used for a relay device of a network.
Hereinafter, a general stream cipher and a relay apparatus that encrypts a packet on the network with the stream cipher will be described.

  FIG. 6 shows the structure of a general stream cipher.

First, the configuration will be described.
101 is a random number generator. The random number generation unit 101 includes an intermediate key 111, an update function 112, and an output function 113.
Reference numeral 102 denotes plain text data.
Reference numeral 103 denotes ciphertext data.
104 is a common key and IV.
Reference numeral 105 denotes a clock.
106 is a random number sequence. The random number sequence 106 is a bit sequence with high randomness output from the output function 113.
Reference numeral 107 denotes an XOR (eXclusive OR) section. The XOR unit 107 generates ciphertext data by performing an exclusive OR of the random number sequence and the plaintext data.

  6 shows the configuration when encrypting plaintext data, the configuration is the same when decrypting ciphertext data, and the positions of plaintext data 102 and ciphertext data 103 in FIG. 6 are switched. It becomes composition.

Next, the operation will be described.
First, appropriate initial values are set for the common key, the IV 104, and the intermediate key 111.
Next, the update function 112 receives the common key, the IV 104, and the intermediate key 111, generates a new intermediate key 111 as an output every time the clock 105 is given, and updates the intermediate key 111 up to that time.
The output function 113 outputs a part of the intermediate key 111 as the random number sequence 106.
The XOR unit 107 performs exclusive OR of the random number sequence 106 and the plaintext data 102 and outputs the result as ciphertext data 103.
Thus, whenever the clock 105 is given, the random number sequence 106 is produced | generated while updating the intermediate key 111 with the update function 112, and the ciphertext packet 103 is output by taking the exclusive OR of it and the plaintext data 102.

In the stream cipher, in order to output the random number once output, it is necessary to give the intermediate key and IV again and give a predetermined number of clocks.
The number of clocks given to re-output the random number increases or decreases depending on the position where the random number is extracted from a series of random numbers, and it takes time to output again as the random number sequence continues to be generated and moved backward. Become.

In addition, since stream ciphers output a series of random numbers in order, it is difficult to generate a random number after skipping some random numbers.
In such a case, first, a random number of a portion to be skipped is generated, and then a desired random number is generated. If you want to use the skipped random number later, you need to save it.

  FIG. 7 shows a general stream cipher packet relay apparatus that relays a packet encrypted with the stream cipher.

First, the configuration will be described.
Reference numeral 201 denotes a relay device that encrypts a packet (hereinafter also simply referred to as an encryption device).
Reference numeral 211 denotes a relay device that decodes a packet (hereinafter also simply referred to as a decoding device).
Reference numerals 202 and 212 denote reception units of the encryption device and the decryption device, respectively.
Reference numerals 203 and 213 denote XOR sections of the encryption device and the decryption device, respectively.
Reference numerals 204 and 214 denote transmission units of the encryption device and the decryption device, respectively.
205 and 215 are clock generation units of the encryption device and the decryption device, respectively.
Reference numerals 206 and 216 denote random number generation units of the encryption device and the decryption device, respectively. The structure and operation of the random number generation units 206 and 216 are as described in the random number generation unit 101 of FIG.
207 and 217 are random number sequences of the encryption device and the decryption device, respectively.
208 and 218 are a common key and IV used by the encryption device and the decryption device, respectively.
Reference numeral 219 denotes a sequence control unit of the decoding device.
220 is a random number buffer of the decoding device.
Reference numeral 231 denotes a plaintext packet.
Reference numeral 232 denotes a ciphertext packet.
Reference numeral 233 denotes a network for transferring the ciphertext packet 232.

  Next, operations of the encryption device 201 and the decryption device 211 will be described.

First, the encryption device 201 and the decryption device 211 share a common key and IVs 208 and 218 between the two devices before performing communication using encrypted packets.
Note that the encryption device 201 and the decryption device 211 are generated on the basis of a single common key and a single IV shared here, as prerequisite operations for both devices to correctly encrypt and decrypt each other. From the series of random number sequences, the amount of random numbers necessary for encryption and decryption of the received packet is sequentially used.
Therefore, in both the encryption device 201 and the decryption device 211, the order of packets to be encrypted and the order of packets to be decrypted need to match.

Next, the operation of the encryption device 201 will be described.
First, when receiving the plaintext packet 231, the reception unit 202 requests the clock generation unit 205 to generate a random number sequence for one packet and transfers the plaintext packet 231 to the XOR unit 203.
Next, the clock generation unit 205 generates a clock for one packet and outputs it to the random number generation unit 206.
Next, the random number generation unit 206 outputs the random number sequence 207 and transfers it to the XOR unit 203.
Next, the XOR unit 203 performs exclusive OR of the random number sequence 207 and the plaintext packet 231 to generate a ciphertext packet 232 and forwards it to the transmission unit 204.
Next, the transmission unit 204 assigns a transfer order number (hereinafter also referred to as a transfer number) for each packet to the header portion of the ciphertext packet 232 and transmits the packet to the network 233.

Next, the operation of the decoding device 211 will be described.
First, when receiving the ciphertext packet 232, the receiving unit 212 confirms the transfer order for each packet.
Here, there are two cases, when the packets are received in order and when the packets are received with the order changed.

First, the operation of the decoding device 211 when packets are received in order will be described.
First, the reception unit 212 notifies the sequence control unit 219 that packets have been received in order. In addition, the reception unit 212 requests the clock generation unit 215 to generate a random number sequence for one packet and transfers the ciphertext packet 232 to the XOR unit 213.
Next, the clock generation unit 215 generates a clock for one packet and outputs it to the random number generation unit 216.
Next, the random number generation unit 216 outputs a random number sequence 217 and transfers it to the order control unit 219.
Next, since the order control unit 219 receives a notification that the packets are received in order from the receiving unit 212, the random number sequence 217 is transferred to the XOR unit 213 as it is.
Next, the XOR unit 213 takes the exclusive OR of the random number sequence 217 and the ciphertext packet 232 to generate a plaintext packet 231 and forward it to the transmission unit 214.
Next, the transmission unit 214 transmits the plaintext packet 231 outside the apparatus. At this time, the transfer sequence number for each packet assigned to the header portion is deleted and restored.

Secondly, the operation of the decoding device 211 when the order of packets is changed and received will be described.
Note that the operation in this case assumes a case where the packet transfer order is changed or a packet is lost due to reasons such as transfer path switching in the network 233 or depletion of the buffer of the relay device.
Here, there are two cases: a case where a packet is received by overtaking another packet, and a case where the overtaken packet is received later.

First, the operation of the decoding device 211 when the packet is received by overtaking will be described.
First, the reception unit 212 notifies the order control unit 219 that the packet has been received by overtaking. In addition, the reception unit 212 requests the clock generation unit 215 to generate a random number sequence for the number of packets that have been overtaken due to a change in the reception order, and a random number sequence for one received packet, and send a ciphertext packet 232 Transfer to the XOR unit 213.
Next, the clock generation unit 215 generates a clock for the number of packets that have been overtaken by switching the reception order and a clock for one packet, and outputs the generated clock to the random number generation unit 216.
Next, the random number generation unit 216 outputs a random number sequence 217 and transfers it to the order control unit 219. Here, since overtaking of the packet transfer order has occurred, a random number sequence 217 necessary for decoding the overtaken packet is first generated, and then a random number sequence 217 necessary for decoding the packet is generated.
Next, since the order control unit 219 receives the notification received by overtaking the packet from the reception unit 212, the sequence control unit 219 first stores the random number sequence 217 necessary for decoding the overtaken packet in the random number buffer 220, and then The random number sequence 217 necessary for decoding the packet is transferred to the XOR unit 213.
Next, the XOR unit 213 obtains an exclusive OR of the random number sequence 217 necessary for decryption of the packet and the ciphertext packet 232, generates a plaintext packet 231, and transfers it to the transmission unit 214.
Next, the transmission unit 214 transmits the plaintext packet 231 outside the apparatus. At this time, the transfer sequence number for each packet assigned to the header portion is deleted and restored.

Secondly, the operation of the decoding device 211 when the overtaken packet is received later will be described.
First, the reception unit 212 notifies the order control unit 219 that the overtaken packet has been received. In addition, the reception unit 212 transfers the ciphertext packet 232 to the XOR unit 213. Since the random number sequence 217 necessary for decoding the packet is already stored in the random number buffer 220, the reception unit 212 does not request the clock generation unit 215 to generate a random number sequence.
Next, since the order control unit 219 receives the notification of receiving the overtaken packet from the reception unit 212, the sequence control unit 219 reads the random number sequence 217 necessary for decoding the packet from the random number buffer 220 and transfers it to the XOR unit 213. To do.
Next, the XOR unit 213 obtains an exclusive OR of the random number sequence 217 necessary for decryption of the packet and the ciphertext packet 232, generates a plaintext packet 231, and transfers it to the transmission unit 214.
Next, the transmission unit 214 transmits the plaintext packet 231 outside the apparatus. At this time, the transfer sequence number for each packet assigned to the header portion is deleted and restored.
JP 2004-180234 A

When communicating between packets relayed on a network using packets encrypted by stream encryption, the order in which the encryption device transmits the packets and the order in which the decryption device receives the packets are switched, and a packet in the decryption device When the packet is received by overtaking another packet, the decoding device needs to generate a random number sequence necessary for decoding the overtaken packet in addition to generating a random number sequence necessary for decoding the received packet.
When overtaking occurs in this way, there is a problem in that the delay is significantly increased compared to a normal state where overtaking does not occur and the relay performance is degraded.

  One of the main objects of the present invention is to solve the above-described problems, and it is a main object of the present invention to decrypt ciphertext data without delay in a decryption device even if the arrival order of ciphertext data is changed. .

The decoding device according to the present invention provides:
The plaintext data is encrypted from the encryption device that encrypts the plaintext data using a random number sequence that is generated by ordering the random number sequence according to a predetermined random number sequence generation algorithm and the order of the plaintext data with the data order determined. A decryption device for receiving encrypted ciphertext data,
A random number generation unit that generates an ordered random number sequence according to the same random number sequence generation algorithm as the random number sequence generation algorithm used by the cryptographic device;
A random number storage unit that stores a plurality of random number sequences generated by the random number generation unit in association with the order;
A decryption unit for decrypting ciphertext data using a random number sequence and extracting plaintext data;
The ciphertext data transmitted from the cipher apparatus is received, a random number sequence in an order matching the data order of the received ciphertext data is read from the random number storage unit, and the read random number sequence and the ciphertext data are decrypted And a receiver that requests the random number generator to generate a new random number sequence,
The random number generator
When the generation of a new random number sequence is requested from the receiving unit, it corresponds to the order after the last sequence in the random number storage unit according to the same random number sequence generation algorithm as the random number sequence generation algorithm used by the encryption device Generate a random number sequence,
The random number storage unit
The random number sequence newly generated by the random number generation unit is stored in place of the random number sequence read by the reception unit with respect to the ciphertext data.

  According to the present invention, a plurality of random number sequences are held, and when a random number sequence is read for use in decryption of the received ciphertext data, a new random number sequence is generated and supplemented to generate the ciphertext data. A plurality of random number sequences that are expected to be used for decryption can always be held, and the ciphertext data can be decrypted without delay even if the arrival order of the ciphertext data is changed.

Embodiment 1 FIG.
FIG. 1 shows a configuration example of a decoding device 311 according to the present embodiment.
Decryption apparatus 311 according to the present embodiment is used in a stream cipher packet relay apparatus that relays a packet encrypted with stream cipher.
The configuration and operation of the encryption device paired with the decryption device 311 are the same as those described in the background art with reference to FIGS.
That is, the encryption device paired with the decryption device 311 according to the present embodiment generates and generates a random number sequence in accordance with a predetermined random number sequence generation algorithm, and for a plaintext packet (plaintext data) in which the data order is determined. This is an encryption device that encrypts a plaintext packet using a random number sequence having the same order.
Then, the decryption apparatus 311 according to the present embodiment receives the ciphertext packet (ciphertext data) obtained by encrypting the plaintext packet from the encryption apparatus, and the random number sequence in the order matching the data order of the ciphertext packet. Is used to perform the decoding process.

First, the configuration of decoding apparatus 311 in the present embodiment will be described.
Reference numeral 312 denotes a receiving unit of the decoding device 311.
Reference numeral 313 denotes an XOR section of the decoding device 311.
Reference numeral 314 denotes a transmission unit of the decoding device 311.
Reference numeral 315 denotes a clock generation unit of the decoding device 311.
Reference numeral 316 denotes a random number generation unit of the decryption device 311. The structure and operation of the random number generation unit 316 are as described for the random number generation unit 101 in FIG.

Reference numeral 317 denotes a random number sequence of the decryption device 311.
Reference numeral 318 denotes the common key and IV of the decryption apparatus 311.
320 is a random number buffer of the decoding device 311. The random number buffer 320 is a buffer for storing a random number sequence for decoding a packet, and can store a random number sequence of N (N ≧ 2) packets.
Reference numeral 321 denotes a transfer number management buffer of the decoding device 311. The transfer number management buffer 321 is a buffer for storing packet transfer numbers, and can store transfer numbers of N packets.
Reference numeral 322 denotes a maximum transfer number register of the decoding device 311. The maximum transfer number register 322 is a register indicating the largest number (number in the last order) among the N transfer numbers stored in the transfer number management buffer 321. The largest number among the N transfer numbers managed in the maximum transfer number register is also expressed as imax.
Reference numeral 331 denotes a plaintext packet.
Reference numeral 332 denotes a ciphertext packet. In the ciphertext packet 332, the transfer number is indicated in the header portion.

In the configuration of FIG. 1, the random number generation unit 316 generates the random number sequence 317 in order according to the same random number sequence generation algorithm as the random number sequence generation algorithm used by the encryption device. That is, as described in the background art, the random number generation unit 316 updates the intermediate key generated in the previous random number sequence generation process to generate the next intermediate key, and generates the next intermediate key. The next random number sequence is generated using at least a part, and thereafter, the intermediate key update and the random number sequence generation are repeated to generate the random number sequence in order.
The random number buffer 320 stores a plurality of random number sequences 317 generated by the random number generation unit 316 in association with the order. The random number buffer 320 is an example of a random number storage unit.
The receiving unit 312 receives the ciphertext packet 332 transmitted from the encryption device, reads a random number sequence in an order that matches the transfer number (data order) of the received ciphertext packet from the random number buffer 320, and The ciphertext packet 332 is output to the XOR unit 313 and the random number generation unit 316 is requested to generate a new random number sequence via the clock generation unit 315.
The XOR unit 313 decrypts the ciphertext packet 332 using the random number sequence output from the reception unit 312 and extracts the plaintext packet 331. The XOR unit 313 is an example of a decoding unit.
In addition, when the reception unit 312 requests generation of a new random number sequence, the random number generation unit 316 determines the last order in the random number buffer 320 according to the same random number sequence generation algorithm as that used by the encryption device. A random number sequence corresponding to the later order is generated, and the random number buffer 320 stores the random number sequence newly generated by the random number generation unit 316 instead of the random number sequence read by the reception unit 312 with respect to the ciphertext packet 332. To do.

FIG. 2 shows the relationship between the random number buffer 320 and the transfer number management buffer 321 in the decoding apparatus according to the present embodiment.
The transfer number management buffer 321 stores the transfer number of the packet, and the random number buffer stores a random number sequence used for decoding the packet of each transfer number corresponding to the order of the transfer number in the transfer number management buffer 321. Has been.
In this manner, the random number buffer 320 stores a plurality of random number sequences in order in association with the packet transfer numbers (data order).

  Next, the operation of decoding apparatus 311 in the present embodiment will be described.

First, the decryption device 311 shares the common key and IV 318 with a pair of encryption devices before performing communication using the encrypted packet.
In addition, as a prerequisite operation for the decryption apparatus 311 to correctly encrypt and decrypt each other with a pair of encryption apparatuses, the decryption apparatus 311 is based on a single common key and a single IV shared here. From the series of random number sequences generated in this way, the random number sequence of the amount necessary for decoding the received packet is used in order.

Further, as a preparation before performing packet communication, the decoding device 311 generates a random number sequence of N packets to be received first and stores it in the random number buffer 320 in advance.
Then, the decrypting device 311 stores the transfer numbers of the N packets prepared with random numbers in the transfer number management buffer 321.

When the above procedure is completed, the decryption device 311 can receive the ciphertext packet 332 transmitted from the encryption device.
Hereinafter, a processing example when the decryption apparatus 311 receives the ciphertext packet 332 and decrypts the ciphertext packet 332 will be described with reference to FIGS. 3 and 4.

First, when the decryption device 311 receives the ciphertext packet 332 (S101), the reception unit 312 checks whether or not the transfer number management buffer 321 has the transfer order (here, i) for each received packet. (S102).
Here, as a result of the confirmation, (1) there is a transfer number that matches the transfer number of the received packet in the transfer number management buffer 321, and (2) there is no transfer number that matches the transfer number of the received packet. If the transfer number of the received packet is smaller than any of the N transfer numbers stored in the transfer number management buffer 321, the transfer number of the received bucket is the first transfer order of the N transfer numbers. (3) N transfer numbers in which there is no transfer number that matches the transfer number of the received packet and the transfer number of the received packet is stored in the buffer. If the transfer number of the received bucket is larger than any one of the N transfer numbers, there are three ways.

First, when a transfer number that matches the transfer number of the received packet exists in the transfer number management buffer 321 (YES in S102), the receiving unit 312 determines that the transfer number is i in the transfer number management buffer 321. If there is a value smaller than the number obtained by subtracting N (YES in S103), it is invalidated (assuming that j are invalidated here) (S104).
Note that the operation in this case is a situation in which the packet sent by the cryptographic device is lost from the network for some reason, or a malicious third party resends the packet once transferred to the network. Assumed. This is an operation of invalidating a random number sequence of a packet that could not be received even after a predetermined time has passed by the decryption apparatus 311.

For example, when a ciphertext packet is received as shown in FIGS. 5A to 5C, the random number sequence corresponding to the transfer number 11 is invalidated in FIG. 5C.
Specifically, when N = 5 and a random number sequence corresponding to transfer numbers 11 to 15 is stored in the random number buffer 320, a packet with transfer number 12 (i = 12) is received (FIG. 5). In (a)), (i−N) is 12−5 = 7, and all transfer numbers have a value larger than (i−N), so there is no random number sequence to be invalidated.
Then, a random number sequence corresponding to the next transfer number 16 is generated, and the random number sequence for the transfer number 16 is stored at the position where the random number sequence of the transfer number 12 was stored. In this state, when the packet with the transfer number 13 (i = 13) is received (FIG. 5B), (i−N) becomes 13−5 = 8, and all the transfer numbers are (i Since the value is larger than -N), no random number sequence is invalidated.
Then, a random number sequence corresponding to the transfer number 17 that is the next number is generated, and the random number sequence for the transfer number 17 is stored at the position where the random number sequence of the transfer number 13 was stored. In this state, when a packet with transfer number 17 (i = 17) is received (FIG. 5C), (i−N) is 17−5 = 12, and transfer number 11 is (i− Since the value is smaller than the value of N), the random number sequence for the transfer number 11 is invalidated.

On the other hand, when there is no transfer number smaller than (i−N) (NO in S103), the receiving unit 312 uses the random number sequence necessary for decoding the packet as a random number based on the transfer number of the packet. The data is read from the buffer 320 and transferred to the XOR unit 313 (S105).
Further, the reception unit 312 requests the clock generation unit 315 to generate a random number sequence for one packet (S106) and transfers the ciphertext packet 332 to the XOR unit 313 (S107).
The random number sequence requested to be generated here is a random number sequence necessary for decoding one packet to be received in the future. If there is a transfer number invalidated in the operation of S104, an additional j packets are added. Request random number sequence.

Next, the receiving unit 312 changes the element (region) having the transfer number i in the transfer number management buffer 321 to a value obtained by adding 1 to the value (imax) indicated by the maximum transfer number register 322 (S108). ).
If there is an invalidated transfer number in the operation of S104, the invalidated j elements are changed to values obtained by adding 2 to j + 1 to the value (imax) indicated by the maximum transfer number register 322, respectively.

Next, the receiving unit 312 adds 1 to the value (imax) of the maximum transfer number register 322 (S109).
If there is an invalid transfer number in the operation of S104, j is further added.

Next, the XOR unit 313 takes the exclusive OR of the random number sequence necessary for decryption of the packet and the ciphertext packet 332, generates a plaintext packet 331, and transfers it to the transmission unit 314 (S110).
Next, the transmission unit 314 transmits the plaintext packet 331 outside the apparatus. At this time, the transfer sequence number for each packet assigned to the header portion is deleted and restored.

  Next, the clock generation unit 315 generates a clock for one packet and outputs it to the random number generation unit 316. If there is an invalid transfer number in the operation of S104, it is generated by adding a clock for j packets to this.

  Next, the random number generation unit 316 generates a random number sequence 317 (S111) and transfers it to the reception unit 312.

Next, the receiving unit 312 writes the random number sequence 317 in the random number buffer 320 (S112).
At this time, the place where the random number sequence 317 is written in the random number buffer 320 is the place where the random number sequence of the packet whose transfer number is i is stored.
If there is a transfer number invalidated in the operation of S104, the random number sequence 317 further includes a random number sequence for j packets, but the random number buffer 320 is where the random number sequence for these j packets is written. Is a position in the random number buffer corresponding to the element in which a value from 2 to j + 1 is newly written in the transfer number management buffer 321, and the receiving unit 312 writes j random number sequences to the respective positions in the order of generation.

Second, if the transfer number of the received packet is smaller than any of the N transfer numbers stored in the transfer number management buffer 321, that is, NO in S <b> 102 and smaller in S <b> 113, the receiving unit 312. Discards the received packet without decoding it (S114).
Note that the operation in this case is not a situation that can normally occur when the decryption device receives the packet after an unnecessarily long time has elapsed since the packet was transmitted from the encryption device.
This is an operation for discarding the packet in consideration of a malicious third party resending the packet.

Third, if the transfer number of the received packet is larger than any of the N transfer numbers stored in the transfer number management buffer 321, that is, NO in S 102 and large in S 113, the receiving unit 312. Includes a random number sequence for decrypting the received packet and newly generates a random number sequence for N packets with consecutive transfer numbers, and replaces the contents of the random number buffer 320.
The operation in this case is an operation that takes into account that the ciphertext packet transmitted from the encryption device due to cable disconnection or the like has been discarded on the network for a certain period.
Hereinafter, the operation will be described in detail.

First, the reception unit 312 requests the clock generation unit 315 to generate a random number sequence for N packets (S115).
Here, the random number sequence for which generation is requested is a random number sequence for N packets including a random number sequence for decoding the received packet and having consecutive transfer numbers.
Note that the transfer numbers of N packets with consecutive transfer numbers are M, M + 1,..., M + N−1.
The transfer number i of the received packet matches one of these.
Further, the reception unit 312 stores the transfer numbers M, M + 1,..., M + N−1 of N packets for which new random numbers are prepared in the transfer number management buffer 321 (S116). That is, the N elements of the transfer number management buffer 321 are changed to correspond to the transfer numbers M to M + N−1.

The random number generation unit 316 at this time holds a state of generating a random number sequence for decoding a packet whose transfer number has a value indicated by the maximum transfer number register 322 as its own internal state.
On the other hand, the clock generation unit 315 continuously gives a clock to the random number generation unit 316 and makes a transition to a state of generating a random number sequence for decoding a packet having a transfer number M.
The receiving unit 312 discards the random number sequence generated during this time.
Next, the clock generation unit 315 generates a clock for N packets and outputs it to the random number generation unit 316.

  Next, the random number generation unit 316 generates a random number sequence 317 (S117) and transfers it to the reception unit 312.

Next, the receiving unit 312 writes the random number sequence 317 in the random number buffer 320 (S118).
At this time, the place where the random number sequence 317 corresponding to the random number of N packets is written in the random number buffer 320 corresponds to the element in which the value from M to M + (N−1) is newly written in the transfer number management buffer 321. The random number generation unit writes N random number sequences to the respective positions in the order in which they are generated.
Next, the receiving unit 312 changes the content of the maximum transfer number register 322 to M + (N−1) (S119).

Next, the receiving unit 312 transfers the ciphertext packet 332 to the XOR unit 313.
The receiving unit 312 reads the random number sequence 317 necessary for decoding the packet from the random number buffer 320 based on the transfer number of the packet, and transfers it to the XOR unit 313 (S105).

Next, the reception unit 312 requests the clock generation unit 315 to generate a random number sequence for one packet (S106).
Here, the random number sequence that is requested to be generated is a random number sequence that is necessary for decoding a packet with a transfer number M + N that will be received in the future.
Further, the receiving unit 312 changes the element having the transfer number i in the transfer number management buffer 321 to a value obtained by adding 1 to the value (imax) indicated by the maximum transfer number register 322 (S108).

Next, the XOR unit 313 takes the exclusive OR of the random number sequence necessary for decryption of the packet and the ciphertext packet 332, generates a plaintext packet 331, and transfers it to the transmission unit 314 (S110).
Next, the transmission unit 314 transmits the plaintext packet 331 outside the apparatus. At this time, the transfer sequence number for each packet assigned to the header portion is deleted and restored.

  Next, the clock generation unit 315 generates a clock for one packet and outputs it to the random number generation unit 316.

  Next, the random number generation unit 316 generates a random number sequence 317 (S111) and transfers it to the reception unit 312.

Next, the receiving unit 312 writes the random number sequence 317 in the random number buffer 320 (S112).
At this time, the place where the random number sequence 317 is written in the random number buffer 320 is the place where the random number sequence of the packet whose transfer number is i is stored.

In order to reduce the delay when the decoding apparatus 311 decodes the packet, it is necessary to enable the operation in the first case where YES is obtained in S102 as much as possible.
For this reason, the amount of the random number sequence stored in the random number buffer 320 takes into account the delay until the packet arrives from the encryption device to the decryption device 311 and the influence of a relay device such as a router existing between the two devices. Select the appropriate one for each network.

  As described above, according to the present embodiment, whether or not the packet has already received the transfer number management buffer and the maximum transfer number so that the random number buffer of the decoding apparatus can store a random number sequence of a plurality of packets. This is a random number sequence for decoding the packet even if the order of arrival of the packets is changed by the decoding device. Is within the range prepared in the random number buffer, the packet can be decoded and relayed without increasing the delay.

  As described above, in the present embodiment, when a predetermined amount of random number sequence generated from the random number generation unit is always prepared in a predetermined buffer and the packet is received and the random number sequence in the buffer is used for decoding, the random number generation unit In the above description, a decryption apparatus has been described in which a random number sequence is newly generated and the buffer is replenished, so that packets encrypted with the stream cipher can be decrypted without increasing the delay even if the arrival order of the packets is changed.

  In the above description, the relay apparatus in IPsec or the like is exemplified as the decoding apparatus, but the decoding apparatus may be a final packet receiving apparatus.

Lastly, a hardware configuration example of the decoding device 311 described in this embodiment will be described.
FIG. 8 is a diagram illustrating an example of hardware resources of the decoding device 311 illustrated in the present embodiment.
The configuration in FIG. 8 is merely an example of the hardware configuration of the decoding device 311. The hardware configuration of the decoding device 311 is not limited to the configuration described in FIG. .

In FIG. 8, the decoding device 311 includes a CPU 911 (also referred to as a central processing unit, a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, and a processor) that executes a program.
The CPU 911 is connected to, for example, a ROM (Read Only Memory) 913, a RAM (Random Access Memory) 914, a communication board 915, a display device 901, a keyboard 902, a mouse 903, and a magnetic disk device 920 via a bus 912. Control hardware devices.
Further, the CPU 911 may be connected to an FDD 904 (Flexible Disk Drive), a compact disk device 905 (CDD), a printer device 906, and a scanner device 907. Further, instead of the magnetic disk device 920, a storage device such as an optical disk device or a memory card (registered trademark) read / write device may be used.
The RAM 914 is an example of a volatile memory. The storage media of the ROM 913, the FDD 904, the CDD 905, and the magnetic disk device 920 are an example of a nonvolatile memory. These are examples of the storage device.
A communication board 915, a keyboard 902, a mouse 903, a scanner device 907, an FDD 904, and the like are examples of input devices.
The communication board 915, the display device 901, the printer device 906, and the like are examples of output devices.

  The communication board 915 is connected to the network. For example, the communication board 915 is connected to a LAN (local area network), the Internet, a WAN (wide area network), or the like.

The magnetic disk device 920 stores an operating system 921 (OS), a window system 922, a program group 923, and a file group 924.
The programs in the program group 923 are executed by the CPU 911 using the operating system 921 and the window system 922.

The RAM 914 temporarily stores at least part of the operating system 921 program and application programs to be executed by the CPU 911.
The RAM 914 stores various data necessary for processing by the CPU 911.

The ROM 913 stores a BIOS (Basic Input Output System) program, and the magnetic disk device 920 stores a boot program.
When the decryption device 311 is activated, the BIOS program in the ROM 913 and the boot program in the magnetic disk device 920 are executed, and the operating system 921 is activated by the BIOS program and the boot program.

  The program group 923 stores programs for executing the functions described as “˜units” in the description of the present embodiment. The program is read and executed by the CPU 911.

In the description of the present embodiment, in the file group 924, “determination of”, “calculation of”, “calculation of”, “comparison of”, “generation of”, “update of”, Information, data, signal values, variable values, and parameters indicating the results of the processing described as “setting of”, “registration of”, “selection of”, etc. are “~ file” or “˜database”. It is memorized as each item.
The “˜file” and “˜database” are stored in a recording medium such as a disk or a memory. Information, data, signal values, variable values, and parameters stored in a storage medium such as a disk or memory are read out to the main memory or cache memory by the CPU 911 via a read / write circuit, and extracted, searched, referenced, compared, and calculated. Used for CPU operations such as calculation, processing, editing, output, printing, and display.
Information, data, signal values, variable values, and parameters are stored in the main memory, registers, cache memory, and buffers during the CPU operations of extraction, search, reference, comparison, calculation, processing, editing, output, printing, and display. It is temporarily stored in a memory or the like.
Also, the arrows in the flowchart described in this embodiment mainly indicate input / output of data and signals, and the data and signal values are the RAM 914 memory, the FDD904 flexible disk, the CDD905 compact disk, and the magnetic disk device. It is recorded on a recording medium such as a 920 magnetic disk, other optical disks, minidisks, and DVDs. Data and signals are transmitted online via a bus 912, signal lines, cables, or other transmission media.

  In addition, what is described as “˜unit” in the description of the present embodiment may be “˜circuit”, “˜device”, “˜device”, and “˜step”, “˜”. “Procedure” and “˜Process” may be used. That is, what is described as “˜unit” may be realized by firmware stored in the ROM 913. Alternatively, it may be implemented only by software, or only by hardware such as elements, devices, substrates, and wirings, by a combination of software and hardware, or by a combination of firmware. Firmware and software are stored as programs in a recording medium such as a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, and a DVD. The program is read by the CPU 911 and executed by the CPU 911. In other words, the program causes the computer to function as “to part” of the present embodiment. Alternatively, the procedure or method of “˜unit” in the present embodiment is executed by a computer.

  As described above, the decoding device 311 described in this embodiment includes a CPU that is a processing device, a memory that is a storage device, a magnetic disk, a keyboard that is an input device, a mouse, a communication board, and a display device that is an output device, a communication board, and the like. As described above, the computer includes the functions indicated as “to part” by using these processing devices, storage devices, input devices, and output devices.

FIG. 3 shows a configuration example of a decoding apparatus according to the first embodiment. FIG. 6 is a diagram for explaining a relationship between a random number buffer and a transfer number management buffer of the decoding device according to the first embodiment. FIG. 6 is a flowchart showing an operation example of the decoding apparatus according to the first embodiment. FIG. 6 is a flowchart showing an operation example of the decoding apparatus according to the first embodiment. FIG. 6 illustrates an example in which a random number sequence is invalidated in the decryption device according to the first embodiment. The figure which shows the structural example of the encryption apparatus of a general stream encryption. The figure which shows a general stream encryption packet relay apparatus. FIG. 3 is a diagram illustrating a hardware configuration example of the decoding device according to the first embodiment.

Explanation of symbols

  311 Decoder, 312 Receiver, 313 XOR, 314 Transmitter, 315 Clock Generator, 316 Random Number Generator, 317 Random Number Sequence, 318 Common Key / IV, 320 Random Number Buffer, 321 Transfer Number Management Buffer, 322 Maximum Transfer Number Register, 331 plaintext packet, 332 ciphertext packet.

Claims (5)

The plaintext data is encrypted from the encryption device that encrypts the plaintext data using a random number sequence that is generated by ordering the random number sequence according to a predetermined random number sequence generation algorithm and the order of the plaintext data with the data order determined. A decryption device for receiving encrypted ciphertext data,
A random number generation unit that generates an ordered random number sequence according to the same random number sequence generation algorithm as the random number sequence generation algorithm used by the cryptographic device;
A random number storage unit that stores N (N ≧ 2) random number sequences generated by the random number generation unit in association with the order;
Receiving the encrypted data transmitted from the previous SL encryptor, when the random number sequence order that matches the data order of the encrypted data received is not stored in the random number memory unit, the data of the ciphertext data received It is determined whether the order is the order before the head order in the random number storage unit or the order after the tail order, and the data order of the received ciphertext is the last order in the random number storage unit A receiving unit that requests the random number generation unit to generate N random number sequences including a random number sequence in an order that matches the data sequence of the ciphertext data in the case of an order later than the order; ,
The random number generator
When generation of N random number sequences is requested from the receiving unit, the data order of the ciphertext data received by the receiving unit is matched according to the same random number sequence generating algorithm as the random number sequence generating algorithm used by the encryption device Generate N random number sequences including random number sequences in order ,
The random number storage unit
Instead of the N random sequence stored to have the decoding apparatus characterized by storing a new N random sequence generated by the random number generating unit. The receiver is
After the N random number sequences are newly generated by the random number generation unit and the new N random number sequences are stored by the random number storage unit, the random number sequence in the order matching the data sequence of the received ciphertext data The decoding device according to claim 1 , wherein the decoding device reads out from the random number storage unit. The receiver is
It received if the data order is the order before the beginning of the sequence in the random number memory unit of ciphertext decryption apparatus according to claim 1 or 2, characterized in that discarding the ciphertext data received. The plaintext data is encrypted from the encryption device that encrypts the plaintext data using a random number sequence that is generated by ordering the random number sequence according to a predetermined random number sequence generation algorithm and the order of the plaintext data with the data order determined. A decryption device for receiving encrypted ciphertext data,
A random number generation unit that generates an ordered random number sequence according to the same random number sequence generation algorithm as the random number sequence generation algorithm used by the cryptographic device;
A random number storage unit that stores N (N ≧ 2) random number sequences generated by the random number generation unit in association with the order;
Receiving the encrypted data transmitted from the previous SL encryptor, with to read out the random number sequence order that matches the data order of the encrypted data received from the random number memory unit, the data order of the encrypted data received It is determined whether or not a random number sequence in an order before a value obtained by subtracting the value N is stored in the random number storage unit, and when the random number sequence is stored in the random number storage unit, the random number sequence is Invalidate and request the random number generator to generate a new random number sequence to replace the read random number sequence with respect to the received ciphertext data, and a new random number to replace the invalid random number sequence A receiving unit that requests generation of a sequence;
The random number generator
When the generation of a new random number sequence is requested from the receiving unit, it corresponds to the order after the last sequence in the random number storage unit according to the same random number sequence generation algorithm as the random number sequence generation algorithm used by the encryption device Generate a random number sequence,
The random number storage unit
The decryption unit stores a random number sequence newly generated by the random number generation unit in place of the random number sequence read by the reception unit with respect to the ciphertext data and the random number sequence invalidated by the reception unit. apparatus. The random number generator
The intermediate key generated in the process of generating the previous random number sequence is updated to generate the next intermediate key, and the next random number sequence is generated using at least a part of the generated next intermediate key and, since, by repeating the generation of updates and random number sequence intermediate key, decoding apparatus according to any one of claims 1 to 4, wherein the generating order the random number sequence.

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