KR20100026722A - Apparatus and method for reduction of encryption overhead in wireless access system - Google Patents

Abstract

PURPOSE: A device and a method for reducing the size of an encoding overhead are provided to reduce the size of the encoding overhead using ROC and PDU_SN instead of PN added at each MPDU(MAC Protocol Data Unit). CONSTITUTION: An MPDU encoding device of a wireless access system includes a transmission data processor(610) and a message generator(612). The transmission data processor generates an uncoded MPDU. A message generator confirms a sequence number for counting the number of the MPDU transmitted in the generation of the uncoded MPDU. The message generator increase a roll over count value for counting a roll over. The message generator generates the encode information using the roll over count value and the sequence number.

Description

Apparatus and method for reducing the size of encryption overhead in a wireless access system {APPARATUS AND METHOD FOR REDUCTION OF ENCRYPTION OVERHEAD IN WIRELESS ACCESS SYSTEM}

The present invention relates to an apparatus and method for reducing the size of encryption overhead in a wireless access system. In particular, when encrypting an MPDU according to the AES-CCM scheme, the size of encryption overhead due to PN added to each MPDU is determined. An apparatus and method for reducing the present invention.

In a wireless access system such as IEEE 802.16, each unicast connection between a terminal and a base station is associated with one security association (SA), and data is encrypted / according to the characteristics / methods / parameters assigned to the SA. By decrypting, the data is protected from attackers. Here, the SA is a collection of information related to data encryption, and includes a traffic encryption key (hereinafter, referred to as 'TEK') used for data encryption.

Currently, the IEEE 802.16 standard uses the CTR mode with CBC-MAC; CTR = CounTeR, CBC-MAC = Cipher-Block Chaining Massage Authentication, among the Advanced Encryption Standard (AES) algorithms as the data encryption / decryption method. Code) method is defined.

According to the AES-CCM method, the MPDU (MAC Protocol Data Unit) is encrypted by the MPDU generating unit as follows. First, when an L-byte plain text MPDU to be encrypted is generated, the MPDU generation unit encrypts the plain text MPDU, and then a 4-byte packet number (PN) in front of a cipher text. ) And an 8-byte integrity check value (hereinafter referred to as 'ICV') at the end of the ciphertext. In this way, the MPDU generation unit generates an encrypted MPDU. Here, the PN is not encrypted. The PN is managed for each SA and used to count the number of MPDUs transmitted for each SA. Therefore, the PN can be used to prepare for a replay attack. Here, the retransmission attack refers to a network attack method that maliciously repeats or delays data transmission.

As described above, when the MPDU is encrypted according to the AES-CCM scheme, a large encryption overhead of 12 bytes (that is, 4 bytes of PN + 8 bytes of ICV) is added to each MPDU. If the number of MPDUs is large, the size of the encryption overhead increases in proportion to the number of MPDUs, which may act as a factor of deteriorating system performance.

Accordingly, there is a need for a proposal for reducing the size of encryption overhead generated when encrypting an MPDU according to the AES-CCM scheme in a wireless access system.

An object of the present invention is to provide an apparatus and method for reducing the size of encryption overhead incurred during data encryption in a wireless access system.

The present invention provides an apparatus and method for reducing the size of encryption overhead due to PN added to each MPDU while maintaining the same security when encrypting an MPDU according to the AES-CCM scheme in a wireless access system. .

The present invention is an apparatus and method for using a roll-over count (ROC) and protocol data unit_sequence number (PDU_SN) in place of a PN added to each MPDU when encrypting an MPDU according to the AES-CCM scheme in a wireless access system. In providing.

According to an embodiment of the present invention to achieve the above object, the MPDU encryption method of a wireless access system, when the plain text MPDU is generated, the process of checking the sequence number (Sequence Number) for counting the number of MPDUs transmitted; When the checked sequence number rolls over, increasing a rollover count value for counting the rollover, and generating encryption information using the sequence number and the rollover count value. Characterized in that it comprises a.

According to an embodiment of the present invention to achieve the above object, in the MPDU decryption method of a wireless access system, when an encrypted MPDU is received, the sequence number for counting the number of MPDUs transmitted in the received encrypted MPDU Extracting a sequence number, a rollover count value for counting the rollover when the sequence number rolls over, and decoding information using the extracted sequence number and rollover count value It characterized in that it comprises a process of generating.

In order to achieve the above object, according to an embodiment of the present invention, the MPDU encryption apparatus of the wireless access system, a transmission data processing unit for generating a plain text MPDU, and when the plain text MPDU is generated, for counting the number of MPDUs transmitted Check the sequence number, increase the rollover count value for counting the rollover when the checked sequence number rolls over, and use the sequence number and rollover count value. It characterized in that it comprises a message generating unit for generating encrypted information.

In order to achieve the above object, according to an embodiment of the present invention, an MPDU decryption apparatus of a wireless access system includes a physical layer receiving unit for receiving an encrypted MPDU, and for counting the number of MPDUs transmitted in the received encrypted MPDU. Extracts a sequence number and a rollover count value for counting the rollover when the sequence number rolls over, and decodes information using the extracted sequence number and rollover count value. Characterized in that it comprises a message processing unit for generating.

In the present invention, when encrypting an MPDU according to the AES-CCM scheme in a wireless access system, by using the ROC and PDU_SN in place of the PN added to each MPDU, the encryption per MPDU due to the PN while maintaining the same security This has the advantage of reducing the size of the overhead. For example, if the ROC is 2 bytes, the overhead of about 2 bytes per MPDU can be reduced.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention uses the Roll-Over Count (ROC) and Protocol Data Unit_Sequence Number (PDU_SN) instead of the PN added to each MPDU when encrypting the MPDU according to the AES-CCM scheme in the radio access system. An apparatus and method for reducing the size of encryption overhead per MPDU due to the above will be described.

Meanwhile, in the radio access system, all MPDUs include PDU_SN for indicating the transmission order of MPDUs. Here, the PDU_SN may be used to count the number of MPDUs that are encrypted and transmitted. Therefore, in the present invention, in order to reduce the encryption overhead of adding 4 bytes of PN to each MPDU when encrypting the MPDU according to the AES-CCM scheme in the radio access system, instead of the PN, always in the MPDU The proposed method uses the included sequence number, that is, PDU_SN, to cope with retransmission attacks using less overhead than the conventional method.

To this end, two counters, a roll-over counter and a retransmission counter, are newly defined as follows. Here, the rollover counter is a counter that increases by one when PDU_SN increases and then reaches 0 again and then goes back to zero. The retransmission counter is a counter used only for retransmission and is a counter indicating the number of retransmissions of the MPDU.

1 is a diagram illustrating a format of an MPDU encrypted according to the AES-CCM scheme in a wireless access system according to the present invention.

Referring to FIG. 1, the L-byte plaintext MPDU 100 to be encrypted includes a protocol data unit_sequence number (PDU_SN) 101 and a plaintext payload indicating a transmission order of the corresponding MPDU. It comprises a 103. Here, after encrypting the plain text payload 103 to generate an encrypted payload (Cipher-text payload) and ICV 113, the PDU_SN (101) and two bytes in front of the encrypted (pay) (encrypted) payload A roll-over count (ROC) 111 is added and an 8-byte ICV 113 is added at the back to generate an encrypted MPDU 110. At this time, the ROC 111 and the PDU_SN 101 are non-encrypted. Here, the ROC 111 and the PDU_SN 101 are managed for each connection, among which the PDU_SN 101 is incremented by one each time the MPDU is transmitted. In addition, the ROC 111 is a value counted by the roll over counter, and is increased by one when the PDU_SN 101 increases and reaches a maximum value and then goes back to zero. The TEK is updated before the ROC 111 mapped to the SA overflows, and when the TEK is updated to a new value, the ROC 111 of all connections of the SA is reset to zero.

Here, when the plain text payload 103 is a retransmission for a previous payload, a 3-bit Re-Tx_COUNT representing a retransmission count of the corresponding MPDU is converted into a general MAC (GMAC) header or the encryption. Not included in the ROC 111 or PDU_SN 101 can be included as one piece of information. If not retransmission, the Re-Tx_COUNT is null (ie, 0). At this time, the Re-Tx_COUNT is also non-encrypted. Here, the encrypted MPDU 110 to be retransmitted continues to use the ROC 111 and PDU_SN 101 used during the initial transmission.

Encrypting MPDUs using the AES-CCM scheme according to the prior art causes a large encryption overhead of 12 bytes (i.e. 4 bytes of PN + 8 bytes of ICV) for each MPDU. However, if the MPDU is encrypted using the AES-CCM scheme proposed in the present invention, in the initial transmission, an encryption overhead of 10 bytes (that is, 2 bytes of ROC + 8 bytes of ICV) occurs for each MPDU, and retransmission is performed. In this case, each MPDU incurs 10 bytes (i.e. 2 bytes of ROC + 8 bytes of ICV) + 3 bits (Re-Tx_COUNT) encryption overhead, which is much more than the encryption overhead incurred in the prior art. It has a small size.

Meanwhile, in the AES-CCM scheme of the current standard, a 13-byte nonce (NONCE) is used as basic information required as an initial value for data encryption / decryption. The nonce according to the present invention is configured, for example, as shown in Table 1 below.

Byte number 0-2 3-7 8 9-10 11-12 Field GMAC Header Reserved Re-Tx_COUNT ROC PDU_SN Contents GMAC Header omitting HCS 0x0000000000 0x00 + Re-Tx_COUNT 0x0000 + ROC 0x0000 + PDU_SN

Here, as shown in Table 1, the nonce used for encrypting / decrypting data in the AES-CCM method according to the present invention is referred to as a 3-byte GMAC header (General MAC header: hereinafter referred to as 'GMH'). ) Field, 5 bytes of Reserved field, 1 byte of Re-Tx_COUNT field, 2 bytes of ROC field, and 2 bytes of PDU_SN field. Herein, the GMH field stores information related to a message. A field indicating a message type except for a header check sum field for checking a header error, and a length of an MPDU. It includes a field to indicate, and a Connection IDentifier (CID) field for identifying a connection. The Re-Tx_COUNT field is included only when retransmitting the corresponding MPDU. In the case of the retransmission, since the ROC and PDU_SN used in the previous transmission are continuously used, the MPDU is transmitted using a different nonce each time the MPDU is transmitted or retransmitted. It can be encrypted.

2A and 2B are flowcharts illustrating a procedure of a method for encrypting an MPDU according to an AES-CCM scheme by a terminal in a wireless access system according to an embodiment of the present invention.

2A and 2B, the UE checks whether a plain text MPDU for transmission occurs in step 201. Here, the plain text MPDU is configured to include PDU_SN, as shown in FIG. 1. When the occurrence of the plaintext MPDU is detected, the terminal checks whether the transmission of the plaintext MPDU in which the occurrence is detected is retransmission in step 203.

When the transmission of the plaintext MPDU in which the occurrence is detected in step 203 is retransmitted, the MPDU must be distinguished from the encrypted MPDU in the previous transmission for security stability. In step 205, the UE re-Tx_COUNT of the retransmission counter. Is incremented by 1 and updated. In step 207, the updated Re-Tx_COUNT is included in the GMAC header. Here, the GMAC header including the updated Re-Tx_COUNT may be transmitted in plain text without being encrypted later, and the updated Re-Tx_COUNT may be included in ROC or PDU_SN instead of the GMAC header.

On the other hand, when the transmission of the plaintext MPDU in which the occurrence is detected in step 203 is the initial transmission, the terminal checks PDU_SN included in the plaintext MPDU in step 209, and the checked PDU_SN is rolled over in step 211. roll over) to check whether it has a value of 0. When the checked PDU_SN is not rolled over, the terminal proceeds to step 219. On the other hand, when the PDU_SN rolls over and has a value of 0, the UE updates the ROC of the rollover counter by 1 in step 213 and updates the updated ROC in step 215. Check whether it is. If the updated ROC has a maximum value, the terminal determines that the TEK currently being used is sufficiently used, and in step 217, transmits a KEY-REQ message requesting the TEK to be updated to the base station. Proceed to step. On the other hand, if the updated ROC does not have a maximum value in step 215, the terminal proceeds directly to step 219.

Thereafter, the terminal checks whether the TEK has been updated in step 219. That is, it is checked whether a KEY-RSP message including a new TEK is received from the base station in response to the KEY-REQ message. When the TEK is updated, the terminal resets ROCs of all the connections included in the corresponding SA to 0 in step 221 and then proceeds to step 223. On the other hand, when the TEK has not been updated, that is, if the TEK update request has not been requested or the KEY-RSP message has not been received yet, the terminal proceeds directly to step 223, where the original Use TEK and ROC.

Thereafter, the terminal generates a nonce using a GMAC header, Re-Tx_COUNT, ROC, and PDU_SN in step 223, and encrypts a payload using TEK and the generated nonce in step 225. Here, in case of retransmission, the ROC and PDU_SN used in the previous transmission are continuously used. The nonce may be configured as shown in Table 1, and when the generated nonce is substituted into an existing AES-CCM cipher, an ICV for integrity check of the encrypted MPDU is generated.

Thereafter, in step 227, the UE adds a ROC and a PDU_SN / ICV to the front / back of the encrypted payload, and adds a GMAC header and a cyclic redundancy check (CRC) in step 229 to the physical layer. To send. In this case, the physical layer transmits the encrypted MPDU to the terminal.

Thereafter, the terminal terminates the algorithm according to the present invention.

3 is a flowchart illustrating a procedure of a method for a base station to decrypt an MPDU encrypted according to an AES-CCM scheme in a wireless access system according to an embodiment of the present invention.

Referring to FIG. 3, the base station determines whether an encrypted MPDU from the terminal is received from the physical layer in step 301. When the encrypted MPDU is received, the base station extracts and acquires an ROC, PDU_SN, Re-Tx_COUNT, and ICV from the received encrypted MPDU in step 303, and in step 305, the extracted ROC, PDU_SN, and Re-Tx_COUNT. Check whether there is a possibility of a Replay Attack using. Here, the Re-Tx_COUNT may be obtained through a GMAC header (or ROC or PDU_SN) of the encrypted MPDU.

If there is a possibility of the retransmission attack, the base station proceeds to step 313 and discards the received MPDU, and then terminates the algorithm according to the present invention. On the other hand, when there is no possibility of the retransmission attack, the base station checks whether the encrypted MPDU is intact using the extracted ICV in step 307. If the encrypted MPDU is not intact, the base station proceeds to step 313 and discards the received MPDU and ends the algorithm according to the present invention.

On the other hand, when the encrypted MPDU is intact, the base station generates a nonce using the GMAC header, Re-Tx_COUNT, ROC, and PDU_SN in step 309, and in step 311, the TEK and the generated terminal of the terminal. A nonce is used to decrypt the payload of the encrypted MPDU, thereby generating a decrypted MPDU. As described above, when the terminal recognizes that the MPDU is encrypted with the updated TEK, the base station also performs encryption / decryption using the updated TEK.

The base station then terminates the algorithm according to the invention.

4A and 4B are flowcharts illustrating a procedure of a method for encrypting an MPDU according to an AES-CCM scheme by a base station in a wireless access system according to an embodiment of the present invention.

Referring to FIGS. 4A and 4B, most of cases are the same as those of the terminals of FIGS. 2A and 2B. However, since the terminal is currently managed by the terminal, the process for the case where the ROC reaches the maximum value, namely, There is a difference in that steps 215 and 217 of FIGS. 2A and 2B are not performed by the base station of FIGS. 4A and 4B. That is, the UE, with reference to the ROC value of the MPDU received from the base station, requests the update of the TEK to the base station through a KEY-REQ message if necessary, and the received base station is a KEY-RSP message including the new TEK. Send to the terminal. The terminal updates the TEK after receiving the KEY-RSP message. In addition, when the base station has encrypted the MPDU received from the terminal with the updated TEK, the base station encrypts the MPDU using the updated TEK thereafter, whereby the TEK of the terminal is updated in steps 415 of FIGS. 4A and 4B. You can check whether or not.

5 is a flowchart illustrating a procedure of a method for a terminal to decrypt an MPDU encrypted according to an AES-CCM scheme in a wireless access system according to an embodiment of the present invention.

Referring to FIG. 5, the terminal is mostly the same as the base station of FIG. 3, except that processing (steps 509 and 517) for the case where the ROC reaches a maximum value is further added. In other words, the terminal checks whether the ROC of the MPDU received in step 509 has the maximum value, and when the ROC has the maximum value, the terminal determines that the currently used TEK is sufficiently used. Sends a KEY-REQ message requesting the TEK update to the base station.

6 is a block diagram illustrating a device configuration of a base station and a terminal in a wireless access system according to an embodiment of the present invention. Since the base station and the terminal according to the present invention have the same device configuration, it will be described in the following description of the operation of the base station and the terminal using a single device configuration.

As shown, the base station and the terminal is a physical layer receiver 600, a message processor 602, a controller 606, a received data processor 608, a transmission data processor 610, a message generator 612, a physical layer It comprises a transmitter 616. Here, the message processing unit 602 includes a decryption unit 604 therein, and the message generator 612 includes an encryption unit 614 therein.

Referring to FIG. 6, the operation of the terminal will be described first.

The physical layer receiver 600 provides a control message and data received from a base station to the message processor 602.

The message processing unit 602 performs an authentication on the control message from the physical layer receiving unit 600 through an internal decoder 604, and if the authentication is successful, provides the control message to the control unit 606. do. In this case, the authentication is performed using the CMAC, and if the authentication fails, the message processing unit 602 discards the control message. If a new TEK is transmitted to the controller 606 through the KEY-RSP message among the control messages, the controller 606 notifies the message generator 612 of the update to the new TEK, thereby generating the message. In section 612, the MPUD is encrypted using the new TEK. In addition, the message processor 602 decodes data from the physical layer receiver 600 through an internal decoder 604 and provides the decoded MPDU to the received data processor 608. In addition, when the ROC included in the encrypted MPDU from the base station is a maximum value, the message processing unit 602 requests the controller 606 to update the TEK. In this case, the controller 606 generates information for requesting an update to a new TEK and provides the message to the message generator 612, and the message generator 612 generates a KEY-REQ message to generate a physical layer transmitter ( 616 is transmitted to the base station.

The received data processor 608 provides the received data to a higher layer.

The transmission data processing unit 610 provides the message generation unit 612 with data to be transmitted.

The message generator 612 generates the plain text MPDU using the transmission data from the transmission data processor 610, encrypts the generated plain text MPDU through an internal encryption unit 614, and then transmits the physical layer transmitter. Provided at 616. At this time, when the usage of the TEK used for the encryption increases, so that the ROC reaches a maximum value, the message generator 612 requests the controller 606 to update the TEK. Here, when the controller 606 generates information for requesting an update to a new TEK and provides the message generator 612 to the message generator 612 according to the TEK update request, the message generator 612 sends a message as authentication information. Generates a KEY-REQ message containing a code used for authentication of the (Cipher-based Message Authentication Code: hereinafter referred to as 'CMAC'), and provides the generated KEY-REQ message to the physical layer transmitter 616 do. In addition, when the message generator 612 receives a response indicating an update to a new TEK through the controller 606 while encrypting the plain text MPDU through the internal encryption unit 614, all connections included in the corresponding SA are received. Their ROCs are reset to zero, and then encrypted using the new TEK.

The physical layer transmitter 616 transmits the control message and data from the message generator 612 to the base station.

Next, the operation of the base station is as follows.

The physical layer receiver 600 provides a control message and data received from a terminal to the message processor 602.

The message processing unit 602 performs an authentication on the control message from the physical layer receiving unit 600 through an internal decoder 604, and if the authentication is successful, provides the control message to the control unit 606. do. In this case, the authentication is performed using the CMAC, and if the authentication fails, the message processing unit 602 discards the control message. If an update request to a new TEK is transmitted to the control unit 606 through a KEY-REQ message among the control messages, the control unit 606 generates a TEK to be updated using a random number, and then, controls the control unit 606. It is provided to the message generating unit 612 through. In this case, the message generator 612 generates a KEY-RSP message including the TEK and transmits the KEY-RSP message to the terminal through the physical layer transmitter 616. In addition, the message processor 602 decodes data from the physical layer receiver 600 through an internal decoder 604 and provides the decoded MPDU to the received data processor 608. In this case, when the data encrypted with the updated TEK is received, the message processing unit 602 provides the updated TEK to the message generating unit 612 through the control unit 606, and the message generating unit ( 612 to encrypt the MPDU using the updated TEK.

The received data processor 608 provides the received data to a higher layer.

The transmission data processing unit 610 provides the message generation unit 612 with data to be transmitted.

The message generator 612 generates the plain text MPDU using the transmission data from the transmission data processor 610, encrypts the generated plain text MPDU through an internal encryption unit 614, and then transmits the physical layer transmitter. Provided at 616. Here, if a new TEK is provided through the controller 606 while encrypting the plain text MPDU, the message generator 612 resets the ROCs of all the connections included in the corresponding SA to 0, and thereafter a new TEK. Encryption is performed using.

The physical layer transmitter 616 transmits the control message and data from the message generator 612 to the terminal.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

1 is a diagram illustrating a format of an MPDU encrypted according to the AES-CCM scheme in a wireless access system according to the present invention;

2A and 2B are flowcharts illustrating a procedure of a method for encrypting an MPDU according to an AES-CCM scheme by a terminal in a wireless access system according to an embodiment of the present invention;

3 is a flowchart illustrating a procedure of a method for a base station to decrypt an MPDU encrypted according to an AES-CCM scheme in a wireless access system according to an embodiment of the present invention;

4A and 4B are flowcharts illustrating a procedure of a method for encrypting an MPDU according to an AES-CCM scheme by a base station in a wireless access system according to an embodiment of the present invention;

5 is a flowchart illustrating a procedure of a method for a terminal to decrypt an MPDU encrypted according to an AES-CCM scheme in a wireless access system according to an embodiment of the present invention;

6 is a block diagram showing the device configuration of a base station and a terminal in a wireless access system according to an embodiment of the present invention.

Claims (26)

In the MPDU (MAC Protocol Data Unit) encryption method of a wireless access system, When a plain text MPDU is generated, checking a sequence number for counting the number of MPDUs transmitted; Increasing a rollover count value for counting the rollover when the identified sequence number rolls over; Generating encryption information using the sequence number and the rollover count value. The method of claim 1, The encryption information is characterized in that the nonce (NONCE). The method of claim 1, The encryption information may include at least one of the sequence number, the rollover count value, a retransmission count count value, and a media access control (MAC) header. The method of claim 1, wherein the operation subject of the encryption method of the MPDU is a terminal. Transmitting a KEY-REQ message requesting an update of a traffic encryption key to a base station when the increased rollover count value is a maximum value; And when a KEY-RSP message including a new traffic encryption key is received from the base station, resetting a rollover count value of connections included in a corresponding security association (SA) to zero. . The method of claim 1, wherein when the operation subject of the encryption method of the MPDU is a base station, When the MPDU encrypted with the new traffic encryption key is received from the terminal, updating the traffic encryption key used for payload encryption with the new traffic encryption key; And resetting the roll over count value of the connections included in the corresponding security association to zero. The method of claim 1, Encrypting a payload using at least one of the generated encryption information and the traffic encryption key; Among the sequence number, the rollover count value, the number of retransmission counts, the MAC (Media Access Control) header, the cyclic redundancy check (CRC), and the integrity check value (ICV) before and after the encrypted payload. Including at least one to generate an encrypted MPDU. The method of claim 1, And when the plain text MPDU is generated for retransmission, including the information on the number of retransmissions in a Media Access Control (MAC) header. In the MPDU (MAC Protocol Data Unit) decoding method of a wireless access system, When an encrypted MPDU is received, a sequence number for counting the number of MPDUs transmitted in the received encrypted MPDU, and counting the rollover when the sequence number rolls over Extracting a rollover count value for Generating decoding information using the extracted sequence number and rollover count value. The method of claim 8, The decoding information is characterized in that the nonce (NONCE). The method of claim 8, The decoding information may include at least one of the sequence number, the rollover count value, a retransmission count count value, and a media access control (MAC) header. The method of claim 8, And decrypting a payload using at least one of the generated decryption information and the traffic decryption key. The method of claim 8, When the encrypted MPDU is received, extracting at least one of a retransmission count count value and an integrity check value (ICV) from the received encrypted MPDU; Checking the possibility of a retransmission attack using at least one of the extracted sequence number, rollover count value, and retransmission count count value; Checking the integrity of the data by using the extracted ICV; Discarding the received MPDU when it is detected that there is a possibility of the retransmission attack or the data is intact. The method of claim 8, wherein when the operation subject of the decoding method of the MPDU is a terminal, And transmitting a KEY-REQ message requesting an update of a traffic decryption key to a base station when the extracted roll over count value is a maximum value. In the MAC Protocol Data Unit (MPDU) encryption apparatus of a wireless access system, A transmission data processing unit for generating the plain text MPDU, When the plaintext MPDU is generated, confirm a sequence number for counting the number of MPDUs transmitted, and roll over for counting the rollover when the identified sequence number is rolled over. And a message generator for generating encryption information using the sequence number and the rollover count value after increasing the count value. The method of claim 14, The encryption information is characterized in that the nonce (NONCE) device. The method of claim 14, The encryption information may include at least one of the sequence number, the roll over count value, a retransmission count count value, and a media access control (MAC) header. 15. The method of claim 14, wherein the operation subject of the MPDU encryption is a terminal, The message generator, when the increased rollover count value is the maximum value, generates a KEY-REQ message requesting the update of the traffic encryption key and transmits it to the base station, and the KEY-RSP including a new traffic encryption key from the base station And when the message is received, resets the rollover count value of the connections included in the corresponding security association (SA) to zero. 15. The method of claim 14, wherein when the operating entity of the MPDU encryption is a base station, When the message generation unit receives an MPDU encrypted with a new traffic encryption key from the terminal, the message generation unit updates the traffic encryption key used for payload encryption with the new traffic encryption key and rolls up connections included in the corresponding security association (SA). And reset the over count value to zero. The method of claim 14, The message generator encrypts a payload using at least one of the generated encryption information and the traffic encryption key, and includes the sequence number, the rollover count value, the number of retransmission counts, before and after the encrypted payload, And generating at least one of a Media Access Control (MAC) header, a Cyclic Redundancy Check (CRC), and an Integrity Check Value (ICV) to generate an encrypted MPDU. The method of claim 14, wherein the message generating unit, And when the plain text MPDU is generated for retransmission, including the information on the number of retransmissions in a MAC (Media Access Control) header. In the MPDU (MAC Protocol Data Unit) decoding apparatus of a wireless access system, A physical layer receiver for receiving an encrypted MPDU; Extracting, from the received encrypted MPDU, a sequence number for counting the number of MPDUs transmitted, and a rollover count value for counting the rollover when the sequence number rolls over; And a message processor for generating decryption information using the extracted sequence number and rollover count value. The method of claim 21, The decoding information is characterized in that the nonce (NONCE) device. The method of claim 21, The decoding information may include at least one of the sequence number, the rollover count value, a retransmission count count value, and a media access control (MAC) header. The method of claim 21, wherein the message processing unit, And decrypting a payload using at least one of the generated decryption information and the traffic decryption key. The method of claim 21, wherein the message processing unit, When the encrypted MPDU is received, at least one of a retransmission count count value and an integrity check value (ICV) is extracted from the received encrypted MPDU, and the extracted sequence number, rollover count value, and retransmission is performed. When the possibility of the retransmission attack is checked by using at least one of the count value, and the integrity of the data is checked by using the extracted ICV, when the possibility of the retransmission attack exists or when the data is detected to be intact. And discarding the received MPDU. The method of claim 21, wherein the operation subject of the MPDU decoding is a terminal. And generating a KEY-REQ message requesting an update of the traffic decryption key and transmitting the generated KEY-REQ message to the base station when the extracted roll over count value is a maximum value.

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