Abstract:
In a wireless communication system, a transmission device includes: a generation section configured to encrypt information shared between the transmission device and a reception device using first encryption information which changes in accordance with the sequence information, and to generate encrypted data for the shared information; a transmission section configured to transmit, to the reception device, the encrypted data for the shared information; a reception section configured to receive, from the reception device, information about a result of a comparison between the shared information and a result of decrypting the encrypted data for the shared information using second encryption information which changes in accordance with the sequence information assigned to the encrypted ciphering-process-target data at the reception device; and a determination section configured to determine, based on the comparison result, whether the first and second encryption information matches or not.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-191017, filed on Jul. 24, 2008, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to a transmission device and a reception device for use in a wireless communications system. 
       BACKGROUND 
       [0003]      FIG. 5  illustrates the network configuration of a 3rd Generation Partnership Project (3GPP) system. This 3GPP system is configured to include Access Gate Ways (aGWs)  11  and  12  each being a host network, Evolved NodeBs (eNBs)  13  to  15 , and a User Equipment device (UE)  16 . 
         [0004]    The aGWs  11  and  12  each correspond to a Mobile Management Entity/User Plane Entity (MME/UPE), and the eNBs  13  to  15  configure an Evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network (E-UTRAN). 
         [0005]    The interface between the aGWs  11  and  12  and the eNBs  13  to  15  is referred to as interface S 1 , and the interfaces among the eNBs  13  to  15  are each referred to as interfaces X 2 . These interfaces may each be wired for physical communications. On the other hand, the interface between the eNBs  13  to  15  and the UE  16  is referred to as an interface Uu, and the interface Uu may be wireless for physical communications. 
         [0006]      FIG. 6  illustrates an example of a user protocol stack between the eNBs and the UE in the above wireless communications system. This user protocol stack includes a physical (PHY) layer, a Media Access Control (MAC) layer, a Radio Link Control (RLC) layer, and a Packet Data Convergence Protocol (PDCP) layer. Between the eNBs and the UE, for preventing communications interception by third parties, the PDCP layer is subjected to a ciphering process. A ciphering process may include both ciphering and deciphering. 
         [0007]      FIG. 7  illustrates a Protocol Data Unit (PDU) format of the PDCP layer, which is hereinafter referred to as PDCP PDU. The PDCP PDU includes elements “D/C”, “PDU Type”, “SN”, and “PDCP SDU” (Service Data Unit). 
         [0008]    The element “D/C” indicates “0” if the PDU is a control PDU, and indicates “1” if the PDU is a data PDU. The element “PDU Type” is made up of three reserved bits. The element “SN” indicates a sequence number, and the element “PDCP SDU” indicates audio data, packet data, and others. Among such elements, the element “PDCP SDU” is the part to be subjected to the ciphering process. 
         [0009]      FIG. 8  illustrates an example of a ciphering process to be executed when the PDCP PDU is transmitted from the UE to any of the eNBs. This ciphering process is executed similarly when the PDCP PDU is transmitted from the eNB to the UE. 
         [0010]    The UE is configured to include a key generation section  21 , and a computation section  22 . The key generation section  21  generates a KEYSTREAM BLOCK from parameters used for the ciphering process (hereinafter, referred to as “encryption information”) under the management of the UE using an f8 algorithm. The encryption information includes parameters “COUNT-C”, “BEARER”, “DIRECTION”, “LENGTH”, and “CK”. 
         [0011]    The computation section  22  encrypts Plain Text data that is a subject to the ciphering process by calculating an exclusive OR of the Plain Text and the KEYSTREAM BLOCK, thereby generating a Cipher Text. The UE sets the resulting Cipher Text in the PDCP SDU, assigns a value to the element “SN,” and transmits the Cipher Text to the eNB. 
         [0012]    The eNB is configured to include a key generation section  23 , and a computation section  24 . The key generation section  23  generates another KEYSTREAM BLOCK from the encryption information under the management of the eNB also using the f8 algorithm. The computation section  24  calculates an exclusive OR of the provided Cipher Text and the KEYSTREAM BLOCK, thereby decrypting the Cipher Text and restoring the Plain Text. 
         [0013]    As to the encryption information under the management of the UE and the eNB, the parameters other than the parameter “COUNT-C” are each fixed in value, and these values are each shared by the UE and the eNB. On the other hand, the parameter “COUNT-C” is configured by an element “long-term Hyper Frame Number (HFN)” and an element “short-term sequence number (SN)”. The value in the element “HFN” is incremented every time the element “short-period SN” goes through all the values in the sequence. The value in the element“SN” here is the value assigned to the element “SN” in the PDCP PDU. That is, the parameter “COUNT-C” under the respective management of the UE and eNB has the same value for any similar PDCP PDU. 
         [0014]    A wireless communications system including a UTRAN as an alternative to the E-UTRAN is also known to execute the ciphering process (see International Publication Pamphlet No. WO2005/025127). 
         [0015]    However, the wireless communications system described above has the following problem. 
         [0016]    In certain circumstances data loss may occur, e.g., when the radio quality is poor, and when the Quality of Service (Qos) control is performed over any wired section, the parameter “COUNT-C” may vary in value between the UE and the eNB. When the parameter “COUNT-C” varies in value as such in the encryption information, the KEYSTREAM BLOCK to be generated may also vary between the transmission and reception ends. As a result, on the reception end, the result of restoration from the provided Cipher Text will not be the same Plain Text as on the transmission end. 
         [0017]      FIG. 9  illustrates how the parameter “COUNT-C” shows a change in the previous wireless communications system. When the element“HFN” indicates 1, the UE transmits the PDCP PDUs respectively assigned with the values of 0 to 4095 for the element “SN” to the eNB. When the element “SN” indicates “0” again after going through all the values in the sequence, the value in the element of “HFN” is incremented to 2, and the PDCP PDUs respectively assigned with the values of 0 to 4095 in the element “SN” are transmitted again to the eNB. The UE repeats such a transmission operation. 
         [0018]    When the element “HFN” is 0 and the element “SN” is 4095, if the eNB is provided with the PDCP PDU in which the element “SN” is 0, the eNB sets the initial value 0 to the element “SN”, and increments the element “HFN” by 1. In this case, when the PDCP PDUs respectively assigned the values 1 to 4095 in the element “SN” are not provided to the eNB, and when the next PDCP PDU assigned with the value 0 in the element “SN” is also not provided to the eNB, the element “SN” in the eNB remains at 0 with no increment. 
         [0019]    Next, when the element “HFN” in the UE is 2, if the eNB is provided with the PDCP PDUs respectively assigned the values 1 to 4095 in the element “SN”, the eNB increments the value in the element “SN”. Thereafter, when the element “SN” is 0 after going through all the values in the sequence, the eNB increments the element “HFN” by 2. At this point in time, however, the element “HFN” in the UE is already 3. 
         [0020]    Thus, in the second or later PDCP PDUs assigned the value 1 for the element “SN”, the parameter “COUNT-C” varies in value between the UE and the eNB, and thus the eNB cannot correctly restore the Plain Text from the provided Cipher Text. 
         [0021]    This occurrence of the Plain Text restoration on the reception end being different from the Plain Text on the transmission end is referred to as “asynchronization of ciphering.” The problem here is that, on the reception end, there may be no way to detect such asynchronization of ciphering because the expected value of the Plain Text is not known. If such asynchronization of ciphering occurs, with the resulting audio service, the audio on the reception end will sound unusual, and with the resulting packet service, the throughput may be reduced. 
       SUMMARY 
       [0022]    According to an aspect of the invention, a transmission device encrypts ciphering-process-target data using encryption information, and assigns sequence information to the encrypted ciphering-process-target data for transmission to a reception device. The transmission device includes a generation section configured to encrypt information shared between the transmission device and the reception device using first encryption information which changes in accordance with the sequence information, and generate encrypted data for the shared information; a transmission section configured to transmit, to the reception device, the encrypted data for the shared information; a reception section configured to receive, from the reception device, information about a result of a comparison between the shared information and a result of decrypting the encrypted data for the shared information using second encryption information which changes in accordance with the sequence information assigned to the encrypted ciphering-process-target data at the reception device; and a determination section configured to determine, based on the information about the comparison result, whether or not a match is observed between the first and second encryption information. 
         [0023]    According to an aspect of the invention, a reception device receives, from a transmission device, ciphering-process-target data encrypted using encryption information and assigned with sequence information. The reception device includes a reception section configured to receive, from the transmission device, information shared between the transmission device and the reception device encrypted by the transmission device using first encryption information which changes in accordance with the sequence information; a determination section configured to decrypt the encrypted data for the shared information using second encryption information which changes in accordance with the sequence information assigned to the encrypted ciphering-process-target data, and compares a result of the decryption result and the shared information; and a transmission section that transmits, to the transmission device, information about a result of the comparison made between the decryption result and the shared information. 
         [0024]    The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0025]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a diagram illustrating the configurations of communications devices of an embodiment; 
           [0027]      FIG. 2  is a diagram illustrating the correlation between PDCP PDUs and encryption information; 
           [0028]      FIG. 3  is a flowchart of determination ciphering synchronization control; 
           [0029]      FIG. 4  is a diagram illustrating a change of a parameter “COUNT-C” in a wireless communications system of the embodiment; 
           [0030]      FIG. 5  is a diagram illustrating the configuration of the wireless communications system; 
           [0031]      FIG. 6  is a diagram illustrating a user protocol stack; 
           [0032]      FIG. 7  is a diagram illustrating a PDCP PDU format; 
           [0033]      FIG. 8  is a diagram illustrating a ciphering process; and 
           [0034]      FIG. 9  is a diagram illustrating a change of the parameter “COUNT-C” in a previous wireless communications system. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    The best mode for carrying out the invention is described in detail below by referring to the accompanying drawings. 
         [0036]    In the embodiment, a communications device transmits data at regular intervals for checking the synchronization of ciphering, and through such data transmission, checks the state of the synchronization of ciphering. When the synchronization of ciphering is not observed, encryption information under the management of the transmission end is transmitted to the reception end for recovering the synchronization of ciphering. 
         [0037]      FIG. 1  is a diagram illustrating configurations of communications devices of the embodiment. In  FIG. 1 , communications devices  101  and  102  respectively correspond to the UE and the eNB. 
         [0038]    The communications device  101  is configured to include a ciphering synchronization determination control section  111 , a user data processing section  112 , a generation section  113 , an analysis section  114 , a transmission section  115 , and a reception section  116 . The ciphering synchronization determination control section  111  includes the key generation section  21  and the computation section  22 , and the user data processing section  112  includes the key generation section  23  and the computation section  24 , as illustrated in  FIG. 8 . 
         [0039]    The ciphering synchronization determination control section  111  generates a cipher text of control data for checking and recovering the synchronization of ciphering. The resulting cipher text is forwarded to the generation section  113 . The user data processing section  112  generates a cipher text of user data subject to the ciphering process, and forwards the resulting cipher text to the generation section  113 . The generation section  113  generates a PDCP PDU in which the element “PDCP SDU” is set with the cipher text of the control data or of the user data, and the transmission section  115  transmits the resulting PDCP PDU to the communications device  102 . 
         [0040]    The reception section  116  receives the PDCP PDU from the communications device  102 . The analysis section  114  analyzes the PDCP PDU and forwards the cipher text of the control data set in the element “PDCP SDU” to the ciphering synchronization determination control section  111 . The analysis section  114  then forwards the cipher text of the user data to the user data processing section  112 . The ciphering synchronization determination control section  111  decrypts the cipher text, and restores the plain text of the control data, thereby performing control for checking and recovering the synchronization of ciphering. The user data processing section  112  decrypts the cipher text, and restores the plain text of the user data, thereby processing the user data. 
         [0041]    The communications device  102  is configured to include a reception section  121 , a transmission section  122 , an analysis section  123 , a generation section  124 , a ciphering synchronization determination control section  125 , and a user data processing section  126 . The ciphering synchronization determination control section  125  includes the key generation section  21  and the computation section  22 , and the user data processing section  126  includes the key generation section  23  and the computation section  24 , as illustrated in  FIG. 8 . 
         [0042]    The reception section  121  is provided with the PDCP PDU from the communications device  101 . The analysis section  123  analyzes the PDCP PDU, and forwards the cipher text of the control data set in the element “PDCP SDU” to the ciphering synchronization determination control section  125 . The analysis section  114  then forwards the cipher text of the user data to the user data processing section  126 . 
         [0043]    The ciphering synchronization determination control section  125  decrypts the cipher text, and restores the plain text of the control data, thereby performing control for checking and recovering the synchronization of ciphering. The ciphering synchronization determination control section  125  generates a cipher text of the control data, and forwards the resulting cipher text to the generation section  124 . The user data processing section  126  decrypts the cipher text, and restores the plain text of the user data, thereby processing the user data. The user data processing section  126  also generates a cipher text of the user data, which is subject to the ciphering process, and forwards the resulting cipher text to the generation section  124 . 
         [0044]    The generation section  124  generates a PDCP PDU in which the element “PDCP SDU” is set with the cipher text of the control data or of the user data, and the transmission section  122  forwards the resulting PDCP PDU to the communications device  101 . 
         [0045]      FIG. 2  is a diagram illustrating the correlation between the PDCP PDUs and the encryption information for use in the wireless communications system of this embodiment. In the ciphering process for any of the PDCP PDUs, the parameters in the encryption information other than the parameter “COUNT-C” take values at the time of a call setup. On the other hand, the parameter “COUNT-C” takes a value in accordance with the type of the corresponding PDCP PDU. 
         [0046]    When the PDCP PDU is user data (D/C=1), the parameter “COUNT-C” takes the value currently in use. The PDCP PDU (D/C=0) of the control data may be classified into four types depending on the value in the element “TYPE”: ciphering synchronization data when the element “TYPE” indicates “010”, ciphering synchronization result data when the element “TYPE” indicates “011”, encryption information data when the element “TYPE” indicates “100”, and encryption information update result data when the element “TYPE” indicates “101”. 
         [0047]    Among such types of data, the ciphering synchronization data takes the value currently in use as the parameter “COUNT-C”, and the remaining data, e.g., the ciphering synchronization result data, the encryption information data, and the encryption information update result data, each take a fixed value determined in advance for use as the parameter “COUNT-C”. 
         [0048]      FIG. 3  is a flowchart of the ciphering synchronization determination control for UE to check if eNB ciphering synchronization is established. In such a case, the UE and the eNB respectively correspond to the communications devices  101  and  102  of  FIG. 2 . For the eNB to check whether the synchronization of ciphering is established with the UE or not, the control similar to  FIG. 3  is performed. 
         [0049]    First of all, the UE generates the ciphering synchronization data, and forwards the resulting data to the eNB (step  301 ). In this case, the ciphering synchronization determination control section  111  uses, as a plain text, a fixed value of shared use between the UE and the eNB, e.g., 0xAAA or others (hereinafter, referred to as “plain-text fixed value”, and generates a cipher text. The parameter “COUNT-C” takes the value currently in use by the user data processing section  112  with respect to the current user data. 
         [0050]    The generation section  113  assigns the value “010” to the element “TYPE” as ciphering synchronization identification information, provides a value to the element “SN”, and sets the cipher text to the element “PDCP SDU”, thereby generating the ciphering synchronization data. The transmission section  115  forwards the resulting ciphering synchronization data to the eNB. 
         [0051]    The transmission section  115  transmits the ciphering synchronization data using the designated value in the element “SN”, for example. Alternatively, the transmission section  115  transmits the ciphering synchronization data at regular intervals of 1 second, 10 seconds, and the like. Note here that the transmission section  115  does not perform such transmission of the ciphering synchronization data at regular intervals during transmission of the encryption information data that will be described later. 
         [0052]    The analysis section  123  of the eNB then determines the type of the data based on the value found in the element of “TYPE” in the provided PDCP PDU (step  311 ). When the element “TYPE” indicates the value “000”, the analysis section  123  of the eNB determines that the data is user data, thereby providing the cipher text to the user data processing section  126 . On the other hand, when the element “TYPE” indicates the value “010”, the analysis section  123  of the eNB determines that the data is the ciphering synchronization data, thereby forwarding the cipher text to the ciphering synchronization determination control section  125 . 
         [0053]    Using the value of the parameter “COUNT-C” currently used by the user data processing section  126  with respect to the current user data, the ciphering synchronization determination control section  125  restores the plain text from the cipher text, thereby checking whether the synchronization of ciphering is being established or not (step  312 ). At this time, the ciphering synchronization determination control section  125  compares the resulting restored plain text with the plain-text fixed value described above, and generates the ciphering synchronization result. When a match is observed therebetween, the ciphering synchronization result is OK, and when no match is observed therebetween, the ciphering synchronization result is NG (Not Good). 
         [0054]    Next, the eNB transmits the resulting ciphering synchronization result to the UE as the ciphering synchronization result data (step  313 ). At this time, using the ciphering synchronization result as a plain text, the ciphering synchronization determination control section  125  generates the cipher text thereof. The fixed value of shared use between the UE and the eNB, e.g., 0xFFFFFFFF, (hereinafter, referred to as “COUNT-C fixed value”) is used as the parameter “COUNT-C”. 
         [0055]    The generation section  124  assigns the value “011” to the element “TYPE” for use as ciphering synchronization result identification information, provides a value to the element “SN”, and sets the cipher text to the element “PDCP SDU”, thereby generating ciphering synchronization result data. The transmission section  122  forwards the resulting ciphering synchronization result data to the UE. 
         [0056]    The analysis section  114  of the UE then determines the type of the data using the value found in the element “TYPE” in the provided PDCP PDU (step  302 ). When the element of “TYPE” indicates the value “000”, the analysis section  114  determines that the data is the user data, and forwards the cipher text to the user data processing section  112 . On the other hand, when the element “TYPE” indicates the value “011”, the analysis section  114  determines that the data is the ciphering synchronization result data, and forwards the cipher text to the ciphering synchronization determination control section  111 . 
         [0057]    Using the COUNT-C fixed value described above, the ciphering synchronization determination control section  111  restores the plain text of the ciphering synchronization result from the cipher text, thereby making a determination about the ciphering synchronization result (step  303 ). When the ciphering synchronization result about the restoration result indicates “OK”, the ciphering synchronization determination control section  111  determines that a match is observed between the UE and the eNB in terms of the value of the parameter “COUNT-C”, and this is the end of the processing. 
         [0058]    When the ciphering synchronization result indicates “NG”, the ciphering synchronization determination control section  111  determines that no match is observed between the UE and the eNB in terms of the value of the parameter “COUNT-C”. When the frequency of receiving the ciphering synchronization result indicating that the ciphering synchronization result is “NG” is not yet reached a specific number of times, the procedure repeats the process from step  301 . 
         [0059]    Note here that when the ciphering synchronization result data does not come from the eNB within a fixed length of time after the ciphering synchronization data is transmitted, the UE determines the situation as a time-over, and goes through the process similar to when the ciphering synchronization result is NG. Accordingly, when the frequency of the ciphering synchronization result indicating NG or the occurrence frequency of the time-over has not yet reached the specific number of times, the procedure repeats the process from step  301 . 
         [0060]    When the ciphering synchronization result continues to indicate “NG”, or the time-over continues to occur in the UE, it is highly likely that the parameter “COUNT-C” currently in use by the eNB has not been incremented normally. In consideration thereof, when the frequency of the ciphering synchronization result indicating “NG” or the occurrence frequency of a time-over reaches the specific number of times, the UE generates the encryption information data for transmission to the eNB to notify the eNB of the current value of the parameter of “COUNT-C” (step  304 ). 
         [0061]    At this time, using, as a plain text, the value of the parameter “COUNT-C” currently used by the user data processing section  112  with respect to the current user data, the ciphering synchronization determination control section  111  generates the cipher text thereof. The COUNT-C fixed value described above is used as the parameter “COUNT-C” to generate the KEYSTREAM BLOCK. 
         [0062]    The generation section  113  assigns the value “100” to the element “TYPE” as encryption information identification information, provides a value to the element “SN”, and sets the cipher text to the element “PDCP SDU”, thereby generating encryption information data. The transmission section  115  then forwards the resulting encryption information data to the eNB. 
         [0063]    The analysis section  123  of the eNB then determines the type of the data based on the value found in the element “TYPE” in the provided PDCP PDU (step  314 ). When the element “TYPE” indicates the value “000”, the analysis section  123  determines that the data is the user data, thereby providing the cipher text to the user data processing section  126 . On the other hand, when the element “TYPE” indicates the value “100”, the analysis section  123  determines that the data is the encryption information data, thereby forwarding the cipher text to the ciphering synchronization determination control section  125 . 
         [0064]    Using the COUNT-C fixed value described above, the ciphering synchronization determination control section  125  restores the plain text from the cipher text, thereby updating the encryption information (step  315 ). At this time, the ciphering synchronization determination control section  125  changes the value of the parameter “COUNT-C” being used by the user data processing section  126  with respect to the current user data to the value of the parameter “COUNT-C” that is the restoration result. As such, the parameter “COUNT-C” in the eNB is updated to the correct value used in the UE. 
         [0065]    After updating the parameter “COUNT-C” as such, the ciphering synchronization determination control section  125  generates the encryption information update result. When such update of the parameter “COUNT-C” is completed normally, the encryption information update result indicates “OK”, and when such update of the parameter “COUNT-C” is not completed normally, the encryption information update result indicates “NG”. 
         [0066]    Next, the eNB transmits the resulting encryption information update result to the UE as encryption information update result data (step  316 ). At this time, using the encryption information update result as a plain text, the ciphering synchronization determination control section  125  generates the cipher text thereof. The COUNT-C fixed value described above is used as the parameter “COUNT-C.”. 
         [0067]    The generation section  124  assigns the value “101” to the element “TYPE” as encryption information update result identification information, provides a value to the element “SN”, and sets the cipher text to the element “PDCP SDU”, thereby generating the encryption information update result data. The transmission section  122  then forwards the resulting encryption information update result data to the UE. 
         [0068]    The analysis section  114  of the UE then determines the type of the data using the value found in the element “TYPE” in the provided PDCP PDU (step  305 ). When the element “TYPE” indicates the value of “000”, the analysis section  114  determines that the data is the user data, and forwards the cipher text to the user data processing section  112 . On the other hand, when the element “TYPE” indicates the value “101”, the analysis section  114  determines that the data is the encryption information update result data, and forwards the cipher text to the ciphering synchronization determination control section  111 . 
         [0069]    Using the COUNT-C fixed value described above, the ciphering synchronization determination control section  111  restores the plain text of the encryption information update result from the cipher text, thereby making a determination about the encryption information update result (step  306 ). When the restored encryption information update result indicates “OK”, the UE resets the frequency of the ciphering synchronization result indicating “NG” or the occurrence of a time-over to “0”, and thus completes the processing. When the encryption information update result indicates “NG”, the procedure repeats the process from step  304 . 
         [0070]    Note here that when the encryption information update result data does not come from the eNB within a fixed length of time after the encryption information data is transmitted, the UE determines that a time-over has occurred, and goes through the process similar to when the encryption information update result is “NG”. Accordingly, when the time-over occurs, the procedure repeats the process from step  304 . 
         [0071]      FIG. 4  is a diagram illustrating a change of the parameter “COUNT-C” used in the user data of both the UE and the eNB. In this example, the specific number of times in step  303  is set to 2, and out of the elements “HFN” and “SN” configuring the parameter “COUNT-C”, the UE and the eNB use only the element “HFN” as a plain text of the encryption information data. 
         [0072]    When the element “HFN” indicates “1”, the UE forwards the PDCP PDUs of the user data respectively assigned with the values of 0 to 4095 in the element “SN” to the eNB. When the element “SN” indicates “0” again after going through all the values, the UE increments the element “HFN” to 2, and transmits the PDCP PDUs of the user data assigned with the values of 0 to 4095 in the element “SN” again to the eNB. 
         [0073]    The UE generates a cipher text of the plain-text fixed value using the parameter “COUNT-C” (elements “HFN” and “SN”) in use at regular time intervals of transmitting the user data with the SN “0”. The UE then generates the PDCP PDU of the ciphering synchronization data assigned with the value “0” in the element “SN”, and transmits the resulting PDCP PDU to the eNB. The UE repeats such a transmission operation. 
         [0074]    When the element “HFN” is “0” and the element “SN” is “4095”, if the eNB is provided with the PDCP PDU assigned with the value “0” in the element “SN”, the eNB sets the initial value of “0” to the value in the element “SN”, and increments the element “HFN” to “1”. When receiving the ciphering synchronization data assigned with the value of “0” in the element “SN”, the eNB restores the plain-text fixed value using the parameter “COUNT-C” currently in use. The eNB then generates a cipher text indicating that the ciphering synchronization result is “OK” using the COUNT-C fixed value, and generates the PDCP PDU of the ciphering synchronization result data assigned with an appropriate value for the element “SN”, e.g., SN=X, for transmission to the UE. 
         [0075]    Using the COUNT-C fixed value, the UE restores the plain text indicating that the ciphering synchronization result is “OK” from the ciphering synchronization result data. Accordingly, the count of the ciphering synchronization results indicating “NG” or of the occurrence of time-overs remains at “0”, and thus the UE does not forward the encryption information data to the eNB. 
         [0076]    After receiving the user data assigned with the value of “1” in the element “SN”, the eNB increments the element “SN” to “1”. Thereafter, when the user data assigned with the values of 2 to 4095 in the element “SN” is not provided to the eNB, and when the user data assigned with the values of 0 to 4095 in the element “SN” is not provided to the eNB after the element “HFN” is set to 2, the element “SN” of the eNB remains at “1” with no increment. 
         [0077]    In this case, the ciphering synchronization data assigned with the value “0” in the element “SN” is also not provided to the eNB, and the UE thus is not provided with the ciphering synchronization result data from the eNB. Accordingly, the UE changes the value of the count of the ciphering synchronization result indicating “NG” or the occurrence of time-overs to “1”. 
         [0078]    When receiving the user data assigned with the value “0” in the element “SN” when the element “HFN” of the UE indicates “3”, the eNB sets “0” for the element “SN”, and sets “2” for the element “HFN”. As a result, the value in the element “SN” of the eNB becomes the same as the value in the element “SN” of the UE, but the value in the element “HFN” of the eNB does not become the same as the value in the element “HFN” of the UE because the element “HFN” of the UE already indicates “3”. 
         [0079]    Using the parameter “COUNT-C” in which the element “HFN” indicates “3” and the element “SN” indicates “0”, the UE generates a cipher text with the plain-text fixed value. The UE then generates the ciphering synchronization data assigned with the value of “0” in the element “SN”, and transmits the resulting data to the eNB. 
         [0080]    Upon reception of the ciphering synchronization data, the eNB restores the plain text from the cipher text using the parameter “COUNT-C” in which the element “HFN” indicates “2”, and the element “SN” indicates “0”. However, because the parameter “COUNT-C” in the eNB is not the same as the parameter “COUNT-C” in the UE, the restoration result does not become the same as the plain-text fixed value, and thus the ciphering synchronization result indicates “NG”. Therefore, the eNB generates a cipher text indicating that the ciphering synchronization result is “NG” using the COUNT-C fixed value, and generates the PDCP PDU of the ciphering synchronization result data assigned with the value “X” in the element “SN” for transmission back to the UE. Moreover, after receiving the user data in which the element “SN” indicates “1” or more, the eNB increments the value in the element “SN” in a sequential manner. 
         [0081]    After receiving the ciphering synchronization result data from the eNB, the UE restores the plain text indicating that the ciphering synchronization result is “NG” from the ciphering synchronization result data using the COUNT-C fixed value, and changes the value of the count of the ciphering synchronization result indicating “NG” or of the occurrence of the time-over to “2”. Herein, because the count indicates “2” which is the specific number of times, the UE generates a cipher text of the encryption information (HFN=3) using the COUNT-C fixed value, and generates the PDCP PDU of the encryption information data assigned with the value of “3” in the element “SN” for transmission to the eNB. 
         [0082]    After receiving the encryption information data, the eNB restores the plain text of the encryption information using the COUNT-C fixed value, and changes the value in the element “HFN” to “3” in accordance with the encryption information restored as such. As a result, the element “HFN” of the eNB indicates the same value as the element “HFN” of the UE, and the value of the parameter “COUNT-C” becomes a normal value again. Thereafter, the eNB generates a cipher text of the encryption information update result indicating “OK” using the COUNT-C fixed value, and generates the PDCP PDU of the encryption information update result data assigned with the value of X in the element of “SN” for transmission to the UE. 
         [0083]    Upon reception of the encryption information update result data, the UE restores the plain text of the encryption information update result indicating “OK” from the encryption information update result data using the COUNT-C fixed value, and resets the count of the ciphering synchronization results indicating “NG” or the count of the time-overs to “0”. 
         [0084]    With the related art wireless communications system, in a section after the third user data assigned with the value “0” in the element “SN”, i.e., section  402 , the parameter “COUNT-C” varies in value between the UE and the eNB, whereby the eNB cannot restore the correct plain text from the cipher text. On the other hand, with the wireless communications system of the embodiment described herein, because the encryption information data is transmitted from the UE to the eNB, the restoration result thus becomes different only in section  401 . After the user data assigned with the value of 3 in the element “SN” in the section  401 , normal communications may be recovered. 
         [0085]    According to an aspect of the embodiment, with such a transmission device and a reception device, the information of shared use between the transmission and reception devices can be used as a basis to determine whether or not a match is observed between the first encryption information in the transmission device and the second encryption information in the reception device. When no match is observed between the first and second encryption information, to achieve the matching therebetween, the transmission device may forward the first encryption information to the reception device, and the second encryption information may be updated based on the provided first encryption information, for example. 
         [0086]    The transmission and reception devices respectively correspond to, for example, communications devices  101  and  102 , and the sequence information and the encryption information respectively correspond to, for example, an element “SN” and a parameter “COUNT-C”. 
         [0087]    According to the transmission and reception devices of the embodiment, an asynchronization of ciphering occurring between the transmission and reception devices can be automatically detected and recovered. Accordingly, the resulting audio service may sound normal, and the resulting packet service may not cause the reduction of the throughput. 
         [0088]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention(s) has(have) been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.