JP2004080071A - Method for preventing excessive use of security key in wireless communication security system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for determining a start value, which is stored in a memory of a wireless communication device. <P>SOLUTION: The start value has a size of x bits, and is used to provide an initial value to an n-bit security count value. The radio communication device establishes a channel with a suitable device, and releases the channel established with the suitable device. Finish values corresponding to all the channels established by the radio communication device are acquired. The finish value of each of the channels is the highest value at which the most significant bit (MSB<SB>x</SB>) of an n-bit security count value corresponding to this channel reaches. Data transmitted through the channels are encrypted by using the security count value. The finally acquired value is the greatest value among all the finish values. Finally, a start value having at least the same size as that of the final value is stored in a memory of the wireless device. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a security count value in a wireless communication system. In particular, the present invention discloses a method for ensuring that the security count generated by a hyper frame number is not reused as much as possible during the life of the security key.
[0002]
[Prior art]
Please refer to FIG. FIG. 1 is a simplified block diagram of a prior art wireless communication system. This communication system includes a first station 10 that performs wireless communication with a second station 20. As an example, the first station 10 may be a mobile such as a mobile phone, and the second station 20 may be a base station. The first station 10 communicates with the second station 20 through a plurality of channels 12. Accordingly, the second station 20 has a plurality of channels 22, one for each of the channels 12. Each channel 12 has a receive buffer 12r that holds a protocol data unit (PDU) 11r received from a corresponding channel 22 of the second station 20. Each channel 12 has a transmission buffer 12t that holds a PDU 11t that is waiting for the second station 20 to transmit to the corresponding channel 22. The PDU 11t is transmitted by the first station 10 via the channel 12 and received by the second station 20 and generates a corresponding PDU 21r in the reception buffer 22r of the corresponding channel 22. Similarly, the PDU 21t is transmitted by the second station 20 via the channel 22 and received by the first station 10 to generate a corresponding PDU 11r in the receiving buffer 12r of the corresponding channel 12.
[0003]
To maintain consistency, the data structure of each PDU 11r, 11t, 21r, 21t passing through the corresponding channel 12, 22 is the same. That is, a transmitted PDU 11t generates the same corresponding received PDU 21r, and vice versa. Further, the first and second stations use the same PDU 11t, 21t data structure. The PDUs 11r, 11t, 21r, 21t passing through the corresponding channels 12 and 22 are the same, but different channels 12 and 22 are different PDUs according to the type of connection adapted to go through the corresponding channels 12 and 22. Data structures may be used. However, in general, all PDUs 11r, 11t, 21r, 21t have sequence numbers 5r, 5t, 6r, 6t. The sequence numbers 5r, 5t, 6r, 6t are m-bit numbers and are incremented for each PDU 11r, 11t, 21r, 21t. The sizes of the sequence numbers 5r, 5t, 6r, 6t indicate the order of the PDUs 11r, 11t, 21r, 21t in the buffers 12r, 12t, 22r, 22t. The sequence numbers 5t, 6t are often explicitly carried by the PDUs 11t, 21t, but are also assigned implicitly by the stations 10,20. For example, in the generally accepted mode settings for the corresponding channels 12 and 22, each transmitted PDU 11t is explicitly acknowledged by the second station 20, and upon successful reception of the PDU 11t, the same corresponding PDU 21r is identified. Generated. The 12-bit sequence number 5t is explicitly carried by each PDU 11t in the transmission of the generally accepted mode. The second station 20 scans the sequence number 6r embedded in the received PDU 21r, determines the order of the PFUs 21r, and determines whether there is any missing PDU 21r. Next, the second station 20 can transmit a message indicating which PDU 21r has been received to the first station 10 by using the sequence number 6r of each received PDU 21r. Alternatively, the second station 20 can request that the PDU 11t be retransmitted by specifying the sequence number 5t of the PDU 11t to be retransmitted. Alternatively, in the so-called transparent transmission mode, the data is never confirmed as successfully received. The sequence numbers 5t and 6t are not explicitly carried in the PDUs 11t and 21t. Instead, the first station 10 internally assigns only a 7-bit sequence number to each PDU 11t. Similarly, upon reception, the second station 20 assigns a 7-bit sequence number 6r to each PDU 21r. Ideally, the sequence number 5t maintained by the first station 10 for the PDU 11t is the same as the corresponding sequence number 6r for the PDU 21r maintained by the second station 20.
[0004]
The hyper frame number (HFN) is also maintained by the first station 10 and the second station 20. The hyper frame number is regarded as the upper bits of the sequence numbers 5t and 6t, and is never physically transmitted together with the PDUs 11t and 21t. An exception to this rule occurs in rare cases where the special signal PDUs 11t, 21t are used for synchronization. In this case, the HFN is not carried as a part of the sequence numbers 11t and 21t, but is carried in the field of the data payload of the signal PDUs 11t and 21t, and thus becomes more appropriate signal data. As each transmitted PDU 11t, 21t generates a corresponding received PDU 21r, 11r, a hyper frame number is also maintained for the received PDU 21r, 11r. Each received PDU 11r, 21r and each transmitted PDU 11t, 21t use sequence numbers 5r, 6r, and 5t, 6t (explicitly or implicitly assigned) as the least significant bits and are further corresponding. A value is assigned that uses the hyper frame number (which is always implicitly assigned) as the most significant bit. Therefore, each channel 12 of the first station 10 receives the received hyper frame number (HFN). _R ) 13r and the transmission hyper frame number (HFN) _T ) 13t. Similarly, the corresponding channel 22 on the second station is HFN _R 23r and HFN _T 23t. When the first station 10 detects the rollover of the sequence number 5r of the PDU 11r in the reception buffer 12r, the HFN _R Increment 13r. When the first station 10 rolls over the sequence number 5t of the transmitted PDU 11t, the HFN _T Increment 13t. On the second station 20, HFN _R 23r and HFN _T A similar process is performed for 23t. Therefore, the HFN of the first station 10 _R 13r is the HFN of the second station 20 _T Synchronize with (ie coincide with) 23t. Similarly, the HFN of the first station 10 _T 13t is the HFN of the second station 20 _R Synchronize with (ie, coincide with) 23r.
[0005]
The PDUs 11t, 21t are not transmitted "out in the open". The security engine 14 on the first station 10 and the corresponding security engine 24 on the second station cooperate to securely and privately exchange data only between the first station 10 and the second station 20. Guarantee. The security engines 14, 24 have two main functions. The first function is to disrupt (ie, encrypt) the data held in the PDUs 11t, 21t such that the corresponding PDUs 11r, 21r present a meaningless random set of numbers to the eavesdropper. That is, so-called encryption). The second function is to verify the integrity of the data contained in the PDUs 11r, 21r. This is used to prevent another unauthorized station from impersonating the first station 10 or the second station 20. By proving the integrity of the data, the first station 10 can confirm that the PDU 11r was actually transmitted by the second station 20, or vice versa. The security engine 14 performs an encryption function on the PDU 11t using the n-bit security count 14c and the key 14k, among other inputs, for the PDU 11 to be transmitted. In order to properly encrypt the corresponding PDU 21r, the security engine 24 must use the same security count 24c and key 24k. Similarly, an n-bit security count is used to verify data integrity on the first station 10. This n-bit security count must be synchronized with the corresponding security count on the second station 20. Since the data integrity security counts are generated in the same manner as the encryption of the security counts 14c, 24c, and encryption is used more frequently, the encryption security counts 14c, 24c are as follows: To be considered. The keys 14k, 24k remain constant over all PDUs 11t, 21t (and thus the corresponding PDUs 21r, 11r) until explicitly changed by both the first station 10 and the second station 20. However, the security counts 14c, 24c change continuously with each PDU 11t, 21t. This constant change in security counts 14c, 24c makes the PDUs 11t, 21t more difficult to decipher (and spoof) because the statistical integrity of the inputs to security engines 14, 24 is compromised. . The sequence number 5t of the PDU 11t is set as the least significant bit of the security count 14c, and the HFN corresponding to the sequence number 5t. _T By using 13t as the most significant bit of security count 14c, security count 14c of PDU 11t is generated. Similarly, the sequence number 5r of the PDU 11r and the HFN of the PDU 11r _R From 13r, a security count 14c of the PDU 11r is generated. A similar process takes place on the second station 20, with sequence number 6r or sequence number 6t and the corresponding HFN _R 23r or HFN _T 23t is used to generate a security count 24c. The security counts 14c and 24c have a fixed bit size of, for example, 32 bits. Since the bit size of the sequence numbers 5r, 6r, 5t, 6t can vary depending on the transmission mode used, the hyper frame number HFN _R 13r, HFN _R 23r, HFN _T 13t and HFN _T The bit size of 23t must be changed correspondingly to produce the fixed bit size of security counts 14c, 24c. For example, the sizes of the sequence numbers 5r, 6r, 5t, and 6t are all 7 bits in the transparent transmission mode. Therefore, the hyper frame number HFN _R 13r, HFN _R 23r, HFN _T 13t and HFN _T 23t is 25 bits in size, and combining these two produces 32-bit security counts 14c and 24c. In the generally accepted transmission mode, the sequence numbers 5r, 6r, 5t, 6t are all 12 bits in size. Therefore, the hyper frame number HFN _R 13r, HFN _R 23r, HFN _T 13t, and HFN _T Since the size of 23t is 20 bits, the combination of the two continues to generate 32-bit security counts 14c and 24c.
[0006]
Initially, channel 12 and channel 22 have not been established between first station 10 and second station 20. Thereafter, the first station 10 establishes a channel with the second station 20. For this purpose, the first station 10 _T 13t and HFN _R An initial value for 13r must be determined. The first station 10 refers to the non-volatile memory 16 such as a flash memory device or a SIM card, obtains a start value 16s, and uses this start value 16s to _T 13t and HFN _R 13r is generated. The starting value 16s is the x most significant bit (MSB) of the hyper frame number from the previous session through channel 12. _x ) Hold. Ideally, x should be a bit size at least as large as the bit size of the smallest hyperframe number (ie, for the above sample, the size of x should be at least 20 Must be a bit). HFN _T 13t and HFN _R The 13B MSBx is set to the starting value 16s, and the remaining low order bits are set to zero. Next, the first station 10 sends the start value 16s to the second station 20 (by a special signal PDU 11t), and the HFN _R , 23r and HFN _T Used as 23t. Thus, HFN _T 13t is HFN _R 23r and HFN _T 23t is HFN _R 13r.
[0007]
The first station 10 can establish a plurality of channels 12 with the second station 20. Each of these channels 12 uses its own sequence numbers 5r, 5t, as well as hyperframe numbers 13r, 13t. When establishing a new channel 12, the first station 10 sends the HFNs of all currently established channels 12. _T 13t and HFN _R 13r, the HFN with the highest value _T 13t or HFN _R Select 13r. Next, the first station 10 determines the MSB of the highest hyper frame number. _x And extract the MSB _x Is incremented by one and the new HFN of the newly established channel 12 _T 13t and HFN _R 13r MSB _x Use as Next, synchronization is performed between the first station 10 and the second station 20, and HFN is transmitted to the second station 20. _R 23r and HFN _T MSB of 23t _x give. In this way, a constantly incrementing spacing is maintained between the security counts 14c of all established channels 12.
[0008]
It is noted that for security, the keys 14k, 24k should be changed after a predetermined interval. This interval is determined by the security counts 14c, 24c. When the security counts 14c and 24c exceed a predetermined value, the first station 10 and the second station 20 start a security command and change the keys 14k and 24k. For the security counts 14c, 24c to reach a predetermined value, the hyperframe number must be remembered during the session (ie, when the first station 10 is turned off and then again when it is turned on). Recall between). This is the purpose of the starting value 16s. When the last channel 12 is released (ie, terminated and there are no other channels established with the second station 20), the HFN of this channel 12 _T 13t or HFN _R 13r MSB _X To (HFN _T 13t or HFN _R ), Increment by one, and then save to the starting value 16s. When the first station 10 is turned on again and attempts to establish the channel 12, the security count 14c is guaranteed to occur continuously by the first station 10 using the starting value 16s.
[0009]
Unfortunately, the HFN of the last released channel 12 _T 13t or HFN _R If the start value 16s is generated using 13r, the change of the security key 14k will be extremely delayed. Typically, the first station 10 establishes a signaling channel 12 with the second station 20. This signaling channel is used to carry special signaling PDUs for the communication protocol. The signaling channel is established very early after the first station 10 is turned on. The signaling channel 12 tends to have a long duration, but typically does not carry much data. Therefore, the HFN of the signaling channel 12 _T 13t and HFN _R 13r has relatively small values. This is because the traffic load of the PDUs 11t and 11r is small, so that the hyper frame numbers 13t and 13r are generated early, and the increment is rarely performed. On the other hand, the data channel 12 may be sporadically established and have a high PDU 11t, 11r throughput. Therefore, the HFN of such a data channel 12 _T 13t or HFN _R 13r is the HFN of the signaling channel 12 _T 13t or HFN _R 13r may be extremely large. However, data channel 12 is released once it has performed its function. Perhaps because the signaling channel 12 will survive, the hyper frame numbers 13t, 13r associated with the data channel 12 will be lost. The data channel 12 has a much larger hyperframe number 13t, 13r than the signaling channel 12, but the last channel released is the signaling channel 12, which is used to generate the start value 16s. HFN of signaling channel 12 _T 13t or HFN _R 13r. As a result, the values of the hyper frame numbers 13t and 13r are excessively used, so that an extra delay occurs between changes of the security key 14k. Thus, security on channel 12 is weakened.
[0010]
[Problems to be solved by the invention]
Accordingly, it is a primary object of the present invention to provide a method for determining a starting value to be stored in a memory of a wireless communication device.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 is a method for determining a start value to be stored in a memory of a wireless communication device, wherein the start value has a size of x bits, and Used to provide a value to an n-bit security count value, wherein the wireless communication device is capable of establishing a plurality of channels and releasing the established channels, the method comprising: Obtaining a corresponding end value for at least two channels established by the wireless communication device, wherein the corresponding channel end value is x maximum of an n-bit security count value associated with the channel. Obtaining the highest value reached by the high-order bit, obtaining the final value that is the largest value among all end values, and having at least the same magnitude as the final value. The open, is summarized in that comprising the step of storing in a memory of the wireless device.
[0012]
The invention as claimed in claim 2 is the method according to claim 1, wherein the last value is previously stored in the memory if the last value is not greater than a starting value previously stored in the memory. The point is to set at least the same value as the starting value.
[0013]
According to a third aspect of the invention, in the method according to the second aspect, the start value stored in the memory is larger than both the final value and the previously stored start value.
[0014]
According to a fourth aspect of the present invention, in the method according to the third aspect, when the final value exceeds a predetermined value, the final value is set to be equal to the predetermined value.
[0015]
According to a fifth aspect of the present invention, in the method according to the fourth aspect, the predetermined value is determined by 2x in order to prevent a roll-over of the start value stored in the memory. .
[0016]
The invention according to claim 6 is a method for managing a start value in a wireless communication device, said start value having a size of x bits and providing an initial value to an n-bit security count value. Used, the communication device is capable of establishing a plurality of channels, each channel having an associated n-bit security count value, and capable of releasing the established channel; The method comprising: for a first established channel, setting the x most significant bits of the n-bit security count value associated with the first established channel to a first value; the first value Is at least as large as the first value stored in the memory of the wireless communication device, and for a subsequently established channel, Setting the MSBx of the n-bit security count value associated with the first channel to a second value, wherein the second value is the sum of all the n-bit security count values associated with all established channels. Being at least as large as the maximum value reached among all the MSBxes, and at least releasing another of the already established channels when establishing another channel, A third value that is at least as large as the maximum value reached among all the MSBx of all the n-bit security count values associated with the released channel and the n-bit security count value associated with the released channel. And storing the third value as the starting value in the memory. The the gist.
[0017]
According to a seventh aspect of the present invention, in the method according to the sixth aspect, the third value stored in the memory is larger than the first value.
The invention according to claim 8 is characterized in that, in the method according to claim 6, when the third value exceeds a predetermined value, the third value is set to be equal to the predetermined value. I do.
[0018]
According to a ninth aspect of the present invention, in the method according to the eighth aspect, the predetermined value is determined by 2x in order to prevent the start value from rolling over.
[0019]
The invention according to claim 10 is the method according to claim 6, wherein the second value is further set so as to be at least as large as the start value stored in the memory. And
[0020]
The invention according to claim 11, wherein in the method according to claim 6, the third value is further set so as to be at least as large as the start value stored in the memory. And
[0021]
Briefly summarized, a preferred embodiment of the present invention discloses a method for storing and managing starting values in a wireless communication device. The size of the starting value is x bits, and the starting value is used to provide an initial value to the n-bit security count value. The wireless communication device can establish a plurality of channels, and can release the established channels. For every channel established by the wireless communication device, a corresponding end value is obtained. The end value of a channel is the highest value reached by the x most significant bits (MSBx) of the n-bit security count value associated with this channel. The final value, which is the maximum of all end values, is obtained. Finally, a start value at least as large as the final value is stored in a memory of the wireless device.
[0022]
An advantage of the present invention is that, according to the method of the present invention, the re-establishment of the security count value by storing the largest MSBx of all the n-bit security count values associated with all established channels. The use is reduced and the security key is changed more quickly. Reuse of the security count value is minimized while maintaining maximum use of the security key. Improve overall transmission security by avoiding the extra delay associated with changing security keys.
[0023]
These and other objects of the present invention will no doubt become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments illustrated in the various figures and drawings.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
In the following description, a station can be a mobile phone, a handheld transceiver, a base station, a personal digital assistant (PDA), a computer, or any other device that requires a wireless exchange of data. It is to be understood that many means are available for the physical layer that performs wireless communication, and any such means can be used in the systems disclosed below.
[0025]
Please refer to FIG. FIG. 2 is a simplified block diagram of the wireless communication system 30 according to the present invention. Wireless communication system 30 is very similar to prior art wireless communication systems. This is because changing the method used to manage the starting value 46s is a primary object of the present invention. Wireless communication system 30 includes a first station 40 that communicates wirelessly with a second station 50 over a plurality of established channels 42. The first station 40 may be a mobile unit capable of establishing a channel 42 and communicating with a second station 50 that is a base station. The second station establishes a corresponding channel 52 for the channel 42 of the first station 40. Also, the first station 40 can release the established channel 42, in which case the second station 50 releases the corresponding channel 52. Each channel 42 has a reception buffer 42r and a transmission buffer 42t. Similarly, in the second station 50, each channel 52 has a reception buffer 52r and a transmission buffer 52t. The reception buffer 42r is used to hold a protocol data unit (PDU) 41r received from the second station 50. The transmission buffer 42t is used to hold the PDU 41t waiting to be transmitted to the second station 50. The PDU 41 t is transmitted to the second station 50 via the channel 42, where it is received and put into the reception buffer 52 r of the corresponding channel 52. Similarly, the PDU 51t is transmitted to the first station 40 via the second station channel 52, where it is received and placed in the receive buffer 42r of the corresponding channel 42. Each PDU 41r, 41t, 51r, 51t has an m-bit sequence number (SN) 35r, 35t, 36r, which indicates a continuous position of the PDU 41r, 41t, 51r, 51t in the buffer 42r, 42t, 52r, 52t. 36t. The PDUs 41r, 41t, 51r, and 51t that are rearward in order have sequence numbers 35r, 35t, 36r, and 36t that are higher in order. Since the sequence numbers 35r, 35t, 36r, and 36t have a fixed bit size of m bits, the sequence numbers 35r, 35t, 36r, and 36t have values of 2 bits. ^m If it exceeds -1, it rolls over to zero. The reception buffers 42r and 52r store the reception hyper frame numbers (HFN _R ) 43r and 53r. This received hyper frame number is incremented by one when such a rollover event of the sequence numbers 35r, 36r of the received PDUs 41r, 51r is detected. Therefore, the HFN associated with each received PDU 41r, 51r _R 43r and 53r function as upper bits (most significant bits) of the sequence numbers 35r and 36r of the received PDUs 41r and 51r. Similarly, each transmission buffer 42t, 52t stores a transmission hyper frame number (HFN) that functions as an upper bit of the sequence numbers 35t, 36t of the received PDUs 41t, 51t, that is, as the most significant bit. _T ) 43t and 53t. The hyper frame numbers 43r, 43t, 53r, 53t are internally managed by the first station 40 and the second station 50 and are explicitly transmitted only during a synchronization event. This is different from the sequence numbers 35t, 36t that are normally carried by the respective PDUs 41t, 51t.
[0026]
The first station 40 has a security engine 44 used to perform encryption / decryption of PDUs 41r, 41t and data integrity check. Two of the multiple inputs to the security engine include, among other things, an n-bit security count 44c and a first encryption key 44k. A corresponding security engine 54 is provided on the second station 50, and the security engine 54 also uses an n-bit security count 54c and a first encryption key 54k. The PDU 41t is encrypted by the security engine 54 using the special security count 44c and the encryption key 44k. To properly decrypt the corresponding received PDU 51r, the security engine 54 uses the same security count 54c as the security count 44c and the same first encryption key 54k as the first encryption key 44k. Must. The synchronized security counts are used to check the integrity of the PDUs 41r, 41t, 51r, and 51t. However, since these integrity security counts are almost always smaller than the encryption security counts 44c and 54c, For the following discussion, encryption security counts 44c, 54c will be considered.
[0027]
The encryption keys 44k, 54k are changed relatively rarely, with a somewhat complicated signaling process between the first station 40 and the second station 50, and ensuring that the respective encryption keys 44k, 54k are synchronized. (Ie, identical). On the other hand, the security counts 44c and 54c continuously change for each PDU 41r, 41t, 51r and 51t passing through the channels 42 and 52. The HFN associated with the PDUs 41r, 41t using the sequence numbers 35r, 35t of the PDUs 41r, 41t as the lower (least significant) bits of the security count 44c, respectively. _R 43r, HFN _T By using 43t as an upper bit of the security count 44c, a security count 44c is generated for each of the PDUs 41r and 41t. The corresponding process is used by the security engine 54 of the second station 50. For a stream of transmitted PDUs 41t, the security count 44c increases continuously with each PDU 41t. Therefore, the same can be said for the stream of the PDU 51t transmitted by the second station 50. The range of security count values 44c used by the various channels 42 can vary very widely. However, in the normal case, all the channels 42 use the same encryption key 44k.
[0028]
Initially, first station 40 does not have an established channel 42 with second station 50. To establish the channel 42 with the second station 50, the first station 40 first extracts a start value 46s from the non-volatile memory 46 of the first station 40, and is to be established using the start value 46s. HFN for channel 42 of _T 43t and HFN _R 43r is generated. The non-volatile memory 46 is used to permanently store data for the first station 40, so that the starting value 46s is not lost when the first station 40 is turned off. The non-volatile memory 46 may be an electrically erasable programmable read only memory (EEPROM), a SIM card, or the like. Ideally, the bit size of the starting value 46s should be equal to the bit size of the hyper frame numbers 43t, 43r. In this case, HFN _T 43t and HFN _R 43r is simply set equal to the start value 46s. However, for the m-bit hyper frames 43t and 43r, the size of the start value 46s is x bits, and if x is smaller than m, the start value 46s is the x most significant bit (MSB) of the hyper frames 43t and 43r. _x ) And HFN _T 43t and HFN _R The remaining lower order bits of 43r are simply cleared. After generating the hyper frame numbers 43t and 43r with the start value 46s, the first station 40 transmits the start value 46s to the second station 50. As a result, the second station 50 sets the HFN of the corresponding channel 52. _R 53r and HFN _T 53t can be set to be equal to the initial values of the hyper frame numbers 43t and 43r. Thus, HFN _T 43t is the corresponding HFN _R 53r and HFN _R 43r is the corresponding HFN _T Synchronized with 53t. The starting value 46s is an x-bit size number, HFN _T Since 43t is used as the most significant bit of the security count 44c for the transmitted PDU 41t, the starting value 46s is the MSB of the n-bit security count 44c. _x Effectively. Where n is HFN _T It is equal to the sum of the bit size of 43t and the bit size of sequence number 35t. This is HFN _R Regarding 43r, the same applies to the case of the security count 44c for the received PDU 41r.
[0029]
After establishing the initial channel 42, many other channels 42 may be established by the first station 40 (or in response to the channel 52 established by the second station 50). When another channel 42 has already been established and a new channel 42 is to be established, the first station 40 firstly establishes the hyperframe number 43t or the hyper frame number 43t having the largest numerical value among all the established channels 42. The frame number 43r is selected. The hyper frame numbers 43r and 43t having the largest numerical values are extracted to generate an x-bit final value 45. The final value 45 of this x bit is 2 ^x If it is less than -1, the final value 45 is incremented by one. Check the final value 45 against the start value 46s. If the final value 45 is smaller than the start value 46s, the final value 45 is set equal to the start value 46s. Next, the HFN of the new channel 42 establishing the final value 45 _T 43t and HFN _R MSB for 43r _x Use as Next, synchronization is performed between the first station 40 and the second station 50, and the HFN _R 43r and HFN _R Establish initial values for 53r.
[0030]
However, of particular importance in connection with the present invention, is that the first station 40 can release the established channel 42. When the established channel 42 is released, the memory used by the channel 42 is released. Therefore, the corresponding reception buffer 42r and transmission buffer 42t are removed, and the HFN _R 43r and HFN _T 43t is lost. Immediately prior to releasing any channel 42 (ie, as part of the process of releasing channel 42), regardless of whether other channels 42 are simultaneously established, the first station 40 HFN reached numerically at the same time _T 43t and HFN _R 43r is selected first. This includes the channel 42 and HFN to be released _T 43t and HFN _R The end value of 43r is also included. The end values of the hyper frame numbers 43r and 43t are the last values reached just before the corresponding channel 42 is released. The MSB of this numerically largest hyper frame number 43t, 43r _x To generate a final value 45 of x bits. The final value 45 of this x bit is 2 ^x If it is less than -1, the final value 45 is incremented by one. When the final value 45 is larger than the start value 46s, the final value 45 is stored in the nonvolatile memory 46 as the start value 46s.
[0031]
Alternatively, upon release of any channel 42, the first station 40 may provide the final value 45 with the HFN of the releasing channel 42. _T 43t or HFN _R MSr of the larger end value of 43r _x May be set to be equal to This final value 45 is 2 ^x If it is less than -1, the final value 45 is incremented by one. When the final value 45 is larger than the start value 46s, the final value 45 is stored in the nonvolatile memory 46 as the start value 46s.
[0032]
Regardless of which of the above methods was used, the net result is that upon release of the last channel 42 (no channel 42 subsequently established), the starting value 46s will be MSB of channel 42 hyperframe numbers 43t and 43r _x Holds one value larger than the highest end value reached. This is the main object of the present invention. The start value 46s is 2 to prevent the start value 46s from rolling over. ^X -1 must not be exceeded.
[0033]
The starting value 46s is the MSB of the largest security count 44c reached by any channel 42 of the first station 40 _X , The first station 40 prevents excessive reuse of the security count value 44c, and the security count 44c increases steadily in all sessions to the previous value. Guarantee that you will not fall back. Since changing the encryption key 44k depends on the size of the security count 44c, the first station 40 ensures that the encryption key 44k will not be used for an excessively long time. This helps to further assure the security of the communication system 30. This is because the periodic change of the encryption keys 44k, 54k makes the cracking of the security engines 44, 54 more difficult.
[0034]
As an example of the present invention, it is assumed that the first station 40 is a mobile telephone and the second station is a base station. For simplicity, it is further assumed that the bit size of the starting value 46s is equal to the bit size of the hyperframe numbers 43r and 43t. The first station 40 is turned on, the first channel 42 is established with the second station 50, and a session is started. In this context, a session refers to the time period from the establishment of the first channel 42 to the release of the last channel 42. The first channel 42 is, in effect, the first channel 42 that the first station establishes with the second station 50, has no other channels 42 established, and responds to the normally on first station 40. . The last channel 42 is the last channel released by the first station, and no other channel 42 is subsequently established with the second station 50. This generally occurs just before the first station 40 is turned off. Assuming that the starting value 46 s retains the initial value of 147, the first station 40 will change the starting value 46 s to the newly established HFN of the first channel 42 after being turned on. _T 43t and HFN _R Used as 43r. Therefore, the HFN of the first channel 42 _T 43t is HFN _R As with 43r, it has a value of 147. Generally, the first channel 42 is typically a signaling channel 42 and tends to have a relatively low transmission rate PDU 41t. After a while, the first station 40 establishes the data channel 42 with the second station 50. Assuming that the first channel 42 does not transmit a large amount of PDU 41t and receives less PDU 41r, HFN _T 43t is the larger one of the hyper frame numbers 43t and 43r of the first channel 42, and can be incremented only once to a value of 148. When establishing the data channel 42, the first station 40 first searches for the largest value among all the hyper frame numbers 43t and 43r of the established channel 42. Since only one channel is currently established, that is, the first channel 42, as a result of this search, the HFN of the first channel 42 is obtained. _T A value of 148 is obtained from 43t. This value is incremented by one and compared to the starting value 46s, and the larger of the two is selected to determine the HFN of data channel 42. _T 43t and HFN _R Used as 43r. Thus, data channel 42 has an HFN with an initial value of 149. _T HFN with an initial value of 43t, and also 149 _R Get 43r. The data channel 42 is finally released after a period of heavy traffic load. HFN for data channel 42 due to the high traffic volume through data channel 42 _R 43r increases from an initial value of 149 to an ending value of 231 and the HFN for data channel 42 _T 43t (ie, the PDU 41r received by the data channel 42 is much larger than the transmitted one). When the data channel 42 is released, the first station 40 _R 43r is compared with a starting value 46s. HFN of data channel 42 _R 43r is greater than the starting value 46s, HFN _R 43r is incremented by one and stored as a starting value 46s. Therefore, the start value 46s holds the value of 232. Therefore, any subsequently established channels 42 will have at least 232 HFNs. _T 43t and HFN _R 43r.
[0035]
The invention differs from the prior art in that the starting value stored in the non-volatile memory can be updated each time an established channel is released. Thus, the maximum x most significant bits reached by the security counts of all established channels are stored in non-volatile memory. Thus, excessive reuse of the security count value is prevented, and the encryption key is not used for an excessive period of time.
[0036]
One skilled in the art will readily recognize that many modifications and alterations of the device may be made while retaining the teachings of the invention. That is, the above disclosure is to be limited only by the appended claims.
[0037]
【The invention's effect】
According to the present invention, there is an excellent effect that transmission security in wireless communication can be improved.
[Brief description of the drawings]
FIG. 1 is a simplified block diagram of a conventional wireless communication system.
FIG. 2 is a simplified block diagram of a wireless communication system according to the present invention.
[Explanation of symbols]
30 wireless communication device, 40 first station, 42 channel, 44c security count, 44k key, 45 final value, 46 nonvolatile memory, 46s start value, 50 second station, 52 Channel, 54c ... security count, 54k ... key

Claims (11)

A method for determining a starting value to store in a memory of a wireless communication device, the starting value having a size of x bits and being used to provide an initial value to an n-bit security count value, The communication device is capable of establishing a plurality of channels and releasing the established channels, the method comprising:
Obtaining a corresponding end value for at least two channels established by the wireless communication device, wherein the corresponding channel end value is x most significant bits of an n-bit security count value associated with the channel; Bit (MSB _x ) being the highest value reached,
Obtaining a final value which is the largest value among all end values;
Storing a starting value at least as large as the final value in a memory of the wireless device. 2. The method of claim 1, wherein the final value is set to be at least as large as the start value previously stored in the memory, if the final value is not greater than the start value previously stored in the memory. the method of. 3. The method of claim 2, wherein the starting value stored in the memory is greater than both the final value and the previously stored starting value. 4. The method according to claim 3, wherein if the final value exceeds a predetermined value, the final value is set to be equal to the predetermined value. To prevent rollover of the start value stored in the memory The method of claim 4, wherein the predetermined value is determined by 2 ^x. A method for managing a start value in a wireless communication device, wherein the start value has a size of x bits and is used to provide an initial value to an n-bit security count value, wherein the communication device comprises a plurality of start values. Channels can be established, each channel has an associated n-bit security count value, and the established channel can be released, the method comprising:
Setting, for a first established channel, the x most significant bit (MSB _x ) of the n-bit security count value associated with the first established channel to a first value; The value is at least as large as the first value stored in the memory of the wireless communication device;
Setting, for a subsequently established channel, the MSB _x of the n-bit security count value associated with the subsequently established channel to a second value; At least as large as the maximum value reached among all the MSBs _x of all the n-bit security count values associated with the established channel;
When releasing any of the already established channels, at least when establishing another channel, the n-bit security count value associated with all the already established channels and the released channel Generating a third value that is at least as large as the maximum value reached among all MSBs _x of the associated n-bit security count value;
Storing said third value as said starting value in said memory. The method of claim 6, wherein a third value stored in the memory is greater than the first value. 7. The method according to claim 6, wherein if the third value exceeds a predetermined value, the third value is set to be equal to the predetermined value. To prevent rollover of the start value, The method of claim 8, wherein the predetermined value is 2 ^x Thus are determined. 7. The method of claim 6, wherein the second value is further set to be at least as large as the starting value stored in the memory. 7. The method of claim 6, wherein the third value is further set to be at least as large as the starting value stored in the memory.

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