CN100442923C - A Periodic Update Method for Transmitting Encryption Key Pair - Google Patents

Abstract

The invention relates to mobile communication technology, in particular to a method for periodically updating a transmission encryption key pair used for air interface encryption, so as to solve the problems of low success rate and waste of air interface resources in the prior art when updating transmission encryption keys. A periodic update method for transmitting encryption key pairs. The life cycle of each TEK is two update cycles. The BS generates a new TEK at the end of each update cycle to supplement the TEK whose life cycle is over, and When receiving the key request message sent by the MS/SS within the TEK Grace Time each time, the current two TEKs are sent to the MS/SS through the key request response message; the starting time of the TEK Grace Time is set at Within two air interface delays before the life cycle of the generated TEK ends.

Description

A Periodic Update Method for Transmitting Encryption Key Pair

technical field

The invention relates to mobile communication technology, in particular to a method for periodically updating a transmission encryption key pair used for air interface encryption.

Background technique

In communication systems, security has always been an important indicator to evaluate the quality of a communication system. With the development of cryptography and cryptanalysis, more available advanced technologies have been provided for the security of communication systems, and more challenges have been posed to the security of the system. Especially in the wireless mobile communication system, due to the openness and mobility of the wireless mobile communication system, an attacker can easily monitor the user's communication on the air interface, so the air interface data needs to be encrypted and authenticated. Moreover, in the process of moving, more restrictions and requirements are put forward on the distribution and management of keys, which makes the security issue particularly important.

The 802.16d/e series protocol defines the standard of wireless broadband fixed and mobile access air interface. In order to ensure the security of air interface data, the protocol defines a security sublayer (Privacy Sublayer) for user authentication and key distribution. management, and encryption and authentication of subsequent data. During the authentication process, BS (Base Station, base station) and MS/SS (Mobile Station, mobile station) (hereinafter referred to as MS) generate, distribute and manage keys through the PKM (Privacy Key Management, security key management) protocol, As a result of the authentication, there is a basic key AK used to derive other key resources between MS and BS. Both parties in communication derive KEK (KeyEncryption Key, key encryption key) from AK according to a secure algorithm. Neither AK nor KEK is directly used for data encryption. The key used for data encryption (TEK Traffic Encryption Key, transmission encryption key) is randomly generated by BS and distributed to MS after being encrypted with KEK. In order to further enhance security, AK and TEK are set to be valid within a certain life cycle. During a protection time before the life cycle of AK expires, MS must complete the re-authentication (Re-authentication) with BS to generate a new AK; within a protection time before the life cycle of TEK ends, MS must pass the message Interactively request a new TEK from the BS. In addition, in 802.16e, when the MS roams to a new target BS, the network re-entry (network re-entry) process must be carried out. key resource.

As shown in Figure 1, in order to ensure the continuity of service transmission during the TEK update process, MS and BS maintain multiple SA (Security Association, secure connection) information synchronously, and the security connection information includes SAID (used to identify a secure connection), corresponding encryption algorithm parameters and TEK key information, etc. On the BS side, new TEKs are periodically generated for each SA to ensure that two available TEKs are maintained for one SA at each moment. The actual usage time of each TEK is shown in the hatched segment in Figure 1. Each TEK The length of the life cycle is the same, but there is an overlap of half the life cycle, such as the overlap between TEK0 and TEK1 in Figure 1, the overlap between TEK1 and TEK2, and the overlap between TEK2 and TEK3. After the MS completes the access and passes the authentication, it needs to request the BS for its authorized security connection information. This process may be completed during the authentication message interaction process, such as in the RSA authentication mode in 802.16d, the BS sends the SA information to the MS through the authentication response message Auth Reply; it may also be through a specific message interaction process after the authentication is completed. Complete, such as in PKMV2 of 802.16e/D8, the distribution of SA information is completed through an SA-TEK three-way handshake message interaction process. In addition, the BS may also send SA information to the MS by actively sending a message, such as an SAAdd message. After the MS obtains the SA information authorized by the BS, the MS or BS specifies a mapping relationship with an SA for the connection as needed when establishing a service connection. After the connection is successfully established, all data transmitted on the connection will use the corresponding SA. Specify the encryption algorithm and key to encrypt. In order to further enhance security, the MS must start requesting new key resources for the currently maintained SA at an appropriate moment. The current 802.16d/e protocol defines a TEK state machine for each SA on the MS, and a TEK Grace Time is defined in the state machine, which represents a time interval field before the end of the TEK life cycle. In this time field The starting point of x and y shown in Figure 1, the MS must initiate a Key Request to request a new key resource, and the BS responds with a Key Reply message after receiving the request message, which contains the KEK-encrypted Two TEKs available at the current moment, along with their respective key serial numbers and remaining lifetime lengths. After receiving the Key Reply, the MS judges according to the key serial number and immediately uses the new TEK to encrypt the uplink data. On the BS, always use the older TEK among the two available TEKs to encrypt the downlink data, the specific process is shown in Figure 1.

The Key Reply message sent by the BS to the MS contains the TEK encrypted with the KEK, the serial number of the TEK, and the remaining life cycle length. According to the analysis, the moment when the BS constructs and sends the message and the MS receives the message and starts to use the new key There is an air interface delay between key moments. That is, there is an air interface delay difference between the two time points a and b in the figure, which is set as Tdelay. Generally, this delay is on the order of milliseconds. However, the TEK Grace Time defined in the current agreement is recommended to be 5 minutes to 3.5 days (see Agreement 10.2 for details), and its end time point is the same as the expiration time of TEK. Therefore, if the Key Request message is sent at time point x, the BS receives the message before time point a in most cases, and before this time point, BS has not generated a new key, so , the BS will send the two available keys at the current moment, for example: TEK0 and TEK1, to the MS again through the Key Reply message. After receiving the Key Reply message, the MS finds that the updated key information is not included, so it will initiate a Key Request again, although the Key Request message sent at a short time before TEK0 expires may reach the BS after time point a , so as to obtain a new key TEK2. However, in most cases, the Key Request message sent by the MS reaches the BS before the time point a, which greatly wastes the air interface resources, and to some extent, the protocol provided in the protocol to ensure the successful completion of the key update The protection time TEK Grace Time is only valid for a short time interval before the old TEK expires. If the Key Request message sent by the MS is lost within this very short protection time, the MS will not be able to obtain a new key, resulting in discontinuity of service data transmission.

Contents of the invention

The invention discloses a method for periodically updating a transmission encryption key pair to solve the problems in the prior art that the success rate is low and air interface resources are wasted when updating the transmission encryption key.

A periodic update method for transmitting encryption key pairs. According to the 802.16d/e protocol, the life cycle of each TEK is two update cycles, and the BS generates a new TEK at the end of each update cycle to supplement its life cycle. The TEK at the end of the cycle; the update method includes the following steps:

The mobile station MS/SS determines the expiration time of the previously generated TEK according to the remaining life cycle lengths of the current two TEKs in the key response message Key Reply obtained from the BS;

The MS/SS sets the starting time of the TEK protection time TEK Grace Time to be greater than or equal to the failure time minus the difference between the two air interface delays and less than or equal to the failure time;

The MS/SS starts sending key request messages at the start time of TEK Grace Time.

Before the MS/SS sets the start time of the TEK protection time TEK Grace Time, it also includes:

The MS/SS uses the acquired two TEKs currently stored on the BS side to update the two TEKs stored locally, and judges whether the two TEKs before and after the update correspond to the same, and if so, sends the key request message to the BS again, Otherwise, clear TEK Grace Time to zero.

The TEK Grace Time is 5 minutes to 3.5 days.

The air interface delay is estimated through measurement statistics or calculation.

A method for periodically updating a transmission encryption key pair. According to the 802.16d/e protocol, the life cycle of each transmission encryption key TEK is two update periods, and the base station BS generates a new TEK at the end of each update period. It is used to supplement the TEK whose life cycle is over; the update method includes the following steps:

The mobile station MS/SS determines the expiration time of the first generated TEK according to the remaining usage time of the current two TEKs in the key response message Key Reply obtained from the BS; the remaining usage time of the TEK is the remaining life cycle length of each TEK Add an extension time, the extension time is greater than or equal to TEK Grace Time minus the difference between the two air interface delays and less than or equal to TEK Grace Time;

The MS/SS sets the starting time of the TEK protection time TEK Grace Time as the failure time minus the TEK Grace Time;

The MS/SS starts sending key request messages at the start time of TEK Grace Time.

The TEK Grace Time is 5 minutes to 3.5 days as stipulated in the agreement.

The air interface delay is estimated through measurement statistics or calculation.

Beneficial effects brought by the technical solution of the present invention: by modifying the time at which the MS side starts to send the key update request message, the probability that the BS receives the request message after generating a new key is improved, thus improving a message interaction The probability that the key can be successfully updated can reduce the waste of air interface resources.

Description of drawings

Figure 1 is a sequence diagram of the TEK update process in the existing protocol;

FIG. 2 is a sequence diagram of the TEK update process in Embodiment 1 of the present invention;

FIG. 3 is a sequence diagram of a TEK update process in Embodiment 2 of the present invention.

Detailed ways

In the definition of TEK Grace Time in the current 802.16d/e protocol, the end time of TEK Grace Time is defined on the expiration time of TEK, and the corresponding start time is the expiration time of TEK minus the length of TEK Grace Time. This has resulted in the problem of wasting air interface resources in the prior art by repeatedly interacting Key Request and Key Reply uselessly before updating the key.

The technical solution provided by the present invention solves the problems existing in the prior art, and ensures that the key request message sent by the MS within an appropriate time interval can be received after the BS generates a new key, thereby successfully completing the key request message. Key update ensures the continuity of business data transmission during the key update process.

In order to realize the purpose of the present invention, it is necessary to modify the strategy of MS initiating a key update request, so that the MS starts to send the key update request message at an appropriate time point, and ensure that in most cases the BS generates a new key The message is received after the key. In this way, when the channel environment is good, only one message exchange is needed between the MS and the BS to successfully complete the key update. At the same time, it is guaranteed that in most cases the key request message sent by the MS reaches the BS after the BS generates a new key. Therefore, even if the current channel environment is poor and messages are lost frequently, as long as the protection time definition is appropriate, the key update can still be successfully completed after multiple message exchanges. According to the above idea, this method provides two specific implementation manners.

Embodiment one:

In order to achieve the purpose of the above invention, it is necessary to modify the definition of TEK GraceTime in the current 802.16d/e protocol. The start time of TEK Grace Time is defined as a certain moment within at most two air interface delays before the end of the old TEK life cycle on the MS side. When the MS sends the Key Request message within this time interval TEK GraceTime, it can ensure that the message is received after the new key is generated on the BS side, so that the returned response message carries the new key, so that the MS can successfully complete the transmission key request. key update. As shown in Figure 2, the implementation method in Figure 2 is to set the starting point of sending the Key Request message at the end of the TEK life cycle. The specific implementation includes the following two steps:

1. The BS respectively determines the remaining life cycle lengths of the current two TEKs and sends them to the MS/SS in the Key Reply message;

2. The MS obtains the remaining life cycle length of each TEK from the Key Reply message and calculates the end time of the generated TEK, for example: the end time of TEK0, TEK1, or TEK2 on the MS/SS side shown in Figure 2, and then Set the start time of TEK Grace Time to the end time minus at least two air interface delays.

Embodiment two:

In order to achieve the purpose of the above invention, the definition of TEK Grace Time in the current protocol may not be modified. It is only necessary for the BS to add the remaining lifetimes of the two currently available TEKs to An extension time, generally speaking, the extension time is required to be greater than or equal to TEK Grace Time minus two air interface delay lengths and less than or equal to TEK Grace Time. In this way, as shown in FIG. 3 , the TEK failure time on the MS will be delayed by an extended time. In this way, the Key Request message initiated by the MS within the TEK Grace Time interval can be guaranteed to be received after the BS generates a new key in most cases. The specific implementation includes the following two steps:

1. The BS determines the remaining usage time of the current two TEKs and sends them to the MS in the Key Reply message. The remaining usage time of the TEK is the remaining life cycle length of each TEK plus an extension time, which is greater than or equal to the TEK Grace Time minus two air interface delay lengths is less than or equal to TEK Grace Time;

2. The MS obtains the remaining usage time of each TEK from the Key Reply message and calculates the expiration time of the generated TEK, and then sets the start time of the TEK Grace Time as the expiration time minus the TEK Grace Time.

In fact, the method of setting the remaining usage time of TEKs to the remaining life cycle length of each TEK plus an extension time is the same as that in Embodiment 1, which is to push back the starting time of TEK Grace Time to avoid After the BS side generates a new key, it receives the Key Request message sent by the MS side, which reduces the message overhead.

Moreover, as shown in Figure 1, due to the timing of exchanging Key Request messages and Key Reply messages between the BS and the MS and the influence of air interface delay, although the TEK with the earlier sequence number expires later on the MS side than on the BS side, due to Due to the impact of air interface delay and scheduling, the MS may receive the data packet encrypted with the corresponding TEK sent by the BS after the TEK expires. At this time, the MS side cannot correctly decrypt the data encrypted by the BS with the earlier TEK. This second embodiment can improve this problem to a certain extent. The reason is that when the BS side extends the remaining life cycle of the TEK, the time for the MS side to retain the TEK with an earlier serial number is relatively extended, and the BS uses the TEK with an earlier serial number to encrypt. When the sent data arrives at the MS side, even if the channel environment or scheduling causes a large delay in data transmission, the MS side can still ensure that the corresponding old TEK is used to decrypt the data correctly, which improves the reliability of data transmission.

In the present invention, the air interface delay is obtained through measurement statistics or calculation estimation.

Beneficial effects brought by the technical solution of the present invention: by modifying the time at which the MS side starts to send the key update request message, the probability that the BS receives the request message after generating a new key is improved, thus increasing the time required for a message interaction. The probability that the key can be successfully updated reduces the waste of air interface resources.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (7)

1, the right periodical update method of a kind of traffic encryption key, life cycle according to each traffic encryption key TEK of 802.16d/e agreement is two update cycles, base station BS generates a new TEK when each update cycle finishes, in order to replenish the wherein TEK of life cycle end; It is characterized in that described update method comprises the steps:

Mobile station MS/SS determines the out-of-service time of the TEK that elder generation generates according to current two TEK residue life cycle length the key response message Key Reply that obtains from BS;

The zero-time that described MS/SS sets TEK guard time TEK Grace Time deducts the difference of two time delays of eating dishes without rice or wine more than or equal to the described out-of-service time and smaller or equal to the described out-of-service time;

Described MS/SS begins to send secret key request message in the zero-time of TEK Grace Time.

2, the method for claim 1 is characterized in that, sets at described MS/SS before the zero-time of TEK guard time TEK Grace Time, also comprises:

Described MS/SS utilizes two TEK of the current preservation of BS side of obtaining to upgrade local two TEK that preserve, and judge whether two TEK before and after described the renewal are corresponding identical, if then send secret key request message once more to BS, otherwise with TEK Grace Time zero clearing.

3, method as claimed in claim 1 or 2 is characterized in that, described TEK Grace Time is 5 minutes～3.5 days.

4, method as claimed in claim 3 is characterized in that, the described time delay of eating dishes without rice or wine is by measuring statistics or calculating and estimate to obtain.

5, the right periodical update method of a kind of traffic encryption key, life cycle according to each traffic encryption key TEK of 802.16d/e agreement is two update cycles, base station BS generates a new TEK when each update cycle finishes, in order to replenish the wherein TEK of life cycle end; It is characterized in that described update method comprises the steps:

Mobile station MS/SS remains service time according to current two TEK the key response message Key Reply that obtains from BS, determines the out-of-service time of the TEK that elder generation generates; Described TEK residue service time, the residue life cycle length for each TEK added a time expand, and this time expand deducts two differences of eating dishes without rice or wine to delay time and is less than or equal to TEK Grace Time more than or equal to TEK Grace Time;

The zero-time that described MS/SS sets TEK guard time TEK GraceTime is to deduct TEK Grace Time the described out-of-service time;

Described MS/SS begins to send secret key request message in the zero-time of TEK Grace Time.

6, as one of any described method of claim 5, it is characterized in that described TEK Grace Time is 5 minutes～3.5 days.

7, method as claimed in claim 6 is characterized in that, the described time delay of eating dishes without rice or wine is by measuring statistics or calculating and estimate to obtain.

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