Abstract:
Disclosed are a system and a method for performing re-authentication in a communication system. A user Authorization, Authentication and Accounting server transmits a user Master Session Key (MSK_U), which is generated by performing user re-authentication for a mobile station (MS) according to a twice Extensible Authentication Protocol scheme, to a device Authorization, Authentication and Accounting server that generates a new user Master Session Key (MSK_U 1 ) by using the MSK_U and a device Master Session Key generated at initial device authentication for the MS. A base station (BS) generates a Pairwise Master Key (PMK) by using the MSK_U 1,  and the MS and BS generate an authorization key by using the PMK.

Description:
PRIORITY  
       [0001]     This application claims priority to an application entitled “Re-Authentication System and Method in Communication System” filed in the Korean Industrial Property Office on Nov. 14, 2005, and assigned Serial No. 2005-108811, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a re-authentication system and a re-authentication method in a communication system, and more particularly to a system and a method for performing re-authentication in a communication system by using a twice Extensible Authentication Protocol (EAP) (hereinafter twice EAP) scheme.  
         [0004]     2. Description of the Related Art  
         [0005]     It is well-known in the art that next-generation communication systems are evolving into communication systems for providing mobile stations with services enabling high-capacity data to be transmitted/received at high speed. A typical example of the next-generation communication system is an IEEE (Institute of Electrical and Electronics Engineer) 802.16e communication system.  
         [0006]      FIG. 1  illustrates the internal structure of an IEEE 802.16e communication system employing a conventional twice EAP scheme. Hereinafter, for the convenience of explanation, the twice EAP scheme will be referred to as an “EAP-in-EAP” scheme, and an operation mode using the EAP-in-EAP scheme will be referred to as an “EAP-in-EAP” mode.  
         [0007]     Referring to  FIG. 1 , the IEEE 802.16e communication system includes a Mobile Station (hereinafter MS)  100 , a Base Station (hereinafter BS)  110 , a device Authorization, Authentication and Accounting (AAA) (hereinafter AAA-D) server  120  and a user AAA (hereinafter AAA-U) server  130 . The MS  100  performs device authentication with the AAA-D server  120  through the BS  110 , and performs user authentication with the AAA-U server  130  through the BS  110 . Since the IEEE 802.16e communication system uses an EAP-in-EAP scheme, authentication according to an EAP scheme is performed twice. Hereinafter, for the convenience of explanation, authentication performed using the EAP scheme will be referred to as “EAP authentication”. Of the two EAP authentications performed, the first EAP authentication is intended to authenticate a user, and the second authentication is intended to authenticate a device after the first authentication is successful.  
         [0008]      FIG. 2  is a signal flowchart illustrating a procedure of performing re-authentication in the IEEE 802.16e communication system employing a conventional EAP-in-EAP scheme.  
         [0009]     Similar to the authentication initially performed, re-authentication in the IEEE 802.16e communication system employing an EAP-in-EAP scheme also requires two EAP authentications, those being user re-authentication and device re-authentication. Hereinafter, for the convenience of explanation, the EAP authentication for re-authentication will be referred to as “EAP re-authentication”.  
         [0010]     Referring to  FIG. 2 , when user re-authentication is needed, a BS  220  transmits an EAP-REQUEST/IDENTITY message, which requests EAP re-authentication, to an MS  200 . Since messages according to an EAP scheme are transmitted/received between the MS  200  and the BS  220  by using a Privacy Key Management (PKM) version 2 (hereinafter”PKMv2)_EAP_TRANSFER (PKMv2_EAP_TRANSFER) message, the BS  220  transmits a PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message to the MS  200  (step  211 ).  
         [0011]     If the PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message is received from the BS  220  to the MS  200 , the MS  200  transmits a PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message to the BS  220  in response to the PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message (step  213 ).  
         [0012]     If the PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message is transmitted from the MS  200  to the BS  220 , the BS  220  forwards intact the received PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message to the AAA-U server  260 . In the IEEE 802.16e communication system, messages according to the EAP scheme are transmitted/received between the BS  220  and the AAA-U server  260  by using a Remote Authentication Dial-In User Service (RADIUS) protocol message, a DIAMETER protocol message or the like. Particularly, it is assumed in  FIG. 2  that messages according to the EAP scheme are transmitted/received between the BS  220  and the AAA-U server  260  by using the RADIUS protocol message. Thus, the BS  220  transmits a RADIUS/ACCESS REQUEST/IDENTITY message to the AAA-U server  260  (step  215 ).  
         [0013]     If the RADIUS/ACCESS REQUEST/IDENTITY message is received from the BS  220  to the AAA-U server  260 , the AAA-U server  260  performs user re-authentication for the MS  200  in such a manner that it re-authenticates the PKMv2_EAP_TRANSFER messages by using a scheme such as an EAP-Message-Digest5 (EAP-MD5) or an EAP-Microsoft Challenge Authentication Protocol version 2 (EAP-MSCHAPv2) scheme (step  217 ). If re-authentication for the MS  200  is completed in this manner, the AAA-U server  260  and the MS  200  share a user Master Session Key (hereinafter MSK_U) (steps  219  and  221 ).  
         [0014]     Subsequently, the AAA-U server  260  transmits a RADIUS/EAP-SUCCESS message containing the MSK_U and indicating that the EAP re-authentication was successful to the AAA-D server  240  (step  223 ). The AAA-D server  240  recognizes success in user re-authentication for the MS  200  by receiving the RADIUS/EAP-SUCCESS message from the AAA-U server  260 , and determines whether the second EAP re-authentication is needed (step  225 ). Since both EAP re-authentication for a user and EAP re-authentication for a device must be performed in the IEEE 802.16e communication system employing the EAP-in-EAP scheme, the AAA-D server determines that the second EAP-re-authentication is necessary.  
         [0015]     The AAA-D server  240 , which has determined that the second EAP re-authentication needs to be performed, transmits a RADIUS/EAP-SUCCESS message, which indicates success in user re-authentication for the MS  200 , to the BS  220  (step  227 ). Here, the RADIUS/EAP-SUCCESS message contains the MSK_U. The BS  220  generates the first Pairwise Master Key (PMK) (hereinafter PMK__ 1 ) by using the MSK_U contained in the RADIUS/EAP-SUCCESS message received from the AAA-D server  240  (step  229 ). The BS  220  also transmits a PKMv2_EAP_TRANSFER/EAP-SUCCESS message indicating success in user re-authentication to the MS  200  (step  231 ). Through steps  211  to  231 , user/first EAP re-authentication for the MS  200  is completed. In addition, when device re-authentication is needed, the BS  220  transmits a PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message to the MS  200  (step  233 ). If the PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message is received from the BS  220  to the MS  200 , the MS  200  transmits a PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message to the BS  220  in response to the PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message (step  235 ).  
         [0016]     If the PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message is received from the MS  200  to the BS  220 , the BS  220  forwards intact the PKMv2_EAP_TRANSFER/EAP-RSPONSE/IDENTITY message in the form of a RADIUS/ACCESS REQUEST/IDENTITY message to the AAA-D server  240  (step  237 ).  
         [0017]     If the RADIUS/ACCESS REQUEST/IDENTITY message is received from the BS  220  to the AAA-D server  240 , the AAA-D server  240  performs device re-authentication for the MS  200  in such a manner that it re-authenticates the PKMv2_EAP_TRANSFER messages by using a scheme such as an EAP-Transport Level Security (EAP-TLS) scheme, an EAP-Transport Level Security Pre-Shared KEY (EAP-TLSPSK) scheme or an EAP-Authentication and Key Agreement (EAP-AKA) scheme (step  239 ). If device re-authentication for the MS  200  is completed in this manner, the AAA-D server  240  and the MS  200  share a device Master Session Key (hereinafter MSK_D) (steps  241  and  243 ).  
         [0018]     Subsequently, the AAA-D server  240  transmits a RADIUS/EAP-SUCCESS message, which indicates success in the EAP re-authentication, to the BS  220  (step  245 ). Here, the RADIUS/EAP-SUCCESS message contains the MSK_D. The BS  220  generates the second PMK (hereinafter PMK__ 2 ) by using the MSK_D contained in the RADIUS/EAP-SUCCESS message received from the AAA-D server  240  (step  247 ). The BS  220  also transmits a PKMv2_EAP_TRANSFER/EAP-SUCCESS message indicating success in device re-authentication to the MS  200  (step  249 ). Through steps  233  to  249 , device/second EAP re-authentication for the MS  200  is completed. If re-authentication up to device re-authentication is completed in this manner, the MS  200  and the BS  220  perform a Security Association &amp; Traffic Encryption Key 3way handshake (hereinafter SA-TEK 3way handshake) operation (step  251 ). If the SA-TEK 3way handshake operation is completed, the MS  200  and the BS  220  generate an Authorization Key (AK) from PMK_ 1  and PMK_ 2  (steps  253  and  255 ).  
         [0019]     Reference will now be made in detail to a procedure of generating the AK by using PMK_ 1  and PMK_ 2 .  
         [0020]     First, the MS  200  and the BS  220  applies PMK_ 1  and PMK_ 2  to an AK generation function such as the Dot16KDF function, thereby generating the AK. Here, the Dot16KDF function can be expressed by the following Equation (1): 
 
 AK =Dot16 KDF ( PMK   — 1 ⊕  PMK   — 2, MSID|BSID|‘AK’, 160)   (1) 
 
         [0021]     In Equation (1), MSID denotes the identifier of an MS  200  for which EAP authentication is presently performed, BSID denotes the identifier of a BS  220 , ‘AK’ represents that a key generated by the Dot16KDF function is an AK, and numeral  160  represents that the length of an AK generated by the Dot16KDF function is 160 bits. That is, the Dot16KDF function generates an AK having a length of 160 bits by using a parameter for an exclusive logical sum (XOR) operation of PMK_ 1  and PMK_ 2  and a parameter for the concatenation of MSID and BSID.  
         [0022]     As stated in connection with  FIG. 2 , in the IEEE 802.16e communication system employing the EAP-in-EAP scheme, EAP re-authentication is performed twice for user authentication and device authentication even when performing re-authentication. Consequently, because of the two EAP re-authentications, the quantity of radio resources consumed increases and re-authentication time lengthens, which results in performance deterioration of the overall system.  
       SUMMARY OF THE INVENTION  
       [0023]     Accordingly, the present invention has been made to solve at least the above-mentioned problem occurring in the prior art, and an object of the present invention is to provide a system and a method for performing re-authentication in a communication system.  
         [0024]     A further object of the present invention is to provide a system and a method for re-authenticating a user and a device together through only one EAP re-authentication in a communication system.  
         [0025]     To accomplish these objects, in accordance with the present invention, there is provided a system for performing re-authentication in a communication system, which system includes an AAA-U server for transmitting an MSK_U, which is generated by performing user re-authentication for a MS according to an EAP-in-EAP scheme, to an AAA-D servern the AAA-D server for generating a new MSK_U termed MSK_U 1 , by using the MSK_U and a MSK_D having been generated at initial device authentication for the MS, and then transmitting the MSK_U 1  to a BS that generates a PMK by using the MSK_U 1 , and generating an AK by using the PMK, and the MS for generating the AK by using the PMK.  
         [0026]     In accordance with the present invention, there is provided a first embodiment of a method for performing re-authentication in a communication system, which method includes transmitting, from an AAA-U server to an AAA-D server, an MSK_U, which is generated by performing user re-authentication for an MS according to an EAP-in-EAP scheme, generating a new MSK__U termed an MSK_U 1 , in the AAA-D server by using the MSK_U and a MSK_D having been generated at initial device authentication for the MS, and then transmitting the MSK_U 1  from the AAA-D server to a BS, generating a PMK in the BS by using the MSK_U 1 , and generating an AK in the MS and the BS by using the PMK.  
         [0027]     In accordance with the present invention, there is provided a second embodiment of a method for performing re-authentication in a communication system, which method includes receiving, from an AAA-U server; an MSK_U, which is generated by performing user re-authentication for an MS according to an EAP-in-EAP scheme, and generating a new MSK_U termed an MSK_U 2 , by using the MSK_U and a MSK_D having been generated at initial device authentication for the MS, transmitting the MSK_U 2  to a BS, and controlling the BS to generate a PMK by using the MSK_U 2 .  
         [0028]     In accordance with the present invention, there is provided a third embodiment of a method for performing re-authentication in a communication system, which method includes receiving an MSK_U and a new MSK_U termed an MSK_U 3 , which is generated by using an MSK_D having been generated at initial device authentication for an MS, from an AAA-D server; generating a PMK by using the MSK_U 3 , and generating an AK by using the PMK, wherein an AAA-U server generates the MSK_U by performing user re-authentication for the MS according to an EAP-in-EAP scheme. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0030]      FIG. 1  is a block diagram illustrating an internal structure of an IEEE 802.16e communication system employing a conventional EAP-in-EAP scheme;  
         [0031]      FIG. 2  is a flowchart illustrating a procedure of performing re-authentication in an IEEE 802.16e communication system employing a conventional EAP-in-EAP scheme; and  
         [0032]      FIG. 3  is a flowchart illustrating a procedure of performing re-authentication in an IEEE 802.16e communication system employing an EAP-in-EAP scheme in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the similar components are designated by similar reference numerals although they are illustrated in different drawings. Also, in the following description, a detailed description of known functions and configurations incorporated herein will be omitted for the sake of clarity and conciseness.  
         [0034]     The present invention discloses a system and a method for re-authenticating a user and a device together through only one EAP re-authentication in an IEEE 802.16e communication system employing a twice EAP scheme. Further, the present invention discloses a system and a method for re-authenticating a user and a device while preventing a Man-in-the-middle-Attack phenomenon even through only one EAP re-authentication in an IEEE 802.16e communication system employing a twice EAP scheme. Here, the Man-in-the-middle-Attack phenomenon refers to a phenomenon in which an abnormal user/device performs EAP-re-authentication by using a normal user/device&#39;s AK by stealth, and a detailed description thereof will be omitted because it is unrelated to the present invention.  
         [0035]     Hereinafter, since the internal structure of an IEEE 802.16e communication system employing the EAP-in-EAP scheme is the same as that described above in the Description of the Related Art with reference with  FIG. 1 , a detailed description thereof will be omitted. In addition, although the IEEE 802.16e communication is exemplified in the following description for the convenience of explanation, the present invention may be applied to communication systems other than the IEEE 802.16e communication system.  
         [0036]      FIG. 3  is a flowchart illustrating a procedure of performing re-authentication in an IEEE 802.16e communication system employing an EAP-in-EAP scheme according to the present invention.  
         [0037]     It is noted that re-authentication in the conventional IEEE 802.16e communication system employing a common EAP-in-EAP scheme also requires user re-authentication and device re-authentication. However, when re-authentication according to the present invention is performed, only one EAP re-authentication (hereinafter EAP re-authentication) is required for user re-authentication and device re-authentication. Referring to  FIG. 3 , when user re-authentication and device re-authentication are needed, a BS  320  transmits an EAP-REQUEST/IDENTITY message, which requests EAP re-authentication, to an MS  300 . In the IEEE 802.16e communication system, since messages according to an EAP scheme are transmitted/received between the MS  300  and the BS  320  by using a PKMv2_EAP_TRANSFER message, the BS  320  transmits a PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message to the MS  300  (step  311 ).  
         [0038]     If the PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message is received from the BS  320  to the MS  300 , the MS  300  transmits a PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message to the BS  320  in response to the PKMv2_EAP_TRANSFER/EAP-REQUEST/IDENTITY message (step  313 ).  
         [0039]     If the PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message is received from the MS  300  to the BS  320 , the BS  320  forwards intact the received PKMv2_EAP_TRANSFER/EAP-RESPONSE/IDENTITY message to an AAA-U server  360 . In the IEEE 802.16e communication system, messages according to the EAP scheme are transmitted/received between the BS  320  and the AAA-U server  360  by using such a message as a Remote Authentication Dial-In User Service (RADIUS) protocol message or a DIAMETER protocol message. Particularly, in  FIG. 3 , messages according to the EAP scheme are transmitted/received between the BS  320  and the AAA-U server  360  by using the RADIUS protocol message. Thus, the BS  320  transmits a RADIUS/ACCESS REQUEST/IDENTITY message to the AAA-U server  360  (step  315 ).  
         [0040]     If the RADIUS/ACCESS REQUEST/IDENTITY message is received from the BS  320  to the AAA-U server  360 , the AAA-U server  360  performs user re-authentication for the MS  300  in such a manner that it re-authenticates the PKMv2_EAP_TRANSFER messages by using a scheme such as an EAP-Message-Digest5 (EAP-MD5) scheme or an EAP-Microsoft Challenge Authentication Protocol version 2 (EAP-MSCHAPv2) scheme (step  317 ). If re-authentication for the MS  300  is completed in this manner, the AAA-U server  360  and the MS  300  share a user Master Session Key (MSK_U) (steps  319  and  321 ).  
         [0041]     Subsequently, the AAA-U server  360  transmits a RADIUS/EAP-SUCCESS message containing the MSK_U and indicating that the EAP re-authentication was successful, to an AAA-D server  340  (step  323 ). The AAA-D server  340  recognizes successful user re-authentication for the MS  300  by receiving the RADIUS/EAP-SUCCESS message from the AAA-U server  360 , and determines whether the second EAP re-authentication is necessary (step  325 ). Since device re-authentication as well as user re-authentication can be performed by only one EAP re-authentication in the present invention, the AAA-D server determines that the second EAP-re-authentication is not necessary. Thereafter, the AAA-D server  340  generates an MSK_U 1  in addition to the MSK_U (step  325 ). The MSK_U 1  is generated by using a KDF (Key Derivation Function) function as given in the following Equation (2): 
 
MSK —   U 1 =KDF ( MSK   —   D, MSK   —   U |‘Combined MSK ’)   (2) 
 
         [0042]     In Equation (2), the KDF function generates the MSD_U 1  by combining an MSK_U and an MSK_D. The MSK_D has been generated at initial authentication for the MS  300 .  
         [0043]     After the MSK_U 1  is generated in this manner, the AAA-D server  340  transmits a RADIUS/EAP-SUCCESS message, which contains the MSK_U 1  and indicates success in user re-authentication and device re-authentication for the MS  300 , to the BS  320  (step  327 ). The BS  320  generates a PMK by using the MSK_U 1  contained in the RADIUS/EAP-SUCCESS message received from the AAA-D server  340  (step  329 ). The BS  320  also transmits a PKMv2_EAP_TRANSFER/EAP-SUCCESS message indicating success in user re-authentication and device-re-authentication to the MS  300  (step  331 ).  
         [0044]     Through steps  311  to  331 , if user re-authentication and device re-authentication for the MS  300  are completed in this manner, the MS  300  and the BS  320  perform a Security Association &amp; Traffic Encryption Key 3way handshake (SA-TEK 3way handshake) operation (step  333 ). If the SA-TEK 3way handshake operation is completed, the MS  300  and the BS  320  generate an Authorization Key (AK) from the PMK (steps  335  and  337 ).  
         [0045]     Reference will now be made in detail to a procedure of generating the AK by using the PMK.  
         [0046]     First, the MS  300  and the BS  320  apply the PMK to an AK generation function such as the Dot16KDF function, thereby generating the AK. The Dot16KDF function can be expressed by the following Equation (3): 
 
 AK =Dot16 KDF ( PMK,MSID|BSID|‘AK’, 160)   (3) 
 
         [0047]     In Equation (3), MSID denotes the identifier of an MS  300  for which EAP authentication is presently performed, BSID denotes the identifier of a BS  320 , ‘AK’ represents that a key generated by the Dot16KDF function is an AK, and numeral  160  represents that the length of an AK generated by the Dot16KDF function is 160 bits. That is, the Dot16KDF function generates an AK having a length of  160  bits by using a parameter for PMK and a parameter for the concatenation of MSID and BSID.  
         [0048]     As represented in Equation (3), the IEEE 802.16e communication system employing the EAP-in-EAP scheme according to this embodiment of the present invention can prevent the Man-in-the-middle-Attack phenomenon because it generates an AK by using a PMK that is generated using both an MSK_U having been generated at user re-authentication and a MSK_D having been generated at initial authentication. Since only one EAP re-authentication enables both user re-authentication and device re-authentication without causing the Man-in-the middle-Attack in the IEEE 802.16e communication system employing the EAP-in-EAP scheme according to this embodiment of the present invention, a resulting increase in the quantity of radio resources consumed and a rise in re-authentication time spent can be avoided, thereby improving the overall system performance.  
         [0049]     As described above, the present invention enables both user re-authentication and device re-authentication to be performed through only one EAP re-authentication without causing the Man-in-the middle-Attack in the IEEE 802.16e communication system employing an EAP-in-EAP scheme. As a result, an increase in the quantity of radio resources consumed and a rise in re-authentication time spent, which result from performing EAP re-authentication twice in the conventional IEEE 802.16e communication system employing a common EAP-in-EAP scheme, can be avoided, which results in an improvement of the overall system performance.  
         [0050]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.