Abstract:
Disclosed is a system for lawful interception using a trusted third party in secure VoIP communication. A VoIP transmit terminal generates a secure packet using a master key received from a trusted third party and then communicates with a VoIP receive terminal. A collection device having received a lawful interception instruction from a key recovering system collects and transmits the secure packet to the key recovering system. The key recovering system decrypts the secure packet using the master key received from the trusted third party and provides the decrypted secure packet to a lawful interception requester or provides the master key received from the trusted third party and the secure packet to the lawful interception requester. It is possible to provide the perfect lawful interception in the secure VoIP communication environment, and to guarantee a perfect forward secrecy since the master key is changed for each call.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims all benefits of Korean Patent Application No. 10-2007-0119164 filed on Nov. 21, 2007 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a system and a method for lawful interception using a trusted third party in secure VoIP (Voice Over Internet Protocol) communication. According to the invention, a VoIP transmit terminal generates a secure packet using a master key received from a trusted third party and then communicates with a VoIP receive terminal. A collection device having received a lawful interception instruction from a key recovering system collects and transmits the secure packet to the key recovering system. The key recovering system decrypts the secure packet using the master key received from the trusted third party and provides the decrypted packet to a lawful interception requester or provides the master key received from the trusted third party and the secure packet to the lawful interception requester. 
         [0004]    2. Description of the Related Art 
         [0005]    Currently, a method for lawfully intercepting call contents between subscribers is widely used in the PSTN (Public Switched Telephone Network). In addition, as a VoIP for transmitting voice information using the IP (Internet Protocol) is widely used, a lawful interception method in the VoIP network is also suggested. 
         [0006]    In the meantime, the trusted third party (TTP) means an institution that is trusted in a user authentication and a key management from users and performs mediation, authentication, verification, management and the like. The trusted third party to manage an encryption key for the purpose of secure communication in the VoIP network is occasionally used. 
         [0007]    The conventional lawful interception method in the VoIP network is to lawfully intercept the general call in the VoIP. However, a technology that performs the lawful interception using the trusted third party has not been disclosed in the secure communication using the trusted third party. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    Accordingly, the present invention has been made to solve the above problems. An object of the invention is to provide a system and a method for lawful interception using a trusted third party in secure VoIP communication. According to the invention, a VoIP transmit terminal generates a secure packet using a master key received from a trusted third party and then communicates with a VoIP receive terminal. During the communication, a collection device having received a lawful interception instruction from a key recovering system collects and transmits the secure packet to the key recovering system. The key recovering system decrypts the secure packet using the master key received from the trusted third party and provides the decrypted secure packet to a lawful interception requester or provides the master key received from the trusted third party and the secure packet to the lawful interception requester. By doing so, it is possible to provide the perfect lawful interception in the secure VoIP communication environment, and to guarantee a perfect forward secrecy since the master key managed by the trusted third party is changed for each call. 
         [0009]    To be more specific, the invention relates to a system for lawful interception using a trusted third party in secure VoIP communication. The system is for lawfully intercepting secure communication using a trusted third party between a VoIP transmit terminal and a VoIP receive terminal and comprises a trusted third party that receives a master key request from the VoIP transmit terminal to generate a master key and transmits the generated master key to the VoIP transmit terminal and a key recovering system; a key recovering system that receives a lawful interception request from a lawful interception requester to instruct a collection device on lawful interception, receives a secure packet from the collection device, receives the master key from the trusted third party, decrypts the secure packet with the master key and provides the decrypted packet to the lawful interception requester or provides the master key and the secure packet to the lawful interception requester; and a collection device that collects the secure packet transmitted/received between the VoIP transmit terminal and the VoIP receive terminal in accordance with the lawful interception instruction received from the key recovering system and transmits the collected secure packet to the key recovering system. 
         [0010]    In addition, the invention relates to a method for lawful interception using a trusted third party in secure VoIP communication. The method is for lawfully intercepting secure communication using a trusted third party between a VoIP transmit terminal and a VoIP receive terminal and comprises the steps of: (a) instructing, at a key recovering system, a collection device on lawful interception in accordance with a lawful interception request from a lawful interception requester; (b) at the trusted third party, receiving a master key request from the VoIP transmit terminal to generate a master key and transmitting the generated master key to the VoIP transmit terminal; (c) exchanging the master key and performing secure communication between the VoIP transmit terminal and the VoIP receive terminal; (d) at the collection device, collecting a secure packet transmitted/received between the VoIP transmit terminal and the VoIP receive terminal and transmitting the secure packet to the key recovering system; and (e) at the key recovering system, receiving the master key from the trusted third party, decrypting the secure packet with the received master key and providing the decrypted packet to the lawful interception requester. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    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: 
           [0012]      FIG. 1  shows a structure of a system for lawful interception using a trusted third party in secure VoIP communication according to an embodiment of the invention; 
           [0013]      FIG. 2  shows a detailed structure of a trusted third party according to an embodiment of the invention; 
           [0014]      FIG. 3  shows a detailed structure of a key recovering system according to an embodiment of the invention; 
           [0015]      FIG. 4  is a flow chart showing a process for lawful interception using a trusted third party in secure VoIP communication according to an embodiment of the invention; and 
           [0016]      FIG. 5  is a flow chart showing a process for lawful interception using a trusted third party in secure VoIP communication according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. 
         [0018]      FIG. 1  shows a structure of a system for lawful interception using a trusted third party in secure VoIP communication according to an embodiment of the invention. 
         [0019]    The system for lawful interception according to the invention comprises a trusted third party  10 , a VoIP transmit terminal  20 , a collection device  30 , a VoIP receive terminal  40  and a key recovering system  50 . 
         [0020]    The trusted third party  10  is an institution that manages an encryption key for the purpose of secure communication between VoIP terminals. 
         [0021]    According to an embodiment, when the trusted third party  10  receives a request for a master key (Traffic Generation Key; TGK) from the VoIP transmit terminal  20 , which master key is a kind of an encryption key necessary for the secure communication with the VoIP receive terminal  40 , the trusted third party  10  generates and then transmits a master key to the VoIP transmit terminal  20 . In addition, the trusted third party  10  also transmits the master key to the key recovering system  50  so that the key recovering system  50  can decrypt a secure packet, as described below. 
         [0022]    Alternatively, when the trusted third party  10  receives a request for a master key from the VoIP transmit terminal  20 , which master key is a kind of an encryption key necessary for the secure communication with the VoIP receive terminal  40 , the trusted third party  10  generates and then transmits a master key to the VoIP transmit terminal  20 . Then, the trusted third party  10  may generate a session key from the master key and transmit the session key to the key recovering system  50 . At this time, the session key is an encryption key that is used to actually encrypt a voice packet between the VoIP transmit terminal  20  and the VoIP receive terminal  40 . 
         [0023]      FIG. 2  shows a detailed structure of a trusted third party according to an embodiment of the invention. To be more specific, the trusted third party  10  comprises a control unit  11 , an encryption key generation unit  12 , a storage unit  13  and a transmit unit  14 . 
         [0024]    When there is a request for an encryption key from the VoIP transmit terminal  20 , the encryption key generation unit  12  generates a master key under the control of control unit  11  and generates a session key from the master key. 
         [0025]    The storage unit  13  stores the master key and the session key that are generated by the encryption key generation unit  12  under the control of control unit  11 . 
         [0026]    The transmit unit  14  transmits the master key and the session key to the VoIP transmit terminal  20  and the key recovering system  50  under the control of control unit  11 , respectively. 
         [0027]    The control unit  11  controls the respective elements constituting the trusted third party  10  and may perform additional functions such as key recovery request record management and monitoring management, as required. 
         [0028]    The collection device  30  collects secure packets transmitted/received between the VoIP transmit terminal  20  and the VoIP receive terminal  40 , which are the objects of the lawful interception, in accordance with a lawful interception instruction received from the key recovering system  50 , and transmits the collected secure packets to the key recovering system  50 . 
         [0029]    The key recovering system  50  receives a request for lawful interception from the lawful interception requester  60  and instructs the collection device  30  on the lawful interception. In addition, the key recovering system  50  receives the secure packet from the collection device  30  and receives the master key or session key from the trusted third party  10 . Then, the key recovering system decrypts the secure packets using the master key or session key and provides the decrypted packets to the lawful interception requester  60 . Alternatively, the key recovering system  50  may provide the master key or session key received from the trusted third key  10  to the lawful interception requester  60  together with the secure packets so that the lawful interception requester  60  can decrypt the secure packets. 
         [0030]      FIG. 3  shows a detailed structure of a key recovering system according to an embodiment of the invention. Specifically, the key recovering system  50  comprises a control unit  51 , a decryption unit  52 , a storage unit  53  and a transmit unit  54 . 
         [0031]    The decryption unit  52  decrypts the secure packets received from the collection device  30  using the master key or session key received from the trusted third party  10 . 
         [0032]    The storage unit  53  stores communication information between the VoIP transmit terminal  20  and the VoIP receive terminal  40  under the control of control unit  51 . For example, the storage unit stores the information such as IDs of the transmit and receive terminals, IP/ports of the transmit and receive terminals, time at which a call is initiated and time at which the call is terminated. At this time, the communication information is extracted from the packets decrypted in the decryption unit  52 . 
         [0033]    The transmit unit  54  receives the secure packets from the collection device  30 , receives the master key or session key from the trusted third key  10  and transmits the decrypted packets to the lawful interception requester  60 . 
         [0034]    The control unit  51  controls the respective elements constituting the key recovering system  50  and may perform additional functions such as key recovery request record management and monitoring management, as required. 
         [0035]    The following describes a method for lawful interception using a trusted third party in secure VoIP communication according to the invention, with reference to  FIGS. 4 and 5 . 
         [0036]      FIG. 4  is a flow chart showing a process for lawful interception using a trusted third party in secure VoIP communication according to an embodiment of the invention. 
         [0037]    First, the lawful interception requester  60  transmits the information about terminals that are objects of the lawful interception to the key recovering system  50  and requests the lawful interception (S 10 ). The information may be for example, IDs of the transmit and receive terminals and IP/ports of the transmit and receive terminals. The key recovering system  50  having received the request for lawful interception transmits the information about the terminals that are objects of the lawful interception to the collection device  40 , thereby instructing the lawful interception (S 11 ). 
         [0038]    Meantime, when the VoIP transmit terminal  20  requests the trusted third party  10  for a master key for the purpose of the secure communication with the VoIP receive terminal  40  (S 12 ), the trusted third party  10  generates and then transmits a master key to the VoIP transmit terminal  20  (S 13 ). 
         [0039]    Then, when the VoIP transmit terminal  20  transmits an INVITE message including the master key to the VoIP receive terminal  40  so as to initiate the secure communication with the VoIP receive terminal  40  (S 14 ), the VoIP receive terminal  40  transmits a response message to the VoIP transmit terminal  20  (S 15 ), so that the secure communication between the VoIP transmit terminal  20  and the VoIP receive terminal  40  is made (S 16 ). 
         [0040]    Like this, during the secure communication between the VoIP transmit terminal  20  and the VoIP receive terminal  40 , the collection device  30  collects the secure packets transmitted/received between the VoIP transmit terminal  20  and the VoIP receive terminal  40  (S 17 ), which are the objects of the lawful interception, and transmits the collected secure packets to the key recovering system  50  (S 18 ). 
         [0041]    Then, the key recovering system  50  receives the master key from the trusted third party  10  (S 19 ), decrypts the secure packets received from the collection device  30  using the master key in real time (S 20 ) and provides the decrypted packets to the lawful interception requester  60  (S 21 ). 
         [0042]    Alternatively, after the step of S 19 , the key recovering system  50  may provide both the master key received from the trusted third party  10  and the secure packets received from the collection device  30  to the lawful interception requester  60  (not shown) so that the lawful interception requester  60  can directly decrypt the secure packets. 
         [0043]      FIG. 5  is a flow chart showing a process for lawful interception using a trusted third party in secure VoIP communication according to another embodiment of the invention. 
         [0044]    First, the lawful interception requester  60  transmits the information about terminals that are objects of the lawful interception to the key recovering system  50  and requests the lawful interception (S 30 ). The information may be for example, IDs of the transmit and receive terminals and IP/ports of the transmit and receive terminals. The key recovering system  50  having received the request for lawful interception transmits the information about the terminals that are objects of the lawful interception to the collection device  30 , thereby instructing the lawful interception (S 31 ). 
         [0045]    Meantime, when the VoIP transmit terminal  20  requests the trusted third party  10  for a master key for the purpose of the secure communication with the VoIP receive terminal  40  (S 32 ), the trusted third party  10  generates and then transmits a master key to the VoIP transmit terminal  20  (S 33 ). 
         [0046]    Then, when the VoIP transmit terminal  20  transmits an INVITE message including the master key to the VoIP receive terminal  40  so as to initiate the secure communication with the VoIP receive terminal  40  (S 34 ), the VoIP receive terminal  40  transmits a response message to the VoIP transmit terminal  20  (S 35 ). 
         [0047]    Then, the trusted third party  10 , the VoIP transmit terminal  20  and the VoIP receive terminal  40  generate a session key from the master key, respectively (S 36 ), so that the secure communication between the VoIP transmit terminal  20  and the VoIP receive terminal  40  is made (S 37 ). 
         [0048]    Like this, during the secure communication between the VoIP transmit terminal  20  and the VoIP receive terminal  40 , the collection device  30  collects the secure packets transmitted/received between the VoIP transmit terminal  20  and the VoIP receive terminal  40  (S 38 ), which are the objects of the lawful interception, and transmits the collected secure packets to the key recovering system  50  (S 39 ). 
         [0049]    Then, the key recovering system  50  receives the session key from the trusted third party  10  (S 40 ), decrypts the secure packets received from the collection device  30  using the session key in real time (S 41 ) and then provides the decrypted packets to the lawful interception requester  60  (S 42 ). 
         [0050]    Alternatively, after the step of S 40 , the key recovering system  50  may provide both the session key received from the trusted third party  10  and the secure packets received from the collection device  30  to the lawful interception requester  60  (not shown) so that the lawful interception requester  60  can directly decrypt the secure packets. 
         [0051]    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 thereto without departing from the spirit and scope of the invention as defined by the appended claims.