Abstract:
A first communication network is used to securely communicate a key that is used for communications over a different network. In one embodiment, a CDMA network is used to securely communicate a key that is used for communications in a data network. The key used in the data network may be used for authentication and/or enciphering or encryption.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to communications; more specifically, the security of the authentication process used in communication systems. 
   2. Description of the Related Art 
     FIG. 1  illustrates a base station  10 , its associated cell  12  and mobile  14  within cell  12 . When mobile station  14  first registers or attempts communications with base station  10 , base station  10  authenticates or verifies the mobile&#39;s identity before allowing the mobile access to the communication network. The authentication of mobile  14  involves communicating with authentication center  16 . Authentication center  16  then accesses a home location register  22  which is associated with mobile  14 . Home location register  22  may be associated with the terminal or mobile by an identifier such as the mobile&#39;s telephone number. The information contained in the home location register is used to generate encryption keys and other information. This information is used to supply base station  10  with information that is transmitted to mobile  14  so that mobile  14  can respond and thereby be authenticated as a mobile that is entitled to receive communication services. 
     FIGS. 2   a  and  2   b  illustrate the authentication process used for an IS-41 compliant network. IS-41 compliant networks are networks that use, for example, AMPS, TDMA or CDMA protocols. In this system, both the mobile and home location register contain a secret value called AKEY. Before the actual authentication process can start, a key update is performed by providing the mobile with keys that will be used with encryption functions for authentication and communication. The AKEY value stored in the home location register associated with the mobile is used to produce the keys. The keys values calculated are the SSDA (Shared Secret Data A) and SSDB (Shared Secret Data B) values. These values are calculated by performing the CAVE algorithm or function using a random number R S  as an input and the value AKEY as the key input. The CAVE algorithm is well known in the art and is specified in the IS-41 standard. The network then updates the key values SSDA and SSDB that will be used by the mobile by transmitting R S  to the mobile. The mobile then calculates SSDA and SSDB in the same fashion as calculated by the authentication center. Now that the mobile and home location register both contain the SSDA and SSDB values, the authentication process may take place. 
     FIG. 2   b  illustrates how a mobile is authenticated to a network after both the mobile and home location register have received the keys SSDA and SSDB. The authentication center challenges the mobile by sending a random number R N  to the mobile. At this point both the mobile and authentication center calculate the value AUTHR, where AUTHR is equal to the output of the CAVE algorithm using the random number R N  as an input and the SSDA value as the key input. The mobile then transmits the calculated value AUTHR to the authentication center. The authentication center compares its calculated value of AUTHR and the value received from the mobile. If the values match, the mobile is authenticated and it is given access to the network. In addition, both the mobile and the authentication center calculate the value of cipher key K C  where the value K C  is equal to the output of the CAVE algorithm using the value R N  as an input and the value SSDB as the key input. At this point, communications between the mobile and network are permitted and may be encrypted using a cryptographic function where the inputs are the message to be encrypted and the key value is K C . 
   As illustrated above, many of today&#39;s wireless voice networks such as CDMA, TDMA, GSM and AMPS networks provide for securely communicating encryption or cipher keys between a network and a mobile terminal. Unfortunately, this capability is not available in other networks. 
   SUMMARY OF THE INVENTION 
   The present invention uses a first communication network to securely communicate a key that is used for communications over a different network. In one embodiment, a CDMA network is used to securely communicate a key that is used for communications in a data network. The key used in the data network may be used for authentication and/or enciphering or encryption. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates communications between a mobile and authentication center; 
       FIGS. 2   a  and  2   b  illustrate the key update and authentication process for an IS-41 compliant network; 
       FIG. 3  illustrates a first network that securely provides a key for use in a second or overlay network; and 
       FIG. 4  illustrates the process for providing a key for communications in an overlay network using secure communications over another network. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  illustrates CDMA network  50  and HDR (Higher Data Rate) network  60 . CDMA network  50  is a network that provides secure communications and user authentication. Network  50  may be a network other than a CDMA network such as a TDMA network, GSM network, AMPS network or another type of wireless voice network. Mobile station  62  communicates with network  50  via base station  64 . Initially, mobile station  62  is authenticated by network  50  as described earlier through communications between base station  64  and authentication center  66  which includes home location register  68 . It is also possible for base station  64  to communicates with authentication center  66  via mobile switching center  70 . If communication network  50  is not mobile station  62 &#39;s home network, the authentication process is carried out through authentication center  72  and visiting location register  74  which communicate with authentication center  76  and home location register  78  in the mobile&#39;s home network. After mobile station  62  has been authenticated by network  50  communicates are carried out through base station  64  and mobile switching center  70  to either public switched telephone network  80  or short message service message center (SMS MC)  90 . 
   In some instances, mobile station  62  may be in communication with or may include application terminal  100  when carrying out data communications. For example, application terminal  100  may be a portable computer in communication with mobile station  62 , or it may be a communication application being run by mobile station  62 . Data communications are typically carried out by application terminal  100  through mobile station  62  via data network  60 . Data network  60  may be a data network such as an HDR radio access network (H-RAN). Network  60  may include elements such as base station  110  and switching center  112 . Switching center  112  allows base station  110  to communicate with internet protocol (IP) network  114  and packet data service network (PDSN)  116 . When involved in data communications, application terminal  100  communicates with the destination application terminal or server  118  via mobile station  62 , base station  110 , switching center  112  and PSDN  116 . 
   Network  50  performs an authentication of mobile station  62  and provides a ciphering key K C  to mobile station  62 . Once mobile station  62  and network  50  have agreed on a cipher key K C , secure communications may be carried out between network  50  and mobile station  62 . The session key that will be used for authentication, and/or enciphering or encryption of communications between application terminal  100  and network  60  is provided to application terminal  100  via a secure communication between network  50  and mobile station  62 . 
     FIG. 4  illustrates the process by which the session key that will be used for communications between application terminal  100  and network  60  is communicated to application terminal  100  using network  50 . Each step in this process is outlined below in reference to  FIG. 4 .
         a) Application terminal (AT) requests the PPP (Point to Point Protocol) connection sending the PPPREQ (PPP Request) message to the Mobile Station (MS).   b) The MS is the combination IS-2000 &amp; HDR terminal. The MS sends the IS-2000 registration to the IS-2000 RAN (Radio Access Network) (MSC/BSC/VLR).   c) The VLR conducts registration and authentication procedure with the HLR.   d) The registration and authentication procedure is complete. The session Ciphering Key (K C ) is available at the VLR/MSC/BSC.   e) The registration session is completed and the K C  is available at the MS.   f) The MS sends the PPPREQ to the HDR RAN. The message is identified by the MS IMSI (A mobile station or user identifier).   g) The HDR RAN selects the random HDR Session Key, HDR-SSD.   h) The HDR RAN generates the IS-41 SMS Delivery Point-to-Point (SMDPP) message addressed to the MS. The message is identified as the HDR_Teleservice_Message. The message contains the HDRSSDUPD (HDR SSD Update Request) and a parameter set to the value of HDR_SSD. The message is sent to the IS-41 SMS MC with instruction for secure delivery. The IS-41 SMS MC forwards the SMS message to the IS-41 VLR/MSC/BSC.   i) The IS-41 VLR/MSC/BSC encrypts the message using the K C  and sends it to the MS over the IS-2000 air interface as encrypted SMS message.   j) The MS decrypts received SMS message and forwards the contents—the HDRSSDUPD Request with the HDR-SSD parameter—to the AT with the MS IMSI included.   k) The AT calculates the digital signature (MAC) of the IMSI using the HDR_SSD as the key, and sends the signature to the MS as the response.   l) The MS assembles the response SMS message for the HDR RAN and sends it to the IS-41 MC. The message contains the Digital Signature of the MS IMSI calculated in step (k).   m) The IS-41 MC sends the smdpp response to the HDR RAN containing the Digital Signature of IMSI.   n) The HDR RAN validates the Digital Signature of IMSI.   o) The HDR RAN sends the PPPREQ (PPP Request) to the PDSN for specific IMSI. Optionally, it may include the HDR_SSD to be used for the session encryption at the PPP level.   p) The PDSN established the PPP and responds to the HDR RAN.   q) The HDR RAN responds to the MS with the pppreq response.   r) The MS forwards the pppreq response to the AT.   s) The PPP session is established between the AT and PDSN and may be encrypted using the HDR_SSD.