Method of establishing a secure tunnel through a proxy server between a user device and a secure server

A method and apparatus for establishing a secure tunnel through a proxy between a user device and a secure server on a network are described. The method comprises storing information retrievable by the proxy server, in the event of the user device sending a request to the proxy server to access the secure server during a current session with the proxy server. The information indicates that the user device wishes to access the secure server. Thereafter, the current session between the user device and the proxy server is terminated. A tunnel is set through the proxy server between the user device and the secure server (via a trusted domain proxy/firewall) in the event of the user device sending a further request to the proxy server to access the secure server.

FIELD OF THE INVENTION

This invention relates to communications over a network. In particular, it relates to a method of establishing a secure tunnel through a proxy server between a user device and a remote secure server on the network.

BACKGROUND

It is desirable when sending sensitive information over a network to keep the information secret. For example, a user may be required to send his/her credit card information over the Internet in order to effect an online purchase. In order to ensure that such sensitive information is kept secret from potential eavesdroppers, the transmission control protocol (TCP/IP) suite on which the World Wide Web (WWW) is based includes secure protocols. For example, the Transport Layer in the TCP/IP suite includes the Transport Layer Security (TLS)/Secure Sockets Layer (SSL) protocols which have been designed specifically to achieve true end-to-end security. Briefly, the way these protocols work is to establish an encryption key which is shared between a user device and a remote secure server on the network. The process of establishing the shared encryption key is known as handshaking. All subsequent data transfer between the user device and the remote secure server are encrypted, both the user device and the secure server being able to decrypt the communications using the shared encryption key.

A special case occurs when a proxy server resides between the user device and the remote secure server. In this case, in order to achieve true end-to-end security, the proxy server must connect the user device to the remote secure server in order for handshaking to take place, at the end of which a shared encryption key is established between the user device and the remote secure server. This encryption key must remain unknown to the proxy server to maintain true end-to-end security.

In order to handle this special case, HyperText Transfer Protocol (HTTP), which is the primary protocol of the WWW, has a special method known as CONNECT. This method is used by a user device to instruct a proxy server to establish a connection with a remote server so that handshaking between the user device and the remote server can take place. At the end of the handshaking a shared encryption key is established between the user device and the remote secure server. Thereafter, all subsequent communications between the user device and the remote secure server are encrypted and sent to the proxy server which then acts only as a data relay between the user device and the remote secure server. This is known as tunneling through the proxy. As the proxy server does not know the encryption key, it cannot examine the data in the communications.

Many wireless devices make use of the Wireless Application Protocol (WAP) instead of the TCP/IP Protocol. The WAP protocol supports the Wireless Session Protocol (WSP) which does not have a method equivalent to the CONNECT method described above. Thus, tunneling through a proxy server in order to achieve true end-to-end secure communication between a wireless device, for example, mobile telephones, personal digital assistants (PDA's), personal information managers (PIM's), and pagers to reach a remote secure server remains a problem.

SUMMARY OF THE INVENTION

The invention provides a method and apparatus for establishing a secure tunnel through a proxy server between a user device and a secure server on a network. The method comprises receiving an initial request from a user device during a current session between the user device and the proxy server; terminating the current session if the initial request is to a secure server; and establishing a tunnel, through the proxy server, between the user device and the secure server upon receipt of a further request on the user device to access the secure server.

DETAILED DESCRIPTION OF THE DRAWINGS

Broadly, the invention provides a method of establishing a tunnel through a proxy server between a user device and a secure server. The method achieves, in a wireless environment, in essence what can be achieved using the HyperText Transfer Protocol (HTTP) CONNECT method which has no equivalent in the protocols used to support wireless devices e.g., Wireless Application Protocol (WAP).

Briefly, the HTTP CONNECT method is used to instruct a proxy to open a connection to a secure server and thereafter to simply copy data in both directions without intervening in the secure transaction. This process is known as tunneling. For example, a user device may send the following method/command to a proxy: Connect Openwave.com: 1080 HTTP/1.0 This command instructs the HTTP proxy to open a connection to “Openwave.com” on port 1080. Once the connection is established, the proxy acts like a simple data relay between the user device and the site Openwave.com.

As mentioned above, the CONNECT method or its equivalent does not exist in WAP.

Accordingly, the invention provides a method of establishing a tunnel through a proxy server using existing protocols supported by a mobile user device. Further, the invention provides a method of operating a proxy server in order to set a tunnel in accordance with the invention.

FIG. 1shows an illustrative network environment100in which various embodiments of the present invention may be practiced. Network environment100includes a wireless network (“Airnet”)102that is coupled to a land-based network (“Landnet”)104via a proxy server106.

Landnet104may be or may include the Internet, an intranet or a data network such as a local area network (LAN). The communications protocol supporting Landnet104may be, for example, HTTP or secure HTTP (SHTTP), which use the Transmission Control Protocol (TCP/IP) suite.

Airnet102may, for example, be a network such as a Cellular Digital Packet Data (CDPD) network, a Global System for Mobile (GSM) network, a Code Division Multiple Access (CDMA) network, or a Time Division Multiple Access Network (TDMA) network. The communications protocol used by the Airnet102may include, for example, Wireless Application Protocol (WAP) and/or Hand-held Device Protocol (HDTP) which use the User Datagram Packet (UDP/IP) protocol. Airnet102includes a transceiver base station108which facilitates wireless communications within its respective cell. As shown, a mobile communications device in the form of a mobile telephone110may operate within the area served by Airnet102.

Airnet102connects to Landnet104via proxy server106. Proxy server106serves to convert communications as they pass between Airnet102and Landnet104and thus functions as a gateway server. Coupled to Landnet104is a trusted domain proxy/firewall server112which forms part of a firewall implementation around a secure server114.

Proxy server106supports communications according to HTTP on the Landnet104side and communications according to HDTP and/or WAP on Airnet102side. Proxy server106also has software and/or hardware to provide various services to the mobile telephone110as will be described in greater detail below. The trusted domain proxy/firewall server112may be a conventional firewall proxy server which provides conventional firewall functionality in the form of a firewall116around the secure server114. The trusted domain proxy/firewall also provides WAP to HTTP protocol conversion.

In order to facilitate ease of discussion, it will be assumed that secure server114is the secure server for a fictitious banking organization known as Fake Bank having a Uniform Resource Locator (URL) HTTP://www.FakeBank.com. It is also be assumed that the Fake Bank has a non-secure mirror server which lies outside the area protected by firewall116. This non-secure server is designated118in FIG.1.

FIG. 2of the drawings shows the sequence of events which occur when a user device in the form of the mobile telephone110attempts to communicate with secure server114. As will be seen, at200mobile telephone110performs a handshake with proxy server106, which in this scenario will be provided by the carrier operator of Airnet102. The handshake is in accordance with a secure protocol known as Wireless Transport Layer Security Protocol (WTLS) which is the security layer of WAP. The goal of the handshake is to establish a shared key, say Key A, between the mobile telephone110and the proxy server106.

The sequence of steps which occur during a typical handshake is shown inFIG. 3of the drawings. Referring now toFIG. 3of the drawings, device D1represents the mobile telephone110and device D2represents proxy server106in the example of the WTLS handshake200(seeFIG. 2of the drawings). The handshake200starts with a “hello message,” which is sent by mobile telephone110to proxy server106. Proxy server106responds to the message with a return “hello message.” In the two hello messages, devices D1, D2agree on the session capabilities. For example, device D1announces the supported encryption algorithms and the trusted certificates known to D1, and device D2responds by determining session properties to be used during the session. After device D1has sent the hello messages, it starts receiving messages until the D2“hello done” message is received. Device D2then sends a server certificate message in which it authenticates itself. Thereafter, device D1sends a “key exchange” message containing either a pre-master secret encrypted with device D2's public key or the information that is required to complete the key exchange. Finally, device D1sends a “finished message” which contains verification of all previous data including the calculated security related information.

Device D2then responds with a “finished message” where it also verifies the exchange and the calculated information. In addition, either device must send a change cipher specification. By means of this message the devices decide that they start using the negotiated session parameters.

WTLS also supports an abbreviated handshake where only the “hello” and the “finished” messages are sent. In this case, both parties must have a shared secret, which is used as a pre-master secret.

As mentioned above, after the WTLS handshake200, both the mobile telephone110and the proxy server106share the encryption key, Key A. At step210, mobile telephone110sends the request GET: HTTPS://www.FakeBank.com, which is a secure HTTP command to access the FakeBank.com website on server114. Proxy server106responds to this instruction by establishing a TCP connection212with the non-secure server118which responds at216with a message indicating that server114is a secure server requiring end-to-end secure data transfer. Thus, proxy server106learns that the request the URL:HTTPS ://www.FakeBank.com is to a end-to-end secure URL. In response, proxy server106terminates the secure session with mobile telephone110at step218. It is to be understood that steps212to216are performed in order for proxy server106to learn that the instruction GET: HTTPS://www.FakeBank.com is directed to a secure server requiring end-to-end secure data transfer. In other embodiments, the proxy server106may be pre-provisioned with a list of secure servers requiring end-to-end secure data transfer against which it would perform a match of the URL for FakeBank.com in order to identify whether the FakeBank.com requires end-to-end secure data transfer or not.

The instruction218to close the WTLS session with mobile telephone110may be performed by sending a standard error message which tells mobile telephone110to resend the request to proxy server106. Thereafter, at step220, mobile telephone110initiates a further WTLS handshake with proxy server106. However, proxy server106now knows that mobile telephone110wishes to communicate with a secure server. As a result, proxy server106responds by going into “tunnel mode” in which it maps the inbound UDP socket to the outbound UDP socket and forwards the data directly to the proxy/firewall112. In essence, this allows mobile telephone110to handshake directly with trusted domain proxy/firewall112. At the end of this handshaking, at222, a shared encryption key, say Key B, is established between mobile telephone110and trusted domain proxy/firewall112. Once Key B has been established, then at226, the message GET: HTTPS://www.FakeBank.com is allowed by trusted domain proxy/firewall112to reach secure server114. All subsequent communications between mobile device110and secure server114are then tunneled through proxy server106using the mapping between the inbound UDP socket and the outbound UDP socket. At step228, a WTLS close is performed in order to end communications between mobile device110and secure server114.

FIG. 4of the drawings shows a flowchart illustrating the invention as described within reference toFIG. 3of the drawings. Referring toFIG. 4, at300, proxy server106receives an initial request from mobile telephone110. At302, proxy server106makes a determination as to whether the mobile telephone110wishes to communicate with a secure server.

As mentioned above, this may be done by communicating with the non-secure server118(see steps212to216, discussed with reference toFIG. 2of the drawings); or by pre-provisioning a list of secure servers in proxy server106. If it is determined that the initial request is not to a secure server, then proxy server106performs its standard proxy services. This is indicated by block304in the flowchart. However, if it is determined that the initial request is directed to a secure server, then at306, proxy server106stores sufficient information in order to identify mobile telephone110and secure server114with which it wishes to communicate. Thereafter at308, proxy server106terminates the secure session with mobile telephone110. This is done by sending a standard error message which, when received by mobile telephone110causes telephone110to send a further request to proxy server106to contact secure server114. At312, proxy server106makes a determination as to whether it should go “tunnel mode” or not. This is done by matching the incoming request with the stored information in order to identify firstly that the request is from mobile telephone110and secondly that it is directed to secure server114. If a positive match is made, then at314proxy server106goes into tunnel mode with a time-to-live delay. In other words, proxy server106will continue to operate in tunnel mode for a predetermined period of time, beyond which it will terminate the tunnel. If, on the other hand, no match is made, then proxy server106will continue to perform standard proxy services in a nontunnel mode. At316, proxy server106will tunnel data between mobile telephone110and secure server114(via the trusted domain proxy/firewall112) until the time to-live-delay has been reached, or it is determined, at318, that the tunnel is to be terminated. Proxy server106is able to determine that the tunnel has to be terminated if mobile telephone110sends a request to a URL other than the URL for the Fake Bank. Alternatively, it can decide to terminate the tunnel if the trusted domain proxy/firewall112generates a non secure error message (on behalf of the secure server114) which is “seen” by proxy server106.

FIG. 5of the drawings shows the sequence of steps in a typical session between mobile device110and secure server114in accordance with the invention. At step400, a user selects the URL for FakeBank.com, which causes a user agent associated with the user device (typically a web browser) to establish a secure session with proxy server106, at402. Thereafter, at404, the message GET: HTTPS://www.FakeBank.com is sent by the user agent to proxy server106. If it is determined by proxy server106that FakeBank.com is a secure site, then at406, the secure session with the user agent it terminated with a standard error message which causes mobile telephone110to re-establish a secure session with proxy server106. This secure session is re-established at408and if proxy server106recognizes that mobile telephone110is trying to reach secure server114, it will go into “tunnel mode,” in which it maps the inbound UDP socket to the outbound UDP socket and forwards the message GET: HTTPS://www.FakeBank.com to the trusted domain proxy/firewall112. After initial handshaking between mobile telephone110and trusted domain proxy/firewall112as described above, a shared encryption key is established therebetween. Thereafter, secure transactions may take place between mobile telephone110and secure server114. At410it is assumed that the user selects the URL for the site Shop.com, which causes, at412, the request GET: http://www.Shop.com to be forwarded by proxy server106to trusted domain proxy/firewall112. It will be appreciated that because of encryption, proxy server106is unable to view the payload portion of data sent in communication between mobile telephone110and secure server118. For this reason proxy server106is unable to ascertain that the request get: http://Shop.com should not be forwarded to the trusted domain proxy/firewall112. In response, trusted domain proxy/firewall112responds with an unencrypted error message which is seen by proxy server106which as a result terminates the tunnel.

Referring now toFIG. 6of the drawings, reference numeral106generally indicates one embodiment of a proxy server in accordance with the invention. Proxy server106includes memory252, which may represent one or more physical memory devices, which may include any type of Random Access Memory (RAM), Read Only Memory (ROM) (which may be programmable), flash memory, non-volatile mass storage device, or a combination of such memory devices. Proxy server106has loaded in memory250, a proxy server application254A and a gateway application254B. The illustrated proxy server106further includes a disk drive256, and a CD-ROM drive258coupled to a peripheral device-and-user interface262via a process bus260. Processor250, memory device252, disk drive256and CD-ROM258are generally known in the art. Peripheral device-and-user interface262provides an interface between processor bus260and various components connected to a peripheral bus268as well as to user interface components, such as display, mouse, and other user interface devices. A wireless network interface264, and a landnet interface266are coupled to peripheral bus268. Each of these interfaces264,266, may comprise a peripheral component card coupled to peripheral bus268. Wireless network interface264couples proxy server106to landnet104and operates according to protocols as previously described. When executing program instructions written according to the principals of the present invention, proxy server106is able to perform the operations described herein, particularly with reference toFIG. 4of the drawings.

One advantage of the present invention is that it allows a mobile communications device to achieve true end-to-end secure communications with a remote server (contained within a trusted domain) by tunneling through an operator proxy. The tunnel is set using existing protocols known to the mobile communications device. This obviates the need to modify or reprogram currently deployed mobile communications devices.

Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that various modification and changes can be made to these embodiments without departing from the broader spirit of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.