VPN enrollment protocol gateway

A virtual private network (VPN) enrollment protocol gateway is described herein. The protocol gateway is implemented as a registration authority that operates as an intermediary between routers and a certificate authority, allowing routers operating in accordance with one protocol to obtain and maintain certificates for a VPN from a certificate authority operating in accordance with another protocol. In accordance with one aspect, the gateway protocol supports various requests from the router, including router enrollment requests, get certificate revocation list request, get certificate requests, get certificate authority certificate requests, and password requests.

TECHNICAL FIELD

This invention relates to secure communications, and more particularly to a protocol gateway allowing routers operating in accordance with one protocol to obtain and maintain certificates for a virtual private network (VPN) from a certificate authority operating in accordance with another protocol.

BACKGROUND OF THE INVENTION

Computer technology is continually advancing, resulting in continually evolving uses for computers. One such use is communicating with other computers over a network, such as the Internet, to obtain or exchange information, purchase or sell goods or services, etc. One particular type of communication that can be established is referred to as a “virtual private network” or “VPN”. In a VPN, portions of a network (such as the Internet) are used to establish secure communications from one computer to another via multiple different routers in the network. The VPN allows users to use the larger network (e.g., the Internet) to connect to another computer as if they were part of a dedicated secure network.

In order to operate as part of a VPN, a router enrolls for a VPN certificate via a certificate authority (CA). This VPN certificate is then provided to other routers that are part of the VPN and is used to authenticate the router and may also be used to securely communicate with the other routers. However, different protocols for enrolling for VPN certificates have arisen, many of which are incompatible with one another. For example, many routers available from Cisco Systems, Inc. of San Jose, Calif. use a proprietary protocol called Simple Certificate Enrollment Protocol (SCEP) for obtaining VPN certificates, while many certificate authorities available from Microsoft Corporation of Redmond, Wash. use an incompatible enrollment protocol based on Public-Key Cryptography Standard (PKCS) #10 and PKCS #7. Thus, a router using SCEP would not be able to enroll for a VPN certificate from a CA using PKCS #10 and PKCS #7.

Additionally, many routers and CAs are already manufactured and in use that operate based on such incompatible protocols. Therefore, re-designing such routers or CAs to be compatible with one another would require the replacement of many such pre-existing devices. Thus, it would be beneficial to provide a solution that allows routers and CAs (including pre-existing routers and CAs) operating based on incompatible protocols to communicate with one another for VPN certificate enrollment.

The VPN enrollment protocol gateway described below addresses these and other disadvantages.

SUMMARY OF THE INVENTION

A virtual private network (VPN) enrollment protocol gateway is described herein. The protocol gateway allows routers operating in accordance with one protocol to obtain and maintain certificates for a VPN from a certificate authority operating in accordance with another protocol.

According to one aspect, the VPN enrollment protocol gateway is implemented as a registration authority that operates as an intermediary between the router and the certificate authority. As a registration authority, the gateway is trusted by the certificate authority. The router communicates with the registration authority as if it were the certificate authority, not realizing that it is communicating with an intermediary.

According to another aspect, the protocol gateway receives a router enrollment request from the router. The protocol gateway decrypts the request, adds an alterative subject name to the request, digitally signs the request, and forwards the signed request to the certificate authority. The certificate authority determines whether to trust the source of the request (the protocol gateway), and proceeds to respond with the requested certificate if it verifies that the gateway can be trusted. The gateway receives the requested certificate, encrypts and digitally signs a response including the certificate, and returns the signed and encrypted response to the router.

According to another aspect, the certificate authority may not be able to immediately issue a certificate, in which case it issues a pending response. The registration authority maintains a mapping of a router transaction ID (identifier) received from the router and a pending response ID received from the certificate authority. This mapping allows subsequent requests from the router with the same transaction ID (e.g., querying whether the certificate has been issued yet) to be properly matched to a request previously submitted to the certificate authority for which a pending response was issued. The registration authority also maintains a mapping of a hash value of the request received from the router to the pending response for that request. This mapping allows the registration authority to determine when a request is resubmitted by the router (e.g., in the event the router never receives a pending response returned to it by the registration authority).

According to another aspect, the protocol gateway receives a get certificate revocation list from the router. The protocol gateway decrypts the request and extracts from the request the certificate serial number of the signing certificate of the request. The protocol gateway then submits a Get Certificate by Serial Number request to the certificate authority, which returns to the protocol gateway the certificate corresponding to the serial number. The protocol gateway extracts a certificate revocation list distribution point from the response, and obtains the certificate revocation list from the distribution point. The protocol gateway then generates a response including the certificate revocation list, encrypts and signs the response, and returns the response to the router.

According to another aspect, the protocol gateway receives a get certificate request from the router. The protocol gateway decrypts the request and extracts from the request the certificate serial number of the signing certificate of the request. The protocol gateway then submits a Get Certificate by Serial Number request to the certificate authority, which returns to the protocol gateway the certificate corresponding to the serial number. The protocol gateway then encrypts and signs a response including the certificate, and returns the response to the router.

According to another aspect, the protocol gateway receives a get certificate authority certificate request from the router. The protocol gateway generates a response message including the signing certificate of the registration authority as well as the encryption certificate of the registration authority, and returns the response message to the router.

According to another aspect, the protocol gateway maintains a record of passwords handed out to a router. A router obtains a password by communicating with the protocol gateway (or another device trusted by the protocol gateway) via an authenticatable mechanism (e.g., SSL (Secure Sockets Layer)). A password is returned to the router, which can then use this password for a request submitted to the protocol gateway. If the password presented by the router is in the router's record, then the request is processed; otherwise, the request is rejected.

DETAILED DESCRIPTION

The discussion herein assumes that the reader is familiar with cryptography. For a basic introduction of cryptography, the reader is directed to a text written by Bruce Schneier and entitled “Applied Cryptography: Protocols, Algorithms, and Source Code in C,” published by John Wiley & Sons with copyright 1994 (or second edition with copyright 1996).

In the discussion below, embodiments of the invention will be described in the general context of computer-executable instructions, such as program modules, being executed by one or more conventional personal computers. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that various embodiments of the invention may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. In a distributed computer environment, program modules may be located in both local and remote memory storage devices.

Alternatively, embodiments of the invention can be implemented in hardware or a combination of hardware, software, and/or firmware. For example, all or part of the invention can be implemented in one or more application specific integrated circuits (ASICs).

FIG. 1shows a virtual private network environment with an enrollment protocol gateway in accordance with certain embodiments of the invention. Generally, one or more client computers102can communicate with one or more server computers104via a public network supporting a conventional virtual private network (VPN)106. Server computers104can be coupled directly to the network supporting VPN106, or alternatively can be coupled to the network supporting VPN106via another network, such as local area network (LAN)108.

VPN106includes one or more routers110,112, and114through which data is passed between client102and server104. Routers110–114are part of a public network, such as the Internet. Routers that are part of other types of networks may also be included in VPN106, such as routers from a LAN or a private wide-area network.

Additionally, other networks may be involved in the communication between client102and server104. By way of example, client102may connect to the public network supporting VPN106via a conventional modem and a Public Switched Telephone Network (PSTN), via a conventional cable modem and cable lines, etc.

Routers110–114can communicate with one another, as well as registration authority118, via any of a wide variety of conventional communications protocols. In one implementation, routers110–114communicate with one another and registration authority118using the Hypertext Transfer Protocol (HTTP).

Each of the routers110–114receives data from one of the other routers110–114or alternatively from another component (e.g., a public network access provider, such as an Internet Service Provider (ISP); client computer102; etc.). The data is then securely passed on to another of the routers110–114or other components.

In order for data to be transmitted among routers110–114, a certificate-based authentication scheme is employed. In such an authentication scheme, each router110–114is assigned a unique certificate that it can use to authenticate itself to other routers or other computing devices (e.g., an ISP, a bridge or gateway, etc.). Additionally, these other computing devices may be part of VPN106and may similarly be assigned unique certificates that can be used for authentication. Such certificates can also optionally be used to encrypt messages between routers and/or other computing devices in any of a variety of conventional manners. For ease of explanation, routers are described as the devices that are obtaining and maintaining certificates for VPN106. The establishment and operation of a VPN is well-known to those skilled in the art, and thus will not be discussed further except as it pertains to the invention.

The certificates used by routers110–114are assigned by a trusted certificate authority (CA)116. The process of obtaining such a certificate is referred to as “enrollment”. In the illustrated example, routers110–114use a different enrollment protocol than is used by certificate authority116. A registration authority118communicates with both routers110–114and certificate authority116and acts as an intermediary for enrollment, translating requests and responses in one protocol to another, as discussed in more detail below.

FIG. 2shows a general example of a computer142that can be used in accordance with certain embodiments of the invention. Computer142is shown as an example of a computer that can perform the functions of a client computer102, a server computer104, a certificate authority116, or a registration authority118ofFIG. 1. Computer142includes one or more processors or processing units144, a system memory146, and a bus148that couples various system components including the system memory146to processors144.

The bus148represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. The system memory includes read only memory (ROM)150and random access memory (RAM)152. A basic input/output system (BIOS)154, containing the basic routines that help to transfer information between elements within computer142, such as during start-up, is stored in ROM150. Computer142further includes a hard disk drive156for reading from and writing to a hard disk, not shown, connected to bus148via a hard disk driver interface157(e.g., a SCSI, ATA, or other type of interface); a magnetic disk drive158for reading from and writing to a removable magnetic disk160, connected to bus148via a magnetic disk drive interface161; and an optical disk drive162for reading from or writing to a removable optical disk164such as a CD ROM, DVD, or other optical media, connected to bus148via an optical drive interface165. The drives and their associated computer-readable media provide nonvolatile storage of computer readable instructions, data structures, program modules and other data for computer142. Although the exemplary environment described herein employs a hard disk, a removable magnetic disk160and a removable optical disk164, it should be appreciated by those skilled in the art that other types of computer readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, random access memories (RAMs) read only memories (ROM), and the like, may also be used in the exemplary operating environment.

A number of program modules may be stored on the hard disk, magnetic disk160, optical disk164, ROM150, or RAM152, including an operating system170, one or more application programs172, other program modules174, and program data176. Operating system170can be any of a variety of operating systems, such as any of the “Windows” family of operating systems available from Microsoft Corporation of Redmond, Wash. A user may enter commands and information into computer142through input devices such as keyboard178and pointing device180. Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are connected to the processing unit144through an interface168(e.g., a serial port interface) that is coupled to the system bus. A monitor184or other type of display device is also connected to the system bus148via an interface, such as a video adapter186. In addition to the monitor, personal computers typically include other peripheral output devices (not shown) such as speakers and printers.

Computer142can operate in a networked environment using logical connections to one or more remote computers, such as a remote computer188. The remote computer188may be another personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to computer142, although only a memory storage device190has been illustrated inFIG. 2. The logical connections depicted inFIG. 2include a local area network (LAN)192and a wide area network (WAN)194. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet. In the described embodiment of the invention, remote computer188executes an Internet Web browser program such as the “Internet Explorer” Web browser manufactured and distributed by Microsoft Corporation of Redmond, Wash.

When used in a LAN networking environment, computer142is connected to the local network192through a network interface or adapter196. When used in a WAN networking environment, computer142typically includes a modem198or other means for establishing communications over the wide area network194, such as the Internet. The modem198, which may be internal or external, is connected to the system bus148via a serial port interface168. In a networked environment, program modules depicted relative to the personal computer142, or portions thereof, may be stored in the remote memory storage device. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used.

FIG. 3is a block diagram illustrating an exemplary registration authority118operating as a protocol gateway between a router210and a certificate authority116. Router210can be, for example, any of routers110–114ofFIG. 1. Router210is configured (e.g., during an installation or setup process) with the address of registration authority118rather than CA116as the certificate authority. In the illustrated example, router210has no other knowledge that it is communicating with registration authority118rather than certificate authority116.

Communication between registration authority118and each of router210and certificate authority116can be carried out using any of a wide variety of conventional encryption and/or digital signing techniques. By way of example, using well-known public key cryptography techniques, a device obtains a private key/public key pair; the public key is made available to other devices while the private key is kept secret by the device. Another device can encrypt a message intended for this device by using a conventional encryption algorithm and this device's public key. The private key/public key pair and the encryption algorithm are chosen such that it is relatively easy to decrypt the message with the private key, but extremely difficult to decrypt the message without the private key. Similarly, a message can be digitally signed by the device using a conventional encryption algorithm and its private key. The digitally signed message can be decrypted by another device using the public key, allowing the other device to verify that the message came from that device. Alternatively, rather than applying an encryption algorithm to the message itself, the encryption algorithm may be applied to a hash value generated based on the message and a known hash function. Different public key/private key pairs can be used for encryption and digital signatures, or alternatively the same public key/private key pair can be used for both encryption and digital signatures.

Registration authority118operates as an enrollment agent for certificate authority116, allowing routers such as router210to enroll for a VPN certificate from certificate authority116via registration authority118. Registration authority118obtains, from certificate authority116, an enrollment agency signature certificate (e.g., by enrolling for an “Offline IPSec” enrollment agent signature certificate) and an encryption certificate (e.g., by enrolling for an “IPSec Encryption” certificate). In the illustrated examples, these certificates are used by registration authority118to digitally sign data sent to both the router210and the certificate authority116, and to encrypt data sent to the router210.

Router210communicates requests212to registration authority118in accordance with the protocol supported by router210. In the illustrated example, router210supports the protocol SCEP. Different types of requests212can be transmitted to registration authority118. In one implementation, registration authority118operates as a protocol gateway for the following types of requests: router enrollment, get certificate revocation list (CRL), get certificate, get certificate authority (CA) certificate, and password registration. The specific manner in which each of these requests is handled by registration authority118is discussed in more detail below.

Upon receipt of an SCEP request212, registration authority118converts the request into an appropriate format for certificate authority116. The converted request is then digitally signed by registration authority118and the signed request214is transmitted to certificate authority116. Certificate authority116, receiving a request in its own protocol (using PKCS #7 and PKCS #10), responds to the request and issues a CA response216. Registration authority118receives the response216, converts the response to the appropriate SCEP format for router210, and transmits an SCEP response218to router210. Alternatively, for some requests registration authority118may generate the response218without forwarding a signed request214to certificate authority116.

Registration authority118includes a protocol converter220. Protocol converter220receives messages from router210and converts them as necessary to the proper protocol for certificate authority116, and similarly receives messages from certificate authority116and converts them to the proper protocol for router210. The manner in which protocol converter220operates is dependent on the particular protocols being used by router210and certificate authority116.

In one implementation, registration authority118operates in accordance with the Internet X.509 Public Key Infrastructure Certificate and CRL Profile (Network Working Group Request for Comments 2459, January 1999). Alternatively, other implementations may operate in accordance with other standards.

Registration authority118also includes a transaction ID table222, a request hash table224, and a password table226. Tables222–226are used by registration authority118to maintain information regarding requests212and responses216in order to conform with the protocols of router210and certificate authority116.

FIG. 4shows an exemplary transaction ID table in accordance with certain embodiments of the invention. Transaction ID table222maintains a mapping of router transaction IDs228to CA request IDs230. A router transaction ID228is received by registration authority118from router210as part of each router enrollment message. Similarly, when certificate authority116returns a pending response to registration authority118, the pending response includes a CA request ID230(also referred to as a “token”). Transaction ID table222allows registration authority118to query certificate authority116for the correct certificate in response to subsequent requests from router210for the certificate the pending response was issued for, as discussed in more detail below.

Each entry in transaction ID table222is removed from table222after a period of time. In one implementation, each entry in table222is kept in table222for one week and then removed. This period of time can optionally be configurable by a user or administrator.

FIG. 5shows an exemplary request hash table in accordance with certain embodiments of the invention. Request hash table224maintains a mapping of certificate authority request IDs232to hash values of the requests234. The hash value of a request is generated using any of a variety of conventional hashing functions, such as MD5 (Message Digest5). A hash function is a mathematical function that, given input data (e.g., the request) generates a unique output hash value based on the input data. Thus, the hash value uniquely identifies a request but requires less storage space than maintaining all of the request. Alternatively, table224could maintain the actual request rather than hash values of the request.

Request hash table224allows registration authority118to “remember” router requests. For example, a pending response may be issued by registration authority118to router210, as discussed in more detail below. If a failure or problem occurs during the transmission (e.g., a network failure), then the pending response may not be received by router210. If router210never receives the response, router210will re-issue the same request. By maintaining table224, registration authority118can determine when a received request is a re-issued request, and need not submit another request for another new certificate to certificate authority116.

Each entry in request hash table224is removed from table224after a period of time. In one implementation, each entry in table224is kept in table224for twenty minutes and then removed. This period of time can optionally be configurable by a user or administrator.

FIG. 6shows an exemplary password table in accordance with certain embodiments of the invention. Password table226maintains passwords236that are issued to router210in a secure manner. Such passwords can subsequently be used by router210to obtain a certificate, providing verification of the identity of router210.

Each password in password table226is removed from table226after a period of time. In one implementation, each password in table226is kept in table226for sixty minutes and then removed. This period of time can optionally be configurable by an administrator.

Returning toFIG. 3, in the illustrated example registration authority118is a dynamically linked library (DLL) referred to as the “MSCEP” DLL. Alternatively, registration authority118may include a DLL referred to as the “MSCEP” DLL. Registration authority118includes a response module238that generates responses for certain requests from router210that do not require forwarding to certificate authority116. The operation of response module238is discussed in more detail below.

Registration authority118further hosts a web site240. Alternatively, registration authority118may have a secure communication link to a server hosting web site240, thereby allowing data to be securely passed between the server and registration authority118, or registration authority118may be software and/or filmware being executed by a server that also hosts web site240. Web site240allows passwords to be securely issued to router210and stored in password table226, as discussed in more detail below.

Router Enrollment Request

FIGS. 7aand7bare a flowchart illustrating an exemplary process for handling a router enrollment request in accordance with certain embodiments of the invention. Acts on the left-hand side ofFIGS. 7aand7bare implemented by registration authority118ofFIG. 3, while acts on the right-hand side are implemented by certificate authority116. The process ofFIGS. 7aand7bmay be performed in software, firmware, hardware, or a combination thereof.FIGS. 7aand7bare described with additional reference to components inFIG. 3.

To participate in a VPN, router210enrolls for a certificate from certificate authority116. Router210enrolls for a certificate by sending, as SCEP request212, a router enrollment message (e.g., a SCEP PKCSReq message) to registration authority118. The router enrollment message includes a certificate enrollment request in accordance with the Public-Key Cryptography Standards (PKCS) #10 standard. The certificate enrollment request is further encrypted (e.g., using the public key of registration authority118) and then digitally signed by router210in accordance with the Public-Key Cryptography Standards (PKCS) #7 standard. Additional information regarding PKCS #7 and PKCS #10 is available from RSA Data Security, Inc. of Bedford, Mass. It should be noted that, although requests from router210use PKCS #7 and PKCS #10, certain information needed by certificate authority116is not included in the requests. Registration authority118resolves this problem, adding information when necessary.

Registration authority118receives, as the router enrollment message, this encrypted and digitally signed request (act242). Upon receipt of the enrollment message, registration authority118verifies the signature of the router enrollment message (act244). If the signature is not verified then the message is ignored (act246). Alternatively, an indication of failure could be returned to router210.

If the signature is verified, then registration authority118decrypts the router enrollment message (e.g., using the private key of registration authority118) and extracts the certificate enrollment request from the message (act248). Registration authority118uses the certificate enrollment request to generate a request to the CA for an enrollment certificate in a format expected by certificate11authority116(act250).

Router210needs a certificate with a subject alternative names extension (SubjectAltName). However, router210does not specifically request the SubjectAltName extension, and certificate authority116does not automatically add the extension. Registration authority118resolves this issue by adding, to the message it transmits to certificate authority116, the SubjectAltName extension in the request.

The PKCS #7 message, including both the subject alternative names extension and the certificate enrollment request extracted from the router enrollment message, is digitally signed by registration authority118(act252). This signed message is then transmitted to certificate authority116as a CA request (act254). Note that the CA request thus includes a PKCS #7 message that is signed by registration authority118, which in turn includes a certificate enrollment request that is signed by router210.

Certificate authority116receives the CA request from registration authority118(act256) and determines, based on the content of the CA request, whether to issue the requested certificate (act258). The manner in which certificate authority116determines whether to issue the requested certificate can vary. In one implementation, certificate authority116determines whether to issue a certificate based on whether the certificate of the registration authority118can be validated up to a trusted valid root and whether the certificate of registration authority118includes an extended key usage indicating that registration authority118can be a registration authority (and thus operate as an enrollment agent). If both of these conditions are satisfied, then a certificate is issued. Otherwise, the certificate is not issued. Additionally, certificate authority116may require that the certificate of registration authority118have been issued directly by a certificate authority (that is, no intermediate certificates in the chain from the registration authority certificate to the certificate authority certificate).

If certificate authority116determines it will not issue a certificate, then certificate authority116generates a CA response indicating failure (act260). However, if certificate authority116determines it will issue a certificate, then certificate authority116generates the requested certificate (act262) and then generates a CA response including the generated certificate (act264).

The CA response generated by certificate authority116has no message content and is referred to as a “degenerated PKCS #7”. The PKCS #7 message, however, allows multiple certificates to be included in a degenerated PKCS #7 message. Certificate authority116returns the newly generated certificate as part of the degenerated PKCS #7 message. Additionally, the entire certificate chain from the generated certificate up to a root certificate may optionally be included in the degenerated PKCS #7 message.

Certificate authority116then transmits the CA response (indicating either failure or with the generated certificate) to registration authority118(act266). Registration authority118receives the CA response (act268) and checks whether the CA response includes a certificate (act270). If no certificate is included, then registration authority118generates an SCEP response message indicating failure (act272). However, if such a certificate is included, then registration authority118extracts the certificate (act274) and generates an SCEP response including the certificate (act276). In the illustrated example, registration authority118extracts only the certificate generated by certificate authority116; the additional certificate chain (if included) is not used by registration authority118. Alternatively, the entire certificate chain could be included if router210desired (or at least could handle) the chain.

Registration authority118then encrypts the SCEP response (act278) and digitally signs the encrypted response (act280). The encrypted and signed response is then transmitted to router210(act282), which in turn can verify the signature and decrypt the response to extract the certificate generated by certificate authority116.

Pending Response Handling

In some situations, certificate authority116may not immediately issue a CA response with either a certificate or an indication that no certificate will be issued. For example, certificate authority116may wait for an administrator to approve the issuing of the certificate. In such situations, certificate authority116issues a CA pending response from certificate authority116.

FIG. 8is a flowchart illustrating an exemplary process for handling pending responses in accordance with certain embodiments of the invention. The process ofFIG. 8is implemented by registration authority118ofFIG. 3, and may be performed in software, firmware, hardware, or a combination thereof.FIG. 8is described with additional reference to components inFIGS. 3–7b.

Registration authority118receives the CA pending response from certificate authority116(act302). Upon receipt of the CA pending response, registration authority118adds entries to its transaction ID table222(act304) and its request hash table224(act306). Registration authority118also generates an encrypted and digitally signed SCEP pending response message (act308) and transmits the encrypted and signed message to router210(act310).

Typically, in response to an SCEP pending response message, router210will re-issue its request for a certificate (e.g., via a GetCertInitial message). Registration authority118waits until it receives an additional SCEP request for the certificate from the router210(act312). Once the additional request is received, registration authority118accesses transaction ID table222to determine the appropriate CA request ID (act314). Registration authority118uses the CA request ID from table222to generate a CA request for a certificate corresponding to the CA request ID and digitally signs the CA request (act316). The signed CA request is then transmitted to certificate authority116(act318).

Upon receiving the CA request, certificate authority116may issue another pending response to registration authority118or alternatively determine whether to issue the certificate (per act258ofFIG. 7adiscussed above). Upon receipt of a response from certificate authority116, registration authority118determines whether the response is another pending response (act320). If the response is another pending response, the registration authority118returns to act308and generates and encrypted and signed SCEP pending response message. However, if the response is not another pending response, then registration authority118proceeds per acts268–282ofFIG. 7bto return an appropriate response to router210.

Use of request hash table224further allows registration authority118to gracefully recover in the event the SCEP pending response message is not received by router210. If router210does not receive the pending response message, then it will resubmit its original request (e.g., an SCEP PKCSReq message). In order to avoid a duplicate request to certificate authority for the certificate, registration authority118generates the hash value for SCEP PKCSReq messages it receives and compares the hash value to the entries in request hash table224. If the hash value matches an entry, then registration authority118uses the CA request ID from table224to generate a CA request for a certificate corresponding to the CA request ID (act316), rather than generating a CA request including a certificate enrollment request (act250ofFIG. 7a). Processing then continues as discussed above with reference toFIG. 8.

Get Certificate Revocation List Request

Returning toFIG. 3, router210may also send a Get Certificate Revocation List (CRL) request as SCEP request212. The request identifies a serial number or similar identifier of a certificate for which the corresponding CRL should be retrieved. The CRL is a list identifying revoked certificates which is made available by the certificate authority (typically in a public repository). The CRL can be checked to determine whether a particular serial number (typically identified in the CRL by its serial number) has been revoked. Registration authority118responds to such a request by obtaining the requested CRL and returning it to router210.

FIG. 9is a flowchart illustrating an exemplary process for handling a Get Certificate Revocation List request in accordance with certain embodiments of the invention. The process ofFIG. 9is implemented by registration authority118ofFIG. 3, and may be performed in software, firmware, hardware, or a combination thereof.FIG. 9is described with additional reference to components inFIG. 3.

Initially, registration authority118receives the Get CRL request (e.g., an SCEP GetCRL message) from router210(act330). Registration authority118decrypts the request (act332), verifies the signature of the decrypted request (act334), and proceeds based on whether the signature is verified (act336). If the signature cannot be successfully verified, then the message is dropped (act338); registration authority118simply ignores the message. Alternatively, registration authority118may return an indication to router210that the signature could not be verified.

However, if the signature is successfully verified, then registration authority118extracts the certificate serial number from the decrypted request (act340). This serial number can be extracted by obtaining the serial number of the certificate used by router210to sign the Get CRL request.

Registration authority118then uses the extracted serial number to generate a Get Certificate by Serial Number request (act342). The Get Certificate by Serial Number request is then digitally signed and transmitted to certificate authority116(act344), which in turn accesses its records to identify the certificate corresponding to the given serial number. This certificate is then returned by certificate authority116to registration authority118(act346).

The certificate returned by certificate authority116includes a CRL distribution point, which is an identifier of a location (e.g., a uniform resource locator (URL)) at which the CRL corresponding to the certificate can be obtained. Upon receipt of the certificate, registration authority118extracts the CRL distribution point from the certificate (act348). Registration authority118then accesses (e.g., via HTTP) the identified location and retrieves the CRL located there (act350).

Upon obtaining the CRL, registration authority118generates an SCEP response message including the CRL (act352). Registration authority118then encrypts and digitally signs the SCEP response message including the CRL, and returns the encrypted and signed SCEP response message to router210(act354).

Alternatively, the Get CRL request received from router210(act330) may include the certificate for which the corresponding CRL is to be obtained. In this situation, the CRL distribution point can be extracted by accessing the included certificate, thereby alleviating the need to access certificate authority116(acts340–346).

Get Certificate Request

Returning toFIG. 3, router210may also send a Get Certificate request as SCEP request212. The request identifies a serial number of a certificate that the router would like returned to it. Router210may make such a request, for example, in situations where it has kept the serial number of a certificate it needs but has not kept the actual certificate. Registration authority118responds to such a request by obtaining the requested certificate and returning it to router210.

FIG. 10is a flowchart illustrating an exemplary process for handling a Get Certificate request in accordance with certain embodiments of the invention. The process ofFIG. 10is implemented by registration authority118ofFIG. 3, and may be performed in software, firmware, hardware, or a combination thereof.FIG. 10is described with additional reference to components inFIG. 3.

Initially, registration authority118receives the Get Certificate request (e.g., an SCEP GetCert message) from router210(act362). Registration authority118decrypts the request (act364), verifies the signature of the decrypted request (act366), and proceeds based on whether the signature is verified (act368). If the signature cannot be successfully verified, then the message is dropped (act370); registration authority118simply ignores the message. Alternatively, registration authority118may return an indication to router210that the signature could not be verified.

However, if the signature is successfully verified, then registration authority118extracts the certificate serial number from the decrypted request (act372). This serial number can be extracted by obtaining the serial number specified in the request (e.g., as the certificate serial number of the signing certificate of the request).

Registration authority118then uses the extracted serial number to generate a Get Certificate by Serial Number request (act374). The Get Certificate by Serial Number request is then digitally signed and transmitted to certificate authority116(act376), which in turn accesses its records to identify the certificate corresponding to the given serial number. This certificate is then returned by certificate authority116to registration authority118(act378).

Registration authority118then generates an SCEP response message including the certificate received in act378(act380). Registration authority118then encrypts and digitally signs the SCEP response message including the certificate, and returns the encrypted and signed SCEP response message to router210(act382).

Get CA Request

Returning toFIG. 3, router210may also send a Get CA request as SCEP request212. The request is an HTTP Get call to a URL hosted by registration authority118. The URL is made available to router210during setup or configuration of router210. Registration authority118responds to such a request by returning the requested certificates to router210.

FIG. 11is a flowchart illustrating an exemplary process for handling a Get Certificate Authority Certificate request in accordance with certain embodiments of the invention. The process ofFIG. 11is implemented by registration authority118ofFIG. 3, and may be performed in software, firmware, hardware, or a combination thereof.FIG. 11is described with additional reference to components inFIG. 3.

Initially, a Get CA request is received by registration authority118from router210(act400). Upon receipt of the request, registration authority118obtains a DLL name identified by the request (act402). In one implementation, an exemplary Get CA request from router210is in the following form:GET mscep.dll/cgi-bin/pkiclient.exe?operation=GetCACert&message=<Base64 encoded authority issuer identifier>
In this implementation, registration authority118is implemented as an IIS (Internet Information Server) ISAPI (Internet Server Application Programming Interface) DLL. Upon receipt of such a request, IIS parses the input through to identify the first DLL and attempts to load that DLL if necessary. Thus, the remainder of the request can be ignored by registration authority118in determining how to respond to the request.

Registration authority118is the identified DLL, which in the illustrated example is “mscep.dll”, and passes the request to response module238(act404). In response to being passed the message (either in its entirety, or a part thereof), response module238generates a degenerated PKCS #7 message including the signing certificate and the encryption certificate of registration authority118(act406), and returns the degenerated PKCS #7 message to the router (act408). Thus, router210requests the certificates for the certificate authority, but receives the certificates for the registration authority instead.

Alternatively, registration authority118may include a certificate chain in the message it generates in act408. By way of example, MSCEP DLL328may send a certificate request to certificate authority116, which returns the certificate of certificate authority116and a certificate chain that extends up to its root certificate.

Password Handling

Returning toFIG. 3, router210may also make use of a password to authenticate itself to certificate authority116(actually registration authority118, but router210is not aware of this). The password allows registration authority118(and thus certificate authority116, which trusts registration authority118) to know that a particular request actually came from the router claiming to have sent it. The password may be used with one or more of the different types of SCEP requests212discussed above. By way of example, the password may be used with the router enrollment request.

FIG. 12is a flowchart illustrating an exemplary process for distributing and verifying passwords in accordance with certain embodiments of the invention. The process ofFIG. 12is implemented by registration authority118ofFIG. 3, and may be performed in software, firmware, hardware, or a combination thereof.FIG. 12is described with additional reference to components inFIG. 3.

Initially, registration authority118receives a request for a password (act430). This request is received via a mechanism that allows registration authority118to authenticate the requester, such as by use of SSL (Secure Sockets Layer) to authenticate the requestor when accessing web site240ofFIG. 3. The requester could be a computer being operated by a router administrator, or alternatively router210. Upon receipt of the request, registration authority118attempts to authenticate the requestor, such as the router administrator, (act432) and proceeds based on whether the authentication is successful (act434). If the requester cannot be authenticated, then the request for a password is denied (act436). The request may simply be ignored, or alternatively an indication may be returned to the requestor that the request for a password is denied.

However, if the router is authenticated, then registration authority118proceeds to generate a password and add the newly generated password to password table226(act438). The password can be generated by registration authority118in any of a wide variety of conventional manners, such as by generating a random (or pseudo-random) number and/or sequence of letters. The generated number may then be placed into a particular format if needed by either router210or certificate authority116, such as hexadecimal format, binary coded decimal format, etc.

The password added to password table226is removed from table226after a period of time. In one implementation, each password in table226is kept in table226for sixty minutes and then removed. This period of time can optionally be configurable by an administrator.

Registration authority118then returns the newly generated password to requestor (act440). This return of the password is done in a secure manner, such as by use of SSL.

Eventually, registration authority118receives a request from router210that includes a password that needs to be verified (act442). Upon receipt of such a request, registration authority118determines whether the received password is in password table226(act444). If the received password is not in password table226, then the request is rejected (act446). The request can simply be ignored, or alternatively a rejection response can be returned to router210(e.g., informing router210that the password it provided was not valid).

However, if the password is in password table226, then the request is processed by registration authority118(act448). Registration authority118may also optionally remove the password from password table226(act450), thereby adding an additional level of security by allowing each password to be used only once.

CONCLUSION

Thus, a VPN enrollment protocol gateway has been described. The protocol gateway is implemented as a registration authority that is trusted by the certificate authority, and operates as an intermediary between the router and the certificate authority. The protocol gateway advantageously allows routers operating in accordance with one protocol to obtain and maintain certificates for a VPN from a certificate authority operating in accordance with another protocol.

Although the description above uses language that is specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the invention.