Patent Grant
7941833
The present invention relates to the field of secure network registration processes that allow two network devices to register with each other, and more particularly to a registration process where two devices learn each other's identities and establish a shared key that can later be used by the devices to mutually authenticate each other and to generate session encryption keys.
The protection of information and secrets over a network requires the use of secure methods to add new devices to the network. It is possible to breach network security and gain access to network information and secrets through interfering with the registration process of devices with the network. One method of interfering with the registration of network devices is through interjecting an imposter device into the registration process. If this imposter device can successfully pose as the legitimate device during the registration process, then it is possible for the imposter device to register with the network and masquerade as the legitimate device. As a result, the imposter device can gain access to the information and secrets stored on the network. It is therefore desirable to develop methods and systems that can provide a secure method for registering a device with a network.
A variety of methods and systems are known to facilitate communications between two devices. One such protocol is the Diffie-Hellman key agreement protocol. The Diffie-Hellman key agreement protocol (also called exponential key agreement) was developed by Diffie and Hellman in 1976 and published in the paper “New Directions in Cryptography.” The protocol allows two users to exchange a secret key over an insecure medium without any prior secrets. The protocol has two system parameters p and g. They are both public and may be used by all the users in a system. Parameter p is a prime number and parameter g (usually called a generator) is an integer less than p, which is capable of generating every element from 1 to p−1 when multiplied by itself a certain number of times, modulo the prime p. The protocol depends on the discrete logarithm problem for its security. It assumes that it is computationally infeasible to calculate the shared secret key k=gab mod p given the two public values ga mod p and gb mod p when the prime p is sufficiently large. Breaking the Diffie-Hellman protocol is equivalent to computing discrete logarithms under certain assumptions.
Another system is the Point-to-Point Protocol (PPP) Extensible Authentication Protocol (EAP). EAP is a general system for PPP authentication that is compatible with a variety of authentication mechanisms. EAP does not select a specific authentication mechanism at a Link Control Phase, but rather postpones this selection until an Authentication Phase. This postponement enables the authenticator to request more information prior to determining the specific authentication mechanism. In addition, this postponement also enables the use of a “back-end” server that actually implements the various mechanisms while the PPP authenticator merely passes through the authentication exchange.
RSA is yet another protocol system that provides an algorithm for public key cryptography. The “key” of an RSA cipher has three numbers: the first is the public exponent, the second is the private exponent, and the third is the modulus. The public key is formed from the public exponent and the modulus. The private key is formed from the private exponent and modulus. If two devices are to engage in encrypted communications, they each generate a pair of keys. These devices then may exchange public keys using a non-secure communications channel. Thereafter, when the devices engage in encrypted communications, one device can encrypt the message using the other devices' public key and send it via a non-secure channel. Since the private keys are not exchanged, decryption by an eves dropper proves difficult.
Consider the case of a wireless network with an access point in infrastructure mode. Suppose a user buys a wireless printer and wants to connect the printer to the network. If Wi-Fi Protected Access (WPA) is enabled on the access point, the user has a variety of options for setting up a secure connection between the access point and printer:
The user can install an 802.11 pre-shared key on the access point and on the printer. Note that pre-shared keys are not device-specific. Also, multiple devices may utilize the same pre-shared key to connect to an access point. Alternatively, if the access point is a client to a Remote Authentication Dial in User Server (RADIUS), or includes the capabilities of a RADIUS server, the printer name and credentials can be added to the RADIUS server database. A RADIUS server is used to authenticate and return parameters including the users IP address, gateway, and DNS server. The printer credentials must also be installed on the printer. The credentials may be a password, key, or certificate. The RADIUS server and printer are also configured to perform the same type of EAP authentication, with the printer acting as the supplicant.
The present invention is for an Enhanced Shared Secret Provisioning Protocol (ESSPP). ESSPP provides a novel method and system for adding devices to a network in a secure manner. With ESSPP, two network devices that are attempting to register with each other and establish a secure communications link are both provided with a mechanism for starting ESSPP. Examples of these network devices include servers, wireless printers, wireless computers, and network access points. The mechanism may be to select a button located on the device that triggers the ESSPP process, a menu selection provided in a Graphical User Interface (GUI) shown on a display provided with the device, or to enter a code on a terminal of the device. When, for example, two devices such as the printer and access point run ESSPP at the same time, the two devices automatically register with each other. The ESSPP process allows for registration of network devices without the need to manually install encrypted keys, passwords, or certificates to add the device to the network.
When a device runs ESSPP, it searches for another device running ESSPP. When two devices running ESSPP detect each other they exchange identities and establish a key that can later be used by the devices to mutually authenticate each other and generate session encryption keys. In a wireless network, the established key can be used as a pre-shared key or it can be used for 802.1x authentication using an Extensible Authentication Protocol (EAP).
Different techniques are utilized to protect against intruder devices. A Shared Secret Provisioning Protocol (SSPP) is used to establish credentials. SSPP is structured such that it is resistant to passive attacks. Additional methods are used to protect against active man-in-the-middle attacks. SSPP is a preferred system for establishing credentials, other types of key exchanges function with ESSPP. For example, an RSA-style key exchange is compatible with ESSPP.
With ESSPP, two ESSPP devices that are attempting to register with each other will only provision a key when they detect that they are the only two ESSPP devices on the wireless network running ESSPP. If additional devices running ESSPP are detected, the ESSPP protocol is either terminated or suspended.
The ESSPP process is initiated when two network devices launch ESSPP within a predetermined time interval of each other. Specifically, when ESSPP is launched at one network device through the pressing of a button or selection of a menu option, there is a window of time during which ESSPP can be launched at the second network device. If ESSPP is not launched within this window of time at the second device, then the ESSPP process terminates. Through providing this temporal requirement that ESSPP launch within a predetermined time interval at both devices, the security of the registration process is enhanced.
In addition, in an alternative embodiment, an ESSPP supplicant device may be labeled with a short PIN. The user is required to enter the PIN on the authenticating device for ESSPP to succeed, thereby providing additional security. In another embodiment, a short PIN may be entered at both devices when ESSPP is run. The user selects a unique PIN that need not be remembered.
ESSPP allows for automatic registration of two devices through a process where each device learns the other's identity and learns that the devices are allowed to communicate with each other. In addition, ESSPP is a button, or menu activated process that does not require a user to manually enter passwords, or install credential files, or certificates. ESSPP provides an optional PIN code support, thereby providing added security in some network environments. The short PIN is used once to establish strong password credentials.
ESSPP also provides protection from passive and active attacks during the protocol exchange. ESSPP utilizes generation of a shared key that can be used to secure the connection between the two devices. There is also an optional generation of pseudonyms that can be used by the devices to identify each other during EAP authentication without revealing their true identities on the network.
ESSPP also provides for an optional anonymous registration that allows two devices to run ESSPP without revealing their identities on the network. ESSPP is an efficient mechanism for changing a shared key once the key is established. Cancellation of a registration is provided for by ESSPP if a device detects more than one other device in ESSPP mode. Further, ESSPP supports methods for authenticating using established credentials.
The present invention is further described in the detailed description which follows, in reference to the noted drawings by way of non-limiting examples of certain embodiments of the present invention, in which like numerals represent like elements throughout the several views of the drawings, and wherein:
The particulars shown here are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
A novel method and system for registering devices with a network in a secure manner is provided through an Enhanced Secure Shared Provisioning Protocol (ESSPP). With ESSPP, two network devices that are attempting to register with each other and establish a secure communications link are both provided with a mechanism for starting ESSPP. In order to launch the ESSPP registration process, these mechanisms are activated together within a predetermined time interval. If both of these devices do not launch ESSPP together within this predetermined time interval, the ESSPP registration protocol does not begin. When launched at both devices within the predetermined time interval, ESSPP enables a secure registration process for the two network devices. Through requiring that these mechanisms for launching ESSPP are activated within the predetermined time interval, the probability that a third device would intrude upon the registration of the two devices is reduced.
A preferred general process flow for ESSPP is provided in protocol flow 1 below. Alternative process flows for ESSPP are provided in protocol flows 2-7 and 9-10. Protocol flow 8 illustrates how credentials established by other flows can be used for authentication. The mathematical terminology used for the purposes of describing the ESSPP process flows is documented in the Internet Engineering Task Force (IETF) Internet Draft “draft-moskowitz-shared-secret-provprotocol-01.txt”. This IETF document describes a Shared Secret Provisioning Protocol. Where possible, the same notation used in SSPP is used here.
Protocol Flow 1
Protocol flow 1 illustrates ESSPP in its simplest form. Two network devices, such as a server and client, exchange addresses and public keys. Both of these devices derive shared key k that they can later use to authenticate each other.
Once shared key k has been established, Server and Client can authenticate each other using the shared key k as the hidden credential.
Referring to step 1 of protocol flow 1 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. ESSPP is launched in step 1 through an activation of a mechanism that is located on both the server and the client. Requiring that ESSPP launch at both network devices within the predetermined time interval reduces the ability of a third network device to intrude and interfere with the ESSPP registration process. This mechanism may be referred to as a trigger, or a simultaneous registration trigger. The actual mechanism on the device can take the form of a button, a menu selection, or other triggering device.
The predetermined time interval has a length that can be set depending upon the application and network environment. Predetermined time intervals on the order of seconds may be appropriate where there is one operator who can trigger each ESSPP launch mechanism supported on each network device. However, where there is one operator who has to trigger both network device mechanisms on devices that are on different floors of a building, the predetermined time interval may have a length on the order of minutes.
In step 1, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices. These startup messages are an initial “handshake” between the two network devices that enable the implementation of ESSPP. For instance, these initial start up messages may include a wireless network device searching for the location of access points on a network.
In steps 2, 3, 4, and 5, information is exchanged and verified between the two network devices to facilitate generation of a shared key k in step 6. In step 2, nonceS is generated and a message sent from the server to the client. In step 3, the parameters sent in the message of step 2 are validated as required by SSPP by the client. NonceC, Zs, and proofC are then generated by the client and sent via message to the server. The values Zs and proofS are generated in step 4. Also in step 4, proofC is validated and proof S is sent via a message to the client. In step 5, the client validates proofS. Generation of shared key k enables encrypted communications between the server and the client. This shared key k along with the address is then stored within a database in step 7.
During the entire process, a monitoring system is provided on both network devices to detect ESSPP communications from a third device that is attempting to intrude and interfere in the ESSPP process running between the server and the client as noted in step 8. If and when these ESSPP communications from a third device are detected, in a preferred embodiment the ESSPP process is terminated. The ESSPP process is then not restarted until such time as the process is reset and the trigger mechanisms on both devices reactivated. Alternatively, with detection of ESSPP communications from the third device, the process may be suspended for such a time and then reinitiated at the same or a previous step at a later time period.
ESSPP messages that are detected by the monitoring system are messages that have a format in accordance with the ESSPP process as outlined above. This format is detected through looking at the structure of the message to determine if it contains ESSPP information as outlined above.
If no such ESSPP communications are detected from the third device, the process flows to step 9 where ESSPP process is completed and stops. When ESSPP is completed and stops in step 9, the registration process is complete and a registration has been established between the server and the client, thereby enabling secure communications between them while avoiding potential man in the middle attacks. In a preferred embodiment, the protocol flow of flow 1 utilizes a Diffie-Hellman key exchange process.
Protecting Against Man-in-the-Middle Attacks
A man-in-the-middle attack would allow an imposter Carol between Alice and Bob. When Alice thinks she is talking to Bob, she in fact is talking to Carol, and when Bob thinks he is talking to Alice, he in fact is talking to Carol. The man-in-the middle attack allows Carol to establish a shared key k1 with Alice and a shared key k2 with Bob. Carol can decipher all traffic between Alice and Bob and can modify messages in the conversation.
The SSPP draft points out the need to protect against man-in-the-middle attacks. ESSPP provides a new approach for protecting against a man-in-the-middle attack that is less burdensome on users than prior art. To protect against a man-in-the-middle attack, only two devices on the network are allowed to run ESSPP at a time. If either the Client or Server receives ESSPP messages from more than one device, the protocol exchange will fail. Client and Server devices keep listening for ESSPP messages for a period of time after a successful registration, trying to detect any other device running ESSPP. If a third device is detected running ESSPP after a successful registration, the detecting device destroys its copy of the generated shared key and attempts to inform the device it registered with that the registration has been discarded. This approach is appropriate on networks where it is not feasible for an attacking device to disrupt traffic between two devices without detection.
Protocol Flow 2
Protocol flow 2 is an alternative flow that illustrates how a PIN can be used with ESSPP. This is useful when ESSPP is run on networks where it is feasible for an attacker to disrupt communications between a Server and Client without detection. The use of a PIN provides additional security to the ESSPP process.
If a device is able to disrupt communications between the Server and Client without detection, the device still has a very low probability of being able to mount a successful man-in-the-middle attack. A successful man-in-the-middle attack would require an attacking device to guess the PIN in a single try during the protocol exchange. Referring to step 1 of protocol flow 2, the PIN number entered at the server and the client is included in the calculations of proofC and proofS. Therefore, the PIN number is utilized once in the ESSPP process. As a result, an attacking device has a single opportunity to correctly guess the PIN number, thereby providing enhanced security for the ESSPP process.
Referring to step 1 of protocol flow 2 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In step 1, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
Note that as with protocol 1, the detection or monitoring of ESSPP communications from a third network device as illustrated in step 8 runs throughout the entire ESSPP process. As a result, for instance, the monitoring systems on the server and client will listen for a second message transmitted in steps 2, 3, or 4. For example, if two proofS messages are received from the client in step 4, then a third network device is participating in the ESSPP registration. As a result, the ESSPP process will terminate without completing the registration between the two network devices.
Note that steps 3 and 4 differ from protocol flow 1 in that the PIN number is used to generate proofC and proofS. Protocol flow 2 is implemented utilizing a Diffie-Hellman key exchange process.
Protocol Flow 3
Protocol flow 3 illustrates an alternative embodiment of ESSPP that is similar to the preferred embodiment illustrated in flow 1, but in this alternative embodiment pseudonyms are derived. The pseudonyms can be used by the Server and Client to identify each other on the network without revealing their true identities.
Flows 1 and 2 dealt with device addresses, but in this flow each device also has an associated identity. The identity is sent in the clear during the ESSPP protocol exchange. The generated pseudonyms can be used by the devices to identify each other once the ESSPP protocol exchange completes.
In step 7, a key derivation function is used to generate pseudonyms. The Client and Server generate each other's pseudonyms and store them so that they can be used as an index into the credential database. The Client and Server can generate their own pseudonyms at any time, because their own pseudonyms are not indexes into the credential database.
Referring to step 1 of protocol flow 3 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In step 1, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
In step 7, the key derivation function kdf is used to generate pseudonymC and pseudonymS. Note however, that these pseudonyms are merely random numbers. In step 8, ESSPP converts these random numbers into an identifier for use on the network through a Base64Encode. Base64Encode converts the random number into a display field character. In this manner, it is then possible for the two network devices, client and server, to identify each other over the network through the use of pseudonyms without having to reveal their true identities.
Note that steps 2 and 3 of protocol flow 3, the network devices reveal their identities to each other. Protocol flow 3 is implemented utilizing a Diffie-Hellman key exchange protocol.
Protocol Flow 4
Protocol flow 4 illustrates an alternative embodiment of the ESSPP protocol flow illustrated in flow 1. Protocol flow 4 is similar to flow 3, but in this case, the two network devices, server and client, commonly referred to as Alice and Bob in cryptographic parlance, do not reveal their identities during the registration process.
Referring to step 1 of protocol flow 4 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another as with protocol flow 1. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In step 1, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
Note that neither the server nor the client, “Alice” and “Bob,” reveal their identities during the process of protocol flow 4. The client and server only are able to identify each other through their respective pseudonyms that are generated in steps 13 and 14. Protocol flow 4 is implemented utilizing a Diffie-Hellman key exchange process.
Protocol Flow 5
Protocol flow 5 uses a different key agreement protocol than the ones used by protocol flows 1-4. Instead of performing a Diffie-Hellman key exchange, RSA encryption is used. Whereas the Diffie-Hellman key exchange requires the same amount of work to be performed by both devices in the exchange, with RSA encryption, one device has less work than the other. One device randomly chooses a shared key k, encrypts it, and sends it to the other device. The other device decrypts the shared key k. RSA encryption is much faster than RSA decryption; so slow devices can be given the task of encrypting while faster devices can perform the decrypting.
Before the exchange begins, Alice generates or somehow acquires an RSA public/private key pair.
There is a need to protect against a man-in-the-middle attacks with protocol flow 5 due to the fact that the RSA public key (RA) is not validated by a certificate authority.
A variety of enhancements can be made to protocol flow 5 such that Alice and Bob prove to each other knowledge of k by generating proof hashes similar to proofS and proofC. A PIN can also be included in the generated proof hashes to provide protection from man-in-the-middle attacks on some types of networks.
Referring to step 1 of protocol flow 5 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In step 1, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
Protocol Flow 6
This flow demonstrates how ESSPP can be performed in an EAP message exchange on a wireless network. The Authenticator runs on an access point device, and the Authentication Server is a RADIUS server that may or may not be running on the access point device. The Authentication Server is managed via a web interface. This web interface has menu selections that allow the Authentication Server to run ESSPP. The supplicant in this case is a headless device that has a button to press to start the execution of ESSPP.
Protocol flow 6 illustrates how ESSPP can be deployed without changing access point (Authenticator) firmware. ESSPP is run between the supplicant and the authentication server.
After the supplicant starts running ESSPP, in step 2 it scans for all access points in its range. The supplicant will attempt to register with each access point in range. If more than one access point starts EAP-ESSPP to begin ESSPP registration (not just to issue a challenge), the supplicant will not activate the registration for any device. This is to avert a potential man-in-the-middle attack.
In step 5, the supplicant sends an EAP-Identity Response message with the user name set to “ESSPP_REGISTERING_DEVICE”. The Authentication Server recognizes this special EAP-Identity Response message as coming from a supplicant in ESSPP mode.
In step 6, the Authentication Server begins the EAP-ESSPP protocol. The Authentication Server will only use this protocol with an unregistered device when it is running ESSPP to register a device.
In step 11, the Authentication Server generates and stores a pseudonym for the registering device, and will allow the device to authenticate using this pseudonym when 802.1x authentication is later performed, allowing the device ID to remain confidential.
Device registration is not activated until ESSPP completes execution. If the ESSPP protocol flow is not completely executed, the registration is not activated and the network device is not registered with the network.
When ESSPP is stopped on the supplicant, the user is given some indication of whether or not the registration was successful. Beeping patterns or light flashing patterns may indicate the result of the registration attempt. Likewise, Authentication Server logs and configuration will contain information about registered devices.
The established shared key may be used as the shared secret to use with an 802.1x authentication protocol (EAP). During the registration process, the registering client and server may use the generated shared key to derive encryption keys for an initial session between the client and server. If the initial session is stopped, the shared key may be used by the client and server to authenticate each other and establish new encryption keys using an 802.1x authentication protocol (EAP). If a shared key already exists, ESSPP can be used for 802.1x authentication without going through the ESSPP registration process.
Referring to step 1 of protocol flow 6 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In steps 2-3, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
Protocol Flow 7
Protocol flow 7 is similar to protocol flow 6, but in this flow, ESSPP is started at the Authenticator instead of at the Authentication Server. The access point (Authenticator) may have a button to press or provide a web-based interface to start ESSPP. When running ESSPP, the access point will include a special ESSPP-Mode attribute with (Access-Request) messages sent to the Authentication Server. The presence of this attribute indicates to the Authentication Server that EAP-ESSPP is allowed. In addition, the access point will include the text “ESSPP_OPEN_FOR_REGISTRATION” in EAP-Identity Request messages. Only one access point should be put into ESSPP mode at a time or registrations will fail.
Referring to step 1 of protocol flow 7 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In steps 2-3, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
Protocol flow 7 involves the use of multiple access points within the ESSPP environment. Referring to step 15 of the supplicant, the process with the current access point is stopped and goes to another access point if EAP-Identity Request does not contain the text “ESSPP_OPEN_FOR REGISTRATION.” Also referring to step 15 of the supplicant, there is a failure in the ESSPP process if EAP-Identity Request contains the text “ESSPP_OPEN_FOR_REGISTRATION.” This message indicates that there is a network device that is not properly registered with the network in spite of steps 1-14 of protocol 7. This message therefore indicates that the device registered in steps 1-14 is an imposter device that must be unregistered and that the device broadcasting the message “ESSPP_OPEN_FOR_REGISTRATION” is in fact the legitimate device that should be registered. Alternatively, the device broadcasting the message “ESSPP_OPEN_FOR_REGISTRATION” may in fact be the imposter device. Since the supplicant can not determine which device is the legitimate device and which device is the imposter device, the registered device is unregistered and sent a message “ESSPP_REGISTRATION_FAILED.”
802.1x Authentication Choices
After EAP-ESSPP is used to establish a shared key between two devices, the devices can authenticate each other using 802.1x authentication. EAP methods that can perform mutual authentication using the generated shared key can be used. Such methods include Lightweight Extensible Authentication Protocol (LEAP) and EAP-SPEKE (Simple Password-Authenticated Exponential Key Exchange). However, the best choice is to use EAP-ESSPP itself, as this must already be available on the client and server. Below is a flow for EAP-ESSPP used for authentication using established credentials.
Protocol Flow 8
When used for authentication, EAP-ESSPP can also periodically regenerate the shared key k. The server somehow detects that the shared key k needs to be regenerated. This may be because a certain amount of time has passed or the shared key k has been used for a certain number of times. Instead of beginning EAP-ESSPP for authentication, the server begins EAP-ESSPP to provision a new key, using the old shared key k as the PIN to protect against attacks.
Protocol Flow 9
This flow shows how ESSPP can be run on an 802.11 network without using EAP. This flow requires additions to the 802.11 standard.
The 802.11 standard specifies two authentication algorithms, Open System, and Shared Key. This flow requires two additional authentication algorithms:
Referring to step 1 of protocol flow 9 illustrated above, the server and the client start ESSPP within a predetermined time interval of one another. Server and client start ESSPP when registration triggers are activated on both server and client together within the predetermined time interval. In steps 2-4, the server and the client broadcast a set of registration protocol startup messages to each other in an exchange in order to initiate the ESSPP between the two devices.
Protocol Flow 10
Sometimes, one-way authentication is used to establish a secure connection. For example, an SSL (Secure Sockets Layer) connection can be established between a Client and a Server with the Client authenticating the Server, but without the Server authenticating the Client. The flow below shows how ESSPP can be run on such a connection to establish credentials that can later be used for mutual authentication by the Client and Server.
An SSL (Secured Sockets Layer) connection can be established between a Client and a Server without the Client providing any credentials. In this case, Server credentials can still be authenticated by the Client, allowing for one-way authentication. When an SSL connection is established in this way, a Server has a certificate that it can send to a Client to identify itself. The certificate contains the server's public key and a digital signature from a trusted party that the Client can verify to make sure the certificate properly identifies the Server. The Client can encrypt a message to the Server using the Server's public key. Only the Server will be able to decrypt the message, because only the Server knows the private key that corresponds to the public key. When an SSL connection is established, the Client authenticates the Server by verifying that the Server knows how to decrypt a message encrypted with the Server's public key. When one-way authentication is used, the Server does not authenticate the Client.
In step 1 of protocol flow 10, the client and server establish a secure connection using SSL, which allows for certain messages to be encrypted. ESSPP can then run over this connection, allowing the Client and Server to establish new credentials. The Client and Server can re-connect using the newly generated credentials instead of SSL. Connection-establishing credentials now allow for mutual authentication with ESSPP instead of one-way authentication with SSL.
In steps 2 and 3 of protocol flow 10, the server and client exchange registration information. This information includes address information AddressS and AddressC, portions of the Diffie-Hellman static key pair Ys and Yc, and random numbers NonceS and NonceC. In steps 3 and 4, the client and server generate a Diffie-Hellman shared secret Zs and exchange messages, proofC and proofS, indicating knowledge of such secret. The server and client validate these proof messages in steps 4 and 5 respectively. In steps 6 and 7, the client and server then generate a shared key, k, and store the key and address information for later use. In protocol 10, client and server generate shared key, k, without requiring a simultaneous triggering of registration processes at the Server and the Client device.
A simpler method of establishing credentials over an SSL connection is also possible. Because the Client and Server communicate over an encrypted connection, in step 2, the Server could pick a value for shared key k and send AddressS and shared key k to the Client. In step 3 the Client would then send the Server AddressC. Steps 4-6 are then skipped, and the Client and Server store credentials in step 7. In this case, if an attacker records the registration messages and later learns the Server's private key, the attacker may be able to decipher the recorded registration to learn the value of shared key k. Whether a Diffie-Hellman exchange is used to establish shared key k or not, the newly established credentials allow the Client and Server to re-connect with mutual authentication instead of one-way SSL authentication.
Transferring Keys
When device one successfully registers with device two using ESSPP, device one will store device two's credentials. Device two's credentials consist of information learned about device two, such as device two's name and address, as well as the generated shared key k. These credentials may be stored in a credential file. In certain environments, a credential file can be copied from device one to another device, such as device three, allowing device three to use the credentials to authenticate with device one. This allows devices that do not support the ESSPP protocol to utilize credentials generated using ESSPP. It also allows an administrator to switch devices in a network without running ESSPP.
ESSPP System Components
Wireless network devices 12-18 are connected to Wi-Fi network through wireless access points 20 and 22 that are respectively numbered 1 and m. In order to support n+1 wireless network devices, network 10 may utilize as many as m wireless access points.
Wireless access points 20 and 22 numbered 1 and m may couple to other network devices 24, a virtual private network 26, as well as an authentication server 28. In addition, wireless access points 20 and 22 may couple to a terminal 30. Coupled to authentication server 28 is a storage facility 32.
Wireless network devices 12-18 are each provided with the mechanism that activates the ESSPP protocol on wireless network devices 12-18 as described in step 1 of protocol flows 1-7 and 9. This mechanism may take the form of a button, a switch, a menu selection on a Graphical User Interface (GUI), or some other embodiment of a trigger. Authentication server 28 is also provided with a mechanism that activates ESSPP protocol on authentication server 28 as described in step 1 of protocol flows 1-6. In protocol flow 7, ESSPP is triggered at the wireless access point and not with the authentication server. In protocol flow 9, ESSPP is also triggered at the wireless access point.
When ESSPP is activated on both one of network devices 12-18 and authentication server 28 within the predetermined time interval, ESSPP proceeds to step 2 as outlined in protocol flows 1-7 and 9. If ESSPP is not activated within the predetermined time interval, the ESSPP terminates at step 1 of protocol flows 1-7 and 9. If ESSPP is activated on one of said network devices 12-18 within a predetermined time interval of an activation of ESSPP on authentication server 28, then the ESSPP process commences and proceeds to step 2 of protocol flows 1-7 and 9.
All ESSPP communications between wireless network devices 12-18 and authentication server 28 occurs through wireless access points 20-22. While network devices 12-18 are illustrated as communicating with authentication server 28 through wireless network 10, other forms of communication are possible, such as via satellite, dial up connection, broadband, cable, fire-wire, an Internet and World Wide Web, as well as other methods.
Monitoring systems supported on authentication server 28 and wireless network device 18 listen for ESSPP communications from man-in-the-middle device 40 in order to detect the man in the middle attack and react according to the ESSPP process as detailed in protocol flows 1-7 and 9. When such communications are detected from man-in-the-middle device 40, the monitoring systems on authentication server 28 and wireless network device 18 trigger authentication server 28 and network device 18 to terminate the ESSPP process in a preferred embodiment. To reinitiate the ESSPP process between authentication server 28 and network device 18, the ESSPP must be restarted with the triggering of the mechanisms to launch ESSPP at step 1. Alternatively, detection of these ESSPP signals from man-in-the-middle device 40 may only cause authentication server 28 and wireless network device 18 to suspend, or pause the ESSPP process at a particular step. At a later time, network device 18 and authentication server 28 may reinitiate ESSPP from where the process was last suspended, or may restart the process at an earlier step.
A block diagram depicting a system that supports the Enhanced Shared Secret Provisioning Protocol is illustrated in
Authentication sever 28 includes an internal database 44 and/or an external database 46. Databases 44 and 46 are provided with authentication server 28 to enable authentication server 28 to store information including network system addresses and identity information, pseudonym information, cryptographic key information, and other related information.
Authentication server 28 supports a registration trigger 48, also referred to as a simultaneous registration trigger 48, that causes authentication server 28 to initiate execution of the ESSPP process when registration trigger 48 is activated. A processor arrangement 50 is provided that couples to database 44 and 46, trigger 48, monitoring system 42, and key generator 40.
A communications system 52 is coupled to server that enables authentication server 28 to communicate with remote network devices 12-18 through wireless access points 20 and 22. Alternatively, other methods of communication are suitable including communication via satellite, a computer network such as the Internet and a World Wide Web, LAN, or Ethernet, and broadband.
A network device 60 seeking to securely register with authentication server 28 is also illustrated. As with authentication server 28, network device 60 also supports a variety of subsystems that enable it to support the Enhanced Shared Secret Provisioning Protocol. Network device 60 includes a registration trigger 62, also referred to as a remote registration trigger 62, and simultaneous registration trigger 62. This trigger 62 initiates execution of the ESSPP process on network device 60 when trigger 62 is activated. Network device 60 includes a key system 64 that supports the cryptographic key in accordance with the ESSPP process. This support can include either generation or receipt and storage of a cryptographic key in accordance with the ESSPP process, such as through a Diffie-Hellman process, an RSA process, or an EAP process. Also, it is possible that server 28 could receive the cryptographic key from network device 60.
Storage system 66 provided on network device 60 provides data storage for network address information, identity information, pseudo names, cryptographic key, and other related information. Monitoring system 68 enables network device 60 to listen for communications from a foreign network device and detect a man-in-the-middle attack. A communications system 70 is provided to enable network device 60 to communicate with authentication server 28 through wireless or other communication methods. A processor arrangement 72 is provided that couples to storage system 66, trigger 62, monitoring system 68, communications system 70, and key system 64.
Diffie-Hellman Key Exchanges
The Diffie-Hellman key exchange is used to generate a key from which session keys can be derived. Wireless devices commonly use 128 bit session keys for symmetric encryption. The Diffie-Hellman key exchanges should therefore be as strong as a 128 bit symmetric key so that the Diffie-Hellman key exchange is not the weak link in the registration and authentication process.
The following table is taken from a recent Internet draft, “More MODP Diffie-Hellman groups for IKE”. It is an equivalency table showing for different Diffie-Hellman prime moduli what symmetric key sizes are required to have equivalent strengths. The strength comparisons are estimates.
The table indicates that a 2048-bit Diffie-Hellman key provides the strength of a symmetric key probably somewhere between 110 and 160 bits in strength. Based on the estimates in this table, a 2048-bit Diffie-Hellman prime modulus is recommended for use with ESSPP on wireless networks.
ESSPP will use prime moduli defined in the IETF draft, “More MODP Diffie-Hellman groups for IKE”. In a wireless network, the Authentication Server may indicate, by group number, which Diffie-Hellman prime modulus may be used. ESSPP devices will likely support groups 5, 14, and 15.
Wei Dai has published benchmarks for Diffie-Hellman key exchanges at: http://www.eskimo.com/˜weidai/benchmarks.html
His measurements indicate that Diffie-Hellman 2048 Key-Pair Generation and Key Agreement takes 49.19 milliseconds on a Celeron 850 MHz processor running Windows 2000 SP1.
The Diffie-Hellman key agreement protocol (also called exponential key agreement) was developed by Diffie and Hellman in 1976 and published in the ground-breaking paper “New Directions in Cryptography.” The protocol allows two users to exchange a secret key over an insecure medium without any prior secrets.
The protocol has two system parameters p and g. They are both public and may be used by all the users in a system. Parameter p is a prime number and parameter g (usually called a generator) is an integer less than p, with the following property: for every number n between 1 and p−1 inclusive, there is a power k of g such that n=gk mod p.
Suppose Alice and Bob want to agree on a shared secret key using the Diffie-Hellman key agreement protocol. They proceed as follows: First, Alice generates a random private value a and Bob generates a random private value b. Both a and b are drawn from the set of integers {1, . . . , p−2}. Then they derive their public values using parameters p and g and their private values. Alice's public value is ga mod p and Bob's public value is gb mod p. They then exchange their public values. Finally, Alice computes gab=(gb)a mod p, and Bob computes gba=(ga)b mod p. Since gab=gba=k, Alice and Bob now have a shared secret key k.
The protocol depends on the discrete logarithm problem for its security. It assumes that it is computationally infeasible to calculate the shared secret key k=gab mod p given the two public values ga mod p and gb mod p when the prime p is sufficiently large. Maurer has shown that breaking the Diffie-Hellman protocol is equivalent to computing discrete logarithms under certain assumptions.
The Diffie-Hellman key exchange is vulnerable to a man-in-the-middle attack. In this attack, an opponent Carol intercepts Alice's public value and sends her own public value to Bob. When Bob transmits his public value, Carol substitutes it with her own and sends it to Alice. Carol and Alice thus agree on one shared key and Carol and Bob agree on another shared key. After this exchange, Carol simply decrypts any messages sent out by Alice or Bob, and then reads and possibly modifies them before re-encrypting with the appropriate key and transmitting them to the other party. This vulnerability is present because Diffie-Hellman key exchange does not authenticate the participants. Possible solutions include the use of digital signatures and other protocol variants.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to certain embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the disclosure, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses.
This application is a continuation of U.S. patent application Ser. No. 10/625,846, filed Jul. 24, 2003 and entitled ENHANCED SHARED SECRET PROVISIONING PROTOCOL, which claims priority to U.S. Provisional Application Ser. No. 60/479,176, filed Jun. 18, 2003, the entirety of which is incorporated herein by reference.
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