Abstract:
The present disclosure relates to the authenticating a client against a pool of servers utilizing a secure authentication protocol, and, more specifically, to the authenticating a client against a pool of servers providing a common service, utilizing the Kerberos secure authentication protocol.

Description:
BACKGROUND 
     1. Field 
     The present disclosure relates to the authenticating a client against a pool of servers utilizing a secure authentication protocol, and, more specifically, to the authenticating a client against a pool of servers providing a common service, utilizing the Kerberos secure authentication protocol. 
     2. Background Information 
     Kerberos is a trusted third-party authentication protocol designed for client/server interactions. J. Kohl and B. Neuman, “ The Kerberos network authentication service  ( version  5),” RFC-1510, 1993. Hereafter, a service that is substantially in compliance with the above Kerberos specification, its derivatives, or antecedents is simply referred to as “Kerberos.” This includes imperfect or corrupted implementations. 
     A Kerberos service allows a person or client to access different machines on a network. Kerberos shares a different secret key with every entity on the network and knowledge of that secret key is considered proof of identity. 
     An example of a Kerberos session is illustrated in  FIG. 1 . A client  100  may wish to access a network service running on network server  120 . In order to do so, it must verify that it has the proper credentials to access the service utilizing the Kerberos Key Distribution Center (KDC)  110 . 
     Arrow  130  illustrates that in this example, when logging onto the network, the client may request a Ticket-Granting-Ticket (TGT) from the Authentication Service (AS)  113 . The client may do this by answering a challenge issued by the AS using a password. Of course, other techniques are often used and this is merely an illustrative example. Once the AS verifies that the client is a valid entity on the domain, arrow  135  illustrates that a Ticket-Granting-Ticket may be issued. This TGT is typically cached on the local machine and used to request network service sessions throughout the network. 
     The Ticket-Granting-Ticket usually includes two parts: a main portion of the TGT which is encrypted with a key that only the TGS  117  can decrypt, and a session key encrypted with the client&#39;s secret key. This session key is used to handle future communications with the KDC. Because the client cannot read the main portion of the TGT contents, it must blindly present the ticket to the Ticket Granting Service  117  for service tickets. In some embodiments, the TGT also includes time-to-live parameters, authorization data, or other data. 
     When the client  100  wishes to access a Network Service  120 , the client presents the Ticket-Granting-Ticket to the Ticket Granting Service (TGS)  117  and requests a Service Ticket, as illustrated by arrow  140 . The TGS receives the TGT and decrypts it using the TGS&#39;s secret key. The TGS determines which server provides the service the client is requesting a ticket for. The TGS then encrypts a session key with that server&#39;s secret key. This encrypted session key is incorporated into the Session Ticket. Arrow  145  illustrates that the TGS may respond to a valid request by returning a valid Service Ticket to the client. 
     Arrow  150  illustrates that this Service ticket may be presented to network server  120  by client  100 . The Network server may then decrypt the session key using the server&#39;s secret key. Arrow  155  illustrates that the client-server session may then be established. During each of the client-KDC and client-server transactions the various tickets may have been also encrypted with the client&#39;s secret key, allowing the KDC and client to verify that the transaction was not intercepted nor involved a spoofed client or KDC. 
     This is merely an illustrative example of a Kerberos transaction. However, it does illustrate that the Kerberos protocol assumes that one, and only one, server provides each service. Therefore, if a service is to utilize a Kerberos protocol, it must be tied to a single server. This prevents the use of a server pool and the ability for a network to perform load balancing, among other tasks. Some techniques avoid this problem by sharing a single password among multiple servers. This technique, however, increases the manageability of the servers, for example, all server passwords must by synchronized, and decreases the security of the server pool, for example, compromising one server eases the compromising of the rest of the server pool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Subject matter is particularly pointed out and distinctly claimed in the concluding portions of the specification. The disclosed subject matter, however, both as to organization and the method of operation, together with objects, features and advantages thereof, may be best understood by a reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1  is a block diagram illustrating an embodiment of a technique for the authenticating a client utilizing the Kerberos protocol; 
         FIG. 2  is a flowchart illustrating an embodiment of a technique for generating a Service Ticket to facilitate a client to authenticate against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter; 
         FIG. 3  is a block diagram illustrating an embodiment of a Service Ticket to facilitate a client to authenticate against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter; 
         FIG. 4  is a flowchart illustrating an embodiment of a technique for authenticating a client against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter; and 
         FIG. 5  is a block diagram illustrating an embodiment of an apparatus and a system that allows for the authenticating a client against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous details are set forth in order to provide a thorough understanding of the present disclosed subject matter. However, it will be understood by those skilled in the art that the disclosed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as to not obscure the disclosed subject matter. 
     Kerberos is a trusted third-party authentication protocol designed for client/server interactions. J. Kohl and B. Neuman, “ The Kerberos network authentication service  ( version  5),” RFC-1510, 1993. Hereafter, a service that is substantially in compliance with the above Kerberos specification, its derivatives, or antecedents is simply referred to as “Kerberos.” This includes imperfect or corrupted implementations. 
       FIG. 2  is a flowchart illustrating an embodiment of a technique for generating a Service Ticket to facilitate a client to authenticate against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter. Block  210  illustrates that a Ticket Granting Service may receive a request for a Service Ticket. The Service Ticket may provide access to a client to a particular network service. In one embodiment, the Ticket Granting Service may, aside from the disclosed subject matter, substantially comply with the Kerberos protocol. It is also contemplated that the service be provided by the same machine as the requesting client. It is further contemplated that the client and server may be any physical or virtual machine including any architecture. 
     Block  220  illustrates that the Ticket Granting Service may determine if the requested service is provided a plurality of servers. In one embodiment, the Ticket Granting Service may utilize a Domain Name Server to determine if a generic domain name is aliased to a plurality of specific domain names. If so, the Granting Service may infer that multiple servers exist. In another embodiment, the Granting Service may refer to another database, such as, for example, a Kerberos Database, to determine if multiple servers exist. These are of course, merely a few non-limiting illustrative examples. It is contemplated that in one embodiment, the standard Kerberos database may be modified to include alias information that would facilitate the mapping of a generic server name to a plurality of specific server names. 
     Block  225  illustrates that, in one embodiment, if the service is provided by a single server, the Service Ticket request may be provided in single server mode. In one embodiment, the single server mode may include strict adherence to the standard Kerberos protocol. In another embodiment, the adherence to the Kerberos protocol may be less strict. It is contemplated that in yet another embodiment another technique may be used. It is also contemplated that in one embodiment, all Service Ticket requests may be processed in the same manner regardless of the number of servers utilized, and block  225  and, possibly, block  220  may not be used. 
     Block  230  illustrates that the Granting service may generate a random session key. Block  240  illustrates that a cipher text may be created or used. This cipher text may be encrypted with the session key. In one embodiment the cipher text may be an authenticator that includes, in one particular embodiment, the name of the client, the network address of the client, and a timestamp. 
     Block  260  illustrates that the session key may be encrypted with the secret key of the server providing the service. Block  250  illustrates that block  260  may be repeated for each providing server. In an illustrative embodiment, if there are, for example, 3 servers capable of providing the requested service, the Granting Service may encrypt the session key with the first server&#39;s secret key, resulting in a first encrypted session key. The session key may be encrypted with the second server&#39;s secret key, resulting in a second encrypted session key. Finally, the session key may be encrypted with the third server&#39;s secret key, resulting in a third encrypted session key. However, it is contemplated that any number of providing servers may be used and the illustrative embodiment is not meant to limit the disclosed subject matter to any particular number of providing severs. 
     In one embodiment, the secret keys of the providing servers may or may not be synchronized across all servers in the server pool. In another embodiment, only a portion of the providing server pool&#39;s secret keys may be synchronized. In another embodiment, sets of servers may be securely defined with one secret key associated with each server. In one illustrative example, specific server ABC may be associated with both generic servers  123  and  789 . Conversely specific server XYZ may only be associated with generic server  123 . Therefore, if a client requests access to generic server  789 , it would only be able to use gain access to specific server ABC, even tough specific servers ABC &amp; XYZ are pooled for generic server  123 . In yet another embodiment, at least a portion of the server pool may function as a cluster server. It is also contemplated that, in some embodiments, the session key may be a one-time key. 
     Block  270  illustrates that a Service Ticket may be created that includes the number of providing servers, an encrypted session key for each server, and the encrypted cipher text. It is contemplated that, in one embodiment, the number of providing severs may be inherently included in the number of encrypted session keys. Therefore, in one embodiment, the Service Ticket may not include a field expressly stating the number of providing servers, but instead, may rely upon the number of encrypted session keys to provide that information. Block  280  illustrates that the Service Ticket may be transmitted, in one embodiment, to the requesting client. 
       FIG. 3  is a block diagram illustrating an embodiment of a Service Ticket  300  to facilitate a client to authenticate against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter. The Service Ticket may include a field  310  expressly denoting the number of encrypted session keys or providing servers. A number of encrypted sessions keys may also be included, illustrated as fields  320 ,  330 , &amp;  380 . While at least 3 encrypted session keys are illustrated in  FIG. 3 , it is understood that the disclosed subject matter is not limited to any number of encrypted session keys. Filed  390  may also include the encrypted cipher text. It is contemplated that the fields may be arranged in any easily determinable order and the disclosed subject matter is not limited to the arrangement illustrated. In one embodiment, the Service Ticket illustrated by  FIG. 3  may have been generated in accordance with the technique illustrated in  FIG. 2 . 
       FIG. 4  is a flowchart illustrating an embodiment of a technique for authenticating a client against a pool of servers utilizing a secure authentication protocol in accordance with the disclosed subject matter. Block  410  illustrates that a providing server may receive a Service Ticket. In one embodiment, the Service Ticket may contain the fields illustrated in  FIG. 3 . However, other arrangements and fields are contemplated and within the scope of the disclosed subject matter. 
     Block  420  illustrates that the received ticket may be examined to determine if it includes encrypted session keys for multiple providing servers. If not, block  425  illustrates that the ticket may be processed in single server mode. In one embodiment, the single server mode may include strict adherence to the standard Kerberos protocol. In another embodiment, the adherence to the Kerberos protocol may be less strict. It is contemplated that in yet another embodiment another technique may be used. It is also contemplated that in one embodiment, all received Service Tickets may be processed in the same manner regardless of the number of servers utilized, and block  425  and, possibly, block  420  may not be used. 
     Block  430  illustrates that the number of encrypted session keys may be determined. In one embodiment the number of encrypted session keys, or servers, may be expressly noted within the Service Ticket. In another embodiment, the number of encrypted session keys may be dynamically determined by examining the Service Ticket. 
     Block  440  illustrates that the server may loop through each encrypted session key until the correct encrypted key is found. Block  445  illustrates that if the correct key is not found and error may be generated. In one embodiment, the server may silently ignore the client&#39;s request for the service. Conversely, in another embodiment, the server may report the unsuccessful access attempt to, for example, the client, or an agent that monitors the network security. However, other responses are contemplated and these are just a few non-limiting examples. 
     In one embodiment, the server may not need to enumerate through the encrypted session keys. For example, each encrypted key may be paired with a particular server identifier field. The server identifier field may express denote which encrypted session key utilizes the secret key of the receiving server. In one embodiment, the server identifying field may denote the Internet Protocol number of each server. The receiving server may then go directly to the encrypted session key associated with the receiving server&#39;s Internet Protocol number. As a result, block  440  would not be needed. In other embodiments, other techniques for determining which encrypted session key is associated with the receiving server may be used. 
     Block  450  illustrates that the server may attempt to decrypt the current encrypted session key with the server&#39;s secret key. Block  460  illustrates that an attempt to decrypt the cipher text may then be made utilizing the decrypted session key. If the session key was successfully decrypted, the cipher text should be successfully decrypted as well. If the session key was not encrypted with the receiving server&#39;s secret key, it will not successfully decrypt and the cipher text will also not successfully decrypt. 
     Block  470  illustrates that the server may determine if the cipher text was successfully decrypted. If not, the server will loop back to block  440  and attempt to decrypt the next encrypted session key, if any exist. If so, block  480  illustrates that client has gained access to the requested service and that the requested client-server transaction may continue. 
       FIG. 5  is a block diagram illustrating an embodiment of an apparatus  501  and a system  500  that allows for the authenticating a client against a pool of servers  550  utilizing a secure authentication protocol in accordance with the disclosed subject matter. In one embodiment, apparatus  501  may include a Key Distribution Center (KDC)  510  capable of generating a multi-server service ticket  540 . In one embodiment, the KDC may be, aside from the capability to generate the multi-server service ticket, substantially in compliance with the Kerberos protocol. 
     Key Distribution Center (KDC)  510  may include an Authentication Service (AS)  520  and a Ticket Granting Service (TGS)  530 . The AS may be capable of authenticating that a client  590  is legitimately accessing the KDC and/or the network domain and be capable of issuing a Ticket-Granting-Ticket to the client. In one embodiment, the AS these capabilities may be provided substantially in compliance with the Kerberos protocol. The TGS may be capable of receiving a request for a Service Ticket and issue a multi-server service ticket  540 . In one embodiment, the TGS may be capable of performing the technique illustrated by  FIG. 2 . In one embodiment, the Multi-Server Service Ticket may include the fields illustrated by  FIG. 3 . In one embodiment, the request for a Service Ticket may include or utilize the Ticket-Granting-Ticket issued by the AS. 
     System  500  may include the apparatus  501  and a pool of servers  550 . The pool of servers may be capable of receiving and utilizing a multi-server service ticket  540 . In one embodiment, the servers in the pool may be capable of performing the technique illustrated in  FIG. 4 . It is contemplated that while  FIG. 5  shows three network servers  553 ,  555 , &amp;  559  in the server pool, the disclosed subject matter is not limited to any particular number of servers. It is contemplated that in a unique embodiment, only one server may exist in the pool at a particular time. 
     In an illustrative example, client  590  may authenticate itself on the network utilizing the Key Distribution Center (KDC)  510 , and in particular, the Authentication Server (AS)  510 . The client may receive a Ticket-Granting-Ticket (TGT). The client may use this TGI to request a Service Ticket from the Ticket Granting Service (TGS)  530 . The TGS may determine that the service is provided by a server pool  550 , and issue a Multi-Server Service Ticket  540 . The client may present this Service Ticket to the server pool. The Second Network Server  555  may be selected by the manager of the server pool to process the client&#39;s request. The Second Network Server may authenticate the client&#39;s ability to receive the service and provide the service to the client. It is understood that the above example is merely one possible embodiment of the use of the apparatus  501  and system  500  and other uses are possible and contemplated. 
     It is also contemplated that the disclosed subject matter is not limited to any particular computing platform. While  FIG. 5  utilizes representations of traditional personal computers the disclosed subject matter is not limited to any particular architecture and may include devices, such as, for example, a laptop computer, a handheld computer, a personal digital assistant, a wireless local area network (WLAN) device, and a computer peripheral, such as, for example, a printer or mouse. However, these are merely a few non-limiting examples of such a device. 
     The techniques described herein are not limited to any particular hardware or software configuration; they may find applicability in any computing or processing environment. The techniques may be implemented in hardware, software, firmware or a combination thereof. The techniques may be implemented in programs executing on programmable machines such as mobile or stationary computers, personal digital assistants, and similar devices that each include a processor, a storage medium readable or accessible by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and one or more output devices. Program code is applied to the data entered using the input device to perform the functions described and to generate output information. The output information may be applied to one or more output devices. 
     Each program may be implemented in a high level procedural or object oriented programming language to communicate with a processing system. However, programs may be implemented in assembly or machine language, if desired. In any case, the language may be compiled or interpreted. 
     Each such program may be stored on a storage medium or device, e.g. compact read only memory (CD-ROM), digital versatile disk (DVD), hard disk, firmware, non-volatile memory, magnetic disk or similar medium or device, that is readable by a general or special purpose programmable machine for configuring and operating the machine when the storage medium or device is read by the computer to perform the procedures described herein. The system may also be considered to be implemented as a machine-readable or accessible storage medium, configured with a program, where the storage medium so configured causes a machine to operate in a specific manner. Other embodiments are within the scope of the following claims. 
     While certain features of the disclosed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the disclosed subject matter.