Credential roaming

<u>RELATED APPLICATION</u>

0001This application is related to co-owned, pending <patcit id="pcit0001" dnum="US36587803A" dnum-type="L"><text>U.S. Patent Application Ser. No. 10/365,878 of David B. Cross, et al., filed on February 13, 2003</text></patcit> for "Digital Identity Management."

<u>TECHNICAL FIELD</u>

0002The described subject matter relates to electronic computing, and more particularly to systems and methods of credential roaming in electronic computing systems.

<u>BACKGROUND</u>

0003Various types of encryption schemes are widely used to secure data (e.g., an email message or file) for communication over a network. For example, in symmetric encryption, both the user that is encrypting data and the user that is decrypting the data need copies of the same encryption key. Asymmetric encryption, also known as public key encryption, uses key pairs (e.g., a public key and a private key). In asymmetric encryption the public keys may be shared but the private keys are not.

0004Encryption keys may be stored on a computer system, e.g., as part of a user profile or other repository for user settings, credentials, etc. The encryption keys may be modified or replaced over time to decrease the likelihood that unauthorized users are able to decipher the encryption scheme. In any event, the user is provided access to the encryption keys after the user is authenticated (e.g., during logon) and the user profile is loaded on the computer system.

0005The user may, however, need access to the encryption keys at more than one computer system (e.g., a personal computer and one or more mobile devices). Although the user may transfer the encryption keys from one computer system to another (e.g., using a diskette or other removable storage media), this is cumbersome and time-consuming. While smartcards may be used, these are expensive. Alternatively, the user profile may be stored on a network server and accessed from a variety of different computer systems every time the user connects to the network. However, the user profile may be large (many megabytes) and downloading the user profile from a network server may slow the logon process. In addition, the user may not be able to logon and use the computer without a locally-stored user profile (when the network is not available).

0006Passlogix: "v-GO Single-Sign On", 8 April 2003 relates to a single sign-on solution for replacing all user IDs and passwords with a single authentication. Users authenticate once and the sign-on program detects and responds to all password-related events to automate every password management task for the end user, including login, password selection, password change and password re-sets. It is further stated that v-GO SSO uses client-side intelligence in conjunction with a locally encrypted database of user credentials to respond to logon requests. Synchronizing user credentials to a directory service or network drive enables mobility. In particular, v-GO SSO supports windows roaming profiles for simple file-level synchronization and backup, and provides a standard API for record-level synchronization of user credentials with any external application or device.

0007Novell: "Novell SecureLogin", 31 October 2003 relates to the Novell SecureLogin program, which is also a single sign-on program eliminating the need for users to remember their user names and passwords beyond the initial network login. Single sign-on stores the user names and passwords that each user needs and then automatically enters them for the user when required. It is further stated that upon authentication, a call is made to eDirectory to acquire/synchronize assigned scripts and stored credentials.

0008<patcit id="pcit0002" dnum="EP1560100A"><text>EP 1 560 100 A</text></patcit> relates to techniques for establishing and managing a distributed credential store. An identity service aggregates identity information from one or more identity stores and maintains the information as a remote credential store. A principal interacts with the principal service for defining or modifying a policy that identifies portions of the remote credential store which are to be synchronized with the local credential store. More precisely, the synchronization policy defines fields of a remote credential store which are to be kept in synch with a local credential store. It is further stated that the identity service is configured to detect when changes to the duplicated records or maintained links are made in the identity stores via a data store event that is trapped and monitored by the identity service. Furthermore, the identity service is in a position to acquire the changes, and transmit the changes to the principal credential store. If there are conflicts between changes of the personal credential store and the newly instantiated enterprise credential store, the conflicts can be resolved by the policy.

0009<nplcit id="ncit0001" npl-type="s"><text>D. Gustafson, M. Just, M. Nystrom: "Securely Available Credentials - Credential Server Framework": IETF Standard-working-draft, Internet Engineering Task Force, IETF, CH, vol. no. 7, November 2003</text></nplcit> relates to credential mobility. A definition of credentials is given, consisting of public/private key pairs, symmetric keys, X.509 public key certificates, attribute certificates, and/or application data. A password is defined as a string of characters known only to a client and used for the purposes of authenticating to a server and/or securing credentials. A password token is defined as being a value derived from a password using a one-way function that may be used by a client to authenticate to a server. Furthermore, secured credentials are mentioned, which have been cryptographically secured, e.g. encrypted/MACed with a passkey.

0010<nplcit id="ncit0002" npl-type="s"><text>E. Brovick, W.C. Wade III: "Windows® 2000 Active Directory ™", 10 February 2000</text></nplcit>, relates to the physical topology of the Active Directory, which is a concept introduced by the client. The domain controllers (DCs) in the Active Directory have a special relationship with at least two other DCs in their site. These other servers are designated as the DCs replication partners. Because Active Directory uses replication partners to improve performance, it is possible that a DC could receive the same replication data from different DCs. To prevent this, Active Directory has implemented what is called propagation dampening. Propagation dampening is the process of only requesting replication changes that have not been replicated. For this purpose, each DC maintains an up-to-date vector. The up-to-date vector is a set of USNs that represents the highest originating update for each server.

0011<patcit id="pcit0003" dnum="US5926816A"><text>US5926816 A</text></patcit> discloses a database synchronizer which performs database synchronization between a client database and a server database using a three-step process. First, the client determines what modifications to the client data have taken place since the last time of synchronization. The modifications detected are the creation of a new data item, an update to the value of an existing data item, and the deletion of a data item. Under one approach, the client detects modifications by comparing the client data with a before-image of the client data. The before-image is effectively a copy of the client data as of the last time it was synchronized. Second, the modifications are propagated to the server, which has determined what changes have taken place to the server data since the last time of synchronization. Finally, the server detects data conflicts, resolves them, and propagates modifications back to the client as refresh data.

0012<patcit id="pcit0004" dnum="US2002029214A1"><text>US 2002/029214 A1</text></patcit> relates to a synchronizable transactional database method and system. The synchronization algorithm starts by asking both databases to compute a single summary of all records lying in the given key interval. The Get_Interval_Hashes function is invoked for this. The remote summary is transferred to the local side and compared with the local summary. If the summaries match, it is concluded that the databases are already synchronized restricted to the given key interval.

0013<patcit id="pcit0005" dnum="US6560655B1"><text>US 6 560 655 B1</text></patcit> relates to a synchronization manager for standardized synchronization of separate programs. It provides a mechanism for managing the synchronization of data between local and remote computers according to user preferences. Applications register respective handlers with a synchronization manager. On a synchronize event, such as a manual request for synchronization, or, based on user preferences, a notification of an event such as logon or logoff, the synchronization manager queues the registered application handlers, and calls the handlers to perform the synchronization of items therein.

SUMMARY

0014It is the object of the present invention to provide a system and method for enabling credential roaming, e.g., among a plurality of different computing devices. An exemplary system may include an event handler which receives event notifications such as, e.g., an interactive or network logon from an operating system. The event handler may invoke a management service in response to receiving an event notification. The management service may include a synchronizing module to synchronize a user's credentials (e.g., encryption credentials) with a remote cache or directory service. Accordingly, the user's credentials are available from any of a number of different computing devices.

0015This object is solved by the subject matter of the independent claims.

0016Embodiments are given in the dependent claims.

0017In some implementations, articles of manufacture are provided as computer program products. One implementation of a computer program product provides a computer program storage medium readable by a computer system and encoding a computer program for credential roaming. Another implementation of a computer program product may be provided in a computer data signal embodied in a carrier wave by a computing system and encoding the computer program for credential roaming.

0018The computer program product encodes a computer program for executing a computer process on a computer system to enumerate local credentials and remote credentials in response to receiving an event notification, and synchronizing the local credentials and remote credentials.

0019In another implementation, a method is provided. An exemplary method includes enumerating local credentials and remote credentials in response to receiving an event notification, and synchronizing the local credentials and remote credentials.

0020In another implementation, a system is provided. An exemplary system includes an event handler to receive event notifications. A synchronizing module is operatively associated with the event handler. The synchronizing module synchronizes local credentials and remote credentials when the event handler receives an event notification if the local and remote credentials are different from one another.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

0021<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a schematic illustration of an exemplary computer network that may implement credential roaming;</li><li><figref idref="f0002">Fig. 2</figref> is a functional block diagram of exemplary modules to implement credential roaming;</li><li><figref idref="f0003">Fig. 3</figref> is another functional block diagram of exemplary modules to implement credential roaming;</li><li><figref idref="f0004">Fig. 4a</figref> illustrates an exemplary state file;</li><li><figref idref="f0004">Fig. 4b</figref> illustrates an exemplary state entry in a state file;</li><li><figref idref="f0005">Fig. 5</figref> illustrates exemplary winner arbitration matrices, wherein (a) is a lenient matrix and (b) is a strict matrix,;</li><li><figref idref="f0006">Fig. 6</figref> is a flowchart illustrating exemplary operations to implement credential roaming; and</li><li><figref idref="f0007">Fig. 7</figref> is a schematic illustration of an exemplary computing device that can be utilized to implement credential roaming.</li></ul>

<u>DETAILED DESCRIPTION</u>

0022Briefly, credential roaming may be implemented to synchronize local credentials (encryption keys, certificates, tokens, etc.) at any number (n) of computing devices. For purposes of illustration, a user may change, modify, add and/or remove credentials at his or her laptop or desktop computer. When the user logs out of the laptop or desktop computer, a management service synchronizes the local credentials with a remote cache. The remote cache may be implemented as a remote directory service, such as, e.g., Active Directory available for the Microsoft WINDOWS® operating environment. Alternatively, the management service may synchronize in response to other events. For example, real-time synchronizing may occur in response to one or more credentials being added, removed and/or modified.

0023Later, the user may use his or her personal digital assistant (PDA) or mobile phone to retrieve email messages. When the user logs onto the mobile device, the user's credentials are synchronized with the remote directory service so that the user has available a current and complete set of credentials, such as, e.g., encryption credentials for sending/receiving email messages.

0024In exemplary implementations, the management service may be automatically invoked (e.g., in response to a system event) and no affirmative action is even required of the user. Furthermore, the user profile may be stored locally, e.g., on the user's desktop or laptop computer, while still allowing the user to have access to a current and complete set of credentials at any of a number of different computing devices. Exemplary implementations may also ensure old or unused credentials are removed from the user's system when these credentials are no longer needed (e.g., by detecting and propagating a deletion or examining time-stamps for the credentials).

<u>Exemplary System</u>

0025<figref idref="f0001"><b>Fig. 1</b></figref> is a schematic illustration of an exemplary networked computing system 100 in which credential roaming may be implemented. The networked computer system 100 may include one or more communication networks 110, such as local area network (LAN) and/or wide area network (WAN). One or more hosts 120 and one or more clients 130a-c may be communicatively coupled over the communication network(s) 110.

0026Host 120 and clients 130a-c (hereinafter generally referred to as clients 130) may connect to a network via a communication connection such as, e.g., an Ethernet connection. Although there are no theoretical limits on the number of devices that can be included in a network such as networked computing system 100, the number of devices are limited primarily by the connectivity implemented in the communication network.

0027The terms "host" and "client" both refer to the hardware and software (the entire computer system) used to perform various computing services. For example, a host may be implemented as a server computer that is dedicated to server applications or that also runs other applications. A client may be implemented as a stand-alone desktop or laptop personal computer (PC), workstation, personal digital assistant (PDA), or any of a wide variety of electronic appliances, to name only a few examples.

0028Credentials 140a-c (hereinafter generally referred to as credentials 140) may be provided at one or more of the clients 130. Credentials may be provided, for example, for symmetric and/or asymmetric encryption/decryption of data for secure communication over network 110, to apply a digital signature to content, or to authenticate to a system, to name only a few examples. Any number of credentials 140 may be stored in a local cache 135a-c (hereinafter generally referred to as local cache 135). Local cache 135 may include a user profile or other repository (e.g., for user settings and credentials) although other implementations are also contemplated.

0029It is noted that the credentials 140 may include any of a wide variety of different types of credentials, such as, e.g., symmetric encryption keys, asymmetric encryption key pairs, X.509 certificates, XrML licenses, tokens, and authentication/authorization credentials to name only a few exemplary credentials. Of course credentials 140 are not limited to these examples and may include other types of credentials now known or later developed.

0030Credentials 140 may be added to the local cache 135, for example, to encrypt/decrypt different types of data. In addition, credentials 140 may be modified or replaced, e.g., to decrease the likelihood that unauthorized users are able to decipher the encryption scheme. Credentials that are no longer used may be removed. If one or more credential 140 is added, modified, replaced, or removed at any one of the clients (e.g., 130a), this change may be propagated to one or more other clients (e.g., 130b, 130c) so that a user has available a current and complete set of encryption credentials at any number (n) of different clients, as described in more detail below.

0031In an exemplary implementation, local credentials 140 may be synchronized with remote credentials 150 provided at a remote cache 125, e.g., at one or more hosts 120 or a shared cache at another client 130 in a workgroup environment. Accordingly, the user has available a current and complete set of credentials when the user logs onto other clients 130.

0032Remote cache 125 may be implemented as a directory service, such as a distributed lightweight directory access protocol (LDAP) or X.500 directory service. The directory service may be monolithic, or it may be distributed as a multi-master implementation or master-slave implementation. Remote cache 125 may stored in a protected or encrypted state so that the remote credentials 150 are not exposed to compromise, theft, or exploit by unauthorized users.

0033An exemplary directory service is the Active Directory available with the Microsoft WINDOWS® operating environment. Active Directory is a directory service that may be deployed in distributed computing environments to provide comprehensive directory services. Active Directory serves as a consolidation point for isolating, migrating, centrally managing, and reducing the number of directories that an enterprise needs. Active Directory also serves as a central authority (CA) for network security.

0034It is noted, however, that remote cache 125 may be implemented in any suitable manner and is not limited to the examples given herein.

0035<figref idref="f0002"><b>Fig. 2</b></figref> is a functional block diagram of exemplary modules to implement credential roaming, e.g., using a notification service. Notification service 200 may be implemented in computer-readable program code (e.g., software and/or firmware) stored in computer-readable storage or memory and executable by a processor (or processing units) at one or more clients (e.g., the clients 130a-c in <figref idref="f0001">Fig. 1</figref>). Notification service 200 receives notification of various system events and invokes a management service 250 to synchronize local and remote credentials for a user. Accordingly, synchronization may be automatic and transparent to the user.

0036Referring to <figref idref="f0002">Fig. 2</figref>, notification service 200 may include an event handler 210. Event handler 210 receives notification of events 220a-c (hereinafter generally referred to as events 220). Events 220 may include, by way of example, startup, shutdown, logon, logoff, lock, unlock, to name only a few exemplary events. Other events may also include, but are not limited to session events (e.g., policy update, running a process, network connection), and timer events (e.g., every 8 hours, once a month). Optionally, an event may also be triggered manually, e.g., by the user requesting credential synchronization.

0037Event handler 210 may generate one or more jobs 230 based at least in part on events 220. Jobs 230 may include calls to other services. For example, a job 230 may call an auto-enrollment service 240. Auto-enrollment is a service that may be used to populate a user profile with credentials, etc., and may be invoked when a user is new to the system (e.g., a guest) to provide limited functionality and access to basic resources without compromising network security. Auto Enrollment automatically "enrolls" a user by requests/renewing the credentials for a user, e.g., based on the system policies for the computing environment. A job 230 may also call a management service 250 to synchronize encryption credentials with a remote cache (e.g., the remote cache 125 in <figref idref="f0001">Fig. 1</figref>), as discussed in more detail below.

0038Jobs 230 may be passed to a dispatcher 260. Job dispatcher 260 may remove jobs 230 from the queue and process jobs 230 in a serialized manner. The job dispatcher 260 determines which program code (or modules) to load for processing the job and when to load the program code. The job dispatcher 260 may also unload program code that is no longer being used.

0039Notification service 200 may also include logic for intelligently managing jobs 230 to reduce unnecessary resource consumption. In an exemplary implementation, job dispatcher 260 determines whether program code (or modules) for processing the job 230 is already loaded. In addition, if the job queue 270 is empty (e.g., there are no pending jobs 230), the job dispatcher 260 releases loaded program code (or modules).

0040In another exemplary implementation, event handler 210 may order jobs 230 that invoke the management service 250 in the queue 270 ahead of jobs 230 that invoke the auto-enrollment service 240. When events 220 trigger jobs 230 to call both the auto-enrollment service 240 and the management service 250, the jobs 230 invoking the auto-enrollment service 240 may be removed from the queue 270 if the management service is able to provide credentials for a user during synchronization.

0041In another exemplary implementation, dampening logic may be implemented to reduce repeated calls to the management service 250 (e.g., when an event 220 triggers other events). For example, dispatcher 260 may examine the job queue 270 and discard any jobs 230 which are duplicative or otherwise unnecessary.

0042Before continuing, it is noted that the notification service 200 is not limited to the exemplary modules shown in <figref idref="f0002">Fig. 2</figref>. For example, the functions do not need to be embodied in separate modules. In yet other implementations, additional functional components may also be included. Regardless of the implementation, notification service may call management service 250 to synchronize local and remote credentials.

0043<figref idref="f0003"><b>Fig. 3</b></figref> is a functional block diagram of exemplary modules to implement credential roaming, e.g., using a management service. Management service 300 may be operatively associated with a notification service 310 (e.g., the notification service described in more detail above with reference to <figref idref="f0002">Fig. 2</figref>). Notification service 310 may invoke management service 300 in response to receiving notification of an event. Management service 300 evaluates and compares local credentials and remote credentials and, if these are different, synchronizes the local and remote credentials so that the user has available a current and complete set of credentials when using any number (n) of different clients.

0044Management service 300 may be implemented in computer-readable program code (e.g., software and/or firmware) stored in computer-readable storage or memory and executable by a processor (or processing units) at one or more clients (e.g., the clients 130a-c in <figref idref="f0001">Fig. 1</figref>). Management service 300 may include a synchronizing module 320 to evaluate credentials, resolve conflict(s), and update the credentials at the local and remote caches.

0045Synchronizing module 320 may be operatively associated with local store manager 330 and remote store manager 340. Local store manager 330 may be operatively associated with one or more local cache 350 for local credentials 355. In addition, local store manager 330 may abstract the procedures to load/save local encryption credentials 355 locally. Remote store manager 340 may be operatively associated with a remote cache 360 (e.g., a directory service) provided via one or more server computers or hosts 370. Remote store manager 340 may also securely bind to the host 370 to access one or more remote credentials 365 via the remote directory service 360, e.g., during synchronizing.

0046Before continuing, it is noted that credentials are not limited to being provided at a host, e.g., via a remote directory service. In another exemplary implementation the remote cache may be a shared cache at another client, e.g., in a workgroup environment. Accordingly, clients in one or more workgroups may synchronize shared credentials among clients in the workgroup.

0047The store managers 330, 340 may enumerate credentials 355, 365 (e.g., as a list of roaming credentials) for the synchronizing module 320 to evaluate. The store managers 330, 340 may also provide information to the synchronizing module 320, such as, e.g., the last time the collections of credentials 355, 365 were changed so that the synchronizing module 320 can resolve any conflict(s).

0048Synchronizing module 320 may operate in conjunction with local store manager 330 and remote store manager 340 to synchronize local encryption credentials 355 and remote encryption credentials 365. For many invocations, there may be no changes to either the local or remote encryption credentials. During other invocations, changes may only need to be made to the local credentials 355 or only to the remote credentials 365. However, there may also be circumstances where may need to be made to both the local credentials 355 and the remote credentials 365. Accordingly, synchronizing module may be implemented to handle each of these scenarios.

0049Evaluating local and remote encryption credentials may be a time-consuming process, particularly if there are several hundred or even several thousand encryption credentials. Accordingly, synchronizing module 320 may first sort the encryption credentials into arrays and then make a linear comparison of the sorted arrays. Of course other implementations are also contemplated, such as but not limited to using a hash and timestamp to determine if there is a change.

0050During the comparison, synchronizing module 320 may encounter conflicts that need to be resolved in order to synchronize the local and remote credentials 355, 365. For example, a local credential (referred to as an "old credential" for purposes of illustration) may be modified or removed/deleted from the local cache 350 because it is no longer needed. When synchronizing module 320 compares the local and remote credentials 355, 365, however, the remote credentials may still include the old credential. Synchronizing module 320 resolves such a conflict so that the old credential is modified or removed from the remote cache 360 and not rewritten to the local cache 350.

0051In an exemplary implementation, credentials that have been modified or removed/deleted are "tagged" or otherwise identified in the remote cache. Accordingly, the modify or delete operation may be persisted across multiple clients. As an example, if the old credential is deleted from a first client, synchronizing module 320 identifies the old credential at the remote cache as having been removed or deleted. When a second client also having a copy of the old credential synchronizes with the remote cache, the old credential is deleted from the second client and not rewritten to the remote cache. As another example, if the old credential is modified at a first client, synchronizing module 320 identifies the old credential at the remote cache as having been modified. When a second client also having a copy of the old credential synchronizes with the remote cache, the old credential is modified at the second client and not returned to its original condition at the remote cache.

0052In an exemplary implementation, synchronizing module 320 maintains one or more state files 395 for conflict resolution. The state file is a per-user persisted data structure (e.g., computer file, database, memory table, log, etc.) and may be used to store the state of local credentials 350. The state file may be stored locally, e.g., in cache 390 operatively associated with the management service 300. In an exemplary implementation, all fields may be stored in binary, native byte-order, although other implementations are also contemplated.

0053<figref idref="f0004"><b>Fig. 4a</b></figref> illustrates an exemplary state file 400 (e.g., a data structure). State file 400 may include a file version 410 and a flag 420. Flag 420 may be used, e.g., to indicate whether the credential is user-protected or can be exchanged on the network. Alternatively, flag 420 (or another flag) may be used to indicate whether a strict or lenient matrix should be used to resolve conflicts.

0054State file 400 may also include one or more credential states 430-432. For example, state file 400 may include the following states: last time synchronization module called (T_S); last time local store changed (T_L), last time when the remote cache changed (T_R). The state file may also include credential state entries 440.

0055<figref idref="f0004"><b>Fig. 4b</b></figref> illustrates an exemplary state entry 450 (e.g., a data structure). State entry 450 may include a list of local states for each credential. Local states may include credential ID 460, flags 470, time-stamp 480, and hash 490.

0056Before continuing, it is noted that the time-stamp is not limited to a clock-based (e.g., physical or system) time. For example, the time-stamp may include counters such as an update sequence number which is changed for every update made. Indeed, a clock-based time-stamp may be used for the local cache and an update sequence number-based time-stamp may be used for the remote cache.

0057In the implementation shown in <figref idref="f0004">Fig. 4</figref>, credential ID 460 is the "compressed" path of the encryption credential file. Credential ID 460 may be expressed as a single-byte ASCII string, although other implementations are also contemplated. In addition, any suitable flags 470 may be defined and may be set (e.g., 1) or off (e.g., 0). For example, a flag may indicate whether the encryption credential is roaming (can be synchronized) or fixed (should not be synchronized).

0058Operations that may be implemented for conflict resolution using state files, such as the state file 400 shown in <figref idref="f0004">Fig. 4</figref>, are described in more detail below. Conflict resolution may be illustrated by arbitration matrices.

0059<figref idref="f0005"><b>Fig. 5a and 5b</b></figref> illustrate exemplary arbitration matrices, wherein the matrix 500 is lenient and the matrix 550 is strict. In the matrices 500, 550, exportable credentials are denoted by the letter "E" and protected (or non-exportable) credentials are denoted by the letter "P", wherein "/E" and "/P" denote opposites. The time-stamps of both the certificates are used to determine which certificate is the most recent. The most recent certificate is used to overwrite the local and remote cache. The other certificate is deleted.

0060It is noted that the exemplary implementations discussed above are provided for purposes of illustration. Still other implementations are also contemplated.

<u>Exemplary Operations</u>

0061Described herein are exemplary methods for implementing encryption credential roaming. The methods described herein may be embodied as logic instructions on one or more computer-readable medium. When executed on a processor, the logic instructions cause a general purpose computing device to be programmed as a special-purpose machine that implements the described methods. In the following exemplary operations, the components and connections depicted in the figures may be used to implement encryption credential roaming.

0062<figref idref="f0006"><b>Fig. 6</b></figref> is a flowchart illustrating exemplary operations that may be implemented for encryption credential roaming. In operation 610, the client may receive an event notification. Event notifications may include, by way of example, a session event, a logon event, a logout event, a lock event, an unlock event, a timer event, a policy application event, and/or a credential update event. In operation 620 local credentials may be enumerated and in operation 630 remote credentials may be enumerated.

0063In operation 640, the local credentials and remote credentials may be compared to determine if there is a conflict. If there is no conflict, operations return as illustrated by arrow 650 to operation 610. Alternatively, a conflict may exist if any one or more of the enumerated local credentials are different than the enumerated remote credentials. For purposes of illustration, the enumerated local credentials may be different than the enumerated remote credentials if a credential has been added, modified, or deleted from a local credential cache and/or a remote credential cache.

0064If a conflict exists, the conflict is resolved in operation 660, e.g., by determining which credentials need to be added/removed in the local and remote credential caches. In an exemplary implementation, the conflict may be resolved based on time-stamps associated with the local and remote credentials. In operation 670, local and/or remote credentials are synchronized, e.g., so that both the local and remote credential caches include a complete, updated set of encryption credentials.

0065For purposes of illustration, operation 660 (conflict resolution) and operation 670 (synchronization) may be implemented as follows:

0066When credential roaming is first enabled for a client, the client may already have the same credentials (e.g. via manual key or PKCS #12 blob import) as in the remote cache. However, the credential storage and linker details may be different depending on how the credential was imported. This initial conflict may be resolved as follows.

0067If the remote credentials have already been downloaded, master keys (e.g., for accessing private keys) may be synchronized before these operations are performed so that private keys that need master keys are available.

0068A management service may then retrieve the creation time of the remote cache, e.g., via attribute's meta-data, and assigns it to T_C. If either or both of the time-stamps for the conflicting certificates are newer than T_C, at least one of the certificates was modified after deployment of credential roaming and the most recent cache is used.

0069Otherwise, both the local and remote caches may have been created before the deployment of credential roaming. The information flags for both certificates are retrieved to determine if the credential is user-protected or exportable. The policy flag may also be retrieved and determined whether a lenient matrix (e.g., matrix 500 in <figref idref="f0005">Fig. 5</figref>) or strict matrix (e.g., matrix 550 in <figref idref="f0005">Fig. 5</figref>) should be used to resolve the conflict.

0070An exemplary implementation of an algorithm for credential roaming is described as follows. According to this implementation, T_L represents the most recent time the entire local cache changed. T_L is based on the local machine's system time and may be compared with the local cache's update time so there is no timer skew. T_R represents the most recent time changes were made to the Update Sequence Number (USN) of the entire remote cache at the last synchronization. T_R may use the USN from the remote cache and may be compared with the remote cache USN so there is no timer skew.

0071First, the current last change time is read from the local cache and the USN is read from the remote cache. Then T_L and T_R are read from the state file header. T_L is compared with the last change time just read from the local cache and T_R is compared with the USN read from the remote cache. If they are both equal, nothing needs to be done. Otherwise, the algorithm may create a local change list C_L and a remote change list C_R, both initially empty.

0072If the last time the local cache was changed is later than T_L, the all the local cache credentials are read and compared with a corresponding entry in the state file. If any of the credentials are different, an entry may be created in C_L recording the credential or the state file entry, the most recent time a credential was updated, and a suggested action (e.g., add to the remote/local cache, modify the corresponding remote/local cache credential, delete the corresponding remote/local cache credential, update state file entry, etc.). Credentials may be deemed to be different if the hash value has changed, if the flag value has changed (e.g., to DELETED, UNWRITEABLE, UNREADABLE), or if the local cache has a credential that the state file does not have a record of, or state file has an entry that local cache does not have a record of.

0073If the remote cache's last USN is different than T_R, all of the remote cache credentials are read and the same operations as just described are performed. The change list C_R may also be updated.

0074Both the C_L and C_R may then be evaluated to determine if actions have been performed on the same credential in both lists. If actions have been performed on the same credential in both lists, these actions may be evaluated to determine if there are any conflicts. For example, there may be a conflict if C_L includes an entry for credential A to "modify remote" while C_R includes an entry for the same credential to "modify local." The conflict may be resolved based on the last change times of both the local and remote credentials. That is, the entry with the earlier change time may be deleted from the list.

0075After resolving the conflicts, if any, the local and remote cache are updated based on the union of C_L and C_R. A flag is set for each entry that failed to update even after a few retries.

0076The state file may then be updated. For example, DELETED flags that have been set for an excessively long time may be identified and removed. The state file header and entries may also be updated based on the resultant C_L and C_R entries. If the state file failed to update even after a few retries, credential roaming may be disabled because a corrupted state file may generate unpredictable results.

0077It is noted that the entries described above may be evaluated as hash values. Hash values provide security, e.g., so that credentials are not duplicated in unnecessary caches, and for performance (hash comparisons are typically fast). However, it is noted that using a hash is only exemplary. For example, if the state file stores the entire credential, it may be used for binary or exact comparison in place of a hash.

0078The last sync time T_S maintained in the state file may be used to determine how to handle the local cache entry that exists in the state file but not in the remote cache. If the time elapsed from T_S until the current time is less than a threshold time, then the remote cache adds this entry. Otherwise the entry may be deleted from the local cache.

0079Error conditions in synchronizing the credentials may also result in partially updated or corrupted credentials. Accordingly, error handling may be provided so that a failure is not propagated, e.g., to the remote cache.

0080In any exemplary implementation, a "Write State" is returned to indicate a completion status of the write operation. The values may be: NONE, PARTIAL and DONE to indicate that the credential is (1) not altered, (2) partially changed or (3) successfully changed, respectfully. If a save operation results in a PARTIAL write state, the state file entry is marked as UNWRITEABLE. If a delete operation results in a NONE or PARTIAL write state, the state file entry is marked as UNWRITEABLE. For any sporadic write or delete failures, write or delete operations may be retired and the state file entry may be marked when all tries for a credential have failed.

0081The synchronization ignores the local change if it is marked as UNWRITEABLE and may retry deleting the local credential if it is marked UNWRITEABLE. If the credential is successfully overwritten when it is marked as UNWRITEABLE, or if it disappeared when state file marks it as UNWRITEABLE, the UNWRITEABLE flag may be cleared from the state file entry.

0082If State file fails to update (e.g., indicating a potentially corrupted state file), the credential roaming may be disabled for the failed client or for a particular user. It may be manually re-enabled if the problem is fixed later. The system may also perform automatic recovery steps to override any bad data by downloading known good data from the remote store at the next invocation interval.

0083Local cache read failures may also be handled. The read failures may be handled more leniently than update failures so that a read failure of a roaming credential does not affect the roaming for other credentials.

0084In an exemplary implementation, a credential having a read failure appears in the roaming credential set returned by a GET ALL operation so that synchronization does not treat it as a deletion. Local cache reads may be retried with delay when any failure occurs. If the failure still exists after a number of retries, a roaming credential is nevertheless generated with the UNREADABLE flag bit set. Informational, warning, and/or error events may be traced or logged to facilitate trouble shooting/maintenance.

0085The operations shown and described herein are merely illustrative of an exemplary implementation of credential roaming. It is noted that the operations are not limited to any particular order. In <figref idref="f0006">Fig. 6</figref> for example, operation 620 may occur before, after, or simultaneously with operation 630. In another example, operations 620-670 may be iterative for individual encryption credentials, different types of encryption credentials, or other groupings (or sets) of encryption credentials. Still other operations may also be implemented to enable credential roaming.

<u>Exemplary Computing Device</u>

0086<figref idref="f0007"><b>Fig. 7</b></figref> is a schematic illustration of an exemplary computing device 700 that can be utilized to implement credential roaming. Computing device 700 includes one or more processors or processing units 732, a system memory 734, and a bus 736 that couples various system components including the system memory 734 to processors 732. The bus 736 represents 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 734 includes read only memory (ROM) 738 and random access memory (RAM) 740. A basic input/output system (BIOS) 742, containing the basic routines that help to transfer information between elements within computing device 700, such as during start-up, is stored in ROM 738.

0087Computing device 700 further includes a hard disk drive 744 for reading from and writing to a hard disk (not shown), and may include a magnetic disk drive 746 for reading from and writing to a removable magnetic disk 748, and an optical disk drive 750 for reading from or writing to a removable optical disk 752 such as a CD ROM or other optical media. The hard disk drive 744, magnetic disk drive 746, and optical disk drive 750 are connected to the bus 736 by appropriate interfaces 754a, 754b, and 754c. The drives and their associated computer-readable media provide nonvolatile storage of computer-readable instructions, data structures, program modules and other data for computing device 700. Although the exemplary environment described herein employs a hard disk, a removable magnetic disk 748 and a removable optical disk 752, other types of computer-readable media such as magnetic cassettes, flash memory cards, digital video disks, random access memories (RAMs), read only memories (ROMs), and the like, may also be used in the exemplary operating environment.

0088A number of program modules may be stored on the hard disk 744, magnetic disk 748, optical disk 752, ROM 738, or RAM 740, including an operating system 758, one or more application programs 760, other program modules 762, and program data 764. A user may enter commands and information into computing device 700 through input devices such as a keyboard 766 and a pointing device 768. 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 unit 732 through an interface 756 that is coupled to the bus 736. A monitor 772 or other type of display device is also connected to the bus 736 via an interface, such as a video adapter 774.

0089Generally, the data processors of computing device 700 are programmed by means of instructions stored at different times in the various computer-readable storage media of the computer. Programs and operating systems may be distributed, for example, on floppy disks, CD-ROMs, or electronically, and are installed or loaded into the secondary memory of a computer. At execution, the programs are loaded at least partially into the computer's primary electronic memory.

0090Computing device 700 may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 776. The remote computer 776 may be a 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 computing device 700. The logical connections depicted in <figref idref="f0007">Fig. 7</figref> include a LAN 780 and a WAN 782.

0091When used in a LAN networking environment, computing device 700 is connected to the local network 780 through a network interface or adapter 784. When used in a WAN networking environment, computing device 700 typically includes a modem 786 or other means for establishing communications over the wide area network 782, such as the Internet. The modem 786, which may be internal or external, is connected to the bus 736 via a serial port interface 756. In a networked environment, program modules depicted relative to the computing device 700, 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.

0092Hosts may include host adapter hardware and software to enable a connection to the communication network. The connection to communication network may be through an optical coupling or more conventional conductive cabling depending on the bandwidth requirements. A host adapter may be implemented as a plug-in card on computing device 700. Hosts may implement any number of host adapters to provide as many connections to communication network as the hardware and software support.

0093In addition to the specific implementations explicitly set forth herein, other aspects and implementations will be apparent to those skilled in the art from consideration of the specification disclosed herein. It is intended that the specification and illustrated implementations be considered as examples only.