Abstract:
Event-based biometric authentication is provided using a mobile device of a user. A user attempting to access a protected resource is authenticated by receiving a request to access the protected resource; collecting biometric information from the user in response to the request using a mobile device of the user; performing biometric authentication of the user using the collected biometric information; and granting access to the protected resource based on the biometric authentication. The authentication optionally comprises an event-based authentication. The mobile device does not have to contain token generating material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is related to U.S. patent application Ser. No. 13/341,160, filed Dec. 30, 2011, entitled “Biometric Authentication with Smart Mobile Device,” (now U.S. Pat. No. 8,752,145), incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates generally to techniques for securing communications over a network and other types of communication systems. 
     BACKGROUND OF THE INVENTION 
     Computer networks, such as those provided at a workplace, university, or another organization, are often configured to allow users to gain network access remotely through virtual private networks (VPNs), customized network settings, and/or other technologies. To gain access, users are generally required to authenticate to the remote network. Authentication may involve users providing various authentication factors, such as passwords, token codes, and personal identification numbers (PINs). Remote networks generally include, or have access to, an authentication server. The authentication server receives authentication requests from users and either grants or denies access, based on whether authentication factors provided with the requests match expected values. For added security, networks often require that multiple authentication factors be entered and verified before access can be granted. 
     A common two-factor authentication scheme involves both a token code and a personal identification number (PIN). The token code, also known as a one-time password, or “OTP,” is generated automatically, such as by a portable device that a user has in his or her possession. The PIN is a number, or possibly an alpha-numeric string, that the user has memorized. Both the token and the PIN have been registered previously in connection with the user at the authentication server. The user enters both the token code and the PIN in one or more fields of a network login screen on the user&#39;s computer. Access to the remote network is only granted to the user&#39;s computer if both the token code (something the user has) and the PIN (something the user knows) can be verified. An example of a portable token is SecurID®, which is available from RSA Security LLC, Bedford, Mass. 
     Recently, software has been introduced to perform the functions of tokens on smart mobile devices, such as smart phones, personal digital assistants (PDAs), and tablets. See, e.g., RSA SecurID, “Software Authenticators,” downloadable form http://www.emc.com/security/rsa-securid/rsa-securid-software-authenticators/iphone-and-ipad.htm. In one example, a user of a computer wishing to access a remote network enters his or her PIN into a field displayed on the user&#39;s mobile device. The mobile device sends the PIN to an authentication server. If the PIN matches an expected value, the authentication server sends back a signal to unlock the mobile device to allow the mobile device to display a token code. The user can then transfer the token code manually to the computer to enable the computer to gain access to the remote network. 
     PINs can be used alone or in combination with token codes or other factors to afford a high level of security. Unfortunately, however, PINs can be inconvenient. For example, users need to register their PINs. In addition, PINs can sometimes compromise security, as users may write down their PINs in presumably safe locations. Malicious parties, however, can sometimes discover and steal the PINs. Furthermore, a user may use only a single PIN for different applications, in an effort to avoid having to remember multiple PINs, thereby increasing the chance that the PIN will be stolen. 
     U.S. patent application Ser. No. 13/341,160, filed Dec. 30, 2011, entitled “Biometric Authentication with Smart Mobile Device,” (now U.S. Pat. No. 8,752,145), incorporated by reference herein, employs the mobile device of a user to obtain picture information of the user and then use the picture information as part of a biometric authentication operation of the user. In some examples, a server stores picture information for different users along with associated PINs. By matching picture information from a user&#39;s mobile device with picture information stored on the server, the user&#39;s PIN can be obtained, without the user having to register or remember the PIN. 
     While such biometric authentication techniques using the smart mobile device of the user have avoided some of the inconvenience and potential security risks associated with conventional PINs, a need still remains for event-based authentication techniques that provide improved security. A further need remains for mobile authentication techniques that do not require the token or token generating material to be stored on the mobile device of the user. 
     SUMMARY OF THE INVENTION 
     The present invention in the illustrative embodiments described herein provides event-based biometric authentication using a mobile device of a user. In accordance with an aspect of the invention, a method is provided for authenticating a user attempting to access a protected resource. The exemplary method comprises the steps of receiving a request to access the protected resource; collecting biometric information from the user in response to the request using a mobile device of the user; performing biometric authentication of the user using the collected biometric information; and granting access to the protected resource based on the biometric authentication. 
     In one exemplary embodiment, the protected resource may comprise a resource requiring use of a one-time passcode generating device to obtain access. A security application on the mobile device of the user receives a request to collect the biometric information and provides the biometric information for the biometric authentication. In addition, a given token code is generated and provided to the security application on the mobile device if the biometric authentication is successful. The user can then enter the given token code to access the protected resource. 
     In another exemplary embodiment, an application associated with the protected resource forwards the request to access the protected resource to a gateway server. A security application on the mobile device of the user forwards an authentication request to a gateway server in response to the request, and the gateway server initiates the collection of biometric information from the user in response to the authentication request. The gateway server then sends a request to the security application to initiate the collection of the biometric information from the user and wherein the gateway server receives the biometric information from the mobile device of the user. The gateway server also provides the received biometric information to an authentication server for biometric authentication. The authentication server requests a given token code from a token server if the biometric authentication is successful. The token server generates a given token code and provides a message to the gateway server granting access to the user. 
     According to a further aspect of the invention, the authentication optionally comprises an event-based authentication. According to yet another aspect of the invention, the mobile device does not have to contain token generating material. In addition, an additional authentication of the user is optionally performed using at least one additional authentication factor. For example, the additional authentication factor can comprise (i) validating that the mobile device is associated with the user; (ii) evaluation of a certificate from the mobile device to authenticate the mobile device; (iii) knowledge-based authentication of the user; and/or (iv) adaptive authentication of one or more of the user and the mobile device. 
     The authentication techniques of the illustrative embodiments overcome one or more of the problems associated with the conventional techniques described previously, and permit users to perform improved biometric authentication using a mobile device. These and other features and advantages of the present invention will become more readily apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example environment in which enhanced authentication techniques employing facial recognition may be conducted; 
         FIG. 2  shows an example mobile device; 
         FIG. 3  shows an example environment in which biometric authentication in accordance with the present invention may be conducted; and 
         FIGS. 4 and 5  illustrate exemplary authentication processes incorporating features of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides improved event-based biometric authentication techniques. According to one aspect of the invention, mobile authentication techniques are provided that do not require the token to be stored on the mobile device of the user. It is noted that collecting biometric information using the mobile device of a user inherently provides two-factor authentication, as the biometrics establish who the user is, and the mobile device is something the user has. 
     Particular embodiments will now be disclosed. It is understood that these embodiments are included by way of example only and are not intended as limiting the manner in which the invention hereof may be practiced. 
       FIG. 1  shows an example environment  100  in which enhanced authentication techniques employing facial recognition may be conducted, in accordance with the teachings of U.S. patent application Ser. No. 13/341,160, filed Dec. 30, 2011, entitled “Biometric Authentication with Smart Mobile Device,” (now U.S. Pat. No. 8,752,145). The environment  100  includes a human user  110 , a mobile device  112 , and a computing device  114 . The mobile device  112  is coupled to a cellular telephone network  124 , and the computing device  114  is coupled to a network  116 , such as the Internet. Also coupled to the network  116  are a picture match server  118 , an authentication manager  120 , and a remote network  122 . The picture match server  118  is also preferably coupled to the cellular network  124 . 
     The mobile device  112  is generally a smart phone, such as an iPhone, Blackberry, Droid, or a similar device; however, the mobile device  112  can be any smart device equipped with a camera and a network connection, which is capable of communicating over the network and running software. 
     The computing device  114  is the device employed by the user  110  to access resources on the remote network  122 . The computing device  114  is therefore generally a computer, such as a desktop or laptop computer. This is not critical, however, and the computing device  114  can be any type of computing device, including a tablet computer or even a smart phone or other mobile device itself. 
     The picture match server  118  and authentication manager  120  are preferably separate servers. They may be included within the remote network  122  or provided outside the remote network  122 . Although the picture match server  118  and authentication manager  120  may be combined on a single computer, they are preferably maintained on physically separate computers, or even on separate networks, for enhanced security. 
       FIG. 2  shows an example mobile device  112 . The mobile device  112  includes a camera  210 , a speaker  212 , and a display area  220 . The mobile device  112  also generally includes a processor  230 , memory  240 , a cell interface  250 , e.g., for communicating wirelessly over the cellular network  124 , and another network interface  260 , e.g., for communicating wirelessly over the network  116 . User input controls  270 , such as buttons and/or a touchpad are also included to allow the user  110  to enter data, such as numbers, letters, and other characters, into the mobile device  112 . The mobile device  112  runs program code including a security application (e.g., an “app”). The app is used to acquire and process pictures of the user  110  and to provide a soft token code that the computing device  114  uses to access the remote network  122 . The app is stored in the memory  240  and is executed on the processor  230 . 
     When running the app on the mobile device  112 , the user  110  sees an image  224  of himself or herself on the display  220 , enabling the user to take a picture. Also, the app preferably displays an indicator  222 . The indicator is superimposed on the image  224  of the user  110  and designates where the user should position his or her face on the display  220  for best photographic results. If the mobile device  112  is equipped only with a rear-facing camera, the mobile device  112  may alternatively generate an audible signal from the speaker  212 , which directs the user to properly position his or her face relative to the field of view of the camera  210 . The audible signal can take a number of forms, such as beeps issued as the user&#39;s face becomes properly aligned, and spoken instructions to direct the user to adjust the camera position, e.g., “left,” “right,” “up,” and “down.” 
     To initiate an authentication request to the remote network  122 , the user  110  opens an application on the computing device  114  to start a VPN client program. The application presents a log-in screen that displays fields into which the user  110  is directed to enter information, such as the user&#39;s user ID, a SecurID® token code, and a PIN, for example. The user  110  then accesses the mobile device  112  and starts the app. The app directs the user  110  to take a picture. The user  110  points the camera (or one of the cameras, where there are more than one) at his or her face and takes a picture. The app on the mobile device  112  processes the picture and extracts facial geometry from the image of the user&#39;s face. 
     The facial geometry may include a large number of reference points, or landmarks, from which the relative size, shape, and position of facial features may be computed. The greater the number of landmarks acquired, the greater the uniqueness of any individual&#39;s facial geometry. Previous work has shown that facial geometry is highly specific to each individual, and the chance of any two individuals, other than identical twins, having the same, or even closely matching, facial geometry is very low. Facial geometry is stored in the mobile device  112  in the form of a data set, which may be provided in a single file, such as a bitmap. 
     With the picture taken and the facial geometry extracted, the mobile device  112  sends a picture match request  130  to the picture match server  118 . The picture match request  130  includes the facial geometry acquired for the picture just taken, as well as a direction for the picture match server  118  to compare the facial geometry with records of facial geometry stored on the picture match server  118 . 
     The picture match server  118  includes a database  118   a . The database  118   a  of the picture match server  118  can be constructed in any suitable way, but generally includes a different record for each user of the remote network  122 . Each record stores, for example, the following fields: 
     an identifier of the user (e.g., an employee number or organization-issued ID number); 
     an identifier of the user&#39;s mobile device (e.g., an IMSI code); 
     the user&#39;s PIN; and 
     a set of facial geometry previously obtained from a picture of the user. 
     Most large companies and many organizations require users to obtain photo ID cards. In one example, facial geometry for populating the database  118   a  can be extracted conveniently from these photo ID cards, at no additional burden to users. In other examples, facial geometry for users may be obtained by other means, such as by separately photographing users or by having users photograph themselves with their own mobile devices and register their pictures with the picture server  118 . 
     The picture match server  118  compares the facial geometry conveyed with the picture match request  130  with one or more records of facial geometry stored in the database  118   a  to determine whether there is a match, i.e., whether the facial geometry of the user substantially matches the facial geometry associated with the user, or with any of the users, whose facial geometry is stored in the database  118   a . The picture match server  118  then issues a picture match response  132 , which is sent back to the mobile device  112 , preferably via the cellular network  124 . The picture match response, which can include a PIN, a command, or other information, can then be used as part of an authentication operation by the user  110  to provide the computing device  114  with access to the remote network  122 . 
     Preferably, the picture match request  130  is sent to the picture match server  118  via the cellular network  124 . Although the mobile device  112  may support other networks, such as the network  116 , the cellular network  124  is generally preferred for sending the picture match request  130 , as the cellular network  124  is separate from the network  116  and thus provides an added measure of security (e.g., a malicious user on the network  116  monitoring the computing device  114  would not necessarily also be monitoring the same cell phone network  124  and coordinating traffic from the two sources). 
       FIG. 3  shows an exemplary environment  300  in which biometric authentication in accordance with the present invention can be performed. The like-numbered elements from  FIG. 3  that are also shown in  FIG. 1  operate in a similar manner to the above discussion in conjunction with  FIG. 1 . 
     In addition, as shown in  FIG. 3 , the exemplary environment  300  further comprises a gateway server  310 , a token server  330 , an authentication server  340 , and a biometric server  350 . Generally, the gateway server  310  serves as a gateway for communications between the mobile device  112  and various servers  330 ,  340 , and  350 . The token server  330  generates token codes and releases token codes to the mobile devices  112 . The authentication server  340  can implement, for example, adaptive authentication to evaluate the location of the mobile device  112  and/or whether the mobile device  112  is associated with the user  110 . 
     The biometric server  350  may be implemented in a similar manner as the picture match server  118  of  FIG. 1 . Generally, the biometric server  350  receives biometric information from the mobile device  112  of the user  110  and performs biometric authentication of the user  110 . 
     As shown in  FIG. 3  and as discussed further below in conjunction with  FIGS. 4 and 5 , once the user  110  and/or the mobile device  112  are authenticated, a token code  332  is returned to the user  110 . For example, if the biometric authentication is a match, one or more of a key, a PIN and an unlock code can be provided to the user  110  and/or the mobile device  112 . 
       FIG. 4  illustrates communications among various system elements  110 ,  112 ,  310 ,  340 ,  330 ,  114 , and  120  of  FIG. 3  at particular points in time for an exemplary biometric authentication process incorporating aspects of the present invention. As shown in  FIG. 4 , at time  410 , the user  110  starts an application with a security application (app) on the mobile device  112 . Thereafter, at time  415 , the security app on the mobile device  112  requests a token from the gateway server  310 , which in turn, requests the authentication server  340  at time  420  to determine if the user  110  is authentic. The authentication performed by the authentication server  340  may be, for example, one or more of biometric authentication, cryptographic authentication, certificate authentication, knowledge-based authentication and adaptive authentication. 
     For a more detailed discussion of suitable biometric authentication systems, see for example, U.S. patent application Ser. No. 13/341,160, filed Dec. 30, 2011, entitled “Biometric Authentication with Smart Mobile Device,”(now U.S. Pat. No. 8,752,145), incorporated by reference herein. For a more detailed discussion of suitable Adaptive Authentication systems, see for example. U.S. patent application Ser. No. 13/246,937, filed Sep. 28, 2011, entitled “Using Baseline Profiles In Adaptive Authentication” (now U.S. Pat. No. 8,621,586) and/or U.S. patent application Ser. No. 12/751,057, filed Mar. 31, 2010 entitled “Techniques for Authenticating Users of Massive Multiplayer Online Role Playing Games Using Adaptive Authentication,” (now U.S. Pat. No. 8,370,389), each incorporated by reference herein. 
     For a more detailed discussion of suitable knowledge-based authentication systems, see for example, U.S. patent application Ser. No. 13/436,125, filed Mar. 30, 2012, entitled “Methods and Apparatus for Fraud Detection and Remediation in Knowledge-Based Authentication,” incorporated by reference herein. 
     Cryptographic authentication and certificate authentication are well-known to those of ordinary skill in the art. 
     At time  425 , the authentication server  340  sends a request to the gateway server  310  to collect authentication data. The gateway server  310 , in turn, sends a collection request to the security app on the mobile device  112  at time  430 . The collection request may comprise, for example, one or more of biographical information, mobile device data, or adaptive authentication information. The security app on the mobile device  112  sends the collected authentication data at time  435  to the gateway server  310 , which sends it to the authentication server  340  at time  440 . The authentication server  340  evaluates the collected authentication data and if the user  110  is authenticated, returns an authentication token to the gateway server  310  at time  445 . The authentication server  340  can be implemented, for example, using RSA Adaptive Authentication and the techniques described in U.S. patent application Ser. No. 13/246,937, filed Sep. 28, 2011, entitled “Using Baseline Profiles In Adaptive Authentication” (now U.S. Pat. No. 8,621,586) and/or U.S. patent application Ser. No. 12/751,057, filed Mar. 31, 2010, entitled “Techniques for Authenticating Users of Massive Multiplayer Online Role Playing Games Using Adaptive Authentication,” (now U.S. Pat. No. 8,370,389), each incorporated by reference herein. 
     Thereafter, the gateway server  310  requests a token code (e.g., an authentication token) from the token server  330  at time  450 . The token server  330  generates a token and returns the token code to the gateway server  310  at time  460 . It is noted that the token server  330  can optionally employ the split-key techniques referenced below and/or detect tampering of the mobile device  112  or communications using the tamper detection techniques referenced below. The gateway server  310  then forwards the token code to the security app on the mobile device  112  at time  465 . 
     The user reads the token code at time  470  and enters the code on an exemplary VPN agent on computing device  114  at time  475 . The authentication request is provided to the authentication manager  120  at time  480 , in a known manner, and the VPN agent is allowed access at time  485 . A VPN session is opened, and the user receives a welcome message at time  495 . 
     For a more detailed discussion of suitable techniques for notifying the authentication manager  120  of tampering with the mobile device  112  or a photograph, see for example, U.S. patent application Ser. No. 13/404,780, filed Feb. 24, 2012, entitled “Method and Apparatus for Embedding Auxiliary Information in One-Time Passcode Authentication Tokens,” incorporated by reference herein. 
       FIG. 5  illustrates communications among various system elements  110 ,  112 ,  310 ,  340 ,  330 , of  FIG. 3  at particular points in time for an exemplary alternative biometric authentication process incorporating aspects of the present invention. As shown in  FIG. 5 , at time  505 , the user  110  starts an app on the mobile device  112  or another device. The app on the mobile device  112  responds to the user at time  510  requesting authentication. The app on the mobile device  112  also sends a request for authentication of the user to the gateway server  310  at time  515 . Meanwhile, the user  110  starts an authentication process with the security app on the mobile device  112  at time  520 , prompting the security app on the mobile device  112  to request authentication with the gateway server  310  at time  525 . 
     At time  530 , the gateway server  310  sends an authentication request to the authentication server  340 . The authentication performed by the authentication server  340  may be, for example, one or more of biometric authentication, cryptographic authentication, certificate authentication, knowledge-based authentication and adaptive authentication, in a similar manner to  FIG. 4 . 
     At time  535 , the authentication server  340  sends a request to the gateway server  310  to collect authentication data. The gateway server  310 , in turn, sends a collection request to the security app on the mobile device  112  at time  540 . The collection request may comprise, for example, one or more of biographical information, mobile device data, or adaptive authentication information. The security app on the mobile device  112  sends the request to collect authentication data to the user  110  at time  545 . The user  110  sends the collected authentication data to the gateway server  310  at time  550 , which in turn sends it to the authentication server  340  for evaluation at time  560 . It is noted that the gateway server  310  can optionally embed an alert in a message to the 340 to alter the authentication server  340  of a potential compromise, as described in U.S. patent application Ser. No. 13/249,957, filed Sep. 30, 2011, entitled “Methods and Apparatus for Secure and Reliable Transmission of Messages Over a Silent Alarm Channel,” and/or U.S. patent application Ser. No. 13/404,788, filed Feb. 24, 2012, entitled “Methods and Apparatus for Silent Alarm Channels Using One-Time Passcode Authentication Tokens,” each incorporated by reference herein. 
     The authentication server  340  evaluates the collected authentication data and if the user  110  is authenticated, returns an authentication token to the gateway server  310  at time  565 . The gateway server  310  then requests a token code at time  570  from the token server  330 . The token server  330  generates the token code and returns it to the gateway server  310  at time  580  indicating that the user has been authenticated. The new app on the mobile device  112  is notified of the authentication at time  585 , and the user  110  receives a welcome message at time  590 . 
     The app running on the mobile device  112  is preferably equipped with safeguards to ensure that the picture of the user  110  is authentic. These safeguards operate to prevent a malicious user from gaining unauthorized access to the remote network  122  by using the mobile device  112  to take a picture of a photograph or video of the user  110 . A variety of safeguards may be used. 
     In one example, the camera  210  on the mobile device  112  is directed to take a sequence of pictures of the user at high frequency and to search for small, rapid changes in the user&#39;s skin color. These changes correspond to the user&#39;s pulse, with small changes alternatively toward red and blue at the proper frequency indicating the ebb and flow of oxygenated blood. If the sequence of pictures reveals this variable coloration pattern, the subject of the picture is most likely a living being as opposed to a picture. 
     Another safeguard monitors infra-red light emitted by the subject of the picture. Although infra-red light is generally regarded as an undesirable side effect of electronic photography, infra-red light can be used to advantage in verifying picture authenticity, as human faces, and not pictures of human faces, give off infrared light in a known pattern. 
     Yet another safeguard applies geographic information about the user  110 . It is common for mobile devices  112  to track their geographic locations. Geographic location can be used as a safeguard to refuse authentication attempts if the mobile device  112  reports that it is outside its home country or state, or even if it is in some unexpected location. 
     As used throughout this document, the words “comprising,” “including,” and “having” are intended to set forth certain items, steps, elements, or aspects of something in an open-ended fashion. Although certain embodiments are disclosed herein, it is understood that these are provided by way of example only and the invention is not limited to these particular embodiments. 
     Having described one embodiment, numerous alternative embodiments or variations can be made. For example, although the examples described above employ facial geometry, other forms of biometric information can be used. These include voice information and fingerprint information, for example. Rather than the mobile device  112  taking a picture of the user  110 , the mobile device  112  can instead obtain a fingerprint or voice sample of the user  110 , which it converts to a data set for comparison with data sets stored in connection with different users in the database  118   a.    
     Also, although the mobile device  112  is described as a general-purpose device, such as a smart phone, PDA, tablet, and the like, it can also be a special purpose device, such as a key fob modified to include a camera, a processor, and memory. According to yet another variant, the mobile device  112  is itself a computer, such as a laptop computer. In some embodiments, the mobile device  112  can be the same as the computing device  114 . 
     Also, although the security program running on the mobile device  112  is specified as being an “app,” this is merely an example. The program can be any software construct running on the mobile device  112 . 
     Although one or more examples described herein involve the use of VPN to access the remote network  122 , this is also merely an example. The techniques described can be used in connection with a wide range of other technologies, such as web technology, remote desktop programs, and others. 
     Further, although the above-described techniques use the mobile device  112  to extract facial geometry from a picture of the user, this is just an example. Alternatively, a file or data stream representing the picture itself can be sent to the picture match server  118 , and the picture match server  118  can extract the user&#39;s facial geometry remotely. 
     Also, although the PIN is described as an independent field of the database  118   a , alternatively, the PIN may be computed from the facial geometry. For example, it can be a hash code of the facial geometry. 
     Further still, the improvement or portions thereof may be embodied as a non-transient computer-readable storage medium, such as a magnetic disk, magnetic tape, compact disk, DVD, optical disk, flash memory, Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA), and the like (shown by way of example as medium  280  in  FIG. 2 ). Multiple computer-readable media may be used. The medium (or media) may be encoded with instructions which, when executed on one or more computers or other processors, perform methods that implement the various processes described herein. Such medium (or media) may be considered an article of manufacture or a machine, and may be transportable from one machine to another. 
     The disclosed biometric authentication techniques permit users to authenticate using a mobile device without requiring token generating material to be stored on the mobile device. In a further variation, however, portions of a key can be stored on the mobile device  112 , and further portions of the key can be stored on a cloud or another storage medium, using the split-key techniques described, for example, in U.S. patent application Ser. No. 13/404,737, filed, Feb. 24, 2012, entitled, “Method and Apparatus for Authenticating a User Using Multi-Server One-Time Passcode Verification,” incorporated by reference herein. As previously indicated, the above-described embodiments of the invention are presented by way of illustrative example only. Numerous variations and other alternative embodiments may be used. 
     Numerous other known password protection techniques can be used in conjunction with the present invention. Additional details regarding certain conventional cryptographic techniques referred to herein may be found in, e.g., A. J. Menezes et al., Handbook of Applied Cryptography, CRC Press, 1997, which is incorporated by reference herein. 
     The term “authentication information” as used herein is intended to include passwords, passcodes, answers to life questions, or other authentication credentials, or values derived from such authentication credentials, or more generally any other information that a user may be required to submit in order to obtain access to an access-controlled application. Although the illustrative embodiments will be described below in the context of passwords, it is to be appreciated that the invention is more broadly applicable to any other type of authentication information. 
     It should be understood that although various embodiments have been described as being methods, software embodying these methods is also included. Thus, one embodiment includes a tangible computer-readable medium (such as, for example, a hard disk, a floppy disk, an optical disk, computer memory, flash memory, etc.) programmed with instructions, which, when performed by a computer or a set of computers, cause one or more of the methods described in various embodiments to be performed. Another embodiment includes a computer which is programmed to perform one or more of the methods described in various embodiments. 
     Furthermore, it should be understood that all embodiments which have been described may be combined in all possible combinations with each other, except to the extent that such combinations have been explicitly excluded. 
     It should again be emphasized that the particular security techniques described above are provided by way of illustration, and should not be construed as limiting the present invention to any specific embodiment or group of embodiments. For example, the particular configuration of system elements shown in  FIG. 3 , and their interactions as shown in  FIGS. 4 and 5  may be varied in other embodiments. Moreover, the various simplifying assumptions made above in the course of describing the illustrative embodiments should also be viewed as exemplary rather than as requirements or limitations of the invention. Numerous alternative embodiments within the scope of the appended claims will be readily apparent to those skilled in the art.