Patent Publication Number: US-6668321-B2

Title: Verification of identity of participant in electronic communication

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/192,008, filed Nov. 13, 1998, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to securely transmitting information over communication networks. In particular, the present invention relates to systems and methods for verifying the identity of a sender and/or a recipient of information transmitted over a communication network. 
     2. Relevant Technology 
     During recent years, there has been tremendous growth in the amount and types of information that are transmitted between remote locations using telecommunication networks. For example, the Internet has become widely used in electronic commerce, education, banking, investing, and many other areas. The Internet and other wide area and local area networks have greatly enhanced the ability to transmit large volumes of information between people. While many segments of the economy have been transformed by the ongoing communication revolution, the finance industry has been particularly affected. For instance, financial transactions have become increasingly cashless as debit cards, credit cards, smart cards and other techniques for authorizing electronic transfer of funds have become widely used. 
     There are several reasons for the increased use of electronic systems and telecommunication systems for transmitting information and conducting business. First, data processing speeds have vastly increased during recent decades to permit large volumes of information to be processed in relatively short periods of time. Likewise, the size, cost, and speed of mass data storage systems have improved, thereby allowing large volumes of information to be conveniently stored and accessed. In addition, the data transmission rates of telecommunication systems have grown equally as fast, which permits large amounts of data to be rapidly transmitted between distant locations. 
     There have been some limiting factors that have prevented electronic communication of information from being fully utilized in many situations. A persistent problem involves the difficulty of verifying the identity of participants in electronic communication. For instance, it is often difficult to determine whether a person receiving a document via email is, in fact, the intended recipient. Likewise, it has often proved impossible to conclusively determine whether a person using a credit card number to execute an electronic transaction is an authorized user of the credit card. In yet another example, it has often been difficult to be certain of the identity of a person creating an electronic document. Thus, in situations where electronically created or transmitted information is particularly sensitive, in, for example, the banking and legal industries, electronic communication has not been practical or fully accepted. Instead, hand-signed hard copies of documents, conventional hand delivery of documents, and face-to-face transactions are still widely used, although their electronic counterparts would often be more efficient were it not for the persistent security limitations. 
     In order to attempt to overcome the aforementioned problems of identifying participants in electronic communication, a variety of approaches have been taken. Often, information is encrypted before it is transmitted over open communication networks such as the Internet, stored on computer-readable media, or otherwise placed in a position where it could be potentially intercepted by unauthorized users. Transmitted encrypted information can be decrypted if the recipient possesses the appropriate decryption key. Otherwise, unauthorized recipients are unable to view or otherwise use the contents of the encrypted information. 
     One commonly used encryption technique is private/public key cryptography, such as RSA, in which each user has a public key published for anyone to see and an associated private key. A sender looks up the recipient&#39;s public key and uses it to encrypt the data to be transmitted. The recipient uses the secret, private key to decrypt the information. While the private/public key approach provides reasonably secure transmission in may circumstances, it has several drawbacks. The use and maintenance of the private and public keys can be quite expensive for organizations. Moreover, if the security of the private key is breached, new private and public keys must be created, with the new public key being published to all interested users, and the old public key being invalidated, wherever it might exist. 
     Another approach to maintaining the security of electronic information involves using passwords to identify users of computer networks, recipients of information, etc. For instance, information transmitted over a communication network to a recipient may be password protected, in that it may not be decrypted, decompressed, or otherwise placed in a usable form unless the recipient possesses a specified password. In other situations, passwords are required to gain access to computer networks in the first instance. Typically, when a user logs onto a computer network, the user is prompted to enter a password that enables the user to gain access to resources of the computer network. 
     The basic concept underlying passwords is that any person possessing the password is assumed to be authorized to access particular information or perform selected operations. In practice, however, it has been found that passwords are often the weak link in an electronic security system. Sometimes, network users select passwords such as birthdays or names of family members that could be easily guessed by unauthorized persons. In other situations, users write their password in plain sight, such as on a note affixed to a computer monitor. Such practices essentially negate the security advantages of passwords. Furthermore, particularly persistent persons could intercept a user&#39;s password by memorizing a series of a few keystrokes while observing the user entering a password into a computer. Thus, many businesses require employees to regularly change their passwords in an attempt to strengthen network security systems. In any event, it has been found that unauthorized persons often successfully obtain users&#39; passwords, thereby compromising any security measures associated with the passwords. 
     A related security technique is the use of personal identification numbers (PINs) in electronic commerce and other situations. A PIN is a number assigned to or selected by a cardholder, for example, in order to verify the identify of a person attempting to execute a transaction. PINs are widely used in automatic teller machines, credit and debit card readers, electronic commerce websites, and other situations where electronic funds transfer is to be initiated. Likewise, access numbers, which are analogous to PINs, are widely used in businesses, the military, and other organizations having sensitive buildings or areas. Persons wishing to gain access to sensitive buildings or areas must enter an access number to an access control device that permits entry only to authorized persons. Like passwords, PINs and access codes are subject to being stolen or otherwise obtained by unauthorized individuals. Because PINs are generally static or, in other words, remain usable in multiple transactions, they are sometimes stolen by an unauthorized person watching a PIN being entered into a keypad. 
     In view of the foregoing, electronic communication and creation of information has been limited in many situations by the failure of conventional security measures to reliably permit the identity of participants to be verified. Thus, it would be an advancement in the art to provide systems and methods for both verifying and authenticating the identity of participants in electronic communication that do not merely rely on password protection, PINs, or public key/private key encryption. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to systems and methods for verifying and authenticating the identity of participants in electronic communication. The invention replaces or supplements the reliance that conventional systems place on passwords to verify the identity of participants in electronic communication. In addition, the invention replaces or supplements the reliance that conventional systems place on PINs and access codes to identify users of communication devices or the authorization of such persons to access resources. 
     In one implementation, a primary key is stored at a sending device and at a recipient device. The primary key and the other keys and passphrases can include a string of characters. The sending device generates a passphrase and an associated secondary key. The secondary key represents an encrypted form of the reconstruction capability of the passphrase that has been encrypted based on the contents of the primary key. The secondary key is transmitted from the sending device to the recipient device when electronic communication is to be performed. The recipient device decrypts the secondary key using the primary key to reconstruct the passphrase. Reconstructing the passphrase can only be performed by recipient devices that possess the primary key. Accordingly, reconstruction of the passphrase demonstrates that the recipient device has received the secondary key and possesses the correct primary key. The passphrase can then be transmitted in return to the sending device or can be used locally at the recipient device to access documents that have been passphrase-protected or to access resources that are conventionally accessible by using passwords. 
     The invention replaces conventional passwords in the foregoing manner. The passphrases differ from conventional passwords in that the passphrases are dynamic. A new passphrase and associated secondary key can be generated each time electronic communication is conducted. Accordingly, passphrases are not memorized by users, nor are they stored permanently in the memory of recipient devices. As such, passphrases are not subject to misappropriation by unauthorized persons who might otherwise memorize keystrokes associated with passwords or discover a written copy of a password. 
     Verification of the identity of a human user of a communication device is accomplished by combining the passphrases of the invention with an authorization code memorized by the user. The authorization code represents an ordered series of character positions of the passphrase. When prompted, the user selects the characters of a displayed passphrase that reside at the character positions specified by the authorization code. The user then uses the selected characters to generate and transmit an input code to a remote communication device. The secondary key with its associated passphrase and the authorization code are stored at the remote communication device, thereby permitting the remote device to determine the expected input code. Users who do not possess the authorization code are unable to generate the expected input code. Thus, when the remote device receives an input code that matches the expected input code, it concludes that the user has been verified and is authorized to gain access to information or other resources. 
     The input codes and associated authorization codes can be used in situations that otherwise require the use of PINs or access codes. In this manner, the input codes replace conventional PINs. The specific content of any particular input code depends on the passphrase from which it is derived. Since passphrases typically change with each transaction, the input codes used in successive transactions are different one from another. In contrast, PINs are static, with the same PIN being used in multiple transactions. Thus, input codes are not subject to many of the security risks involved with static PINs, such as interception by unauthorized persons observing a PIN being entered by a user. 
     The primary key, on which the secondary keys and passphrases are based, can be conveniently replaced as desired. For instance, if a client computer having stored thereon a copy of the primary key is stolen, the security of the particular primary key may be compromised. However, a new primary key can easily be generated in response to the possible breach of primary key security. Once the new primary key is generated and stored at the sending and recipient devices, the invention can be practiced as if the security of the key had never been breached. In contrast, conventional public/private key cryptology is not capable of responding in a cost-effective manner to the security of a private key being compromised. If a conventional PKI private key is published, the owner of the private key can be subjected to the significant expense of obtaining a new public/private key combination and making the new public key available to interested users, plus invalidating the old public key wherever it resides. 
     Subsequent communication between the sending device and the recipient device can include a document that is passphrase-protected as well as encrypted with a symmetrical encryption algorithm using the same generated passphrase. In other words, the recipient of the passphrase-protected document must obtain the passphrase to access the document. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIG. 1 is a schematic diagram illustrating the use of primary keys, secondary keys, and passphrases to securely communicate between a sending device and a recipient device according to the invention. 
     FIG. 2 a  is a schematic diagram depicting a passphrase-protected document being sent from a sending device. 
     FIG. 2 b  is a schematic diagram illustrating the passphrase-protected document of FIG. 2 a  being received by a recipient device. 
     FIG. 3 is a schematic diagram illustrating a series of primary keys distributed among a server and multiple clients in a network environment in order to permit selective communication between the server and individual clients. 
     FIG. 4 a  is a schematic diagram showing the methods of the invention for verifying and authenticating the identity of a participant in electronic communication as applied to a financial transaction. 
     FIG. 4 b  is a schematic diagram depicting one example of the use of an authorization code and a passphrase to verify and authenticate the identity of a participant in electronic communication. 
     FIG. 4 c  is a schematic diagram further illustrating the enablement of a financial transaction based on the use of an authorization code and a passphrase. 
     FIGS. 5 a  and  5   b  are flow diagrams illustrating methods of the invention for verifying the identity of participants in electronic communication. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to systems and methods for verifying and authenticating the identity of participants in electronic communication. Participants can include computers, telecommunications devices, or the human users of computers or telecommunication devices. In one embodiment, communication between a sending communication device and a recipient communication device can be regulated using the invention. A primary key is stored at both the sending device and at the recipient device. The sending device generates a passphrase recreating process and an associated secondary key. The secondary key represents an encrypted form of the passphrase recreating process that has been encrypted based on the contents of the primary key. Subsequent communication between the sending device and the recipient device can include a document that is passphrase-protected and/or symmetrically encrypted using the generated passphrase. In other words, the recipient of the passphrase-protected document must obtain the passphrase to access the document. 
     The passphrase-protected document is transmitted from the sending device to the recipient device along with a copy of the secondary key. The recipient device, which possesses the primary key, uses the primary key to decrypt the secondary key, thereby reconstructing the passphrase. The reconstructed passphrase can then be used to access the document. Other recipients, such as unauthorized persons who might intercept the passphrase-protected document, do not possess the primary key and cannot reconstruct the passphrase. In subsequent communication between the sending and recipient devices, new passphrases and associated secondary keys can be generated. Accordingly, the passphrases of the invention can be dynamic in the sense that they can change with each transaction, unlike conventional passwords, which are used repeatedly. 
     In one embodiment, the invention includes features for further identifying a user operating either the sending device or the recipient device. Each user is assigned or chooses an authorization code, which includes an ordered series of character positions of the passphrases to be used in the electronic communication. A copy of the authorization code is stored at the communication device (i.e., the sending or recipient device) that is remote with respect to the user. When communication is to be conducted, the user is shown a copy of the passphrase and instructed to select the characters thereof that reside at the character positions specified in the authorization code. The identity of the characters selected using the authorization code is transmitted to the remote communication device, which can then verify whether the user possesses the correct authorization code. Unlike conventional PINs, which are static, the authorization codes of the invention result in a completely different set of characters being selected in every transaction, based on the changeable nature of the passphrases of the invention. 
     As used herein, the terms “sending device” and “recipient device” are used to describe communication devices that transmit electronic information. Of course, in many situations, electronic communication is two-way. Thus, a specific communication device can alternatingly be seen as a sending device and a recipient device. While some of the specific embodiments of the invention are disclosed in the context of identifying a recipient device or the user of a sending device, the invention is equally applicable to identifying either or both of the sending device and the recipient device, and any users thereof. 
     Embodiments of the invention include or are incorporated in computer-readable media having computer-executable instructions or data structures stored thereon. Examples of computer-readable media include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium capable of storing instructions or data structures and capable of being accessed by a general purpose or special purpose computer. Computer-readable media also encompasses combinations of the foregoing structures. Computer-executable instructions comprise, for example, instructions and data that cause a general purpose computer, special purpose computer, or special purpose processing device to execute a certain function or group of functions. The computer-executable instructions and associated data structures represent an example of program code means for executing the steps of the invention disclosed herein. 
     The invention further extends to computer systems and telecommunication systems for verifying the identity of participants in electronic communication. Those skilled in the art will understand that the invention may be practiced in computing environments with many types of computer system configurations, including personal computers, multi-processor systems, network PCs, minicomputers, mainframe computers, and the like. The invention will be described herein in reference to a distributed computing environment, such as the Internet, where tasks are performed by remote processing devices that are linked through a communication network. In the distributed computing environment, computer-executable instructions and program modules for performing the features of the invention may be located in both local and remote memory storage devices. 
     FIG. 1 illustrates an example of the architecture of communication network in which the identity of a recipient device will be verified. As used herein, sending devices and recipient devices are to be broadly construed to extend to any general purpose computer, special purpose computer, processing device, telecommunication device, and the like that is used to transmit or receive information. 
     In FIG. 1, sending device  10  is linked to recipient device  12  by means of communication network  14 . Communication network  14  may be any wide area or local area network by which special-purpose or general-purpose computers communicate one with another. In addition, communication network  14  may be a public telephone network or any other system that permits communication between telecommunication devices. Those skilled in the art will recognize that the invention described herein has wide applicability to a variety of implementations and is not to be limited to the specific embodiments disclosed herein. 
     One part of the techniques for enabling verification of the identity of the participant in electronic communication involves a storing a copy  16 A of a primary key at sending device  10  and a copy  16 B of the primary key at recipient device  12 . In one embodiment, primary keys, the secondary keys, the passphrases, and the master keys disclosed herein include a string of characters. The characters of the primary keys, secondary keys, passphrases, and master keys can be alphanumeric, ASCII, alphabetic, numeric, or any other desired characters or combination of the foregoing. 
     In the embodiment of FIG. 1, sending device  10  includes a key generation module  18 . Key generation module  18  includes processing means for generating a secondary key  20 A and a passphrase  22 A based at least in part on the contents of primary key  16 A. For instance, key generation module  18  can include algorithms for selecting a passphrase  22 A that is derived from primary key  16 A. The passphrase generated by key generation module  18  will be different each time sending device  10  is used. In the embodiment of FIG. 1, passphrase  22 A can be a string of seven characters that can be used later to enable a user of recipient device  12  to access information transmitted over communication network  14 , or to otherwise verify the identity sending device  10 , recipient device  12 , or users of the devices. In other embodiments, the length of the string of characters that constitute the passphrases of the invention can be shorter or longer. 
     As shown in FIG. 1, key generation module  18  generates passphrase  22 A. Key generation module  18  also generates secondary key  20 A, which in this embodiment, includes an encrypted form of the string of characters that constitute passphrase  22 A. In other words, secondary key  20 A includes the information needed to enable one who possesses primary key  16  to decrypt or otherwise reconstruct passphrase  22 . Therefore, a recipient of secondary key  20  who possesses primary key  16  and the appropriate decryption algorithm can reconstruct passphrase  22 . Accordingly, key generation module  18  can include algorithms for encrypting the string of characters that constitute passphrase  22  to generate secondary key  20 . Those skilled in the art will understand, when learning of the disclosure made herein, how to construct the primary keys, the secondary keys and the passphrases of the invention and how to create the algorithms included in the key generation module. 
     As shown in FIG. 1, secondary key  20 A is transmitted over communication network  14  to recipient device  12 . Thus, as shown in FIG. 1, recipient device  12  obtains a copy  20 B of secondary key. Recipient device  12  includes a passphrase reconstruction module  24  that uses secondary key  20 B and primary key  16 B to reconstruct passphrase  22 . Thus, recipient device  12  is capable of reconstructing a copy  22 B of the passphrase when it receives secondary key  20 B over communication network  14 . Since secondary key  20 B includes an encrypted form of the reconstruction process of passphrase  22 , passphrase reconstruction module  24  can include the appropriate decryption algorithm to decrypt the passphrase based on the contents of primary key  16 B. Thus, those skilled in the art will understand how to reconstruct passphrase  22 B using passphrase reconstruction module  24 A upon learning of the disclosure made herein. 
     The above-described process of reconstructing passphrase  22 B at recipient device  12  has the effect of verifying that the recipient device possesses primary key  16 B. Without a copy  16 B of the primary key, recipient device  12  is unable to use passphrase reconstruction module  24  to reconstruct the appropriate passphrase  22 B. Unauthorized recipients of secondary key  20 B cannot generate passphrase  22 B. Reconstructing passphrase  22 B at recipient device  12  can have many applications. In the example illustrated in FIGS. 2A and 2B, the passphrase is used as a substitute for a password in the transmission of secure documents. As shown in FIG. 2A, sending device  10  can be used to construct information to be included in a data transmission  26 . For instance, sending device  10  can be a personal computer capable of transmitting an e-mail and an attached text document over the Internet. 
     In this example, data transmission  26  includes a passphrase-protected document  28  and secondary key  20 . Passphrase-protected document  28  is any desired data structure that is to be transmitted from sending device  10  to recipient device  12 . Passphrase-protected document  28  can be compressed and/or encrypted using any desired compression or encryption software or techniques. By way of example, and not limitation, document  28  can be compressed using Pkzip produced by PKWARE, Inc. or WinZip produced by WinZip, et al. Document  28  is thus encoded in manner such that it will not be accessible by recipient device  12  unless the recipient device obtains the appropriate passphrase  22 . Document  28  can be passphrase-protected by processing the document using conventional password protection software. For instance, password protection can be performed by the software that encrypts or compresses document  28 . From the standpoint of the password protection software, passphrase  22  is treated as a conventional password to protect document  28  from unauthorized use. Secondary key  20  and passphrase  22  of FIG. 2A can be generated from primary key  16  as described previously in reference to FIG.  1 . 
     As used herein, the term “passphrase” is defined to include any string of characters that enable access to electronic information or to computer networks or telecommunication networks. Thus, passphrases are similar to conventional passwords to the extent that they can enable access to information or to networks. However, unlike conventional passwords, the passphrases of the invention need not be memorized by a user at recipient device  12  or permanently stored at recipient device. Instead, the passphrases according to this embodiment are generated using the primary key at the sending device and are reconstructed at the recipient device as has been described in reference to FIG.  1 . The passphrases of the invention further depart from conventional passwords in that a new passphrase can be generated each time data is transmitted from a sending device to a recipient device. In contrast, conventional passwords are static, with the same password being repeatedly used by a user of a recipient device until the user or a network administrator establishes a new password. 
     As shown in FIGS. 2A and 2B, data transmission  26 , including secondary key  20  and passphrase-protected document  28 , is transmitted from sending device  10  to recipient device  12  via communication network  14 . Upon receiving data transmission  26 , a user of recipient device is unable to access passphrase-protected document  28 , which is protected by passphrase  22 , until it retrieves secondary key  20  and performs the operations described in FIG.  2 B. In contrast, however, the user of recipient device  12  is able to freely access secondary key  20 . For instance, secondary key  20  may be attached to data transmission  26  as a comment, as a file, or in any other manner that does not require use of a password or a passphrase. Recipient device  12  then inputs secondary key  20  and primary key  16  to passphrase reconstruction module  24  to reconstruct passphrase  22 . Reconstruction of passphrase  22  can be accomplished according to the techniques described above in reference to FIG.  1 . The reconstructed passphrase  22  is then used to access passphrase-protected document  28  as shown in FIG.  2 B. For instance, if the passphrase-protected document is compressed by Pkzip or WinZip software, the passphrase is inputted to the software as a substitute to a conventional password. 
     In the example of FIGS. 2A and 2B, the use of secondary key  20  and primary key  16  to reconstruct passphrase  22  can be accomplished only by recipient devices  12  that have a copy of primary key  16  stored thereon. Unauthorized recipients of password-protected document  28  are unable to reconstruct password  28 . 
     One advantage of the invention is understood by contrasting the example of FIGS. 2A and 2B with conventional password-protected communication. In the absence of the invention, document  28  could be protected by a password. However, password protection of document  28  would require the user of recipient device  12  to enter a conventional password or a prior agreed upon password or to telephone the recipient to divulge the password, or would require the conventional password to be permanently stored at recipient device  12 . The use of conventional passwords is inherently insecure, since passwords are often stolen or divulged to unauthorized persons. In contrast, there is no password to be memorized or learned by the recipient according to the example of FIGS. 2A and 2B. A different passphrase can be generated at sending device  10  each time a data transmission  26  is made. Thus, the passphrase techniques of the invention are dynamic, whereas conventional passwords are static, in that they are repeatedly used by a user of the recipient device. 
     The present invention can be adapted to respond to the theft of recipient device  12  or the publication of primary key  16  stored thereon. As shown in FIG. 3, the primary keys from which the passphrases and secondary keys of the invention are generated can be replaced at will. Thus, if the security of any single primary key is somehow breached, the compromised primary key can be conveniently replaced without undue expense or effort. In FIG. 3, a server computer  30  is linked with a plurality of client computers  32 A- 32 E by means of communication network  14 . Server  30  has stored thereon copies of a plurality of primary keys  34 A- 34 E that correspond with copies of primary keys A-E ( 34 A- 34 E) stored individually on client computers  32 A- 32 E. In this embodiment, the primary keys are generated using a master key  36  that is stored at a secure location at server  30  or separately therefrom. To illustrate, if the security of primary key  34 D is breached, primary key  34 D can be easily replaced. For example, master key  36  can generate a new primary key  34 D′, which is transmitted and stored at server  30  and in turn at client  32 D. 
     FIG. 3 also illustrates another optional feature of the invention, whereby individuals or subsets of a plurality of clients or other recipient devices are assigned different primary keys. Accordingly, if a data transmission similar to data transmission  26  of FIGS. 2A and 2B is sent, for example, from server  30  to client  32 A of FIG. 3, the data transmission would be protected by a passphrase generated from primary key  34 A. Clients  34 B- 34 E, which do not possess primary key  34 A, would be unable to generate the appropriate passphrase and cannot gain access to the data transmission. In this manner, the invention provides the flexibility to specify the access credentials of various recipient devices by disclosing particular primary keys thereto. Moreover, the invention is flexible enough to permit the convenient replacement of any primary key whose security is breached. 
     FIGS. 4A-4C illustrate additional features of one embodiment of the invention, whereby the identity of a user of a recipient or sending device is tested. As described below, such an embodiment of the invention provides a dynamic alternative to conventional static PINs and access codes. The example of FIGS. 4A-4C illustrates the execution of a financial transaction using electronic transmission of information over a communication network. In FIG. 4A, a user  140  has been issued a bank card  142  by a financial institution such as a bank  144 . Bank card  142  can be a credit card, a debit card, a smart card, or another instrument for identifying, verifying, and authenticating (IVA) an account of the financial institution and gaining access to the account. While this embodiment of the invention is described in the context of bank cards and financial transactions, the techniques disclosed herein for IVA a party participating in electronic communication can be extended to a wide variety of other situations. By way of example and not limitation, the invention can be used to provide IVA access codes to buildings, to IVA the holder of a telephone calling card or identity card ( 10 ), and to IVA the recipient of information of a computer network. 
     In the example of FIG. 4A, bank card  142  has been issued to user  140  with a copy  116 A of a primary key stored thereon. A copy of  116 B of primary key is stored at bank  144 . Primary key  116  can be generated and replaced as described in reference to FIGS. 1-3. When user  140  desires to execute a transaction using bank card  142 , the user swipes the bank card through ATM  146  or another card reading device. Primary key  116 A is input to key generation module  118  that generates a passphrase  122 A and a secondary key  120 A. In this manner, ATM  146 , key generation module  118 , passphrase  122 , and secondary key  120  are analogous to the corresponding elements  10 ,  18 ,  22 , and  20  of FIG.  1 . 
     ATM  146  transmits secondary key  120 A to bank  144  via communication network  114 . Bank  144  thereby obtains a copy  120 B of the secondary key. As previously disclosed herein, each transaction or transmission of information can be associated with a new secondary key  120  that has been generated by key generation module  118  based on primary key  116 . 
     Bank  144  includes a passphrase reconstruction module  124 , which receives the input of secondary key  120 B and primary key  116 B to reconstruct a copy of  122 B of the passphrase. In this manner bank  144 , passphrase reconstruction module  124 , secondary key  120 B, and primary key  116 B are analogous to the corresponding elements  12 ,  24 ,  20 B, and  16 B of FIG.  1 . 
     It can be appreciated that, in the context of the electronic transaction being executed in FIG. 4A, the primary concern is typically not the identity of the receiving device (bank  144 ), but is instead the IVA of the person operating the sending device (ATM  146 ). Conventional systems often use PINs to attempt to verify that the holder of a bank card or another instrument is authorized to use the instrument to execute transactions. However, PINs, which are static in the sense that they are repeatedly used to transmit a code to a recipient device in multiple transactions, can be breached in a variety of ways as has been disclosed herein. In contrast, user  140  of FIG. 4A is issued an authorization code  148  by bank  144 . The authorization code  148 , which is described in greater detail in reference to FIG. 4B below, permits user  140  to select and enter an appropriate input code to ATM  146 . The input codes are dynamic, in that user  140  will enter different transactions in each of a series of transactions. Authorization code  148  provides instructions to user  140  that enable the user to select the appropriate input code for the particular transaction based on the content of the passphrase. 
     Turning now to FIG. 4B, the use of the authorization codes and input codes is further described. After the user has swiped the bank card, the ATM or the other card reader provides display  150  to the user. Display  150  prompts the user to enter an input code  152  at the same stage of the transaction as, for example, a PIN would be entered in a conventional electronic transaction. 
     In this embodiment, authorization code  148  includes an ordered series of character positions of the characters included in the passphrase. In order to further describe the nature of the authorization code and its relation to the passphrase and input code, a specific example is presented in FIG.  4 B. In this example, the user has been issued an authorization code  148 A that specifies an ordered series of character positions that consist of the sixth character position, the first character position, and the third character position. The user memorizes the authorization code, and a copy of the authorization code is stored at the bank or any other issuing entity as a non-repudiation device. When display  150  prompts the user to enter the input code  152 , display  150  presents passphrase  122 A to the user. In this example, passphrase  122 A consists of the characters L-K-E-B-N-J-H and has been generated by key generation module  118  of FIG. 4A based on the contents of primary key  116 A. Furthermore, passphrase  122 A has character positions  1 - 7  illustrated by FIG.  4 B. As ATM  146  is repeatedly used to execute successive electronic transactions, different passphrases  122 A will be generated. 
     Returning to FIG. 4B, the user selects the appropriate input code by applying authorization code  148 A to passphrase  122 A. In particular, in this example, the user identifies the character residing in the sixth character position of passphrase  122 A. In this case, the character is J. The user then presses the appropriate one of input keys  154  of input device  156 . In this case, the character J is represented by button  4 , which enters the digit  4  as the first digit of input code  152 . Likewise, the authorization code is used to select the first and third character positions of passphrase  122 A. Accordingly, digits  5  and  2  are successively entered using input keys  154  and form the remainder of input code  152 . 
     While the input code in this example is  452 , it is highly likely that a different input code will be selected in subsequent transactions, because a new passphrase  122 A will be generated for each transaction. In this manner, a static authorization code  148 A memorized by the user results in a different input code in successive transactions. This provides significant advantages, since an unauthorized person cannot misappropriate the authorization code by memorizing the key stroke entered by the user, in contrast to the problems associated with static PINs. 
     Optionally, as shown in FIG. 4B, display  150  does not display the fourth character position of passphrase  122 , although all seven characters of the passphrase exist internally in the ATM. Alternatively, any other one or more character positions can be selected to be hidden from view on display  150 . However, any such hidden character positions would be ineligible for use in authorization codes distributed to users. Hiding selected character positions from the view of users provides an added layer of security and prevents participants in transactions from learning the entire passphrase. 
     FIG. 4C further illustrates a method according to this embodiment for using the input code to enable a transaction after the input code has been entered. User  140  has entered input code  152  to ATM  146  as described above in reference to FIG.  4 B. Input code  152  of FIG. 4C is transmitted via communication network  114  to bank  144 . Bank  144  thereby obtains a copy  152 B of the input code. A copy  148 B of the authorization code is stored at bank  144 . Bank  144  also has a copy  122 B of the passphrase, which was obtained after the user swiped the bank card as shown in FIG.  4 A. Bank  144  of FIG. 4C is able to calculate the expected input code  152 ′, which must be received from ATM  146  in order to proceed with the desired transaction. Expected input code  152 ′ is generated by applying authorization code  148 B to passphrase  122 B in much the same manner as input code  152  was generated in FIG.  4 B. Typically, however, expected input code  152 ′ of FIG. 4C is generated automatically by computer-executable instructions at bank  144 . 
     After receiving input code  152 B, bank  144  can compare received input code  152 B with expected input code  152 ′ using an identity verification module  158 . If received input code  152 B matches expected input code  152 ′, bank  144  presumes that an authorized person has initiated the current transaction. Specifically, received input code  152 B matches expected input code  152 ′ only when a person who possesses authorization code  148  enters the input code at ATM  146 . When received input code  152 B matches expected input code  152 ′, a transaction enablement module  160  permits user  140  to proceed with any desired transaction. 
     If the received input code  152 B does not match expected input code  152 ′, any of a number of conditions can be responsible. For example, the user may have mistakenly entered an incorrect input code. Instead, an unauthorized user may have attempted to gain access to an account. Depending on the nature of the transaction, any appropriate action can be taken when the received input code  152   b  does not match expected input code  152 ′. For instance, the card reader can retain the bank card that has been incorrectly used. In some instances, it may be desirable to notify law enforcement authorities to investigate. 
     The use of the authorization code can be associated with a corresponding emergency code, that when applied to the passphrase to generate an input code, notifies authorities that the bank card or other instrument has been inappropriately used. For example, the authorization code  148 A (“613”) of FIG. 4B can be associated with an emergency code “316” by reversing the order of the character positions. If the holder of authorization code  148 A is ever forced under duress to divulge the authorization code, the holder has the option of divulging instead the emergency code. If an unauthorized person attempts to access the holder&#39;s account using the divulged emergency code, authorities are automatically notified that the use of the account is unauthorized. 
     FIGS. 5A and 5B summarize one embodiment of the methods for determining whether a recipient device is authorized to participate in electronic communication and verifying the identity of the user of one of the communication devices. In step  202 , a master key is used to generate one or more primary keys. The primary key is stored at the sending device and the recipient device in step  204 . When electronic communication is to be conducted, a secondary key is generated by the sending device according to the techniques disclosed herein. The secondary key can be described as including an encrypted form of the passphrase reconstruction process that is also generated at the sending device. 
     In step  208 , the secondary key is transmitted to the recipient device, along with any desired electronic communication, that may be encrypted, compressed, or otherwise encoded to be inaccessible by any recipient that does not possess or obtain the passphrase. As shown at step  210 , the recipient device, which possesses the primary key, reproduces the passphrase using the primary key and the secondary key. The passphrase then may be used in any desired manner or for any desired purpose, such as to gain access to a transmitted or stored document that has been passphrase-protected by the sending device. 
     As shown at decision block  212 , the method can proceed to dynamically identify the user of a communication device using the passphrase and the authorization code. If identification of the user is not desired, the method advances to decision block  214 . According to decision block  214 , if another electronic communication is to be performed, the method advances to decision block  216 . According to decision block  216 , if a new primary key is to be created, the method advances again to step  202 . New primary keys can be created if there is there is reason to believe that the security of the primary key at the sending device or the recipient device has been compromised. Alternatively, new primary keys can be created at regular intervals. If a new primary key is not needed, the method advances from decision block  216  to step  206 . Steps  206  and  208  are then conducted so as to create a new secondary key and a new associated passphrase in each successive transaction or communication. 
     Referring now to decision block  212 , if verification of the identity of a user of a communication device is desired, the method proceeds to step  218  of FIG.  5 B. In step  218 , the user is prompted to apply an authorization code memorized by the user to the passphrase displayed to the user. In  220 , the user enters the resulting input code. The input code is then transmitted to the sending device to the recipient device (or vice versa, if the identity of the recipient device is to be verified) as shown in step  222 . 
     The recipient device then determines according to decision block  224  whether the input code entered by the user matches the expected input code. If the input code is correct, the method proceeds to step  226 , in which the identity of the user has been both verified and authenticated. At this stage, any appropriate access to network resources, financial services, or the like, can be granted. If the input code is not correct, the method advances to step  228 , in which any appropriate measures can be taken to restrict access to any resources or communication. 
     While the methods and systems disclosed herein successfully replace conventional passwords and PINs, the invention can be implemented by layering the security features with conventional security features. For example, any encryption technology can be supplemented with the passphrases and other security techniques of the invention to further ensure that only authorized persons gain access to information. Another possible password management system that could be replaced by the invention is a secure fax. 
     While the combination of the methods for verifying the identity of a communication device using the primary key and the secondary key with the methods for verifying and authenticating the identity of a user of a communication device using the passphrase and the authorization code can be used advantageously in many cases, the invention may be practiced using either of the two foregoing aspects of the invention separately. For instance, the primary key and the secondary key can be used to determine if a computer receiving an e-mail message is authorized without using an authorization code to verify the identity of a user. Conversely, the passphrase and the authorization code can be used to determine whether a participant in an electronic transaction is authorized without verifying that the card reader (i.e., the sending device) and the bank (i.e., the recipient device) are authorized. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.