Patent Publication Number: US-7222107-B2

Title: Method for inter-enterprise role-based authorization

Description:
FIELD OF THE INVENTION 
   This invention relates to e-commerce transactions, and, more particularly, to a method of both authorizing and verifying the authorization of transactions between enterprises over both public and private networks. 
   BACKGROUND OF THE INVENTION 
   Large-scale deployment of e-commerce solutions between various enterprises over public networks requires careful consideration of security issues. This is best explained through an example. 
   Two companies, company A and company B, have a formal agreement for making business transactions (i.e., any legally binding action between persons or organizations), such as an offer, an order or a cancellation. The possible set of transaction types between A and B may be denoted by T(A,B)={T 1 , T 2 , . . . , Tn} where for example T ∈ T(A,B) may denote
 
T→“purchase X units of product Y at price P per unit”.
 
   The transaction types denoted by the set T(A, B) may be assumed to be general, and at the actual time when the particular transaction takes place, additional details beyond those given in the transaction descriptions of T(A,B) must be provided. For example, for transaction T, the requester will supply values for X, Y, and P, which are expected to vary over time. 
   The problem of specifying the set of transactions T(A, B), how they will be performed, the data exchanged and so on, could be solved using Electronic Data Interchange (&lt;&lt;EDI&gt;&gt;) syntax, such as in ISO 9735, available at http://www.r3.ch/standards/edifact/index.html. Further, these companies must coordinate over the Internet to fulfill their general transactions as specified in the set T(A,B). 
   A typical situation would be for a user UA of company A to receive a transaction of type T ∈ T(A,B) from a user UB, that purports to be under the control of company B. Let us assume that UA is presented with a request from company B for company A to make X=1000 units of product Y at price P=$1 per unit and further that the user operates through software operating through a public network. Since the request originates from a public network, there are at least three security issues that UA may consider: (1) should the details (X, Y, P, UA, UB) of the transactions be confidential and encoded for integrity? (2) how does one verify that the user UB requesting the transaction is in fact controlled by company B? and (3) even if it is known that the user UB requesting the transaction is employed by company B, it is not clear how one verifies that UB is in fact authorized to request such a transaction for the given values of X, Y and P. 
   The first two points can be addressed using standard security protocols and cryptographic algorithms, as described in A. Menezes, P. van Oorschot, and S. Vanstone;  Handbook of Applied Cryptography , CRC press, 1996. In particular, with public key cryptography each user Ux can be issued with one or several certificates (such as those described in ISO/IEC 9594, Information Technology—Open Systems Interconnection—The Directory: Authentication Framework, 1993) that can be used to demonstrate their identity through the use of digital signatures. 
   If UA and UB are acquainted personally then that existing trust relationship may be sufficient for UA to accept the request from UB as authorized, and this is how many inter-enterprise transactions are currently conducted. In this case, UA and UB have established some trust relationship, either specifically for the purpose of conducting future transactions, or perhaps the trust has been gained by successful previous transactions. However, general e-commerce will bring together people and companies who will have no prior business or trust relationships, and the transaction then must somehow be ‘self-authorizing’. Traditionally authorization to data, applications, resources, or more generally simply objects, is administered using some form of access control. See D. E. Denning;  Cryptography and Data Security . Addison—Wesley Publishing Company, 1982. In its most general form, there exists an access control matrix M that explicitly lists the access rights each user has with respect to each object O. As there may be many users Ui and objects Oj, the access control matrix M can be difficult to manage. 
   Perhaps the most common type of authorization is for there to be a general written document/form describing a transaction T, where certain details are provided by the requester at the time of the request, and the requester is then required to collect a set of handwritten signatures on the paper form, from one or several people who are able to approve transactions or requests of type T. For example, T may be a travel request form, which requires that the destination, duration of stay, expected costs and methods of transport be provided. The requester fills in these details, signs the request, and then takes the form to various superiors for their signatures in the appropriate places provided on the form. Typically the places in the form where a signature is required are labeled by the role of the people whose signatures are required, such as manager, department head or CEO. 
   This form of authorization is called the form-signature model, or authorization by co-signatures, or co-signing data. For example, the travel request transaction (T=‘travel request’) may require the signature of the requester, the requester&#39;s manager and then the department head of the requester. Once the required signatures have been collected, the requester uses the signed document to authorize the transaction, say to have a travel agent book flights or hotels. Usually the travel agent is not concerned with verifying the details of the travel request, other than general checks such as the return date is after the departure date, or that some threshold of expense is not exceeded. What is of importance to the travel agent is the set of signatures accompanying the request, and the roles represented by these signatures. For many office tasks that do not involve significant amounts of funds, the form-signature model is adequate for granting task authorization. However, where more significant amounts of funds or resources are committed by the transaction, it becomes important to be certain that each signature is both authentic, and that the collection of signatures does, in fact, bind the company. In these cases, it becomes necessary to obtain direct approval of every transaction from an enterprise authority (i.e., Transaction Administrator such as the President, comptroller, or other officer) for confirmation that the lower level employees had authority to authorize the transaction. 
   A form-signature model for e-commerce includes: (1) an electronic representation of the task and the information required to perform the task (such as dates, costs, names), (2) a signature mechanism, and (3) a mechanism to relate the signatures accompanying the electronic task data to privilege for granting authorization for the task. Generally speaking, (1) and (2) can be solved directly using current methods and technology, while (3) has not yet be adequately addressed. With respect to (1) and (2), paper-based forms can be represented electronically as HTML or word-processor documents, and for a task T, let D(T) denote the electronic form/template of task T. If T is a ‘travel request’ then for example D(T) may be a HTML document requesting details of the trip to be taken, and there will also be a list of roles where users acting in these roles must sign the travel request details. Also there are several schemes for providing digital signatures, such as RSA or DSS, so the basic tools to implement the form-signature model in e-commerce are available. The more difficult part in the e-commerce form-signature model is to determine or verify that the set of collected signatures implies authorization for the task. 
   If a user U digitally signs data, it is implied that U has a public key Pub(U) and a private key Pri(U) such that Pub(U) is stored in a certificate, which we will denote as Cert(U). The certificate Cert(U) is stored in a public database or directory, so anyone may retrieve it and verify a signature purportedly produced by U with Pri(U). The certificate Cert(U) contains one or several names/identifiers for U, so U can be uniquely identified as the user who produced the signature. However in considering if another user is verified to request transaction T by examining a set of signatures on D(T), the important aspect is not so much who produced each signature but whether they have the authority to authorize T. 
   Therefore, what is needed is a method that frees the enterprise authority from having to verify every transaction and which enables efficient authorization and verification of authorization of e-commerce contracts, using standard security or cryptographic protocols, over an insecure public network. Still further, what is needed is a method for performing inter-enterprise authorization that reveals minimal information about the decision structures of the respective companies. 
   SUMMARY OF THE INVENTION 
   A transaction authorization method is provided which operates over a computer network comprising a plurality of interconnected computers and a plurality of resources, each computer including a processor, memory and input/output devices, each resource operatively coupled to at least one of the computers and executing at least one of the activities in the process flow. The method assembles an electronic authorization of a transaction in a manner that is verifiable by extracting and verifying whether role certificates of at least one type, associated with the authorization, are themselves authentic. The method eliminates the need of having to authorize each and every signature on a transaction individually by providing an authorization structure based on roles, this structure being accessible on a public network for verification that the transaction is authorized. 
   The method is applicable in both an intra-enterprise and an inter-enterprise context, because it makes anonymous authorization decisions based on roles, represented by anonymous role certificates. In this manner, the identities of the employees need not be divulged when verifying the authenticity of the transaction. 
   Further, the method uses an authorization tree for a particular transaction that determines what combination of roles can authorize transactions of that type. 
   In another feature involving inter-enterprise authorization, a hashed version of the authorization tree is used, thus providing proof that a given user is authorized to perform a transaction while revealing minimal information about the approval structures of the company. In this manner, the method allows verification of a company&#39;s decision structures in such a manner as to obscure the details of this structure. 
   An object of the invention is to promote e-commerce by providing a convenient and computerized means of ensuring that transactions are properly authorized and therefore enforceable. 
   Another object of the invention, where the hash table is used, is to reduce space requirements and to obscure the decision procedure information in the authorization tree while still permitting the transactions to be authorized, thus making the method particularly useful for intra-enterprise transactions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail with specific reference to the appended drawings wherein: 
       FIG. 1  is a block diagram of a computer system of the invention; 
       FIG. 2  is a schematic diagram of a network encoded with the method of the invention; 
       FIG. 3  is a schematic diagram of a transaction; 
       FIG. 4  is a detailed flow diagram of the method of the invention; 
       FIG. 5  is a flow chart of a verification submethod of the invention; 
       FIG. 6  is a schematic diagram of a travel request document used in the method; 
       FIG. 7  is a block diagram showing the transaction authority of the method; 
       FIG. 8  is a block diagram showing the authorization structure of the method; 
       FIG. 9  is an authorization tree for a travel request; 
       FIG. 10  is a block diagram showing an interaction of the method with role certificates; 
       FIG. 11  is a block diagram showing the interaction of the TAM with various databases in the method; 
       FIG. 12  is a schematic diagram of the completed travel request; 
       FIG. 13  is a schematic diagram showing the role certificates in the travel request; 
       FIG. 14  is a schematic diagram showing the transfer of the request to the verifier; and 
       FIG. 15  is a hash of the tree of  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , a Transaction Authorization Method (“TAM”)  2  provides a means of ensuring the validity of contracts  4  in e-commerce by constructing such contracts in a manner such that their validity can be easily verified. 
   The TAM  2  has a message exchange mechanism that operates within the distributed workflow management system  6 . The method  2  has the properties of (1) being accessible by users  8  to authorize requests  10 ; (2) having access to several databases  70 ,  82 ,  96  or  202  (shown in  FIG. 11 ); and (3) contacting users to request signatures  18 . 
   The TAM  2  operates on a computer system  20  in a distributed system  21  over a computer network  25  and/or  31  (shown in  FIG. 3 ) comprising a plurality of interconnected computers  22  and a plurality of resources  23 . The TAM  2  is encoded on computer-readable media and operates on the computer system  20  and/or between computer systems and one or more servers  54   a  or  54   b  (shown in  FIG. 2 ) on an intranet  25  or the Internet  31 . 
   The computer system  20  typically includes a computer  22 , a display device  24 , an input device  26  such as a keyboard, a primary storage device  30  and a secondary storage device  32 . After loading of software encoded with the TAM  2  of the invention or after accessing the server  25  or  54  through a browser such as Internet Explore 5.0, as the case may be, the display device  24  displays a graphical user interface (“GUI”)  34  for facilitating the display of text and graphics associated with the method to the user. Display devices  24  include printers and computer display screens such as a CRT, LED displays, LCDs, flat screens, screen phones, and projectors. Input devices  26  are numerous and include keyboards and pointing devices such as a mouse  27  having a left mouse button  28  and a right mouse button  29 , a trackball, lightpens, thumbwheels, digitizing tablets, microphones using voice recognition software, and touch screens and pads. 
   Each resource  23  is operatively coupled to at least one of the computers  22  and executes at least one of the activities in the process flow of the method  2 . Resources  23  include, but are not limited to, printers, databases, special-purpose servers, security devices, modems, etc. 
   The GUI  34  provides input fields for data input and control of the TAM  2 , as well as an output window for displays of status and other information, which facilitates management and operation of the workflow system. The TAM  2  accesses a database  33  including information associated with transactions, discussed in detail below. 
   The computer  22  includes a CPU  36  as well as other components with which all who are skilled in the art are familiar. For a detailed discussion of these components and their interaction, see U.S. Pat. No. 5,787,254, the content of which is incorporated by reference. The secondary storage  32  supports the TAM  2 , preferably HTTP-compliant, as well as a number of Internet access tools. The CPU  36  fetches computer instructions from primary storage  30  through an interface  41  such as an input/output subsystem connected to a bus  42 . The computer  22  can be, but is not limited to, an “IBM APTIVA” computer, a product of International Business Machines Corporation of Armonk, N.Y., or any computer compatible with the IBM PC computer systems based on the X86 or Pentium(™) series processor of Intel Corporation or compatible processors, or any other suitable computer. The CPU  36  utilizes an operating system that, depending on the hardware used, may be DOS, “WINDOWS 3.X”, “WINDOWS XXXX”, “NT”, “OS/X”, “AIX”, “LINUX”, or any other suitable operating system. The CPU  36  executes these fetched computer instructions. Executing these instructions enables the CPU  36  to retrieve data or write data to the primary storage  30 , display information, such as the statistical displays of the TAM  2 , on one or more display devices  24 , receive command signals from one or more input devices  26 , or transfer data to secondary storage  32  or even other computer systems which collectively form a computer network  25  (shown in  FIG. 2 ). Those skilled in the art understand that primary storage  30  and secondary storage  32  can include any type of computer storage including RAM, ROM, application specific integrated circuits (“ASIC”) and storage devices that include magnetic and optical storage media such as a CD-ROM. 
   Referring now to  FIG. 3  there are many classes of transactions  40  that are to be carried out online in the course of conducting e-commerce. In the context of this disclosure, each transaction  40  takes place between a requester  42  and a verifier/value provider  44  The requester  42  desires a product or service  46  and the value provider  44  wishes to be sure that the e-documentation  50 , upon which the requester&#39;s request  52  is based, is properly authorized. Thus, the value provider  44  wishes to verify the authenticity of the document  50 . In the most general context, the requester  42  and verifier  44  may or may not be employed by the same company. 
   For example, the document  50  associated with the request  52  may be a contract for products or services, such as a travel request document  54  (shown in  FIG. 6 ) from an employee of the requesting company to the company&#39;s travel agent, or from the employee to the financial officer of the same company to determine if the required funds for the travel are available. 
   Now referring to  FIG. 4 , in which a more detailed flow diagram of the method is shown, the TAM  2  executes the following steps. In a first step  60 , an employee  62  requests a transaction  40  from the TAM  2 . In a second step  62 , the TAM  2  requests the HTML representation  64  of details  66  of the transaction  40  from the Digital Document Database  70  (shown in  FIG. 7 ). In a third step  72 , the Digital Document Database  70  returns the HTML representation  64  of the transaction details  66  to the TAM  2 . In a fourth step  74 , the TAM  2  requests the role certificate  76  of the TA  80  from a Role Certificate Database  82  comprised of &lt;&lt;anonymous&gt;&gt; role certificates (the anonymity is implied since the user&#39;s name is not included in the certificate), including the role certificates of the TA  80  (this is discussed in more detail below). In a fifth step  84 , the Role Certificate Database  82  returns the certificate  76  of the TA  80  and the TAM  2  verifies the signature  126  of the TA on the HTML representation  64  of the transaction request details  60  returned from the Digital Document Database  70 . In step six  86 , the TAM  2  returns the HTML transaction details  66  to the requester  42 . In step seven  90 , the requester  42  views the HTML representation  64 , completes the details  66  specified (e.g., name, destination, costs, etc.), signs the completed HTML representation  64  and returns the signed HTML representation to the TAM  2  to collect any remaining signatures  106 . In an eighth step  92 , the TAM  2  requests the AS  94  for the transaction from the Authorization Structure Database  96 . The returned AS  94  is pre-signed by the TA  80  and the signature is verified by the TAM  2 . The TAM  2  chooses a permission set  100  of role names  102 , and a collection of users to contact to sign in these role names. In step nine  104 , the TAM  2  forwards details  66  of the transaction request  52  with the signature  106  of the regular-employee requester  42  to others having roles corresponding to the chosen permission set  100  and collect signatures of each role indicated in the permission set  100 . For example the signature of a manager and a department manager is collected each signing the document  64  in his respective role. In step ten  110 , the TAM  2  requests the role certificates  76  for each member of the permission set  100  and respective signature. In step eleven  112 , the TAM  2  forwards the document  54  including the signatures  106  and role certificates  76  to the requester  42 . Thus, a digital document  114  is created including all the authorization details  66  required in order to confirm the validity of the transaction  40 . In step  116 , optionally, the method  2  verifies the signed document  114 . 
   Referring now to  FIG. 9 , in the method  2 , the anonymous role certificate  76  is an association between a signature verification key  120  and a role  122 . This differs from the standard certificate described in ITU-T X.509 (1997 E)(hereinafter &lt;&lt;X509&gt;&gt;), which is an association between a signature  106  verification key  120  and a name (not shown). More accurately stated, X509 is the association between a public key and a name, where the public key can be used for both encryption and signature verification. The method  2  of the invention, however, is not concerned with users performing encryption in the capacity of a role  122 , but rather is concerned with users producing signatures  106  in the capacity of a role. The certificate  76  will be anonymous by not having any linking information to owner of the certificate. The ‘owner’ of a certificate Cert is implicitly defined as the user who has the private key that corresponds to the public key embodied in the certificate. 
   A role certificate  76  plays an important role in the method  2 . It is assumed that within any company C there exists a set of well-defined roles RC={R 1 , R 2 , . . . , Rm}, and that each user U in the company C is assigned one or several roles UR ⊂RC. For the purposes of the method  2 , it is assumed that each user has a X.509 public key certificate CertCA(U) that contains their name, public key and other fields, signed by some local certificate authority CA. As X.509 certificates contain extension fields for general information such as an e-mail address, alternative names, and policy information for example, it is possible that a designated role  122  could be included as an extension field. However the role  122  and owner of the certificate are linked explicitly since the certificate contains a name field. An IETF working group is also currently developing the concept of an attribute certificate (AC) (see S. Farrell;  An Internet Attribute Certificate Profile for Authorization , Aug. 20, 1998) that binds attributes such as roles  122 , group memberships and security clearance to a name. However, attribute certificates contain no public key, and that the name specified in the AC is meant to provide supplemental information related to an individual U named in an existing X.509 CertCA(U). Since the name of the certificate holder is included in the AC, then the name and role are linked directly. For the purposes of the method  2 , both certificates  76  and ACs are acceptable because the method uses a certificate containing a role  122  to authorize an action, however, in the method, it is desirable that the role not be associated directly to the user it is assigned to. 
   Therefore, the method  2  uses an anonymous role certificate 76 (CertCA(U,R)) for user U, which is an X.509v3 certificate with the following changes: (1) the name field represents a fictitious user; (2) there is an extension field containing the role  122  for U ; (3) there is an extension field that contains a forward reference from Cert(U) to Cert(U, R). 
   The forward reference for example may take the form of E(C, U, passwd) that denotes the public key encryption of the concatenation of U and a password by the company C&#39;s public key or the local CA&#39;s public key. The forward reference is simply a mechanism for the company to be able to identify the owner of a role certificate, and it has no other importance to the method of the invention. If U has several roles  122  then there will be a role certificate  76  for each role. It is important to note that each role certificate has a public and corresponding private key so that users may produce signatures in their role capacities. Thus each user will have at least two certificates, a standard X.509v3 certificate CertCA(U) that binds their name to a public key, and then an anonymous role certificate 76 (CertCA(U,R)) that binds their role to a public key. CertCA(U) is linked to CertCA(U,R) by a forward reference, but given CertCA(U,R) there is no obvious way to determine CertCA(U) or the identity of U. For the purposes of the method  2 , a signature  106  produced by a private key  124  associated with a role certificate 76 CertCA(U,R) is defined as a role signature  126 . 
   Thus, if a user produced a signature  126  on a transaction  40 , then a verifier  130  is interested in the role  122  that the user has in the company, such as whether user is a manager or department head, and how this role relates to the given task, if at all. The identity or name of user is in fact not important, as only the role  122  assumed by user is of concern in verifying if a task has been authorized. 
   Referring now to  FIG. 5 , in order to accomplish the task of verification, the TAM  2  includes a verification submethod  116  that enables the verification of the created and signed document  114 . In a first step  132 , the role signatures  126 , are checked on the document  114 . In a second step  134 , the transaction type itself is checked to ensure that it is an authorized transaction. In a substep  136  of the second step  134 , the role names  122  are extracted from the role certificates  76 . In a second substep  140  of the second step  134 , the names  122  are hashed. In a third substep  142  of the second step  134 , the computed hash value of the transaction  40  is checked to ensure that it is equal to the value of the transaction  40  received in the AS  94 . In a fourth substep  144  of the second step  134 , the signature  126  of the TA  80  on the transaction  40  is checked to ensure that it is correct. If so, the transaction  40  has been verified and notice of this fact is sent to the requester  42 . 
   Thus, verification is simply the process of checking signatures, and that the verifier  130  is not concerned with the details  66  of the transaction  40 . It is assumed that the signatories have checked the details  66  of the transaction  40  and would withhold their signature  106  if these details deviated from company policy in regard to transactions of the given type T. This assumption is again inherent in the form-signature model, where the verifier  130  is typically more concerned with the signatures provided as opposed to details of the signed form. 
   In the remainder of this detailed description, a travel request transaction is used to illustrate the steps of the TAM  2 . 
   Referring now to  FIG. 6 , the structure of an IBM travel request document  54  is shown. Traditionally, paper documents have been used for various transactions, in particular for authorizing a travel request. It is the task of a Transaction Authority  80  (&lt;&lt;TA&gt;&gt;) (shown in  FIG. 7 ) to convert these paper forms into digital documents  64  (preferably in HTML form, although there are several possible formats). For each form, the TA  80  separates out what may be considered as transaction details  66 , and what may be considered as authorization information  146 . For the travel request document  54 , the transaction details  66  include the requester name, destination, the trip cost, dates out of the office, etc. On the paper form, and the HTML document  64  constructed from it, most of the transaction details  66  are simply placeholders for information to be supplied by the requester  42 . 
   The authorization details  146  generally consist of a list of roles  122  of persons who are required to jointly authorize the transaction  40 . &lt;&lt;Authorizing&gt;&gt; the paper form usually means to sign it, and for the HTML document  64 , the authorization details  66  will indicate which persons acting in which roles  122  may authorize the transaction  40 . For the travel request document  54 , the authorization details  66  that correspond to a permission set  100  for authorizing a travel request, consists of the electronic signatures  106  of the requester  165 , a manager  167  and a departmental manager  169  (shown in  FIG. 9 ) This means that the requester  42 , a person acting in the role  122  of manager, and a person acting in the role  122  of departmental manager must digitally sign the HTML form  64  for it to be considered authorized. 
   Referring now to  FIG. 7 , for the travel request document  64 , the TA  80  creates the travel transaction details  66  in HTML, signs these details and stores the signed document in the Digital Document Database  70 . Thus it is necessary to assign the role of the TA  80  to a person who is issued a TA role certificate  76  (shown in  FIG. 8 ) that contains an associated signature verification key  120 . The TA  80  will also be issued separately with the matching signing key  150 . Signatures produced with the TA  80  signing key  150  are verified with the verification key  120  in the TA role certificate  76  (shown in  FIG. 10 ). 
   The TA  80  creates the Authorization Structure  94  for the travel request document  64 , signs the document, and then stores it in the Authorization Structure Database  96 . The Authorization Structure  94  is a representation of the roles that may be used to authorize the transaction  40 . 
   The information in the Digital Document Database  70  and the Authorization Structure Database  96  are not required to be secret as such. However, it is necessary that the information be integrity protected. For this reason, the TA  80  must sign such documents. 
   Referring now to  FIG. 8 , details regarding how the Authorization Structure  98  (&lt;&lt;AS&gt;&gt;) is created depend on social and strategic management factors that are not the subject of the invention. The main property of the AS  98  is that its construction depends on the concept of a permission set  100 . To illustrate what is meant by a permission set  100 , let the set PT, 1 ={U, M, DH} be the permission set for transaction T. In this example, the transaction T has only one permission set, but in general a transaction may have several permission sets denoted PT, 1 , PT, 2 , . . . , PT,i. Each permission set  100  consists of a set of roles  122  (that is, PT,i⊂R, potentially a multi-set), with the meaning that any user U is authorized for transaction T represented by D(T,U), if for some permission set PT,i={R 1 , R 2 , . . . , Rm} of T, m users in the roles R 1 , R 2 , . . . , Rm sign D(T,U) using their respective role certificates. 
   Permission sets  100 , (PT,i), then represent sets of roles  122  whose joint authority is deemed sufficient to authorize transactions  40  of type T. A tree  154  (shown in  FIG. 9 ) is used to represent the permission sets  100  PT={PT,  1 , PT,  2 , . . . , PT, k}, of a transaction T. With respect to the form-signature model, PT describes the decision procedure for authorizing transactions of type T. U.S. Pat. No. 4,309,569 to Merkle, the content of which is incorporated by reference, describes the general use of such trees  154 . 
   Referring now to  FIG. 9 , for each transaction type T, an authorization tree  154 , AT, is created such that there are k nodes  156  at a first level  160  from the root  162 , corresponding to the k permission sets  100 , PT={PT,  1 , PT,  2 , . . . , PT, i}, for transaction type T. The nodes at a second level  164  are leaves  166 , and represent the roles  122  of each permission set  100 . 
   If the permission sets  100 , PT, for T are PT, 1 ={R 1 , R 2 }, PT, 2 ={R 3 , R 4 , R 5 } and PT, 3 ={R 6 }, then AT  154  has two levels where the first level  160  represents PT, 1 , PT, 2  and PT, 3  with 3 nodes  156  and each PT,i  100  has the same number of leaves  166  as there are roles  122  in its permission set. So for example then PT, 1   100  would have two children (both leaves  166 ) representing R 1  and R 2 , as shown in  FIG. 10 . 
   Since transaction  40  is considered authorized if, for at least one permission set  100 , PT,i, signatures are acquired for each role  122  in PT,i, the nodes  156  representing the PT,i may be considered as “AND” nodes  170  and the root  162  of AT  154  as an “OR” node  172 . An AND node  170  means that all children of the node must agree to the request D(T,U) (all roles  122  of a permission set  100  must sign) while an OR node  172  means at least one child must agree to the request D(T,U) (at least one permission set must jointly sign). Alternatively, AT  80  may be interpreted as a disjunctive representation of the roles  122  that can authorize a transaction  40 . 
   Referring again to  FIG. 8 , with the travel request document  64 , the permission set  100  consists of the requester  42 , a manager and a departmental manager. These will be described in more detail later. 
   Referring now to  FIG. 10 , since the AS  98  is based on permission sets  100 , and these sets consist of named roles  122 , each user will be issued with one or more roles designated by a role name. Since users are required to sign in their capacity under a given role name  122 , users are then issued with role certificates  76 . A role certificate  76  consists of the role name  122 , a signature verification key  120 , a Role Manager signature  106  on the role certificate  76 , and other administrative information (such as time at which the role certificate was issued, when it will expire etc.). When a user is given a role certificate  76 , there is also given the corresponding signing key  150  that matches the verification key  120  in the role certificate. In fact, a user demonstrates that he owns a given role certificate  76  by possessing the corresponding signing key  150 . Consequently the signing key  150  must be kept secret by the user it is issued to. Each signed role certificate  76  is also stored in the role certificate database  82  (&lt;&lt;RCD&gt;&gt;). 
   The above completes the initialization of the method  2  of the invention. In summary, the initialization involved the conversion of paper forms into digital documents  64 , and their signing by the Transaction Authority  80 . Further, the TA  80  also determined the Authorization Structure  98  (AS) for each transaction  40 , and has signed this AS as well. The information in the AS  98  is based on named roles and the Role Authority  180  issues each user with one or more role certificates  76 . The set of named roles  122  issued by the Role Authority  180  were used by the TA  80  in the construction of the AS  98 . 
   Referring now to  FIG. 11 , an example of authorizing a travel request  64  is considered. Assume a user wishes to make a travel request and have it authorized. The user, the requester  42  of the travel authorization, will accomplish this through the help of the TAM  2 . In the preferred embodiment, the TAM  2  is a server application on the company intranet  25 , and can be contacted via a Web interface such as a browser. The user thus is able to contact the TAM  2  via its URL and indicates that he/she wishes to make a travel request  64 . Here, the travel request requester  42  is acting in the role  122  of &lt;&lt;regular employee&gt;&gt;. 
   In a first step  182 , the user/employee  42  requests a travel request transaction  40  from the TAM  2 . The TAM  2  receives the travel request  52  from the user  42 , and contacts the Digital Document Database  70  to obtain a copy of the transaction details  66  for this class of transaction  40 . The Digital Document Database  70  returns the details  66 , represented in HTML, to the TAM  2 . The HTML was previously signed by the Transaction Authority (TA)  80 . 
   In the second step  184 , the TAM  2  requests the HTML representation  64  of the transaction details  66  from the Digital Document Database  70 . To check that the HTML details are correct, the TAM  2  requests the role certificate  76  of the TA  80  from the Role Certificate Database  82  (which also includes role certificates of a &lt;&lt;regular employee&gt;&gt;  165 , a &lt;&lt;manager&gt;&gt;  67 , &lt;&lt;department manager&gt;&gt;  169  and other roles of employees and management at differing levels within the company), and then verifies the signature  106 . If the signature  106  is correct, the TAM  2  proceeds. 
   In a third step  186  the Digital Document Database  70  returns the HTML representation  64  of the travel request transaction details  66 . 
   In a fourth step  190 , the TAM  2  requests the role certificate  76  of the TA  80  from the Role Certificate Database  82 . In a fifth step  192 , the Role Certificate Database  82  returns the certificate  76  of the TA  80  and the TAM  2  verifies the signature  106  of the TA on the HTML representation  64  of the transaction request details  66 , returned from the Digital Document Database  70 . 
   In step six  194 , the TAM  2  returns the HTML transaction details  66  to the requester  42 , and the requester&#39;s browser displays the details as a HTML form  64  that is requesting input. The requested input constitutes the transaction details  66  for the travel request  54 . In step seven  196 , the requester  42  views the HTML representation  64 , completes the details  66  specified (e.g., name, destination, costs, etc.) through the browser, signs the completed HTML representation  64 . The user/requester  42  has signed with their role certificate  76  that indicates the role &lt;&lt;regular employee&gt;&gt;. The requester  42  returns this signed HTML representation  64  to the TAM  2  to collect any remaining signatures  106 . 
   In an eighth step  200 , the TAM  2  receives the signed requester input (i.e., the signed HTML representation) from the user  42 , and then contacts the Authorization Structure Database  96  to obtain the authorization structure  98  for the travel request transaction  40 . The TAM  2  receives the authorization structure  98  from the database  96  and checks the signature  106  of the TA  80  on the structure. From the authorization structure  98 , the TAM  2  extracts a permission set  100  of role names  122 , and a collection of users to contact to sign in these role names. In this case there is only one, which is the regular employee/requester  42 , manager and departmental manager. 
   At this point, the object of the TAM  2  is to obtain a collection of signatures  106  from persons whose joint roles  122  constitute a permission set  100 . The requester  42  has already provided the signature  106  for the role &lt;&lt;regular employee&gt;&gt;, and the TAM  2  must obtain two signatures in the roles &lt;&lt;manager&gt;&gt;  167  and &lt;&lt;departmental manager&gt;&gt;. 
   The TAM  2  accesses a User Directory Database  202  that lists users and their roles  122  and, for example, selects user &lt;&lt;John Brown&gt;&gt;; in role &lt;&lt;manager&gt;&gt; for one signature  106 , and user &lt;&lt;Sue Smith&gt;&gt; in role &lt;&lt;departmental manager&gt;&gt; for the other signature. 
   In step nine, the TAM  2  forwards the transaction request details  66  with the signature  106  of the regular-employee requester  42  to a manager of the requester, John Brown. John Brown&#39;s browser displays the HTML travel form  64  with the requester&#39;s transaction details  66  filled in, and an indication that the signature  106  provided by the requester  42  is correct. John Brown then decides whether to authorize the travel request  54 . If authorization is granted, John Brown signs the HTML of the travel request  54 , and the travel details  66  provided by the requester  42 , which are returned to the TAM  2 . 
   In step ten, the TAM  2  forwards the transaction request document  64  with the signatures  106  to the &lt;&lt;department manager&gt;&gt; Sue Smith, who is presented with the details  66  of the travel request  54  and the set of previous signatures on the request (in this case the signature by the requester  42  and that of John Brown). If all is in order, Sue Smith then signs all the information she received in her role as department manager, and sends this back to the TAM  2 . 
   In step eleven, the TAM  2  receives a set of signatures  106  that purport to constitute a permission set  100 . To check that this is in fact the case, the TAM  2  retrieves the role certificates  76  for the requester  42 , John Brown as Manager and Sue Smith as Departmental Manager, and then verifies all the signatures. In step twelve, if the signatures  106  verify as being valid, the TAM  2  forwards the document  64  including the signatures and role certificates  76  to the requester  42 . Thus, a digital document  114 , shown in  FIG. 12 , is created including all the authorization details  66  required in order to confirm the validity of the transaction  40 . The requester  42  now holds a set of signatures  106  on a travel request that constitute a permission set  100  for this class of transaction  40 . This information is to be used in convincing another user, denoted as a verifier  130 , that the requester  42  is in fact authorized to make the travel request  54 . 
   Referring now to  FIG. 12 , the completed transaction  40  is depicted, having transaction details  66  and the signatures  106  held by the requester  42 , including (1) the HTML of the transaction details signed by the TA  80 , (2) the user-supplied input, both of which are signed by the requester  42 , and (3) this information being over-signed by the a manager, and all being over-signed by a departmental manager. 
   Referring now to  FIG. 13 , the role certificates  76  and authorization structure  98  held by the requester  42  are shown. 
   Referring now to  FIG. 14 , the steps involving requester  42  forwarding the travel request  54  to the verifier  130 , for transaction processing, is discussed. This method is called a verification submethod  116 . 
   To better understand this method of verification, it is important to understand details of how the Authorization Structure  98  is constructed. The verification submethod  116  makes use of cryptographic hash functions, which map arbitrary strings to fixed length outputs of say 16 or 20 bytes. In the case of the travel request  54 , the Authorization Structure  98  is constructed by hashing the three roles  122  (thus hashing the actual authorization structure of the company) that constitute the permission set to yield: H 1 =hash(&lt;&lt;regular employee&gt;&gt;); H 2 =hash(&lt;&lt;manager&gt;&gt;); and H 3 =hash(&lt;&lt;departmental manager&gt;&gt;). 
   For example, H 1  is said to be the hash of the string (&lt;regular employee&gt;&gt;. Finally, H 1 , H 2 , and H 3  are treated as strings, concatenated and then hashed as T=hash(H 1 , H 2 , H 3 ). The phrase is “the Transaction Authority  80  (TA) signs the Authorization Structure  98 ”, means that the TA signs the value of T″ the transaction  40 . Thus the TA  80  is signing a “hash of hashes”. 
   All users are aware of this general method for signing an Authorization Structure  98  (AS), in that they know that the AS signed by the TA  80  is derived from first hashing a collection of roles  122 , and then hashing these values once more. 
   Referring specifically to the travel request example, the requester  42  sends (1) the travel request  54  in HTML signed by the TA  80 ; (2) three role certificates  76  corresponding to three users in roles &lt;&lt;regular employee&gt;&gt;, &lt;&lt;manager&gt;&gt; and &lt;&lt;departmental manager&gt;&gt;; (3) the transaction details  66  as shown in  FIG. 12  which are first signed by the regular employee, then the manager, then the departmental manager; and (4) the signature  106  on the hashed roles  122  as created in  FIG. 15 . 
   Referring again to  FIG. 5 , the TAM  2  includes a verification submethod  116  that enables the verifier  130  to verify the created and signed document  114 . The verifier  130  is primarily interested in verifying that the requester  42  is authorized to make the transaction  40 , which in this case is a travel request  54 . The requester  42  sends to the verifier  130  the transaction HTML (signed by the TA  80 ), a collection of role certificates  76 , the transaction details  66  signed by each of the signing keys  150  corresponding to the verification keys  120  in the role certificates, and the Authorization Structure  98 . Recall from  FIG. 8  that each role certificate  122  is signed by the Role Authority  180  (RA). In a first step  132 , the verifier  130  uses the verification key  120  of the RA  180  to check each certificate  76  on the document  114 . In a second step  134 , the verifier  130  then checks the signatures  106  on the transaction details  66  using the verification keys  120  in the supplied role certificates  76 . In a substep  136  of the second step  134 , to check that the requester  42  is authorized, the verifier  130  extracts the named roles  122  from the role certificates  76  In a second substep  140  of the second step  134 , the names are hashed using the hash-of-hashes process (as described above). In a third substep  142  of the second step  134 , the computed hash value of transaction  40  is checked against that was originally signed by the Transaction Authority  80  to ensure that it is equal to the value for transaction  40  received in the AS  98 . The output of the hash-of-hashes process is then used as input to check the signature  106  on the hash-of-hashes process. In a fourth substep  144  of the second step  134 , if the produced hash-of-hashes string matches the hashed string signed by the TA  80 , then the verifier  130 , assumes that the request  52  is authorized. If so, the transaction  40  has been verified and notice of this fact is sent to the requester  42 . 
   In the above submethod  116 , the TAM  2  transfers the information from the requester  42  to the verifier  130 . Optionally, the transfer from the requester  42  to the verifier  130  may be done via e-mail. The requester  42  gathers all the authorization details  66  locally using the TAM  2  and then sends all this information via e-mail to the verifier  130 . For instance, all the signatures  106  and costs are gathered and then the request  52  is e-mailed to a travel agent who proceeds to make the booking. 
   As of yet, it has not been assumed that the requester  42  and the verifier  130  are in the same company. This is not necessary because the method  2  functions regardless of whether the verifier  130  is in the same company or not. If they are in the same company, they may be connected by the intranet  25  and thus share the same server  54   a . The location of the verifier  130  is not important as such. The role  122  of the verifier  130  is to verify the information provided by the requester  42 . 
   In order to verify the validity of the transaction  40 , the verifier  130  needs the following:
     (1) the signature verification key  120  of the Role Authority  180  that is used to check the correctness of the signatures  106  on the role certificates  76  used in the transaction  40 ;   (2) the signature verification key  120  of the Transaction Authority  80  to check the correctness of the signature  106  on the Authorization Structure  98  (the hash-of-hashes process); and   (3) knowledge of how to take a collection of named roles  122  and perform the hash-of-hashes process so that the signature of the Transaction Authority  80  on the Authorization Structure  98  can be checked.   

   The signature verification keys  120  of the Role Authority  180  and Transaction Authority  80  are public information, in that they need not be made secret. Therefore, they are assumed to be available and thus verifiable by all. The hash-of-hashes process needs to be understood by all potential verifiers  130  using the method  2  of the invention. 
   The hash-of-hashes process is quite simple in the example of the travel request  54  given above, because there is only one permission set  100 . However, the basic method  2  can be extended as follows to include several permission sets  100 . For example, a travel request  54  can also be authorized by the CEO and the CEO secretary, so that the two permission sets (P 1  and P 2 ) for a travel request are P 1 ={regular employee, manager, departmental manager}; P 2 ={CEO, CEO secretary}. 
   The permission sets  100  and the roles  122  they consist of can be arranged into an Authorization Tree  154  (AT), as shown in  FIG. 9 . The AT  154  is an example of an Authorization Structure. For the Transaction Authority  80  to sign the AT  98 , the AT must first be converted into a string, which is done by using a hash-of-hashes process similar to that described above. 
   First, each role name  122  is hashed to give H 1 , H 2 , H 3 , H 4 , H 5  as follows:
         H 1 =hash(&lt;&lt;regular employee&gt;&gt;)   H 2 =hash(&lt;&lt;manager&gt;&gt;);   H 3 =hash(&lt;&lt;departmental manager&gt;&gt;);   H 4 =hash(&lt;&lt;CEO&gt;&gt;);   H 5 =hash(&lt;&lt;CEO secretary&gt;&gt;).
 
These values must now be hashed in order to obtain one hash for each permission set, as follows: H 6  =hash(H 1 , H 2 , H 3 ); and H 7 =hash(H 4 , H 5 ). H 6  is the hash for permission set P 1 , and H 7  is the hash (P 2 ′) on permission set P 2 . Thus there is one hash for each permission set  100 ; these are called permission set hashes. Note that hash(H 1 , H 2 , H 3 ) means that H 1 , H 2 , and H 3  are strings that are concatenated and then hashed. Finally, the hash for the tree is produced as T=hash(H 6 , H 7 ).
       

   This hashing process is represented in  FIG. 15 . It is the value of transaction  40  that is signed by the Transaction Authority  80 . 
   The verifier  130  uses a signature on transaction  40  to check that a requester  42  is authorized for a given transaction  40  (travel request  54  in this case) in a similar manner as in the example given above with one permission set  100 . 
   To verity the signature  106  on transaction  40 , the verifier  130  repeats all or part of the tree hashing process described with respect to  FIGS. 9 and 15 . Note that in  FIG. 15  , hashed referenced items are differentiated from those of  FIG. 9  by means of a prime following the unhashed referenced number. Assume that the requester  42  has obtained signatures  106  from persons acting in roles that constitute permission set P 1 . In this case, the requester  42  will be sending the verifier  130  three role certificates  76  from which the verifier can extract the roles names &lt;&lt;regular employee&gt;&gt;, &lt;&lt;manager&gt;&gt;, and &lt;&lt;departmental manager&gt;&gt;. The verifier  130  can then form H 1 , H 2 , H 3  and H 6  as described above. Thus the verifier  130  can form the permission set hash of the permission set  100  that authorized the transaction  40 . 
   To complete the signature verification on the Authorization Tree  154 , the requester  42  will need to provide the verifier  130  with the permission set hashes of all other permission sets  100  besides the one that is authorizing the transaction  40 . In the example above, because P 1  is authorizing the transaction  40 , then the hash of P 2  must be provided, which in this case is equal to H 7  as described above. 
   When given H 7 , the verifier  130  can now form T because the verifier can form H 6 , and the signature  106  on T can be checked. Thus, for the purposes of checking the signature  106  on the Authorization Tree  154 , the requester  42  sends the verifier  130  role certificates  76  from which roles  122  can be extracted and hashed to form the hash of the permission set  100  that is authorizing the transaction; and the hash of each permission set that is not authorizing the transaction. With these two pieces of information, the verifier  130  can compute the hash value of transaction  40  and then check the signature  106 . 
   In the travel request above, the TAM  2  is contacted through the World Wide Web, and thus the TAM can be thought of as a web server process. In the workflow system of the method, users preferably contact the TAM through a dedicated network channel. Both embodiments are essentially identical: the TAM  2  exists somewhere on the computer system  20  which can be accessed by users; the TAM can also access databases  70 ,  82 ,  46  and  202 , and other users. As understood in the prior art, this may be accomplished by e-mail or via an intranet or Internet connection to the web, for example. 
   The TA  80  is trusted by the requester  42  and verifier  130  in that the signatures  106  produced by the TA are trusted. In this sense, the TA  80  is trusted to correctly form the HTML representation  64  of the transaction  40  and sign it, and to also form the Authorization Structure  98  for a transaction and sign it. However, in a broader sense, the TAM  2  need not be trusted. Although a user may trust the TAM  2  to perform some security functions on their behalf, the user may instead use a local process to verify that all the work performed by the TAM is correct. 
   In the web embodiment, the TAM  2  is neutral (i.e., trusted by all) in that it is an independent server  54   b  accessible by both verifiers  130  and requesters  42  on the Internet  31 . Specifically, the components in which trust really resides is with the Transaction Authority  80  (to create digital transactions, to create Authorization structures), and the Role Authority  180  (to allocate role certificates  76  to persons who can act in the stated role). Thus, the verifier  130  need only trust the signatures  106  produced by the Transaction Authority  80  on the HTML representation  64  and Authorization Structure  98 , and the Role Authority  180  for signatures on the role certificates  76 . 
   In the travel request  54  described above, the TAM  2  is performing a trusted role on behalf of the requester  42  since the TAM is fetching information and checking signatures  106 . However it should be clear that all information sits in public databases (the Digital Document Database  70 , the Authorization Structure Database  96  and the Role Certificate Database  82 ) resident on the server  54   b , for example. The requester  42  could access the Digital Document Database  70  and get the travel request HTML document  64  directly, and check the signature  106  of the TA  80  on it (the verification key  120  of the TA  80  is available to everyone). The requester  42  could then contact users for signatures  106  to form a permission set  100 , check the signatures by accessing the Role Certificate Database  82  and so on. 
   It should be clear that when the TAM  2  performs the database fetching and signature collection, this, besides being how the method works in practice, is simply a convenience for the requester  42 . If convenience and not trust is the overriding consideration to a user, then the TAM  2  need not be trusted by all parties. 
   As mentioned above, the main distinction between intra-enterprise and inter-enterprise authorization is that, in the former case, the company is less concerned about revealing its authorization structures  98  to the verifier  130 . In the inter-enterprise context, the authorization structure is the authorization tree  154  for a given task, and thus access to the database containing the collection of all authorization trees, should be restricted to users outside the company. 
   There are several ways to adapt the method  2  as already described to an inter-enterprise scenario. Returning to our original example of a transaction  40  between companies A and B, represented by users UA and UB respectively, the most direct approach would be for each company to have an enterprise authority EA, with a public key that can be used to verify signatures  106  produced by the EA on behalf of the company. The EA authorizes all inter-enterprise transactions by being the verifier  130  of all transactions originating in the company; if a transaction is authorized, then the EA signs a statement to this effect which can be verified by a user in another company. 
   Further, although the TAM  2  preferably operates within the distributed workflow management system  6 , the method may simply consist of a message exchange mechanism. In this embodiment, the message exchange mechanism that does not operate as a traditional workflow management system  6 , but instead, manages electronic message flow such as e-mail with attachments or HTML e-mail between the requester  42  and persons having certain roles within the company. The management of such a mechanism being realized through something as simple as PC-resident role-based programs (i.e., programs customized to suit the particular role of the user  8 ) using file-server type databases (analogous to databases  70 ,  96 ,  82  and  202  shown in  FIG. 11 ) and pull down menus and submenus organized so as to follow the relational structure of the databases. A typical menu item is, for example “transaction type”, which opens a submenu listing different types of transactions (such as “travel request”). Activating a particular transaction  40  can open another submenu showing the permission sets  100  required for such transaction. Activating a permission set  100  then opens up an e-mail having transaction details  66  in an attachment. The e-mail is pre-addressed to all those persons in the permission set  100 , making further distribution for signature and verification simple. 
   The embodiment using the hash of the authorization tree  154  described in  FIG. 15  has the advantage that the verifier  130  learns only a small amount of information about the decision structures of the user&#39;s company, except that a user in role UR can request a transaction  40 . On the other hand, the EA server becomes a potential bottleneck, as every inter-enterprise request must go to EA for verification and signature. An alternate solution is to make the authorization trees  154  available outside the company on the public Internet  31  for the purposes of verification by other companies. The main problem of course is that by revealing an AT  154  directly, much information about the decision process within a company is revealed. In the next section, several modifications to the method  2  that makes it more suitable for inter-enterprise authorization. 
   For example, instead of having to obtain direct approval of every transaction  40  from an enterprise authority (i.e., Transaction Administrator  80  for confirmation that the lower level employees had authority to authorize the transaction, the enterprise authority need only approve of an authorization structure  98 . Now, verification of authorization need not always go to through the enterprise authority—rather, the authorizations need only fulfill the requirements of the authorization structure  98 . 
   In another advantage, once the TA  80  has created transactions  40  and authorization structures  98 , and the RA  180  has created role certificates  76 , the system  20  becomes very reliable in that contracts created using the method  2  can easily and automatically be verified. 
   It should be understood that the method  2  functions with one-role permission sets  100 . However, an advantage of further reliability in the authorization result is obtained where more than one role  122  is specified in a permission set  100 . Further, a lower resource-intensive embodiment of the method  2  may be obtained by providing for the extraction and verification of a single, say, the first listed role certificate  76  in a permission set  100  comprised of several roles  122 . Defining the structure of a permission set  100  such that the role certificate  76  of the higher-level employee is listed first, improves the reliability of this embodiment. Nevertheless, such an embodiment is inherently less reliable as compared to an embodiment that extracts and verifies all of the role certificates  76 , as well as the role content of the permission set  100  itself (i.e., that the role certificates  76  on a transaction  40  do indeed correspond to the specific roles  122  required to authorize the transaction). 
   Multiple variations and modifications are possible in the embodiments of the invention described here. Although certain illustrative embodiments of the invention have been shown and described here, a wide range of modifications, changes, and substitutions is contemplated in the foregoing disclosure. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the foregoing description be construed broadly and understood as being given by way of illustration and example only, the spirit and scope of the invention being limited only by the appended claims.