Signature Data Object

The invention relates to a machine-readable data structure encoding security information for use in authenticating electronic documents (sometimes referred to herein as electronic business documents or "EBD") and to methods for using the data structure.

Systems for handling electronic documents within a computer system must address the problems of creation, routing, tracking, and approval of such documents in contexts such as a wide-area network (WAN) environment across multiple desktops (i.e., multiple workstations on a network). It is known for business applications utilizing online electronic business documents to permit the "signature" of a document through the affixation of a special code indicating, e.g., approval or disapproval of specific matters set out in the document. Additional background information concerning some techniques that can be useful in generating and validating such signatures, such as public/private key encryption and the use of certificates of authority, are discussed in commonly assigned and co-pending application Ser. No. 589,925, "Delegation to Session Key," filed Sep. 28, 1990, now U.S. Pat. No. 5,224,163 which is incorporated herein by reference for background purposes.

In accordance with the invention, a "signature data object" (SDO) is a machine-readable structured data record that is created by data acquisition techniques described below and associated with a document. Each SDO data record comprises three required encoded parts, each of which in turn includes its own encoded elements:

1. The Signature Header;

2. The Signature Data; and

3. The Signature Proof Block.

The SDO can encode the following:

That a specific individual ("signer")

acting within a specific role

on a given time and date

generated a signal encoding a unique mark

that was applied to the specific parent object

indicating approval/denial/or other specified judgment

qualified with/without a free text comment,

and optionally binding the future validation of the mark

to specific contents and/or attachments of the parent object

permitting the same or other users of the parent object

to perform subsequent tests

that the mark is authentic and remains valid by its own criteria

where ever in the network the parent object has been routed.

A signature data object can be appended to, and thus serve as a part of, an arbitrary data structure or other object such as a document stored in binary form, e.g., in disk storage. Alternatively, the SDO can include a pointer referring to an arbitrary "object" in a data repository of suitable form, e.g.,

The signature data object is analogous in function to that of a handwritten signature on a paper business document, although it has additional properties which make it more powerful than a traditional signature in a business environment. The SDO may also contain additional application-specific elements which could also be SIC encoded. These application extensions to the basic function of the signature provide further flexibility and evolvability of the SDO design.

The signature data object is an application-level construct that can be implemented on top of the various security mechanisms of different operating systems and networks and incorporated into usage by different application systems. An advantageous aspect of a signature data object is that a single parent object can have multiple SDOs applied to it with differing levels of semantic tags. For example, multiple SDOs might be applied by multiple versions of an evolving software application.

In use, the signature data object provides a framework for forward and backward compatibility of business function. The basic design of the SDO is independent of the underlying (and frequently changing) end user authentication technologies that may be in use within a given computer system. In particular, an advantageous aspect of the signature data object is that it is not bound to any specific level of security implementation or technology, but rather allows for a range of deployments based on differing technologies which provide different levels of security and authentication services.

FIG. 1 illustrates one way in which one or more signature data objects in accordance with the invention may be incorporated as part of an electronic document or other parent object;

FIG. 2 is a similar illustration of signature data objects that refer to a parent object.

FIG. 3 is a block diagram of a specification of required and optional parts of a signature data object in an exemplar embodiment of the invention.

Reference numerals in FIG. 3 correspond to numbered parts of the signature data object as described below.

As shown in FIGS. 1 through 3, a signature data object SDO is a structured record of data that is attached to, or references, some object such as a business document in the storage of a computer system. The object to which an SDO is applied is referred to as its "parent object."

The SDO is a formatted data record; character-string fields in the data may be encoded in a TAG-LENGTH-VALUE (TLV) format or other suitable abstract syntax notation. As is well known to those of ordinary skill, a data record encoded in Tag-Length-Value format can comprise an arbitrary number of fields of arbitrary length, each field comprising a tag to identify the field (e.g., "Last Name"); a length indicator (e.g., "20" to indicate a field length of 20 characters); and the value of the field (e.g., "Smith"). Depending on the implementation, the data record may also be encoded in other convenient formats such as a frame- or object-oriented structure.

In the discussion below, certain data are described as being obtained from the signer. It will be immediately recognized by those of ordinary skill having the benefit of this disclosure that a wide variety of data entry devices and approaches may be used, e.g., keyboard entry of alphanumeric characters; pen-based entry of characters or other symbols; selection from menus presented on a display screen; voice input; and the like. Data may be obtained on a real-time basis as needed, and/or obtained at a convenient time and stored for later retrieval as needed.

Other data are described as being obtained from the computer system, e.g., from the operating system. Those of ordinary skill having the benefit of this disclosure will recognize that nearly all modern operating systems have access to a considerable quantity of data about the computer system (e.g., hardware and software components in use) and about end users (e.g., data obtained at login about a user's identity, which then is commonly used to retrieve previously-stored data about user access privileges, preferences, and the like).

The Signature Header comprises SIC-encoded meta data describing the specific signature instance and its meaning in the context of the particular implementation, e.g., the business meaning of the signature instance. As shown in FIG. 3, in an illustrative implementation the required elements of the Signature Header are defined to be the following (although other required elements may be defined for other implementations):

1. a Signature Unique Identifier (SID) for the SDO that is unique over time and space within the universe of possible SDOs defined for the implementation in question, which may be generated in any convenient manner such as through a hash function of, e.g., the date, time, session identification, etc. In the illustrative implementation, the SID is a simple unsigned integer value that is generated to be unique within the parent document of which it is a part. The parent document has its own more globally-unique identifier. The unique identifier of the parent document in the illustrative implementation comprises three fields: An unsigned short field that holds the type code of the object (e.g., a type value of "template" or "object"); an unsigned-long value holding a pseudo-random number seeded with the time of application initialization; and an unsigned-long value holding the time stamp of creation of the document;

2. a date and time stamp of the creation of the SDO, which may be obtained in conventional fashion from the computer system clock or in any other convenient manner;

3. an identifier of the application software which created the SDO, which normally can be obtained from the operating system or alternatively may be obtained from the signer;

4. the major:minor version numbers of that application software, obtained in like manner;

5. a principal identifier of the signer, e.g., "John Quimby," which may be obtained, e.g., from the operating system or from the signer; and

6. a message code representative of a semantic value for the signature, e.g., "approval," "disapproval," or "abstention," or the like, which typically is obtained from the signer.

In the illustrative implementation, the Signature Header may also include the following optional elements:

7. user profile data of the individual applying the signature, e.g., an employee badge number and telephone number, which may be obtained from the operating system or from the signer;

8. a text string qualifying any role behavior of the signer, e.g., "signing as EBDS architect," which may be obtained, e.g., from the signer or from the operating system;

9. a principal identifier of an associated end user on whose behalf the signature was applied, e.g., the name of a superior who is on vacation, which may be obtained from the signer;

10. the identity of the submitting session if other than that of the signer, which may be obtained from the operating system;

11. an identifier of a security domain from which the SDO was created, which may be obtained from the operating system or from the signer;

12. a Signature Unique Identifier (SID) of another signature data object for the same parent object that is superseded by the SDO, which may be obtained from the operating system or the signer. The interpretation (including its appropriateness), of the supersede semantic will depend on the specific application and the business policy in effect. The SDO model itself does not constrain the signature policies supported; and

13. one or more comment strings or other application-specific data elements specified by the user or submitting session.

The Signature Data is an SIC-encoded group of data elements that describe the object to which the signature's validity is bound, along with any additional application-specific data contained within the SDO itself such as a "signature comment." In an illustrative implementation, the single required element of the Signature Data is one or both of the following:

14.1 a unique identifier of the parent object (for use when the SDO is a subordinate part of the parent object); and/or

14.2 a descriptor of the parent object, e.g., a full-path specification of an electronic-document parent object (for use when the SDO is maintained separately from the parent object).

In addition, optional elements of the Signature Data in the illustrative implementation may include:

15. a descriptor for each of one or more identified parts of the parent object and, for each descriptor, a value expression specification of the data elements. For example, an SDO may include a descriptor of a "total value" field of a purchase order document as well as a value specification that the total value is equal to $4,892.00. As another example, the SDO may have a descriptor for the "total value" field of the purchase order but may have a value specification that the total value is less than $5,000.00. A descriptor may point to a field within the parent document with a specific value, e.g., $4,892.00. Alternatively, a descriptor may point to a field and evaluate the value within a simple expression, e.g., "is the value of the field less than or equal to $5,000.00?". In the latter case the value of the expression is used;

16. One or more descriptors of subordinate parts or attachments of the parent object to whose contents or value the signature data object is bound. This "contents of" semantic allows for binding of an SDO to a specific revision of separate modifiable parts of the parent object;

17. One or more descriptors of subordinate parts or attachments of the parent object to whose presence (as opposed to contents or value) the signature data object is bound. This "presence of" semantic allows for part of the parent object to be revised and still fulfill the binding requirement, e.g., a justification memo attached to an expense voucher can be revised without affecting the validity of a signature data object that is bound to the expense voucher and that has a presence-of descriptor for the justification memo; and

18. One or more descriptors (encoded as SIDs) to other existing SDOs on this parent object to whose presence and validity this SDO is also bound.

The Signature Proof Block contains TLV-encoded elements which describe any security and validation methods used in the construction of the signature (e.g., major and minor version number again) and any data associated with the proof of validity (e.g., a certificate for the signature data object as a whole). In the illustrative implementation, the single required element of the Signature Proof Block is one of the following:

19.1 Signature target hash (the tag of this element indicates which hash technique was used). In the illustrative implementation, during signature validation a string is formed by concatenating all of the bound elements pointed to by descriptors in the signature data section of the SDO. This string is then reduced to a target hash using the hash technique specified. (e.g. Message Digest V4.0) The target hash can then be compared against the stored hash value in the signature proof block. If they are equal, then the signature is considered valid according to the data and proof block contents; or

19.2 A certificate of authentication of the SDO itself. Such a certificate provides a level of assurance that the signature has not been tampered with since it was applied by the application.

Optional elements of the Signature Proof Block in the illustrative implementation may include:

20. a date-and-time stamp denoting a timeout value for the signature, discussed in more detail below. To be valid, this must post date the date of signature creation;

21. a certificate of authentication of the principal signer;

22. an optional certificate of delegation from an associated user on whose behave the signer is constructing the signature.

Creation of a signature data object is straightforward and involves two stages: Data collection and writing of a structured data record to appropriate storage such as disk storage. Data collection may be accomplished in any manner convenient to the operating system and application(s) in use.

A principal use of the signature data object is validation. Once applied to a parent object, an SDO may be tested for validity multiple times during the life of the parent object. The validation does not alter the SDO, and may be performed either at an end user's specific request through an application user interface or by the application itself as a result of some triggering event. An advantage of the SDO design is that individual SDO's can bind to specific contents of the parent object which may change over time, invalidating the SDO.

SDO Validation Based on Form: A first level of validation is whether the SDO is well formed, i.e., whether it includes all required parts (such as the three required parts of the illustrative implementation). If all of the required parts are not present, the signature is determined to be invalid due to bad form.

SDO Validation Based on Timeout: A second level of validation is derived by examining the optional timeout value of the signature in the signature proof block. If the timeout is specified and its value predates the current time, the signature is determined to be invalid due to timeout.

SDO Validation Based on Data and Proof Block Contents: A subsequent validation process may be driven by the contents of the Signature Data and Signature Proof Block elements. A signature is considered valid if it meets all the criteria established by these elements. For example, all elements within the Signature Proof Block, including any optional elements and application-specific elements, must be valid in order for the SDO as a whole to be valid. This allows varying implementations to provide more sophisticated levels of validation on an incremental basis according to changing needs.

The model does not constrain the meaning that an application may place on upon discovery of one or more invalidated SDO's on a parent object. For some applications this may be a perfectly normal, everyday occurrence, whereas for some other applications the discovery may indicate that the parent object or the SDO itself has been maliciously violated. Further, an application might not make the determination, but the policy of usage of an application might specify a judgment on the presence of invalid signatures. In any case, the SDO provides a convenient means for making a determination of validity.

In some implementations a signature in an electronic document will contain at a minimum the three basic elements described above, namely the Signature Header, Signature Data, and Signature Proof Block. Additional application-specific elements (or parts within these elements) may be added as long as the additional elements are well-behaved, i.e., as long as they do not invalidate the meaning of existing elements or invalidate signatures already on parent objects. An additional element that satisfies the following constraints should be well-behaved:

1. The additional element does not alter the functional behavior of a previously defined element;

2. The additional element does not invalidate the usage of a previously defined element; and

3. The additional element does not presume consistency of element types across multiple signatures on the same parent object.

In the interest of clarity, not all features of an actual implementation are described. It will of course be appreciated that in the development of any such actual implementation (as in any software development project), numerous programming decisions must be made to achieve the developers' specific goals and subgoals (e.g., compliance with system- and business-related constraints), which will vary from one implementation to another. Moreover, attention will necessarily be paid to, e.g., proper serialization to handle concurrent events, boundary detection, error trapping and -handling, and the like. It will be appreciated that such a development effort would be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill having the benefit of this disclosure.