Abstract:
A method and system for transmission of digital content via e-mail with point of use digital rights management is disclosed. The secured access rights to the digital content may be customized for individual recipients by the sender, and may evolve over time. The access rights are enforced according to a time-dependent scheme. A key server is used to arbitrate session keys for the encrypted content, eliminating the requirement to exchange public keys prior to transmission of the digital content. During the entire process of transmitting and receiving e-mail messages and documents, the exchange of cryptographic keys remains totally transparent to the users of the system. Additionally, electronic documents may be digitally signed with authentication of the signature.

Description:
This patent application is a continuation of U.S. patent application Ser. No. 14/162,979 filed on Jan. 24, 2014. U.S. patent application Ser. No. 14/162,979 is a continuation of U.S. patent application Ser. No. 13/538,637 filed on Jun. 29, 2012. U.S. patent application Ser. No. 13/538,637 is a continuation of U.S. patent application Ser. No. 11/237,564 filed on Sep. 28, 2005. U.S. patent application Ser. Nos. 14/162,979, 13/538,637 and 11/237,564 are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates in general to securing transmitted electronic documents and, more particularly, to enforcing a rights management policy on transmitted electronic documents. 
     BACKGROUND INFORMATION 
     Security of transmitted electronic documents has been the subject of great attention in the data processing industry. The misuse or misappropriation of confidential information is a serious threat to electronic commerce. Even the perceived risk of insufficient integrity will render a data processing method unworthy for commercial use. System administrators and service providers have been responsible for creating policies and implementing procedures for ensuring the security of files transferred over a network. The majority of security measures has been focused on controlling access to infrastructure, such as a network domain or a storage media. For example, securing documents sent by e-mail was primarily accomplished by restricting access to a given e-mail account. Another common method is to compress or encrypt documents sent via e-mail. However, due to the unsecured nature of e-mail, many forms of business and transactions are still not conducted using e-mail messages and documents. Also, these kinds of policies do not have any effect on a user or a file after the document has been received via e-mail and made available for further processing. 
     Therefore, newer security architectures have emphasized providing security in the user environment at the application level, when the document is manipulated by the receiving party. Typically, point of use security methods require global coverage of an IT system with the corresponding installation of central tools and distributed agents. This kind of additional digital rights management infrastructure added to an IT system requires a large initial investment and significant administration effort over time. A centralized system can also be very inflexible and may not meet the specific needs of individual stakeholders. For example, if the system architecture requires that every document be registered with the authenticating server, then the system must rely upon the authenticating server for rights management policies. Such an architecture is inherently limited to securing participants within the domain, which inherently limits the scope of the security provided. Thus, there is a need for a simplified, decentralized method for securing e-mail messages and documents at their point of use, that can be universally used by any recipient of an e-mail message. 
     A common problem of practicality when transmitting encrypted content is that the sender and recipient are required to exchange keys in advance of the actual transmission. If a sender wants to send an encrypted document securely to a recipient, prior art methods have required that the sender possess the public key of the recipient before the encrypted content is transmitted. 
     Another aspect of digital rights management that has yet to be addressed is the time-dependent nature of many usage rights policies. When the digital rights to a document that already has been transmitted need to be changed, prior art systems have not offered simple, transparent solutions. For example, a frequent requirement in business communications is the widespread distribution of documents in advance of a specific date when such documents may be accessed by a large number of recipients. There has been no solution available that provides a robust, integrated, and automated solution to this common scenario. 
     Therefore, there is a need for a simple, flexible digital rights management system for transmitting documents and messages via e-mail, such that users may freely exchange encrypted data. The system should be decentralized and enable flexible management of digital rights over time, without requiring a global IT installation and additional administration. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the foregoing needs by providing a solution with point of use digital rights management for transmission of files via e-mail. The present invention utilizes a cryptocontainer, having a unique structure and properties, for packaging digital content upon transmission via e-mail. The digital content may comprise electronic documents and data files, or any other type of digital media content. The sender of the secured documents configures the cryptocontainer using an authoring tool for generating and distributing cryptocontainers, whereby the authoring tool applies a public key belonging to a key server. The authoring tool provides for assigning specific access rights to individual documents that may very over time. The access rights may be customized for individual recipients of the cryptocontainer. Only after validated authorization and decryption may the e-mail recipient of the cryptocontainer be granted their access rights to specific content in the cryptocontainer. 
     The present invention additionally solves the problem of a sender wanting to send an encrypted document securely to a recipient, whose public key the sendor does not possess. The present invention employs a key server to deciper a session key for the encrypted content. Instead of encrypting the session key for the recipient, the session key is encrypted for the key server. The key server authenticates the recipient independently (from an authenticating entity) and releases the session key to the recipient only after the recipient&#39;s authentication certificate is obtained. 
     The access rights are enforced according to the time-dependent scheme defined in the authoring tool of the cryptocontainer for that specific user. During the entire process of transmitting and receiving e-mail messages and documents, the exchange of cryptographic keys remains totally transparent to the users of the system. There is no requirement that senders and recipients manually exchange keys. The present invention provides additional security in that the transmitted content of a cryptocontainer is only decrypted in a second decryption step, only after an initial decryption has provided authentication of the recipient&#39;s identity. Otherwise, the transmitted content is not decrypted. Senders of e-mail may be so assured that the digital content transmitted may only be received by an authorized user and may only be further processed subject to the conditions of use as designated by the sender. 
     Additionally, the present invention provides for digitally signing electronic documents with authentication of the signature. The electronic signature in the present invention relies upon and is compliant with 15 U.S.C. §7001, ELECTRONIC RECORDS AND SIGNATURES IN COMMERCE, General Rule of Validity, of which subsection (a) recites:
         15 U.S.C. §7001. General rule of validity   In general   Notwithstanding any statute, regulation, or other rule of law (other than this subchapter and subchapter II of this chapter), with respect to any transaction in or affecting interstate or foreign commerce—   a signature, contract, or other record relating to such transaction may not be denied legal effect, validity, or enforceability solely because it is in electronic form; and   a contract relating to such transaction may not be denied legal effect, validity, or enforceability solely because an electronic signature or electronic record was used in its formation.
 
The intent of each signature may be further specified by the signing individual with a text entry accompanying the signature.
       

     In one example of the present invention, a marketing department may use the usage rights timeline to make an upcoming brochure unavailable until a given date. On the given date only the recipients in the user groups “Internal Sales” and “Management” can have rights to view and print the brochure. A week after “External Sales” is given rights to view and distribute the brochure in “view only” form. Two-weeks later on the pre-determined release date the brochure can be freely distributed and printed by its recipients. 
     In another example of the present invention, a financial service sends an e-mail listing the latest quarterly earning reports of “ACME Company” to its distribution list 24-hours before its public release. The service company utilizes the usage rights timeline to ensure that the information is disclosed to all of its recipients at the same time. Employees of the financial service are given permission to only view, but not distribute, the information some hours before its public disclosure. At the given pubic release time, the employees will be able to freely distribute the “ACME Company” earnings report to members of the public. 
     Thus an object of the present invention is to enable the widespread and transparent use of e-mail documents and messages for highly secure applications. 
     Another object of the present invention is to provide for decryption of content in a second step following an initial authentication of recipient on receipt of an e-mail message, and to deny decryption of content in case the recipient cannot be authenticated. 
     Another object of the present invention is to provide a secure mechanism for digital rights management of documents transmitted over a network using a transactional authentication methodology for enforcement of usage rights policies, such that access to a server is only required for initiating access granted to secured documents. 
     An object of the present invention is to provide a mechanism whereby senders of secured e-mail messages may rely upon an e-mail address for identifying an authenticated recipient, without the requirement of contacting the recipient or exchanging keys with the recipient in advance of sending an e-mail message. 
     An additional object of the present invention is to provide a means for displaying the security rating of an e-mail client over a given time period. 
     Another object of the present invention is to provide a means for assigning usage permissions to individuals and user groups of selected individuals. 
     A further object of the present invention is to provide time-dependent digital rights for digital content transmitted via e-mail, such that the user-specific rights may change or evolve as a function of elapsed time. 
     A further object of the present invention is to provide time-dependent digital rights for digital content transmitted via e-mail, such that the user-specific rights may be modified in response to actions by the user of the digital content or by third-parties. 
     Another object of the present invention is to provide a mechanism for digitally authenticating an electronic signature transmitted via e-mail. The electronic signature may be augmented with a text line where the signer may specify the intent of the signature. 
     An additional object of the present invention is to provide for the migration and back-up of encrypted data and encryption tools to another physical hardware platform. 
     Another object of the present invention is to prohibit the circumvention of restricted processing rights for digital content by using a hardware overlay technique for rendering the digital content visible on a display device. 
     A further object of the present invention is to provide an audit trail of all documents sent and received using a secured e-mail transmission system. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a flow chart of an encryption process in an embodiment of the present invention; 
         FIG. 2  is a flow chart of a decryption process in an embodiment of the present invention; 
         FIG. 3  is a display of a security rating of an e-mail client in an embodiment of the present invention; 
         FIG. 4  illustrates a graphical user interface element for defining usage rights in an embodiment of the present invention; 
         FIGS. 5 and 5A  illustrate graphical user interfaces for electronic signatures in an embodiment of the present invention; 
         FIGS. 6-12  illustrate a graphical user interface in an embodiment of the present invention; 
         FIG. 13  illustrates network components in one embodiment of the present invention; and 
         FIGS. 14A-F  illustrate a graphical user interface in an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth such as specific word or byte lengths, etc. to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details concerning timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art. 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
     The present invention provides a solution with point of use digital rights management for transmission of files via e-mail. The present invention utilizes a cryptocontainer, having a unique structure and properties, for packaging digital content upon transmission via e-mail. The digital content may comprise electronic documents and data files, or any other type of digital media. Any reference herein to electronic documents, documents, files, messages, data, media, and other content may be used interchangeably and refers universally to digital content which may be transmitted over a network or stored in a memory or storage device. The sender of the secured documents configures the cryptocontainer using an authoring tool for generating and distributing cryptocontainers, whereby the authoring tool applies a public key belonging to an key server. The authoring tool provides for assigning specific access rights, which may vary over time, to individual documents. The access rights may be customized for individual recipients of the cryptocontainer. Only after validated authorization and decryption may the e-mail recipient be granted access rights to specific content in the cryptocontainer. 
     In  FIG. 13 , network components in one embodiment of the present invention are illustrated. A sending platform  320  runs the authoring tool and is operated by the author. The author creates a cryptocontainer, symbolized by  325 , and sends it via e-mail to the recipient operating the receiving platform  321 , which runs the viewing tool. A server  330  may provide services to the sending platform  320  or to the receiving platform  321 . The server  330  may represent a public web server that both platforms  320 ,  321  may connect to via the Internet. In one embodiment, the server  330  is a public web server for accessing the authoring tool or the viewing tool as web services. The server  330  may rely upon an key server  340  to perform the operations of the present invention. In one embodiment, the server  330  and key server  340  represent network services that are executed on a single physical platform, such that servers  330  and key server  340  are combined into a single entity. The key server  340  may rely upon an authenticating server  350  for authenticating e-mail addresses of authors and recipients of cryptocontainers  325 . The authentication server  350  may be operated by a third-party as a public commercial service for authenticating users via e-mail addresses for clients. 
     Referring to  FIG. 1 , a process  115 ,  120  for sending encrypted content according to an embodiment of the present invention is illustrated in flow chart form, from begin  101  to end  150 . An initial configuration process  115  must be performed before the authoring and sending process  120  may be executed, if not previously carried out, according to a determination  110 . In one example of practicing the present invention, the entire procedure of  115  may be omitted after one instance of installation  115  has been performed. In another example, the determination if the authoring tool is installed  110  may result in either steps  111  and  122 , singly or in combination, being executed for the purpose of updating a prior installation or recertifying a prior authentication. 
     The installation of the authoring tool  111  comprises all actions required for obtaining an installable, licensed version of the authoring tool, for performing an installation, and for configuring an authoring tool for use on a given sending platform  320 . The installation step  111  may also include steps for verifying the network connection of the sending platform  320 , comprising configuration of hardware and software components, such that an e-mail service is made bi-directionally operational on the sending platform. Additionally, step  111  may also encompass communicating with an key server  340  for obtaining or validating the key server&#39;s public key, which is used by the authoring tool on the sending platform  320 . In one example, installation  111  of the authoring tool is performed by installing the authoring tool as an application to be executed on the sending platform  320 . In another example, installation  111  of the authoring tool is performed by activating a license to use the authoring tool as web service to be executed on an Internet server  330 . 
     The author is an individual who operates the authoring tool on the sending platform  320  for creating, modifying, and distributing cryptocontainers  325 , containing electronic documents and digital data. The author is also the individual who assigns the usage rights  128  for each document in the cryptocontainer  325 . The author is therefore the author and also the sender of the cryptocontainer  325 , however, no assumption is made herein as to the authoring of the actual digital content transmitted in the cryptocontainer  325  in various embodiments of the present invention. 
     The step of authenticating an author  122  may be performed by the key server  340  on the basis of the author&#39;s e-mail address from an authenticating server  350 . The key server  340  creates a user license for the author, signs the author&#39;s license and public key with the key server&#39;s private key, and stores this as a hash value for authenticating messages from the author (step  122 ). In one embodiment of the present invention, the authoring tool may be installed for use by the author on a sending platform  320 , such as a computer system, such that the authentication of the author  122  involves sending a hardware fingerprint, which identifies the sending platform, to the key server  340  for authentication by an authenticating server  350 . The hardware fingerprint may comprise the following information unique to the computer on which the authoring tool is installed: BIOS version number, video card BIOS creation date, primary HDD serial number, MAC address of a network adapter. In another example, the hardware fingerprint may comprise a unique identifier of the CPU, main system board, or other component of the sending platform computer  320 . 
     In another embodiment of the present invention, the authoring tool may be installed on server  330  and used as a web service in an Internet browser, such that the authentication of the author  122  relies upon a unique biometric identification of the author that is sent to the key server  340  for authentication by an authentication server  350 . In one example a biometric USB device installed on a public computer system may be used by the author for generating the unique biometric identification. The biometric identification is used by the key server  340  to obtain the author&#39;s license from the authenticating server  350  in the same manner as the hardware fingerprint. In another example of practicing the present invention, the authoring tool is integrated as an additional feature in a standard e-mail client program. 
     After the installation steps  115  have been completed at least once without error, the process in  120  may be repeated as required to send a plurality of secured e-mail messages containing cryptocontainers  325 . According to another embodiment of the present invention, installation of the authoring tool  111  may also comprise the transferring (or migration) of an existing installation of a working version of the authoring tool from a previous sending platform to the current sending platform  320 . The transferring (or migration) may include all existing data and archived documents along with the necessary re-validation and re-authentication (as in  122 ) on the current sending platform  320 . 
     The sending process is illustrated by the process steps  120  in  FIG. 1 . Upon authentication  122  by an authenticating server  350 , the author is granted full access to the authoring tool on the sending platform  320  by the key server  340 . One first step may be entry of the recipient list  124 . Individual recipients may be assigned membership to one or more user groups  610 ,  613  (see  FIG. 6 ), which may be used for managing usage rights for each document in the cryptocontainer  325 . After entry of the recipient list, the author may add the digital content to the cryptocontainer  325  by selecting the required files  125 . In  127  the author may also optionally choose to electronically sign certain documents (see  FIGS. 5 and 12 ). The authoring tool generates a symmetric session key  126  for each cryptocontainer  325 . In the recipient list section of the cryptocontainer  325 , a session key and a list of recipients&#39; e-mail addresses is recorded. This entire section of the cryptocontainer  325  is encrypted not for the recipients but for the key server  340 . The key server&#39;s public key is used to encrypt the recipient list section using asymmetric encryption. In alternative embodiments of the sending process  120 , the order of the steps  124 - 127  may be rearranged to accommodate a flexible workflow. The order of the steps  124 - 127  is generally not constrained by the authoring tool. 
     For each document and recipient, a usage rights timeline may be defined by the author in step  128 . The usage rights timeline gives an author the ability to set usage permissions on digital content (digital rights management controls, see  FIG. 4 ) which evolve in accordance with time or specific actions. In its simplest form, the usage rights timeline can be used to deny access to files on a specific time and date. In its full use, the usage rights timeline can be used to quickly set complex usage permission structures that change with time. Using the usage rights timeline, authors can create keyframes  1110  (see  FIG. 11 ), which are sets of predefined rights states that exist for a specified period of time. Different usage permissions can be applied to each keyframe  1110 , enabling usage states to evolve in a pre-determined fashion. The usage rights timeline is enforced by the viewing tool, installed in process  220  (see  FIG. 2 ). 
     After the author determines the recipients, content, and usage rights for the cryptocontainer  325 , encryption  130  is performed by the authoring tool. During encryption  130  of the cryptocontainer  325 , the recipient list section and the content payload are encrypted separately with different session keys. The session keys are encrypted with the public key of a the key server  340 . In one embodiment of the current invention, the key server  340  is maintained by a service provider who also provides the license for the authoring tool on the sending platform  320 , and public access rights to the key server  340  are restricted to license holders of the authoring tool. In another embodiment, the viewing tool is distributed freely to the public, including access rights to the key server  340  for viewing documents sent in cryptocontainers  325  according to their assigned usage rights. 
     In one embodiment of the present invention, each individual operation performed on a cryptocontainer  325 , such as obtaining a session license from an authorizing server or adding a document for viewing or printing encrypted in the cryptocontainer  325 , is recorded in a log which may serve as an audit trail  131  for reconstructing events that occurred involving the cryptocontainer  325 . The audit trail  131  may also include each time that usage rights keyframes  1110  were defined and the files and recipients to which those keyframes  1110  were assigned. 
     The final step in the sending process  120  is transmitting the cryptocontainer  325  via e-mail  132 . The cryptocontainer  325  may be sent  132  with an standard e-mail client program from the sender to each recipient on the recipient list. In one embodiment of the present invention, the authentication process requires the author to use the computer that has been certified from the key server  340  for the author&#39;s sending e-mail address. In another example, a biometric identification has been performed to authenticate the sender, which in turn, permits the sender to work on any suitable public sending platform  320 . In one case, the sender may use a unique biometric identification with a web service version of the authoring tool on the sending platform  320 . The transmission of the cryptocontainer from the sending platform  320  may be performed with any wired or wireless network connection that supports e-mail transmission. In one example, the sending platform is a handheld wireless device that provides a suitable e-mail client service. In another example, the cryptocontainer may be sent to an intermediary, from where the cryptocontainer is further distributed to the recipients on the recipient list. 
     Referring to  FIG. 2 , a process  220  for receiving encrypted content according to an embodiment of the present invention is illustrated in flow chart form, from begin  201  to end  250 . An initial configuration process  215  must be performed before the receiving process  220  may be executed, if not previously carried out, according to a determination  210 . In one example of practicing the present invention, the entire procedure of  215  may be omitted after one instance of installation  215  has been performed. In another example, the determination if the viewing tool is installed  210  may result in either steps  211  and  222 , singly or in combination, being executed for the purpose of updating a prior installation or recertifying a prior authentication. 
     The installation of the viewing tool  211  comprises all actions required for obtaining an installable, licensed version of the viewing tool, for performing the installation, and for configuring the viewing tool for use on a given receiving platform  321 . The installation step  211  may also include steps for verifying the network connection of the receiving platform  321 , comprising configuration of hardware and software components, such that an e-mail service is made bi-directionally operational on the receiving platform. In one example, installation  211  of the viewing tool is performed by installing the viewing tool as an application to be executed on the receiving platform  321 . In another example, installation  211  of the viewing tool is performed by activating a license to use the viewing tool as service executed on web server  330  in a web browser, whereby the web browser is used to access a web e-mail client. Next, authentication of the recipient  222  is performed by the key server  340  using an authentication server  350 . 
     In one embodiment of the present invention, the viewing tool is installed for use by the recipient on a receiving platform  321 , such as a computer system, such that the authentication of the recipient  222  involves sending a hardware fingerprint, which identifies the sending platform  321 , to the key server  340  for authentication by an authenticating server  350 . Step  222  may encompass communicating with an key server  340  for validating the recipient&#39;s identity and transmitting a passport certificate, obtained from an authenticating server  350 , identifying the recipient&#39;s computer (with a hardware fingerprint) and registering the recipient&#39;s computer passport and e-mail address. 
     In another embodiment of the present invention, the viewing tool may be installed on the web server  330  and used as a web service in an Internet browser, such that the authentication of the recipient  222  relies upon a unique biometric identification that is sent to the key server  340  for authentication by an authenticating server  350 . In one example, the recipient may use a web mail service to access a primary e-mail account held by the recipient, whereby a biometric USB device is installed on a public computer system used by the recipient for generating the biometric identification. The unique biometric identification is used by the authenticating server  350  to generate the recipient&#39;s license in the same manner as the hardware fingerprint. In another example of practicing the present invention, the viewing tool is integrated as an additional feature in a standard e-mail client program. 
     In one example of the present invention, after the installation  215  has been completed once without error, the process in  220  may be repeated as required to receive a plurality of secured e-mail messages on the receiving platform  321 . According to another embodiment of the present invention, installation of the viewing tool  211  may also comprise the transferring (or migration) of an existing installation of a working version of the viewing tool from a previous receiving platform to a current receiving platform  321 . The transferring (or migration) may include all existing data and archived documents and be accompanied with a required re-validation and re-authentication (as in  222 ) on the current receiving platform  321 . 
     In  FIG. 2 , the core receiving process is illustrated by the process steps  220 . The entire receiving process in  FIG. 2  is triggered by receipt of the cryptocontainer  325  via e-mail  205  by the recipient. Note that the recipient is not required to be in possession of any public keys. If the recipient is not authenticated and no viewing tool is installed, the installation process  215  will automatically be triggered upon accessing the cryptocontainer  325 . This process requires only a standard e-mail client. If the recipient is authenticated and a viewing tool is installed, process  220  may be initiated. 
     The authentication step  222  may be precluded to some extent when a recipient already possesses a valid public key. This preauthentication begins when the viewing tool sends a certificate that authenticates the recipient to the key server  340  from the sending platform  321 . In one case, an acceptable certificate is signed by an authentication server  350  and contains the recipient&#39;s e-mail address. This is taken as valid proof by the key server  340 , that at some point in the past, the process has taken place by which the recipient had obtained that certificate and there is confidence that it could only have been obtained from a known authentication server  350 . If the key server  340  receives a certificate for a recipient containing a public key and an e-mail address that is signed by a known authenticating server  340 , then the recipient&#39;s identity is considered authentic. The recipient is preauthenticated by issuing the certificate. When the recipient actually contacts the key server  340  for a session key, reauthenticate is not required. 
     As a first step in process  220 , a decryption of the recipient list  224  is performed. Step  224  begins with the author&#39;s public key, signed by the server&#39;s private key, being sent to the key server  340  by the viewing tool from the receiving platform  321 . Then the encrypted recipient list and session keys are sent to the key server  340  by the viewing tool from the receiving platform  321 . The recipient list is decrypted  224  by the key server  340 . Next, the key server  340  compares  226  the recipient&#39;s identity with the recipient list of the cryptocontainer  325 . If there is no match, then the recipient is denied access  230  to the cryptocontainer  325  by the key server  340  and no further action may be taken by the recipient on the cryptocontainer  325 . The denial of access  230  is enforced by the viewing tool on the receiving platform  321 . In this case  230 , no session key is issued to the recipient by the key server  340  for the cryptocontainer  325 . If the recipient does match the recipient list, then the key server  340  will issue  228  a session license for the recipient to open the contents of the cryptocontainer  325  on the receiving platform  321 . In step  228 , the key server  340  re-encrypts the session keys with the recipient&#39;s public key and sends the re-encrypted session keys back to the recipient&#39;s viewing tool on the receiving platform  321 . The recipient&#39;s viewing tool receives the re-encrypted session keys and the decrypts them only when they are required to access a particular file in the cryptocontainer  325 . The recipient may now decrypt and access  232  the content in the cryptocontainer  325  on the receiving platform  321 . However, a recipient&#39;s access to individual documents may further be restricted by a usage rights timeline that is used to enforce  234  the policies in individual keyframes applicable to the recipient. If the content is closed by the recipient, the steps in process  220  may be repeated for each access to the cryptocontainer  325  on the receiving platform  321 . 
     The usage rights timeline is enforced  234  by the viewing tool, installed in process  211 . When the recipient opens a cryptocontainer  325 , the viewing tool checks the time from a local time source or from a secured Internet time server. The viewing tool then enforces the rights schema  234  as designated by the content author using the usage rights timeline for the current time. As long as the viewing tool is active, it periodically checks the time and enforces the usage rights  234  for the given time. In one example, a secured time server is the primary time source and a secondary, local time source is used only when the primary time source is unavailable, thereby ensuring enforcements of rights schema  234 , regardless if a network connection is maintained or not by the receiving platform  321 . 
     One particularly unique aspect of the enforcement  234  of usage rights in process  220  is the use of a hardware-overlay technique for displaying secured documents. The viewing tool may use hardware overlay to render files directly from video hardware rather than by using software rendering. The advantage of this approach is that it helps to defeat many popular screen-capture products in a relatively simple fashion. In one embodiment of the present invention, during enforcement of usage rights  234 , each individual operation performed on a cryptocontainer  325 , such as obtaining a session license from an authorizing server or opening a document for viewing or printing encrypted in the cryptocontainer  325 , is recorded in a log which may serve as an audit trail  235  for reconstructing events that occurred involving the cryptocontainer  325 . The audit trail  235  may also include each time the content was accessed and each time access to the cryptocontainer  325  was denied  230  or each time usage rights were restricted  234 . 
     Of particular significance is the transactional nature of the involvement of the authentication server  350  and the key server  340  in processes  120  and  220 . The transactional authentication methodology, as described in the embodiments of the present invention illustrated in  FIGS. 1 and 2 , limits the involvement of the authentication server  350  and the key server  340  to a minimum, which, in turn, serves to make the entire system very flexible and efficient. In the sending process  120 , there is no requirement for the key server  340  to participate once an author has been authenticated by an authentication server  350  in  122 . The receiving process  220  requires active participation from the key server  340  only for discrete steps  224 ,  226 , and  228  upon receipt of the cryptocontainer  325 , once a recipient has been authenticated by an authentication server  350  in  222 . Of particular importance in certain embodiments of the present invention is that the enforcement of usage rights timeline policies is performed by the viewing tool on the receiving platform  321 , and does not require any involvement by the key server  340 . This unique feature of the present invention enables widespread distribution and use of secured digital rights management for e-mail documents by providing a practical and efficient architecture. 
     Referring now to  FIG. 3 , a display  300  of the security rating of an e-mail client is shown. The display  300  shows the values of the total number of e-mail messages sent as well as the number of those that were secured items. The values may be reset after a time period has elapsed. The display  300  also shows a ratio of the secured items sent. In one example, the percentage of secured items sent is used to calculate a security rating. 
     In  FIG. 4 , a graphical user interface element  400  is illustrated for defining usage rights in an embodiment of the present invention. The interface panel permits the definition of usage rights for specific files. Usage rights are presented in one example of a graphical user interface in a spreadsheet format  410  with files  411  on the left side and the usage rights  412  related to a specific data element  413  selected on the top. Tabs are used to toggle between the different data elements  413 : Files, Folders, User Groups, Signature Lines and Containers. The exemplary user interface  400  is shown with the tab data element  413  (Files  411 ) selected. To allow a particular usage right  412 , a check is entered in the associated box. The interface  400  provides the ability to assign a wide variety of usage rights  412  to files, folders, user groups, signature lines and the cryptocontainer  325  itself. In one example, the usage rights for files comprise: viewing, printing, export, delete, item visible, show thumbnail, rename, move. In one example, the usage rights for folders comprise: folder visible, delete, export, rename, file visible, move, open. In one example, the usage rights for folders comprise: folder visible, delete, export, rename, file visible, move, open. 
     In  FIG. 5 , a graphical user interface  500  is illustrated for electronic signatures in an embodiment of the present invention. The electronic signature for a given document  511  may include an additional qualifier for the signature as a text field  510 . In one example the purpose of the signature may be entered in this text field. In another example, the signer may choose from a predefined list of signature qualifiers. The electronic signature in the present invention relies upon and is compliant with 15 U.S.C. §7001. In  FIG. 5A , a confirmation panel  550  is illustrated of a valid electronic signature. The purpose and terms of the signature  552  are shown along with the e-mail address of the signee  551 , and the document  511  for which the signature is valid. 
       FIG. 6  illustrates a graphical user interface  600  of an authoring tool in a default state in an embodiment of the present invention. The authoring tool is used to construct and distribute a cryptocontainer  325 . At the top, the authenticated e-mail address  614  of the author is shown. This is the sending e-mail address of the cryptocontainer  325 . The panel  600  is the basic screen where all common tasks are performed in the authoring tool. To the left panels User Groups  610 ,  613 , Files  611 , and Signatures  612  can be added. The Files panel  611  displays the files to be protected and in panel  611  each file is identified by a filename and a filepath or network location path to that filename, such that the aggregate filepath identifying the file is unique and valid. The Signatures panel  612  displays any electronic signatures that have been performed on specific files in  611  by the author. The main workspace is defined by tabs which indicate the currently selected User Group  610 ,  613 . In the default state, only Authors and Recipients are defined as User Groups  610 ,  613 . Within a single user group, for example as shown in  600 , Recipients, the list of authorized recipients within the selected User Group may be listed in the Group Members  615  panel. The permissions panel  616  corresponds to the usage rights user interface  400  in  FIG. 4 . Below, the Rights Timeline panel  617  indicates the time span to which the selected permissions apply. Each element in panel  617  is a keyframe in the usage rights timeline. 
       FIG. 7  illustrates a graphical user interface  700  of an authoring tool during entry of files  710  to a cryptocontainer  325  in an embodiment of the present invention. Files  710  may be added to Files panel  611  using the Import File or Import Folder button, or by dragging and dropping over panel  611 . When the author saves the cryptocontainer, the files will be securely encrypted inside a cryptocontainer  325 . The permissions panel  616  displays each individual file  710  as a separate line item  711 . The permissions panel  616  corresponds to the usage rights user interface  400  in  FIG. 4 . 
       FIG. 8  illustrates a graphical user interface  800  of an authoring tool during entry of recipients  810  to a cryptocontainer  325  in an embodiment of the present invention. The list of recipient e-mail addresses  810  may be entered in the group members panel  615 . This ensures that the files  710 ,  711  will be seen only by recipients  810  that are approved by the author. 
       FIG. 9  illustrates a graphical user interface  900  of an authoring tool during entry of user groups  613  to a cryptocontainer  325  in an embodiment of the present invention. Recipients  810  can be categorized into groups  613 , which are created in the, User Groups panel  610 . Sorting recipients  810  into user groups  613  enables advanced control of usage rights  412  for each group  613 . 
       FIG. 10  illustrates a graphical user interface  1000  of an authoring tool during assignment of user rights  412  for user groups  613  in a cryptocontainer  325  in an embodiment of the present invention. After sorting recipients  810  into user groups  613 , each user group  613  can be assigned different user rights  412  to individual files  710 ,  711 . This permits cryptocontainer  325  files to be sent to multiple recipients  810  who have different usage rights  412 . 
       FIG. 11  illustrates a graphical user interface  1100  of an authoring tool during assignment of user rights  412  over time in a cryptocontainer  325  in an embodiment of the present invention. For files  710  that are time sensitive, individual keyframes  1110  in the Rights Timeline panel  617  define the exact days, hours, and seconds that files  710  may be accessed. The Rights Timeline panel  617  indicates the time span to which the selected usage rights  412  apply. Each element in panel  617  is a keyframe  1100  in the usage rights timeline. 
       FIG. 12  illustrates a graphical user interface  1200  of an authoring tool performing an electronic signature  511  in a cryptocontainer  325  in an embodiment of the present invention. The signature panel  500  enables the author to electronically sign  511  individual files  710  in the cryptocontainer  325 . The electronic signature in the present invention relies upon and is compliant with 15 U.S.C. §7001. 
     In another embodiment of the present invention, the functionality of the authoring tool may be adapted for a quick method for creating a cryptocontainer from within a host application. As illustrated in  FIGS. 14A and 14B , an adapted version of the authoring tool is accessible via a user interface toolbar  1402 . This toolbar automates the inclusion all of cryptocontainer data elements that are required for configuring the cryptocontainer to be accessible by authorized recipients. The cryptocontainer data elements from the toolbar comprise: email addresses of the intended recipients  1405 , data files  1407 , usage permissions  1411  and timeline settings  1412 . 
     In  FIG. 14A , one embodiment of the toolbar interface  1402  is shown as an add-in feature  1400  to a commercially available host e-mail client program (Outlook® by Microsoft Corp., Redmond, Wash.). The recipient list  1405  and data files  1407  are entered directly in the host application and are copied automatically by the toolbar interface  1402 . A rights template  1411  may be selected along with the timeline settings  1412  for the selected rights. The process of creating and sending the cryptocontainer is executed by a single user command button  1410 . 
     In  FIG. 14B , an embodiment of the toolbar interface  1402  is shown as an add-in feature  1401  to a commercially available host document processing program (Word by Microsoft Corp., Redmond, Wash.). In this example, the toolbar interface  1402  assumes that the document  1415  being processed by the host application comprises the digital content to be sent. A rights template  1411  may be selected along with the timeline settings  1412  for the selected rights. The process of creating and sending the cryptocontainer is triggered by the user command button  1410 . The recipient list may be entered into a dialog panel. 
     In  FIG. 14C , a simplified timeline entry dialog  1403  is illustrated. The timeline  1412  is specified for a given rights profile  1411  and is stored with the rights profile  1411 . The simplified timeline  1403  comprises three keyframes. The first keyframe  1417  is “Do Not Open Until” and represents the activation time for the data files in the cryptocontainer. The second keyframe is the viewing keyframe (not shown) between the first  1417  and third  1418  keyframes and represents the usage period by the recipient. The third keyframe  1418  is “Expire After” and represent the expiration date of the usage rights in the profile  1411 . 
     The toolbar interface  1402  allows authors retrieve usage permissions from a pre-defined template. The process for generating a pre-defined template using the authoring tool (see  FIGS. 14D-14F ) is separate from the standard cryptocontainer creation process, as previously described above. An author may select a pre-defined rights profile template directly from a drop-down menu  1411  in the toolbar interface  1402 . In one example, the toolbar interface  1402  comprises default rights templates for “View Only” and “Encrypt Only” access to the cryptocontainer. 
     The toolbar interface  1402  may exist as a plug-in to a host software application  1401  or to an e-mail client  1400  that provides for the addition of third party plug-ins. The toolbar interface  1402  may be used with a web mail e-mail client or with a locally installed e-mail client program. In one embodiment of the toolbar interface  1402 , a single mouse click (on button  1410 ) may suffice for creating a cryptocontainer, for assigning access rights to documents sent with a cryptocontainer, and for sending a cryptocontainer within an e-mail application program. In another example, from host application programs such as document, spreadsheet or graphic applications, the author may be required to enter the e-mail addresses of the recipients before the cryptocontainer is created. In that case, the toolbar interface  1402  may assume that the author is attempting to send the current document  1415  being processed in the host application in a cryptocontainer. When the appropriate button  1410  on the toolbar interface is clicked, the required cryptocontainer elements are retrieved by the host application program that the toolbar interface  1402  resides in. In one example, a “Send secure” button  1410  represents the toolbar interface  1402  in a host application, as illustrated in  FIGS. 14A and 14B . The source of the required cryptocontainer elements may comprise the following items: 
     1. E-mail Client Host Applications  1400 
         a. Recipients list is gathered from the e-mail addresses  1405  entered in the “to:”, “cc:”, and “bcc:” fields;   b. Files are gathered from the “File Attachments” field  1407  and/or the email message body and are included in the cryptocontainer as separate files which can be assigned usage rights;   c. Usage permissions are gathered from the template chosen in the toolbar interface  1402  drop-down menu  1411 ; and   d. Timeline rights are gathered from time and date data entered into a dialog window  1403  by the author. The data elements provided are “Do not open until” and “Expires on”. When complete these elements create 3 keyframes that will be applied to the cryptocontainer elements  1405 ,  1407 .       

     2. Other Host Applications  1401 
         a. Recipients list is gathered from the e-mail addresses entered by the author from a prompted dialog window interface.   b. Files comprise the current document(s)  1415  that the author is processing in the host application. The author may be prompted to save the current document(s)  1415  before inclusion in the cryptocontainer.   c. Usage permissions are gathered from the template chosen in the toolbar drop-down menu  1411  by the author.   d. Timeline rights are gathered from time and date data  1412  entered into a dialog window by the author.       

     In one embodiment of the toolbar interface  1402 , all recipients are included into the same User Group. Also, included files  1407 ,  1415  may be assigned usage rights according to the chosen template setting  1411  (i.e. View Only, Encrypt Only). Timeline rights  1412  may be assigned to any rights template  1411 . In another example embodiment of the toolbar interface  1402 , the creation of rights timeline templates  1411 , wherein the times and dates of settings are relative to the date and time they are applied, may be specified and stored in advance. For example, an author may create a plurality of keyframes, each with a set of associated rights. When saved in advance as a template  1411 , only the relative difference to an arbitrary start time for each starting and ending times of each keyframe is stored, thereby allowing authors to create complex usage scenarios that may be rapidly retrieved and reused on demand at any time in the future. 
     As basic examples of rights templates  1411 , “View Only” and “Encrypt Only” may be pre-defined as default selections for rights templates  1411  in the toolbar interface  1402 . The “View Only” template (see  FIGS. 14D-14F ) may have the following rights enabled: View, Item Visible and Show Thumbnails. The “Encrypt Only” template may have the following rights enabled: View, Item Visible, Show Thumbnails and Extract. In one example, the “Encrypt Only” template merely assures the safe transmission of the files between the sender (i.e. the author of the cryptocontainer) and the recipient, without applying further usage rights that are enforced by the viewing tool. 
     Users may additionally create new rights templates by operating the authoring tool and choosing a selected rights schema within the Usage Permissions window. In  FIG. 14D , a template entry is illustrated for the “Do Not Open Until” keyframe  1417 ,  1420  (see  FIG. 14C ) in the “View Only” rights profile template  1411 . As reflected in the first cryptocontainer keyframe  1417 ,  1420 , Item Visible and Show Thumbnails are the only enabled rights  1421 . In  FIG. 14E , a template entry is illustrated for the viewing keyframe  1425  in the “View Only” rights profile template  1411 . As reflected in the second cryptocontainer keyframe  1425 , Item Visible, Show Thumbnails and Viewing are the only enabled rights  1426 . In  FIG. 14E , a template entry is illustrated for the “Expire After” keyframe  1418 ,  1430  (see  FIG. 14C ) in the “View Only” rights profile template  1411 . As reflected in the third cryptocontainer keyframe  1418 ,  1430 , Item Visible and Show Thumbnails are the only enabled rights  1431 . 
     The author may then select the “Save as Template” command in the authoring tool, whereby the chosen rights schema will then be saved as a template that automatically populates the toolbar interface drop-down menu  1411 . The rights template exists as a unique entity independent of the other cryptocontainer elements to which it will be applied. In one example embodiment of a rights template, an author may choose to create a template entitled “View &amp; Print,” which would allow recipients rights only for viewing and printing files in the cryptocontainer (but not forwarding, editing, copying, etc.). Other templates may be created with any combination of user rights and timeline settings as required. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.