System and Method for Controlling Access Rights to and Security of Digital Content in a Distributed Information System, e.g., Internet

1. Field of the Invention

This invention relates to information systems. More particularly, the invention relates to systems and methods for controlling access rights to digital contents in a Distributed Information System (DIS), e.g., the Internet.

2. Description of Prior Art

Owners of digital content stored and available to the public in an information system would like to ensure that payment has been received in some form and use restrictions observed prior to granting access rights to use the contents. Such access rights can be limited to a particular user for a limited period of time. Information handlers which enforce an owner's content restrictions, for example, restricting the user's right to save content to a storage device are presently available to owners. However, in order to make use of such content restrictions practical in a widely-distributed environment, such as the Internet, there must be a mechanism by which the appropriate information-handler can be readily identified and supplied with contents in a secure manner. A trusted information handler is a mechanism that permits limited access to digital content as specified by the owner of that content. Such trusted information handler should be easily replaced enabling new forms of content to be accessed in a secure manner. Also, such mechanism should permit the easy addition and replacement of such handlers.

Prior art related to limiting access rights to digital content in an information system includes the following:

U.S. Pat. No. 5,436,972 discloses a method for preventing inadvertent betrayal by a trustee of escrowed digital secrets. After unique identification data describing a user has been entered into a computer system, the user is asked to select a password to protect the system. All personal identifying data, together with the password, is encrypted with a trustee's public key and stored, for example, in the user's computer system as an escrow security record. The password is then used to encrypt all data on the user's disk. If at some point in time, the user forgets the password, the user contacts the trustee's, for example, the vendor or the manufacturer. The trustee utilizes documentary evidence presented by the alleged legitimate user and determines whether such evidence matches with the previously encrypted escrowed information stored in the escrow records created by the user. If the records agree, then the trustee has confidence that the true owner is making request and that revealing the secret password will not betray the owner's interest.

U.S. Pat. No. 5,557,518 issued Sept. 17, 1996, discloses a system to open electronic commerce using trusted agents. A customer-trusted agent securely communicates with a first money module. A merchant-trusted agent securely communicates with a second money module. Both trusted agents are capable of establishing a first cryptographically-secure session. Both money modules are capable of establishing a second cryptographically-secure session. The merchant-trusted agent transfers electronic merchandise to the customer-trusted agent, and the first money module transfers electronic money to the second money module. The money module informs the trusted agents of the successful completion of payment and the customer may use the purchased electronic merchandise.

U.S. Pat. No. 5,557,765 discloses a system and method for data recovery. An encrypting user encrypts a method using a secret storage key (KS) and attaches a Data Recovery Field (DRF), including an Access Rule Index (ARI) and the KS to the encrypted message. The DRF and the encrypted message are stored in a storage device. To recover the storage key (KS) a decrypting user extracts and sends the DRF to a Data Recover Center (DRC) and issues a challenge based on Access Rules (ARs) originally defined by the encrypting user. If the encrypting user meets the challenge, the DRC sends the KS in a message to the encrypting user. Generally, KS need not be an encryption key but could represent any piece of confidential information that can fit inside the DRF. In all cases, the DRC limits access to decrypting users who can meet the challenge to find in either the ARs defined by the encrypting user or the ARs defined for override access.

U.S. Pat. No. 5,590,199 issued Dec. 31, 1996, filed Oct. 12, 1993, discloses a system for authenticating and authorizing a user to access services on a heterogenous computer network. The system includes at least one workstation and one authorization server connected to each other through a network. A user couples a personally protectable coprocessor (smart card) to the workstation by means of a bidirectional communications channel. The coprocessor is adapted to receive signals including first encrypted authentication information and decrypt the first encrypted authentication information using a preselected first key. The coprocessor is further adapted to assemble and encrypt second authentication information using a preselected second key and to transmit the encrypted second encrypted authentication information to the workstation. The workstation then communicates the information on to the network whereby the user is authenticated to access the network computer or service.

U.S. Pat. No. 4,827,508; U.S. Pat. 4,977,594 issued Dec. 11, 1990, a division of the '508 patent, and U.S. Pat. No. 5,050,213 issued Sept. 17, 1991, a continuation of the '594 patent, disclose a database access system and method at a user site which permits authorized users to access and use the database and prevent unauthorized database use and copying. A facility is disclosed for measuring usage of the on-site database for purposes of billing the user according to the amount the database has been used. Periodically, the measured usage information is conveyed to the database owner while preventing the user from tampering with the measured usage information.

None of the prior art discloses a system and method for using a trusted information handler and a digital container techniques in an information network which assures that an owner's digital content is not accessed without the owner's permission and use restrictions observed, thereby enabling valuable digital content to be transferred and/or sold electronically with the assurance that the owner's rights are fully protected.

An object of the invention is a system and method for limiting access to digital content in an information system.

Another object is a trusted information handler in an information system which controls access to digital content by a client, according to an owner's restrictions.

Another object is a trusted information handler in an information network which uses cryptographic techniques in limiting access to digital content in the network.

Another object is a system and method of validating a trusted information handler's authorization to limit access to an owner's digital content.

Another object is a trusted information handler in an information network which decrypts digital content for distribution to a client in accordance with an owner's requirements.

These and other objects, features and advantages are achieved in an information network including a server for providing access to an owner's digital content under the control of a trusted information handler (TIH). When a client accesses the server to acquire the digital content encrypted in a Document Encryption Key (DEK), the server encrypts the DEK with a Server Public Key using a Public/Private key pair algorithm and places the encrypted content in a digital container for storing and transferring information in an information system in a secure manner. The client opens the container and uses a client program to transmit transaction data to the TIH which signs the data using a digital signature; identifies the type of signing algorithm; and provides a certificate of authority to the client program. (In the event any transaction exchanged between the client and server requires confidentiality, then well know encryption/decryption techniques may be used to implement confidentiality, including but not limited to public key encryption; "shared secret" encryption and symmetric encryption with public key protecting the symmetric cipher key.) The client returns to the server the server encrypted DEK, the TIH certificate, the transaction data, a client signature, and the type of signing algorithm used by the TIH together with a client Public Key in a TIH public/private key. The server re-creates the transaction data and checks for reasonability; authenticates the TIH by (i) confirming the TIH is a known information handler; (ii) validates the TIH certificate, and (iii) confirms the transaction data signature produced by the TIH. After authentication, the server decrypts the DEK with its private key; encrypts the newly encrypted DEK with TIH's public key; encrypts the decrypted key with the client's public key; and returns the doubly encrypted DEK to the client. The client decrypts the DEK with his private key and passes it along with the encrypted digital content to the TIH which proceeds to decrypt the digital content for distribution to the client in accordance with the owner's requirement. The encrypted digital content may be supplied in its' entirety or in discrete amounts, the latter facilitating any metering requirements imposed by the content owner via the TIH.

The invention will be further understood from the following detailed description of a preferred embodiment taken in conjunction with an appended drawing, in which:

FIG. 1 is a block diagram of a prior art server in an information system which provides secure content delivery in a digital container and ensures payment is received from a particular client before the content is decrypted.

FIG. 2 is a representation of a prior art digital container used in the system of FIG. 1

FIG. 3 is a flow diagram of a prior art process for securing content within the digital container of FIG. 1.

FIG. 4 is a block diagram of an information system providing limited access to digital content in a digital container and incorporating the principles of the present invention.

FIG. 5 is a flow diagram of a process for limiting access to digital content in the system of FIG. 3.

In FIG. 1, a portion of a prior art information system 10 is shown for providing secure content delivery and ensuring payment is received from a client before the content can be decrypted and displayed to the client. Such a system is described in Ser. No. 08/625,475 filed Mar. 29, 1996, assigned to the same assignee as that of the present invention and fully incorporated herein by reference in the present information to ensure the information content is always protected within a secure environment. The prior art system 10 may be part of the Internet or a public switch telephone network (PSTN) and includes a conventional server 12 coupled to a conventional storage device, e.g., disk drive, memory unit, or the like, in which the digital content is stored with limited access for a client(s) or user(s) at a workstation 16 including a display 18. The digital content is transferred in process steps 1-6, as will be described hereinafter, and made available to clients or users within a digital container which in one form may be a cryptolope container 11 shown in FIG. 2. The container 11 is a digital envelope containing a collection of files including the digital content in encrypted form, meta-information about the content, and meta-information about the container itself. Specifically, the container includes encrypted document parts 13 which are the "valuable contents" to be purchased by a client or user; an associated encrypted public encryption key 15 for the parts; a list of container parts 17 and a digital signature 21 for the list. The envelope is a grouping of information parts compatible with a large number of grouping technologies, for example Microsoft's OLE. The cryptolope provides security for the digital content in transit to clients and users. It should be understood, however, that in addition to cryptolope containers there are other digital containers available for transferring information between an information source and client or user in a secure manner in an information system. One such digital container is described in copending application Ser. No. 08/866,305, filed May 5, 1997, assigned to the same assignee as that of the present invention and fully incorporated herein by reference. The information transferred in the container of Ser. No. 08/866,305, referred to as an information objects container, includes application programs and data in addition to documents and text requested by a client or user. In such transfers, the information owner has an increased security interest to limit distribution and usage to such clients or users through the information objects container and other means, such as the trusted information handler of the present invention, as will be described hereinafter. For purposes of description, however, the present invention will be described in terms of the cryptolope container of Ser. No. 08/625,475, but the digital information objects container of Ser. No. 08/866,305 is equally applicable for use in the present invention.

In FIG. 3, a prior art process is described by which digital content is secured within a cryptolope container transferred to and then acquired by a client in steps 1-6, as follows:

In step 1, the digital content is encrypted off-line using a randomly generated key, also known as a Document Encryption Key (DEK), and after encryption, stored in the storage unit 14 (See FIG. 1).

In step 2, the DEK is encrypted within the server's 12 public key, using a public/private key pair algorithm, such as the well known RSA cipher.

In step 3, the encrypted DEK is placed within a cryptolope container as part of the meta-information within the container. The above cited Ser. No. 08/625,475 filed Mar. 29, 1996, provides the details for forming the cryptolope container and storing the encrypted digital content in the storage unit 14.

In step 4, the container is distributed to one or more users requesting the digital content with limited access.

In step 5, a client program opens the container and displays the meta-information to a user. The client program has its own public/private key pair which was generated at installation time or received out of band from an external provider (Certificate Authority) using an algorithm which is recognized by the server. If the user wishes to purchase the contents of the container, the client program sends all DEK's back to the server along with the public key from the client's public key/private key pair.

In step 6, if all purchase criteria are met, the server decrypts the decrypted DEK with the corresponding server private key, providing a clear DEK.

In step 7, the DEK is then re-encrypted with the client's public key, thus personalizing the digital content to the client which is returned in a crypotolope container to the client in the newly-encrypted DEK.

In step 8, the client program decrypts the DEK with its private key, producing the clear DEK. The client then proceeds to decrypt the content which can be processed as usual by an appropriate information handler, after which the process ends.

In order to be certain that the digital content with limited access remains in a secure environment and protected from unauthorized use once decrypted, a trusted information handler (TIH) 20, as shown in FIG. 4, is installed in the client environment of FIG. 1. The handler 20 is known to the server 12 and assures the owner the content in the digital container will be securely transferred and decrypted in process steps 1-7 under the appropriate owner conditions, as will be described hereinafter. Under the system of FIG. 4, content owners can specify the appropriate TIH to process the meta-information contained in the cryptolope container. The handler 20 has its own public/private key pair and the ability to sign arbitrary data using a signing algorithm known to the server. The public/private key pair of the handler 20 may be protected by a variety of mechanisms, including, but not necessarily limited to tamper-resistant smart cards, PCMCIA cards or software obfuscation. The owner of the content determines the security requirements for the content and the TIH provider demonstrates that level of conformance prior to being recognized as a "Trusted Information Handler".

In FIG. 5, a process is shown for further protecting the digital content with limited access from unauthorized use after decryption using the system 10' of FIG. 3, as follows:

Steps 1-3 of FIG. 3 are repeated, after which in step 4 a client program opens the container and displays the meta-information contained in the container to the user. At some time prior to step 4, the client program generates key pairs and submits the public key to a Certificate Authority (CA) along with "personal" information pertinent to the type of certificate requested. The CA uses the "personal" information to discern if the client is suitable to receive a certificate for which the client has applied. If the client is suitable, a certificate is created by the CA and encapsulates the client's public key. The public key is used to authenticate signatures of the client. In addition, the CA signs the certificate. In general, well known CAs publicize their public keys so certificates generated by CAs can be authenticated.

If the user wishes to purchase the digital content in the container, step 4a activates a client program to create arbitrary data descriptive of the transaction, after which the handler 20 is requested to provide a digital signature to the transaction data. The handler 20 returns both the transaction digital signature and the type of signing algorithm used by the handler in generating the digital signature.

In step 4b, the handler presents its Certificate of Authority to the client program.

In step 4c, the client program sends all DEK's back to the server 12 along with the public key from its own public key/private key pair; the handler's certificate; the transaction data; the digital signature; and the type of signing algorithm used by the handler 20.

In step 5, when the server processes the transaction for the acquisition of the digital content, the server re-creates the transaction data generated by the client; checks the data for "reasonability", after which the server authenticates the handler 20.

In step 5a, the server confirms that the information handler 20 is a known handler using the name found in the certificate of authority and comparing the name to an approved known specified by the owner.

In step 5b, the server confirms the transaction data signal was produced by the handler 20 after which the certificate of authority for the handler is validated. Validating the certificate may involve validating "issuing" certificates. It is a usual CA practice to create a certificate hierarchy such that not all certificates are signed by the same entity. Thus, multiple certificates may be submitted which represent a trust hierarchy and is commonly referred to as a certificate "chain". Validating certificates in this chain can terminate when a "trusted" certificate is encountered. Applications commonly maintain lists of "trusted" certificates ("trusted" is defined to mean an application assumes the certificates are genuine).

In step 6, after the handler is authenticated by the server and all purchase criteria are met, the server decrypts the encrypted DEK with its corresponding private key, providing a clear DEK in step 6a.

In step 6b, the DEK is re-encrypted with the handler's public key ensuring that only the handler can process and disseminate the digital content.

In step 6c, the server encrypts the newly encrypted DEK again with the client's public key, thus personalizing the digital content to the client and the newly encrypted DEK is returned to the client in step 6d.

In step 7, the client program decrypts the DEK with its private key and passes the key along with the encrypted content to the handler 20 which decrypts the DEK with its private key and proceeds to decrypt the content, after which the digital content can be made available to the client under the owner's conditions ensuring the owner that a known handler is protecting the digital content from unauthorized use after decryption.

The system of FIGS. 4 and 5 provide the following advantages over the system of FIGS. 1 and 2, as follows:

Content owners can be assured that only "known" applications will be permitted access to their content since the application must be known to the server and some sort of registration process (and implicit approval) of the trusted information handler (TIH) has previously taken place.

If a trusted information handler is some how compromised, the handler can be removed from interfacing with the server, effectively disabling the handler from future use.

The encrypted DEK cannot be decoded by any other client and trusted information handler combination since both the client and the handler must use their own private encryption keys to encrypt the DEK for access to the content.

While the invention has been shown and described in connection with a preferred embodiment, various modifications may be made without departing from the spirit and scope of the invention, as described in the appended claims, in which: