Metering: A Pre-pay Technique
`
`Russell Housley
`
`Jan Dolphin
`
`WYkU$, Incorporated
`P.O. Box 1198, Herndon, Virginia 20172
`
`WYkU, Incorporated
`2460 N. First Street, Suite 100, San Jose, California 95131
`
`ABSTRACT
`
`The YkU Metering System allows intellectual property suppliers to control access to electronic information with content-
`based meters. Information is distributed to users in encrypted form, and each user has a hardware token that contains the
`cryptographic keys necessary to decrypt the information as well as the meters that control the use of each key. The hardware
`token will not grant access to the information by decrypting it unless the supplier provided meter constraints are met. Since
`the hardware token includes a built-in real time clock, time-based meters can be enforced without relying on the easily
`modified computer system clock.
`
`Keywords: metering, key management, encryption, hardware token
`
`1. INTRODUCTION
`
`Intellectual property suppliers want to distribute information to users in electronic form, either on physical media or over
`popular networks like the Internet. At the same time, the suppliers require protection so that the electronic information is not
`misused. Protection may prevent copying, alteration, or prevent access altogether. Today's on-line Internet environment has
`generated new requirements. Many parents want to prohibit "X rated" World Wide Web (WWW) pages from being
`downloaded by their children. Employers are concerned about the amount of time that their employees spend "browsing" the
`WWW during work hours. In the first example, access must be limited based on the content itself, and in the second
`example, access must be limited based on time of day without keeping people from doing their job. Technical solutions to
`protect intellectual property in this networked, multimedia environment must be available before business can use electronic
`distribution effectively.
`
`The WYkU$ Metering System allows suppliers to protect the information, then distribute it via any media. The information is
`distributed in encrypted form, thus only authorized users are able to decrypt the information.
`
`Hardware tokens are used. The high assurance hardware tokens implement the cryptographic algorithms, store the keys, and
`enforce the meters. Use of the hardware token ensures that the user cannot bypass the meter checks and decrypt the
`information. Since the hardware token includes a battery-operated real time clock, time-based meters can be enforced
`without relying on the easily modified computer system clock. Additionally, since each user will have their own token, the
`token can provide the user with other services as well. For example, the cryptographic algorithms on the card can be used to
`provide the user with a digital signature capability for electronic mail or fax services; the hardware token can provide
`authentication to WWW sites or firewails; and the hardware token can be used to provide end-to-end network security
`services beyond those provided by firewalls.
`
`Within the last year, user acceptance of PCMCIA PC Card and Smart Card tokens has significantly increased. One
`significant event in this area is the definition of the Microsoft Internet Security Framework which provides a standardized
`cryptographic interface for user tokens on all Windows 95 and Windows NT platforms. The Microsoft architecture includes a
`Cryptographic Service Provider (CSP) under the standardized interface. The CSP provides a "Plug and Play" solution to
`seamlessly integrate applications with hardware tokens. Standardization at this level, on these platforms, opens the
`floodgates to technical solutions to protect electronic intellectual properties.
`
`2. METERS
`
`Like the gas or electric meter attached to a house, the user maintains possession of the metering token. The hardware token
`will not grant the user access to the information by decrypting it unless the meter constraints established by the publisher are
`met. Conversely, the token may not grant a user access to particular content, based on the user identification. Depending on
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`the complexity of the system, meters may take on many different forms, and meters may be coupled with different
`communications or storage functions. Meter can be contained in PCMCIA PC Cards, Smart Cards, or computer boards to
`meet higher input/output performance requirements. For example, a meter combined with a modem allows the application to
`invoke the modem ftinctions when billing or audit information needs to be transferred. For environments requiring large
`amount of meter use information, they can be coupled with multi-megabytes of flash storage. Looking into the future, as
`smart card processors evolve, the use of downloadable meters to maintain user functions such as customer loyalty programs is
`easily achievable.
`
`As described earlier, meters may be based on many different attributes. Attributes are built into and monitored by the
`hardware token. The meters can be associated with any symmetric or asymmetric key on the hardware token. Symmetric
`keys can be used to encrypt intellectual property prior to distribution, and asymmetric signature keys can be used for remote
`authentication. Attributes that a meter can monitor include:
`
`The name or alias ofthe key holder;
`
`SubscriptionCounter;
`Access time ofday; and
`Access calendar date.
`
`.
`. Description ofthe key;
`. Activationdate ofthe key;
`. Expirationdate ofthe key;
`. Number ofuses ofthe key;
`. Data usage;
`.
`.
`.
`In addition, arbitrary attributes can be supported by the application. In this case, the application tells the hardware token
`when to increment the meter. In this way, LYNK aware applications tell the hardware token when meter relevant events occur,
`and the meters are tracked inside the protected memory of the hardware token. The user has no way to decrement the meter,
`thus the hardware token will refuse to decrypt additional information once the meter threshold is reached. This functions is
`particularly useful for implementing a "30 day free trial use" function. In one system, this function was used to provide a
`thirty day free sample period for a word processing program. This was implemented with a key that expired in thirty days.
`Once the key expired, the word processing application disabled certain functions such as copy and print. When the user
`purchased the application key, these functions were re-enabled.
`
`The hardware token associates some user information with the data. As examples, this feature may be used to track user
`accesses to certain types of data and track the amount of information accessed during a session. The hardware token contains
`a limited amount of audit information. This audit information is periodically downloaded from the hardware token to the
`publisher's Billing/Audit Center. This audit information allows the publisher to understand how and when their information
`is used. This audit information is readily available, and extensively used, by publishers with on-line systems; however,
`obtaining this audit information from off-line systems is quite difficult. Alternate hardware token packaging could provide
`large amounts of audit information to the publisher if the system includes a convenient way to transfer the audit information
`from the user to the publisher.
`
`3. METERING SYSTEM COMPONENTS
`
`The WYkU metering system has four components: the Personalization Workstation, the Billing/Audit Center, the Publisher,
`and the Authenticator. Figure 1 illustrates the relationships between these four components. The Personalization
`Workstation is responsible for hardware token initialization and enrollment of users. The Billing/Audit Center is responsible
`for hardware token registration and meter distribution. The Publisher creates meters, assigns access controls, and encrypts the
`information. Lastly, the Authenticator requests meters and decrypts the protected information for the user. In many cases, the
`Authenticator is embedded in another application.
`
`Together, these components support electronic publication and payment, yet user misuse of the information is prevented.
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`Personalization Workstation
`. Initialize Hardware Tokens
`. Authenticate Users
`
`$
`Billing/Audit Center
`U Hardware Token Registration
`. Meter Distribution
`U Audit Information Collection
`
`Publisher
`I Assign Meters and Access
`Controls
`U Encrypt Information
`
`.
`
`.
`
`Meter and Audit Request I Transfer
`
`_____
`
`__________________
`Authenticator
`• Request Meters
`• Access I Decrypt Data
`
`Data Transfer
`
`Figure 1. YkU$ Metering System Components.
`
`4. PUBLISHiNG
`
`Prior to publication of the information, the Publisher must decide on the attributes of the meter. Theses attributes are
`determined by the publisher's payment model. Does the publisher want to charge for information access based on time,
`quantity, or events? If the publisher wants to charge for WWW page access based on time, then the publisher may allow a
`user access to their WWW pages for thirty days or access it in the month of February. If the publisher wants to charge for
`access to a image repository based on quantity, a user may be granted access to 10,000,000 bytes ofphotographic information.
`Ifthe publisher wants to charge for database access based on events, the publisher may allow 250 database queries. The key
`point is that the Publisher determines how much data is protected with each key and establishes the metering parameters prior
`to publication. The Publisher could protect a single file, a whole directory, an arbitrary collection of files, an entire CD-
`ROM, or a WWW page. The metering system does not impose any limitations on the creativeness of the publisher. Further,
`when publishers use LYMK aware applications there are no limit on the publisher's creativeness to define the billable event.
`
`For example, the metering system can use keys to implement a magazine subscription service. Each magazine issue is
`encrypted in a different key. The key from the previous magazine issue is used to derive the key for the subsequent issue by
`applying a one-way update ftmction. The one-way update function is applied to the first issue key to obtain the second issue
`key; the one-way update function is applied to the second issue key to obtain the third issue key; and so on. The meter
`contains the number of updates that are permitted. In this way, the meter determines which magazine issues that a particular
`user may read. Renewals may be implemented by distributing the key for the first magazine issue in the renewal period and
`permitting the number ofupdates that are permitted. This approach allows a user to joint the subscription at any point.
`
`The meters are tightly coupled with the cryptographic keys, and the distribution of the keys and the meters to the user is all
`that is necessary for the user to access the information. Therefore, if payment is required for the information, payment must
`be received before the key and associated meter is provided to the user.
`
`5. PAYMENT
`
`Payment is tightly coupled with key management. That is, keys and associated meter are distributed after payment is
`received. For example, the Publisher may put many products on a single CD-ROM, and associate a separate key and meter
`attributes with each product. When a user purchases one product, the CD-ROM containing all of the products is sent to the
`user, but the user is sent only one key and the associated meter. When the user purchases a second product, the user is sent
`the key and associated meter for the second product. There is no reason to send the CD-ROM again, so the second delivery
`may be accomplished electronically with a small message.
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`During the life of the subscription service, the Billing/Audit Center communicates with the hardware token and securely
`updates the meter status. The cryptography contained within the hardware token is used to provide secure communications,
`and audit information as well as the meter state is received by the Billing/Audit Center. This information is distributed to the
`associated information publishers to plot histograms associated with information usage. Also, the secure communications can
`be used in the evolution of new services or promotions. A publisher can change the meter or give away a "free month" to any
`information user. The hardware token audit information can contain access thresholds that support brand loyalty programs.
`After a fixed amount of access to a particular WWW site or use of a particular software package, the publisher can provide
`free upgrades or other promotional information to foster customer loyalty.
`
`Even though pre-payment is most easily supported by this scheme, "try before you buy" is still accommodated. A "try before
`you buy" meter might limit on-line access to non-prime time, limit access to a subset of the available data, limit the number
`ofbytes that can be decrypted, or limit the number ofdatabase queries.
`
`The Billing/Audit Center can be maintained by the publisher, or the payment center can be provided by a third party.
`
`6. USER APPLICATIONS
`
`Current meter information on the hardware token must be accessible to the user. This capability is provided by the meter
`reader application. All keys and information maintained by the hardware token have an associated alias name that is human
`readable, and this alias name allows the user to determine time or events remaining on a particular meter. Bundled with this
`application is the electronic order form to purchase new services and sign the purchase request prior to sending it to the
`Publisher or Billing/Audit Center.
`
`Another application, Authenticator, is a transparent application responsible for decrypting the information in accordance with
`the meter, transparently to the user.
`
`7. WORKED EXAMPLES
`
`WYkU has used the metering technology described in several projects. Two projects are briefly described in the following
`sections.
`
`7.1 CD-ROMDistribution and Access Control
`
`For the Navy, WYkU developed a system that protects CD-ROM images. The ISO 9660 CD-ROM image encryption standard
`is used. The WYkU Authenticator is implemented as an interposing device driver, so the user can continue to use CD-ROMs
`with any software application. The WYRU Authenticator verifies the Publisher's signature on the CD-ROM, providing
`authentication of the source of the information. The system allows the users to query the CD-ROM jukebox to obtain the
`table of contents and list of required keys, and, if authorized, to download the appropriate keys from a key distribution
`system. The YkU system provides access control to critical information and also provides authenticates information sources
`and dates ofinformation for critical ftmctions.
`
`Figure 2 illustrates the Graphical User Interface used to associates meters with CD-ROM files.
`
`7.2 Copyright Initiative
`
`The National Research and Education Network (NREN) copyright initiative is using this type oftechnology to limit
`redistribution of electronic documents, assure that copies remain unmodified, and to identify the attributes of alternate data
`distribution modes. Using a "sealed envelope" and digital signature based on public key cryptography, meters provide:
`• Authentication - source of the information;
`• Limit redistribution - meters restrict the number of copies that may be printed to the number purchased;
`•
`Protection against plagiarism and change - mechanism to ensure that the materials are used with jeopardizing
`authenticity; and
`Remuneration - metering for subscription fee, license fee, contract fees, or fee for services.
`
`•
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`8. FREQUENTLY ASKED QUESTIONS
`
`One important question that is frequently asked by system developers is: "How do I recover the cost of the hardware token?"
`One can look at the pay per view television market for one solution. In that environment, the decryption box in the user's
`home is provided as part ofthe service. Likewise, a software distribution company can provide hardware tokens as part of the
`subscription to their service. Every month, instead of sending out a set of floppies or a CD-ROM, they can post the encrypted
`application on their WWW page. Alternatively, physical distribution of a CD-ROM could be used more efficiently by
`sending out a single CD-ROM with all ofthe distributions managed by the company. Each subscriber would be limited to the
`software that is part of their subscription or subscriptions. In either case, the meters stored on the hardware token permit
`access to their subscription, and they can also contain their individual maintenance subscription keys for the maintenance
`releases to software which has already been purchased. In the future, several companies might collaborate and share the cost
`ofthe hardware token. For example, one hardware token could serve as a bank card, rental car company card, airline frequent
`flyer card, and computer software store card. In this case, the user's bank card is the hardware token, and it can be used to
`purchase software products while encouraging brand ioyalty.
`
`Another important question is: "How do I connect the hardware token to my computer?" Most laptop computers come with
`slots for PCMCIA PC Cards. Recently, Microsoft has announced support for a Smart Card reader embedded in keyboards.
`So, many computers have or will have easy access to hardware tokens. Also, low cost readers are available that connect to
`serial ports, parallel ports, or the SCSI bus.
`
`An interesting question is: "How will the use of digital signatures effect this technology?" Digital signatures are being used
`to provide authentication and non-repudiation services. The use of hardware tokens to protect the private key needed to
`digitally sign information is strongly recommended to reduce the possibility of masquerade. As digital signatures become
`more prolific, the binding of meters to signature private keys and signature values is an exciting possibility. For example,
`threshold meters can ensure that two people are needed to sign purchase orders over a particular value.
`
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