Models and Languages for Digital Rights C. Gunter, S. Weeks, A. Wright 34th Annual Hawaii International Conference on System Sciences ( HICSS-34)-Volume 9 January , 2001

Outline Introduction A Semantic Model for DRM Standard Licenses Language DRM Enforcement and Audit Functions Conclusion

Introduction(1/2) A Digital Rights Management (DRM) system governs rendering of content. an ongoing-service-model may be better than the sale-of-good-model  Cause the new distribution techniques: bigger capability of media and Internet(bulk transfers, streaming)  selling the right to hear songs at a low fixed price per rendering V.S. selling a set of hundreds of CDs at a high fixed price  Periodical payment, like electricity or a cell phone service  different characteristics of digital goods, need new appropriate service models.

Introduction(2/2) The aim of this paper  make progress on developing a model and a language for describing licenses to digital works. begin by studing simple licenses that consist only of payment and rendering events. mathematical model  capturing the meanings of a wide variety of such licenses with precision language of licenses  whose semantics is defined by reference to the model. Insure  Unambiguous-interpretation license defined without reference to any particular implementation of a DRM system.

A Semantic Model for DRM Action a:  a ::= render[w, d] | pay[x] render[w; d] : rendering of work w by rights-enabled device d pay[x] : a payment of amount x of some currency from a licensee to a license issuer. Event e:  e ::= t : a a pair of a time t, and an action a t : render[w; d] : at time t, work w was rendered on device d t : pay[x] : at time t, a payment of amount x was made

A Semantic Model for DRM Reality r:  r  Reality = { E  P(Event) | E is finite and for all t : a  E if t : a’  E then a = a’ } a finite set of events, such that all events occur at distinct times require events to occur at distinct times so that we may use their times to identify them  r  t = { t’:a  r | t’  t } represent the prefix of r that occurs at or before time t  r  r’ :r is a prefix of r’, there exists a t such that r = r  t

A Semantic Model for DRM License l:  l  License = P(Reality) set of realities Ex:  l A = { {8:00 : pay[$1], 8:01 : render[w1, d1]}, {8:00 : pay[$1], 8:02 : render[w1, d1] }, {8:00 : pay[$1], 8:03 : render[w1, d1], 8:04 : render[w1, d1] }, {8:00 : pay[$1] } }

A Semantic Model for DRM r : the (unique) complete reality that actually occurs over the entire lifetime of the DRM system  A DRM system must attribute every event of r to a license, and should not attribute any event to more than one license r[l] : events of r attributed to license l

A Semantic Model for DRM Definition: Reality r  l of license l is viable for r[l] at t iff r[l]  t  r Definition: License l is fulfilled by r[l] at t iff r[l]  t  l. Definition: License l is breached by r[l] at t iff there does not exist r  l that is viable for r[l] at t.

A Semantic Model for DRM Ex1:  r[l A ] = { 8:00 : pay[$1], 8:01 : render[w1, d1], 8:05 : render[w1, d1] } All four realities of license l A are viable for r[l A ] at t < 8:01. Only the first reality is viable for 8:01  t < 8:05. No reality is viable for t  8:05. License l A is unfulfilled by r[l A ] for t < 8:00, fulfilled for 8:00  t < 8:05, and breached for t  8:05. l A = { {8:00 : pay[$1], 8:01 : render[w1, d1]}, {8:00 : pay[$1], 8:02 : render[w1, d1] }, {8:00 : pay[$1], 8:03 : render[w1, d1], 8:04 : render[w1, d1] }, {8:00 : pay[$1] } }

A Semantic Model for DRM Ex2:  r’[l A ] = {8:00 : pay[$1], 8:03 : render[w1, d1] } license l A is unfulfilled for t < 8:00, fulfilled for 8:00  t < 8:03, unfulfilled for 8:03  t < 8:04, and breached for t  8:04 Note that a license that is fulfilled at time t can be unfulfilled at a later time t’ > t. A license that is breached at time t is breached for all t’  t. A license can never be both fulfilled and breached.

Standard Licenses (simple licenses) The “Up Front” license provides access to any work in set W  P(Work) on any device in set D  P(Device) beginning at time t 0 for period p, for an up-front payment of x.  UpFront(t 0, x, p,W,D) = { t 0 : pay[x], t 1 : render[w 1, d 1 ],…, t n : render[w n, d n ] | n  0, t 0 < t 1 < … < t n < t 0 + p, w 1,…,w n  W, d 1,…,d n  D }  Ex: admission to a theme park, cable television

Standard Licenses (simple licenses) The “Flat Rate” license provides access to any work in set W on any device in set D beginning at time t 0 for period p, for a payment of x at the end of the period  FlatRate (t 0,, x, p,W,D) = { t 1 : render[w 1, d 1 ],…, t n : render[w n, d n ], t n+1 : pay[x] | n  0, t 0 < t 1 < … < t n < t n+1 < t 0 + p, w 1,…,w n  W, d 1,…,d n  D }  Ex: paying for a meal at a restaurant with a fixed-price menu. The price is known in advance

Standard Licenses (simple licenses) the “Per Use” license provides access to any work in set W on any device in set D beginning at time t 0 for a period p, for a payment of x per use at the end of the period  PerUse (t 0,, x, p,W,D) = { t 1 : render[w 1, d 1 ],…, t n : render[w n, d n ], t n+1 : pay[nx] | n  0, t 0 < t 1 < … < t n < t n+1 < t 0 + p, w 1,…,w n  W, d 1,…,d n  D }  Ex: a utility bill like telephone or electricity minus any fixed or minimum per-period charge.

Standard Licenses (more than simple licenses) simple licenses, specific starting time. More complicated licenses, consumer can accept any time before some future date  Ex:  t 0 <t expire UpFront(t 0, x, p,W,D) The license allows the period of use to begin anytime prior to t expire

Standard Licenses (more than simple licenses) simple licenses, only a single service period. multi-period noncancellable licenses : holds for a number of service periods.  let l 1  l 2 = { r 1  r 2 | r 1  l 1, r 2  l 2 }  UpFront  (t 0, x, p,W,D,m) = UpFront(t 0, x, p,W,D)  …  UpFront(t m-1, x, p,W,D) where t i = t 0 + ip for i from 0 to m-1 similar to the lease on an apartment A multi-period PerUse noncancellable license  similar to a telephone contract

Standard Licenses (more than simple licenses) cancellable multi-period licenses:not renewable  let l 1  l 2 = { r 1  r 2 | r 1  l 1, r 1 , r 2  l 2 }  {  }  UpFront  (t 0, x, p,W,D,m) = UpFront(t 0, x, p,W,D)  …  UpFront(t m-1, x, p,W,D) where t i = t 0 + ip for i from 0 to m-1 similar to a renter with rent protection.  Also cancellable FlatRate and PerUse licenses

Language DigitalRights, is defined by the following grammar:  e ::= (at t | until t) (for p | for [up to] mp) pay x (upfront | flatrate | peruse) for W on D  Ex: until 01/01/03 for up to 12 months pay $10.00 upfront for “Jazz Classics” on “devices registered to the license holder”

Language

DRM Enforcement and Audit Functions licenses that cannot be practically enforced are not useful for DRMs.  A DRM system is used to prevent or detect a breach in a license  Limits of DRM protection mechanisms will determine which licenses are implementable the language provides an avenue for classification. The licenses in this paper are ones for which practical DRM enforcement mechanisms are anticipated.

Conclusion a mathematical model and a simple language  for describing licenses for digital rights management systems. toward developing more sophisticated DRM languages with precise semantics, while leaving DRM vendors free to choose different methods of enforcement.