2008/08/08 by Joseph Y. Halpern, Halpern, Joseph Y., Vicky Weissman +1
Computer Science · #Cryptography and Security (cs.CR) #D.4.6 #Digital Rights Management and Security #F.3 #FOS: Computer and information sciences #H.2.7 #K.4.4 #K.6.5 #Logic in Computer Science (cs.LO) #Mathematics, Computing, and Information Processing #cs.CR #cs.LO
paper · pdf · doi:10.48550/arxiv.0808.1215
arxiv created 2008/08/08 · openalex publication_date 2008/08/08 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
XrML is becoming a popular language in industry for writing software licenses. The semantics for XrML is implicitly given by an algorithm that determines if a permission follows from a set of licenses. We focus on a fragment of the language and use it to highlight some problematic aspects of the algorithm. We then correct the problems, introduce formal semantics, and show that our semantics captures the (corrected) algorithm. Next, we consider the complexity of determining if a permission is implied by a set of XrML licenses. We prove that the general problem is undecidable, but it is polynomial-time computable for an expressive fragment of the language. We extend XrML to capture a wider range of licenses by adding negation to the language. Finally, we discuss the key differences between XrML and MPEG-21, an international standard based on XrML.