Abstract
Recently-introduced Publicly Posted Composite Documents (PPCDs) address the problem of composite documents with different formats and differential access control participating in cross-organizational workflows distributed over potentially non-secure channels. An early version of the PPCD only considered two simplest workflow types: ordered and unordered. In real life, however, fragments of such pure types are likely to be combined into mixed workflows with interleaved ordered and unordered workflow steps. In the current paper, we introduce a payload matrix for a generic mixed workflow. We provide a computationally beneficial solution for enforcing access in ordered workflows by reducing the volume of data that needs to be encrypted and then subsequently decrypted. Furthermore, we address the problem of enforcing order in transitions between different types of workflow steps: from an unordered step to ordered steps and vice versa, and from one unordered step to another. This prevents the participants of any workflow step from being able to access a PPCD document prior to their workflow step.