There is disclosed in an example, a computing apparatus, including: a trusted execution environment (TEE); and one or more logic elements providing a collaboration engine within the TEE, operable to: receive a change to a secured document via a trusted channel; apply a change to the secured document; log the change to a ledger; and display the document to a client device via a protected audio-video path (PAVP). There is also disclosed a method of providing a collaboration engine, and a computer-readable medium having stored thereon executable instructions for providing a collaboration engine.