I have reviewed this document as part of the security directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written primarily for the benefit of the security area directors. Document editors and WG chairs should treat these comments just like any other last call comments. This is informational, and documents a system in use (and quite successfully so) by Apple. It's a well-written description that appears to be thorough, and I have to trust that it's accurate and complete (it seems to be). Because it's documenting what's already there, it wouldn't be appropriate to look to change things, in general, except to ask for clarifications -- and there's nothing I think I want clarified. And for what it's worth, the security aspects of the BTMM service look quite solid. It's ready to publish. Barry