of counterintelligence, preventing an adversary to intercept sensitive information that is transmitted, especially through free space, but also through wired networks capable of being wiretapped. It includes several disciplines, both including those for protecting the hostile acquisition of information either from the patterns of flow of messages, or the content of messages (e.g., encryption. It also includes a number of disciplines that protect against the inadvertent emanation of unprotected information from communications systems. Physical security This article discusses physical security in the context of information cycle security; see Physical security for a more general view of the topic. Protection of both sensitive information in human-readable form, as well as of cryptographic equipment and keys, is the complement of communications security. The strongest cryptography in the world cannot protect information that, when not being sent through strong cryptographic channels, is left in an area where it can be copied or stolen. It's useful to look at some of the extremes of physical security, to have a standard of reference. A U.S. Sensitive Compartmented Intelligence Facility (SCIF) is a room or set of rooms, with stringent construction standards, to contain the most sensitive materials, and where discussions of any security level can take place. A SCIF is not a bunker, and might slow down, but certainly not stop, a determined entry attempt that used explosives. There can be individual variations in construction based on specific conditions; the standards for one inside a secure building inside a military base in the continental US are not quite as stringent as one in an office building in a hostile country. While, in the past, it was assumed that the SCIF itself and a good deal of electronics in it needed specialized and expensive shielding, and other methods, to protect against eavesdropping—most of these are under the unclassified code word TEMPEST, TEMPEST has generally been waived for facilities in the continental U.S. At the other extreme, the secure conference and work area in the US Embassy in Moscow, where the new building was full of electronic bugs, had extra security measures making it a "bubble" inside as secure a room as was possible. In each case, however, the plans must be preapproved by a qualified security expert, and the SCIF inspected before use, and periodically reinspected. Facilities for less sensitive material do not need the physical protection provided by a SCIF. While the most recent policies