Eligibility for access to SCI is determined by a Single Scope Background Investigation or periodic reinvestigation. Because the same investigation is used to grant Top Secret security clearances, the two are often written together as TS/SCI. Eligibility alone does not confer access to any specific SCI material; it is simply a qualification. One must receive explicit permission to access an SCI control system or compartment. This process may include a polygraph or other approved investigative or adjudicative action. Once it is determined a person should have access to an SCI compartment, they sign a nondisclosure agreement, are "read in" or indoctrinated, and the fact of this access is recorded in a local access register or in a computer database. Upon termination from a particular compartment, the employee again signs the nondisclosure agreement.
Control systems
SCI is divided into control systems, which are further subdivided into compartments and sub-compartments. These systems and compartments are usually identified by a classified codeword. Several such codewords have been declassified. The following SCI control systems, with their abbreviations and compartments, are known: ;Special Intelligence : Special Intelligence is the control system covering communications intelligence. Special Intelligence is a term for communications intercepts. The previous title for this control system was COMINT, but this was deprecated in 2011. ;STELLARWIND : This codeword was revealed on June 27, 2013, when The Guardian published a draft report from the NSA Inspector General about the electronic surveillance program STELLARWIND. This program was started by President George W. Bush shortly after the 9/11 attacks. For information about this program, a new security compartment was created which was given STELLARWIND as its permanent cover term on October 31, 2001. ;ENDSEAL : This U.S. Navy's control system was revealed in the 2013 Classification Manual. ENDSEAL information must always be classified as Special Intelligence, so probably it is related to SIGINT or ELINT. It has two subcompartments: ECRU and NONBOOK. ;TALENT KEYHOLE : TK covers space-based IMINT, SIGINT, and MASINT collection platforms; related processing and analysis techniques; and research, design, and operation of these platforms. The original TALENT compartment was created in the mid-1950s for the U-2. In 1960, it was broadened to cover all national aerial reconnaissance and the KEYHOLE compartment was created for satellite intelligence. TALENT KEYHOLE is now a top-level control system; KEYHOLE is no longer a distinct compartment. Known compartments include RUFF, ZARF, and CHESS. The KEYHOLE series KH-1 through KH-4b were part of the new TALENT-KEYHOLE designation. ;HUMINT Control System :HCS is the HUMINT Control System. This system was simply designated "HUMINT" until confusion arose between collateral HUMINT and the control system. The current nomenclature was chosen to eliminate the ambiguity. There are two compartments HCS-O and HCS-P. HCS-O-P marking was also used in "Review of the Unauthorized Disclosures of Former National Security Agency Contractor Edward Snowden". ;KLONDIKE : KLONDIKE protects sensitive geospatial intelligence. It has three main subcompartments: KDK BLUEFISH, KDK IDITAROD and KDK KANDIK. ;RESERVE : RESERVE is the control system for National Reconnaissance Office compartments protecting new sources and methods during the research, development, and acquisition process. RSV-XXX, XXX represents 3 alphanumeric characters to indicate sub Reserve compartments. ;BYEMAN : BYEMAN is a retired control system covering certain overhead collection systems, including CORONA and OXCART. Most BYE content was transferred to TK. BYE Special Handling content was transferred to Reserve.
Markings
SCI control system markings are placed immediately after the classification level markings in a banner line or portion marking. Sometimes, especially on older documents, they are stamped. The following banner line and portion marking describe a top secret document containing information from the notional SI-GAMMA 1234 subcompartment, the notional SI-MANSION compartment, and the notional TALENT KEYHOLE-LANTERN compartment:
TOP SECRET//SI-GAMMA 1234-MANSION/TALENT KEYHOLE-LANTERN//NOFORN
Older documents were marked with HANDLE VIA xxxx CONTROL CHANNELS, HANDLE VIA xxxx CHANNELS ONLY, or HANDLE VIA xxxx CHANNELS JOINTLY, but this requirement was rescinded in 2006. For example, COMINT documents were marked as HANDLE VIA COMINT CHANNELS ONLY. This marking led to the use of the caveat CCO in portion markings, but CCO is also obsolete.
