Resilient On-board Timing

Techniques Addressed by Countermeasure

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ID		Name	Description
EX-0014		Spoofing	Threat actors may attempt to spoof the various sensor and controller data that is depended upon by various subsystems within the victim SV. Subsystems rely on this data to perform automated tasks, process gather data, and return important information to the ground controllers. By spoofing this information, threat actors could trigger automated tasks to fire when they are not needed to, potentially causing the SV to behave erratically. Further, the data could be processed erroneously, causing ground controllers to receive incorrect telemetry or scientific data, threatening the SV's reliability and integrity.
	.01	Time Spoof	Threat actors may attempt to target the internal timers onboard the victim SV and spoof their data. The Spacecraft Event Time (SCET) is used for various programs within the SV and control when specific events are set to occur. Ground controllers use these timed events to perform automated processes as the SV is in orbit in order for it to fulfill it's purpose. Threat actors that target this particular system and attempt to spoof it's data could cause these processes to trigger early or late.

Space Threats Addressed by Countermeasure

ID	Description

Low-Level Requirements

Requirement	Rationale/Additional Guidance/Notes
The [spacecraft] shall monitor security relevant telemetry points for malicious commanding attempts.{AC-17,AC-17(1),AC-17(10),AU-3(1),RA-10,SC-7,SC-16,SC-16(2),SC-16(3),SI-3(8),SI-4,SI-4(1),SI-4(13),SI-4(24),SI-4(25),SI-10(6)}
The [spacecraft] shall authenticate the ground station (and all commands) and other spacecraft before establishing remote connections using bidirectional authentication that is cryptographically based.{SV-AC-1,SV-AC-2}{AC-3,AC-17,AC-17(2),AC-17(10),AC-18(1),AC-20,IA-3(1),IA-4,IA-4(9),IA-7,IA-9,SA-8(18),SA-8(19),SA-9(2),SC-7(11),SC-16(1),SC-16(2),SC-16(3),SC-23(3),SI-3(9)}	Authorization can include embedding opcodes in command strings, using trusted authentication protocols, identifying proper link characteristics such as emitter location, expected range of receive power, expected modulation, data rates, communication protocols, beamwidth, etc.; and tracking command counter increments against expected values.
The [spacecraft] shall implement relay and replay-resistant authentication mechanisms for establishing a remote connection.{SV-AC-1,SV-AC-2}{AC-3,IA-2(8),IA-2(9),SA-8(18),SC-8(1),SC-16(1),SC-16(2),SC-23(3),SC-40(4)}
The [spacecraft] shall not employ a mode of operations where cryptography on the TT&C link can be disabled (i.e., crypto-bypass mode).{SV-AC-1,SV-CF-1,SV-CF-2}{AC-3(10),SA-8(18),SA-8(19),SC-16(2),SC-16(3),SC-40(4)}
The [spacecraft] shall synchronize the internal system clocks for each processor to the authoritative time source when the time difference is greater than the FSW-defined interval.{SV-AV-2}{AU-8(1),SC-45,SC-45(1),SC-45(2)}
The [spacecraft] shall internally monitor PNT performance so that changes or interruptions in the navigation or timing are flagged.{AU-8(1),SC-45(1)}
The [spacecraft] shall incorporate backup sources for navigation and timing.{SV-IT-1}{AU-8(1),SC-45(1),SC-45(2)}
The [spacecraft] shall have fault-tolerant authoritative time sourcing for the platform's clock.{SV-IT-1}{AU-8(2),SC-45,SC-45(1),SC-45(2),SI-13}	* Adopt voting schemes (triple modular redundancy) that include inputs from backup sources. Consider providing a second reference frame against which short-term changes or interferences can be compared. * Atomic clocks, crystal oscillators and/or GPS receivers are often used as time sources. GPS should not be used as the only source due to spoofing/jamming concerns.
All [spacecraft] commands which have unrecoverable consequence must have dual authentication prior to command execution.{AU-9(5),IA-3,IA-4,IA-10,PE-3,PM-12,SA-8(15),SA-8(21),SC-16(2),SC-16(3),SI-3(8),SI-3(9),SI-4(13),SI-4(25),SI-7(12),SI-10(6),SI-13}
The [spacecraft] shall have a method to ensure the integrity of these commands and validate their authenticity before execution.{AU-9(5),IA-3,IA-4,IA-10,PE-3,PM-12,SA-8(15),SA-8(21),SC-16(2),SC-16(3),SI-3(8),SI-3(9),SI-4(13),SI-4(25),SI-7(12),SI-10(6),SI-13}
The [spacecraft] shall utilize TRANSEC.{SV-AV-1}{CP-8,RA-5(4),SA-8(18),SA-8(19),SC-8(1),SC-8(4),SC-16,SC-16(1),SC-16(2),SC-16(3),SC-40(4)}	Transmission Security (TRANSEC) is used to ensure the availability of transmissions and limit intelligence collection from the transmissions. TRANSEC is secured through burst encoding, frequency hopping, or spread spectrum methods where the required pseudorandom sequence generation is controlled by a cryptographic algorithm and key. Such keys are known as transmission security keys (TSK). The objectives of transmission security are low probability of interception (LPI), low probability of detection (LPD), and antijam which means resistance to jamming (EPM or ECCM).
The [spacecraft] shall discriminate between valid and invalid input into the software and rejects invalid input.{SC-16(2),SI-3(8),SI-10,SI-10(3),SI-10(6)}
The [spacecraft] shall identify and reject commands received out-of-sequence when the out-of-sequence commands can cause a hazard/failure or degrade the control of a hazard or mission.{SC-16(2),SI-4(13),SI-4(25),SI-10,SI-10(6),SI-13}
If Spacewire is utilized, the [spacecraft] shall adhere to [organization]-defined time synchronization standard/protocol to synchronize time across a Spacewire network with an accuracy around 1 microsecond.{SV-AV-8}{SC-45,SC-45(1),SC-45(2)}	Example for time synchronization is Time Distribution Protocol (http://spacewire.esa.int/WG/Spacewire/SpW-WG-Mtg17-Proceedings/Documents/ISC_2011%20CCSDS%20Time%20Distribution%20over%20SpaceWire.pdf & https://amstel.estec.esa.int/tecedm/ipcores/time_sync_protocol.pdf). These activities by ESA are looking to perform standardization of a time distribution protocol, synchronization, and handling of latency, jitter, and drift
The [organization] shall ensure synchronization of system clocks within and between systems and system components..{SV-AV-3}{SC-45,SC-45(1),SC-45(2)}
The [spacecraft] shall internally monitor GPS performance so that changes or interruptions in the navigation or timing are flagged.{SV-IT-1}{SC-45(1)}