Security Protocol Engine
CCSDS SDLS / SDLS-EP Security Protocol Implementation
CCSDS Space Data Link Security (SDLS) and SDLS Extended Procedures (SDLS-EP) protocol implementation, providing the standardized framework for authentication, integrity, and encryption services at the data link layer for TM, TC, and AOS frames.
Purpose
Provide interoperable, standards-compliant security at the link layer, allowing the Ark to communicate securely with any CCSDS-compliant ground station and lunar relay, while integrating per-frame authentication and replay protection into the existing frame structure.
Context
Sits between L3-COM-EARTH-PROC (frame processing) and the crypto primitives in L3-COM-CRYPT-ENC and L3-COM-CRYPT-AUTH. Manages Security Associations (SAs), per-SA sequence counters, and security-related frame fields. Conforms to CCSDS 355.0-B-2 (SDLS) and 355.1-B (SDLS-EP).
Principles
- ▸Security Association (SA) is the unit of policy: defines algorithms, keys, sequence counters, and security parameters for a class of traffic
- ▸Per-frame Security Header includes SA identifier and sequence counter; Security Trailer carries the authentication tag (and optional encrypted payload)
- ▸Three protection services: authentication-only, encryption-only (rare), authenticated-encryption (typical)
- ▸Sequence counter prevents replay: receiver maintains expected counter window and rejects out-of-window frames
- ▸Multiple SAs allow per-VC (Virtual Channel) and per-MAP (Multiplexer Access Point) policy — e.g., commanding uses authenticated-encryption, public telemetry may be unsigned
- ▸SDLS-EP adds key management messages within the standard frame structure for in-band key rotation
Typical implementations
- ▸CCSDS 355.0-B-2 SDLS Blue Book (Recommended Standard)
- ▸CCSDS 355.1-B SDLS-EP (Extended Procedures Blue Book)
- ▸ESA Cryptolib reference implementation, used on JUICE, Sentinel
- ▸NASA Cryptography Application IP (CAI)
- ▸Three-agency interoperability testing (CNES, ESA, NASA) validated the protocol
- ▸Open-source projects: GSFC NOS3, cFS sc_cryptolib
Lunar considerations
- ▸SA configuration must support multiple lunar relay paths (LCRNS, Moonlight) with different operator trust models
- ▸Long-duration mission means SAs may be rotated through many generations of keys — SDLS-EP key management essential
- ▸Operator handover (NASA → ESA → commercial) over 100 years may require SA migration without service interruption
- ▸Storage for SA state on L1-DVT must survive radiation and reboot
- ▸Mesh networking via Bundle Protocol introduces an additional layer of authentication beyond SDLS — design must avoid conflict
Specifications
Functional
| primary function | Apply CCSDS SDLS security services to TM/TC/AOS frames |
| inputs | Transfer frames from L3-COM-EARTH-PROC (outgoing), Transfer frames from L3-COM-EARTH-MOD (incoming), Crypto services from L3-COM-CRYPT-ENC and L3-COM-CRYPT-AUTH, SA configuration commands from L3-CDH-SW |
| outputs | Protected frames with Security Header/Trailer to L3-COM-EARTH-PROC, Verified+decrypted frame payloads to L3-COM-EARTH-PROC, SA usage telemetry (counter values, rotation events), Security violation alerts (out-of-window counter, MAC failure) |
| supported standards | CCSDS 355.0-B-2 SDLS, CCSDS 355.1-B SDLS-EP |
| concurrent security associations | 32 |
| max throughput mbps | 50 |
| sequence counter check window | 1024 |
| key rotation method | SDLS-EP in-band |
Physical
| mass kg | 0.0 |
| dimensions | Software on L3-CDH-PROC |
| materials | Code on rad-hard NOR flash |
| operating temperature c | -40, 70 |
Operational
| power consumption w | 1 |
| thermal range c | -40, 70 |
| lifetime years | 100 |
| mtbf hours | 500000 |
Interfaces
Provides
- SDLS-protected frames and decryption/verification results
- Security violation events
Requires
- Encryption/decryption operations
- MAC computation/verification
- SA keys and configuration
- Persistent SA state storage
Cite this entry
Lunar Ark Codex. "Security Protocol Engine" (L3-COM-CRYPT-PROT). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-COM-CRYPT-PROT
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.