Conformance Statement for pkg/sdls, CCSDS 355.0-B-2
A1.1 GENERAL INFORMATION
A1.1.1 Identification of PICS
| Field | Value |
|---|---|
| Date of Statement (DD/MM/YYYY) | 23/08/2026 |
| PICS Serial Number | ASTRO-SDLS-PICS-001 |
| System Conformance Statement Cross-Reference | This document |
A1.1.2 Identification of Implementation Under Test (IUT)
| Field | Value |
|---|---|
| Implementation Name | astro/pkg/sdls |
| Implementation Version | See go.mod / latest commit on main |
| Special Configuration | None |
| Other Information | Go library implementing the CCSDS Space Data Link Security Protocol. Ships the annex baselines: AES-256-GCM authenticated encryption with a 96-bit IV and a 128-bit MAC (clause E1/clause E3/clause E4), and AES-CMAC authentication for telecommand (clause E2). Also offers GMAC, the authentication-only companion of the GCM baselines, not an annex baseline itself. Composes with pkg/tmdl, pkg/tcdl, pkg/aos, and pkg/usdl from the outside, the protected data field is built here and handed to the frame constructor. |
A1.1.3 Identification of Supplier
| Field | Value |
|---|---|
| Supplier | Ravi Suhag |
| Contact Point for Queries | GitHub, github.com/ravisuhag/astro |
| Implementation Name(s) and Version(s) | astro/pkg/sdls (Go package) |
| System Name(s) | Astro |
A1.1.4 Identification of Specification
| Field | Value |
|---|---|
| Specification | CCSDS 355.0-B-2 (Space Data Link Security Protocol, Blue Book, Issue 2, July 2022) |
| Have any exceptions been required? | Yes [X] No [ ], see A1.5 |
A1.2 PROTOCOL DATA UNITS
| Feature | Reference | Status | Support |
|---|---|---|---|
| Security Header | clause 4.1.1 | M | Y: SPI, IV, Sequence Number, Pad Length, contiguous and in that order |
| Security Parameter Index | clause 4.1.1.2 | M | Y: 16 bits, big-endian, leading field |
| SPI reserved values rejected | clause 4.1.1.2.3 | M | Y: 0 and 65535 rejected by SecurityAssociation.Validate |
| Initialization Vector field | clause 4.1.1.3 | O | Y: width managed per SA; 12 octets for the GCM baseline |
| Sequence Number field | clause 4.1.1.4 | O | Y: width managed per SA; zero octets when the IV serves as the counter |
| Pad Length field | clause 4.1.1.5 | O | Y: carried and honored on receive; never generated (GCM needs no padding) |
| Security Header maximum 64 octets | clause 4.1.1.1.4 | M | Y: enforced by FieldLengths.Validate |
| Security Trailer | clause 4.1.2 | O | Y: MAC, fixed length per SA |
A1.3 SECURITY ASSOCIATION
| Feature | Reference | Status | Support |
|---|---|---|---|
| One service type per SA | clause 4.2.2.4 | M | |
Y: Mode is exactly one of authentication, encryption, authenticated encryption | |||
| Common SA parameters | clause 4.2.2.5 | M | |
Y: SPI plus IV, Sequence Number, Pad Length, and MAC widths | |||
| Authentication algorithm and mode | clause 4.2.2.6.1 a | M | |
Y: AES-256-GCM, GMAC, or AES-CMAC per Auth | |||
| Authentication bit mask | clause 4.2.2.6.1 b, clause 4.2.2.6.2 | M | |
Y: AuthMask, applied bitwise-AND before MAC computation. Per-frame-type constructors (Baseline) build masks with the mandatory exclusions: TM Master Channel Frame Count, AOS Frame Header Error Control, Insert Zone, and the IV. A nil mask authenticates every header octet, which for TM and AOS is stricter than the mandatory exclusions permit, use the constructors. | |||
| SA bound to GVCID / GMAP_ID | clause 4.2.2.2 | M | |
Y: Channels lists the agreed channel set; enforced by Process | |||
| IV excluded from authenticated data | clause 4.2.2.6.2 h | M | |
Y: enforced in code regardless of the mask supplied | |||
| Managed anti-replay sequence number | clause 4.2.2.6.1 c | M | |
Y: sender counter; receiver stored value | |||
| Managed sequence number window | clause 4.2.2.6.1 d | M | |
Y: SeqWindow | |||
| Managed initialization vector | clause 4.2.2.7 b | M | |
Y: big-endian counter, never reused | |||
A1.4 PROCEDURES
| Feature | Reference | Status | Support |
|---|---|---|---|
| Apply | clause 4.2.3.2.2.1 | O | |
N: see A1.5 | |||
| Apply | clause 4.2.3.2.2.2 | O | |
Y: data field unencrypted, MAC in the trailer | |||
| Apply | clause 4.2.3.2.2.3 | O | |
Y: AEAD split: data field is plaintext, masked prefix is the AAD | |||
| Sequence number incremented per frame | clause 4.2.3.4 a | M | |
Y | |||
| Authentication bit mask applied | clause 4.2.3.4 d | M | |
Y | |||
| MAC truncation to trailer width | clause 4.2.3.4 f | O | |
Y: most significant bits kept. GCM/GMAC: 12 to 16 octets (Go's crypto/ refuses shorter GCM tags). CMAC: 1 to 16 octets, since SP 800-38B clause 6.4 permits any truncation. Both baselines specify 16. | |||
| Process | clause 4.2.4.3 | M | |
Partial: the SPI is always verified before any cryptographic work. Verifying that the SA is the one agreed for the receiving channel needs channel context: Process enforces it against the SA's Channels list. Plain Process has no channel context, so that part of the check falls to the caller. | |||
| Process | clause 4.2.4.2.3.1 | O | |
Y | |||
| Process | clause 4.2.4.2.3.2 | O | |
Y | |||
| No data returned on verification failure | clause 4.2.4.2.3 | M | |
Y: every failure path returns a nil data field | |||
| Anti-replay check | clause 2.3.2.3 | M | |
Y: applied only after the MAC verifies | |||
A1.5 EXCEPTIONS AND UNSUPPORTED FEATURES
| Feature | Reference | Support | Rationale |
|---|---|---|---|
| Encryption without authentication | clause 2.3.3, clause 4.2.3.2.2.1 | N | |
Apply returns Err. Clause 2.3.3 itself warns that encryption without authentication can give a false sense of security. | |||
| Block padding generation | clause 4.2.3.3 b | N | |
GCM is a stream mode and needs none (clause E1.2 note 2). A non-zero Pad Length is still honored on receive. | |||
| SDLS Extended Procedures (key management, OTAR) | CCSDS 355.1 | N | |
A separate standard, out of scope for this package. | |||
| Over-the-air SA negotiation | clause 2.3.1.5 note | N | |
An Application Layer function, undefined by the standard. | |||
A1.6 BASELINE MODE CONFORMANCE
All four baselines are supported in full: Clause E1 (TM), clause E2 (TC), clause E3 (AOS) and Clause E4 (USLP).
clause E1, clause E3 and clause E4, AES-GCM
| Baseline parameter | Reference | Value | Support |
|---|---|---|---|
| Algorithm | clause E1.1 | AES-GCM | Y |
| Key length | clause E1.1 a | 256 bits | Y: exactly 32 octets, enforced |
| IV length | clause E1.1 b | 96 bits, transmitted in-line | Y |
| MAC length | clause E1.1 c | 128 bits | Y |
| Security Header length | clause E1.2 | 14 octets | Y |
| Security Trailer length | clause E1.3 | 16 octets | Y |
| Sequence Number field | clause E1.2 note 1 | 0 octets, IV serves as the counter | Y |
| Pad Length field | clause E1.2 note 2 | 0 octets | Y |
clause E2, AES-CMAC (telecommand)
Selected with SecurityAssociation.AuthAlgorithm = AuthCMAC.
| Baseline parameter | Reference | Value | Support |
|---|---|---|---|
| Algorithm | clause E2.1 | AES-CMAC | Y: internal/cmac, NIST SP 800-38B |
| Key length | clause E2.1 a | 256 bits | Y: exactly 32 octets, enforced |
| Sequence number | clause E2.1 b | 32 bits, transmitted in-line | Y |
| MAC length | clause E2.1 c | 128 bits | Y |
| Security Header length | clause E2.2 | 6 octets | Y |
| Initialization Vector field | clause E2.2 note | 0 octets | Y: a non-zero IV is rejected by Validate |
| Pad Length field | clause E2.2 note | 0 octets | Y |
AES-CMAC is absent from the Go standard library, so it is implemented in
internal/cmac rather than taken as a dependency. It is verified against the
AES-128 vectors of RFC 4493 clause 4 and the CMAC-AES256 vectors of the NIST
SP 800-38B example set, eight published vectors in all, the AES-256 ones being
the sizes clause E2.1 a actually requires.
Wire test vectors
The octets backing this statement live in the vector corpus — 7 vectors. Each vector names the clause it comes from and carries the derivation that produced it.
| File | |
|---|---|
sdls/protected-frame.json | 7 vectors |
These are data files, so any implementation can check itself against the same octets. See CONTRACT.md for how, and how this is verified for what rests on a published vector versus a reading of the clause.