🐛 [BUG] - SA Create Does Not Validate SA State (Conformance issue)

[VissaMoutafis]

Description

Description

The sa_rekey() / SA-Create handler in
src/sa/internal/sa_interface_inmemory.template.c overwrites an existing Security
Association entry without first verifying that the target SPI is in SA_NONE state.
This means an operator can silently replace a live, operational SA — including its cryptographic
parameters — while the SA remains in service.

According to the CCSDS SDLS-EP standard (CCSDS 355.2-B-1, §3.3.1), the SA Create
procedure is only permitted when the target SPI is in the Unoccupied (NONE) state. All
other states must cause the command to be rejected.

Status on dev/main (as of 2026-03-31): The state-check guard (if (temp_sa->sa_state != SA_NONE) { return CRYPTO_LIB_ERROR; }) does not appear in
the current dev branch's sa_interface_inmemory.template.c. This issue should be
considered unpatched in the current dev branch.

---

Branch / Affected Version

• Affected: v1.4.2 (src/sa/internal/sa_interface_inmemory.template.c, ~line 1453)
• Latest tested dev commit: dev branch as of 2026-03-31

---

Reproduction Steps

Use the following packet sequence. Observe that Packet 3 (SA Create for SPI
20) succeeds unconditionally even if SPI 20 already exists in any state other than
SA_NONE.

Packet 1 – Key OTAR

002c104c000000000102000000000000000000000000000000719405af7fcd82f5c1073e5c81455b28e37b2e8b4cada60ec40bd3eea8585e2fb2e22726654fed87b83a4a912feffdf35b9c1422

Packet 2 – Key Activate

002c100e0000000002001000828a33

Packet 3 – SA Create (SPI 20) — send twice to demonstrate no state guard

002c1046000000001101d00014cc001001010c00000000000000000000000001010020000000000000000000000000000000000000000000000000000000000000000000002384

1. Send Packet 1 and Packet 2 as prerequisites.
2. Send Packet 3 the first time — SPI 20 is created successfully (sa_state = 0x1 UNKEYED).
3. Advance SPI 20 to OPERATIONAL (Packets 4, 5 below).
4. Send Packet 3 again — SPI 20 is overwritten without error. An operational SA is
   silently replaced.

---

Expected Behaviour

The second SA Create for SPI 20 (already in a non-NONE state) should be rejected with an
error code (e.g. CRYPTO_LIB_ERROR_SA) and the existing SA should be left untouched.

Actual Behaviour

The SA Create succeeds unconditionally, silently overwriting the live SA entry and resetting
all of its cryptographic parameters.

---

Logs

SA Create
spi = 20
SA status:
     spi        = 20
     sa_state   = 0x1      ← UNKEYED, regardless of prior state
     est        = 0x1
     ast        = 0x1
     shivf_len  = 12
     ...
Status code: 0             ← no error even when overwriting an operational SA

---

Proposed Fix

In src/sa/internal/sa_interface_inmemory.template.c, immediately after the lpid field
is populated (around line 1458 in v1.4.2, offsets may differ in dev), add a state-guard
block:

*** 1453,1458 ****
--- 1456,1470 ----
  // 5-8 : Procedure Identification Field (pid)
  temp_sa->lpid = (sdls_frame.tlv_pdu.hdr.type << 7) |
                  (sdls_frame.tlv_pdu.hdr.uf   << 6) |
                  (sdls_frame.tlv_pdu.hdr.sg   << 4) |
                   sdls_frame.tlv_pdu.hdr.pid;
+
+ // Check that the SA is in NONE state before creating
+ if (temp_sa->sa_state != SA_NONE)
+ {
+ #ifdef DEBUG
+     printf(KRED "ERROR: SPI %d is not in the NONE state.\n" RESET, spi);
+ #endif
+     return CRYPTO_LIB_ERROR_SA;
+ }
 
  // Write SA Configuration
  temp_sa->est = ...

---

References

• CCSDS 355.2-B-1 – SDLS Extended Procedures, §3.3.1 (SA Create state machine
  requirements)
• CCSDS 355.0-B-2 – Space Data Link Security Protocol, §4 (SA state transitions)

---

Environment

• OS: Linux (Ubuntu 22.04 / tested in Docker)
• CryptoLib version: v1.4.2
• Crypto backend: LibGcrypt 1.4.1 (internal SA/Key)
• Build flags: TC_PROCESS_SDLS_PDUS_TRUE, CRYPTO_EPROC=1

Branch Name

v1.4.2 and dev

Reproduction steps

Use the following packet sequence. Observe that **Packet 3** (SA Create for SPI
20) succeeds unconditionally even if SPI 20 already exists in any state other than
`SA_NONE`.
 
**Packet 1 – Key OTAR**

002c104c000000000102000000000000000000000000000000719405af7fcd82f5c1073e5c81455b28e37b2e8b4cada60ec40bd3eea8585e2fb2e22726654fed87b83a4a912feffdf35b9c1422

**Packet 2 – Key Activate**

002c100e0000000002001000828a33

**Packet 3 – SA Create (SPI 20) — send twice to demonstrate no state guard**

002c1046000000001101d00014cc001001010c00000000000000000000000001010020000000000000000000000000000000000000000000000000000000000000000000002384

1. Send Packet 1 and Packet 2 as prerequisites.
2. Send Packet 3 the first time — SPI 20 is created successfully (`sa_state = 0x1 UNKEYED`).
3. Advance SPI 20 to `OPERATIONAL` (Packets 4, 5 below).
4. Send **Packet 3 again** — SPI 20 is overwritten without error. An operational SA is
   silently replaced.

Screenshots

Logs

OS

Linux