ClassificationGateCheck

What it does

5-level architectural enforcement of the standard US-government classification ladder. The gate refuses if caller_clearance < data_classification.

Stage

ADMISSION — runs before the request is forwarded upstream.

The ladder

Level	Ordinal	Aliases accepted
UNCLASS	0	UNCLASSIFIED, U
CUI	1	FOUO (legacy)
SECRET	2	S
TS	3	TOP SECRET, TOPSECRET
TS/SCI	4	TS-SCI, TS_SCI, SCI

Comparison is total: SECRET >= CUI, TS/SCI >= TS, etc. Higher ordinal = more sensitive.

Headers

Header	Purpose
X-Classification	Data classification this request operates on
X-Caller-Clearance	Caller's asserted clearance level

Both default to UNCLASS when absent.

Configuration

from signet.checks import ClassificationGateCheck, ClassificationLevel

# Defaults — UNCLASS / UNCLASS, US-gov ladder
ClassificationGateCheck()

# Customize default classification when header is absent
ClassificationGateCheck(default_classification=ClassificationLevel.SECRET)

# Customize header names (rare)
ClassificationGateCheck(
    classification_header="X-Data-Tier",
    clearance_header="X-Caller-Tier",
)

For non-government hierarchies (corporate confidential / restricted / public, or healthcare PHI / PII / public), construct with your own enum or remap aliases — see source for the alias table.

Decision matrix

Data	Caller UNCLASS	Caller CUI	Caller SECRET	Caller TS	Caller TS/SCI
UNCLASS	✓	✓	✓	✓	✓
CUI	✗	✓	✓	✓	✓
SECRET	✗	✗	✓	✓	✓
TS	✗	✗	✗	✓	✓
TS/SCI	✗	✗	✗	✗	✓

✗ = HTTP 403, audit row recorded with reason "caller clearance X insufficient for data classification Y".

Pair with ScopeDriftCheck

ADMISSION-stage classification checks the declared level. The model can still try to produce output above the declared level — leaking SECRET marker strings into a UNCLASS response. ScopeDriftCheck at INSPECTION stage catches this case: it scans the accumulated output for classification markers and aborts the stream when one above the request's declared level appears.

Recommended pair:

pipeline = Pipeline(checks=[
    OwnerResolutionCheck(),
    ClassificationGateCheck(),       # ADMISSION: refuse SECRET request from UNCLASS caller
    ScopeDriftCheck(),               # INSPECTION: refuse SECRET output for UNCLASS request
    # ...
])

Common bypass attempts (and why they fail)

Attempt	Result
Omit headers	Both default to UNCLASS → allowed for UNCLASS data
Spoof X-Caller-Clearance: TS/SCI	Allowed — but identity is on the audit row. Like owner resolution, this is enforcement layered on top of platform auth.
Send X-Classification: SEEKRET	Decision.BLOCK ("unrecognized classification header value") — no fuzzy matching
Send mixed-case X-CLASSIFICATION: secret	Headers and values are case-insensitive; same as X-Classification: SECRET

Audit row example

Block:

{
  "check_name": "classification_gate",
  "decision": "block",
  "reason": "caller clearance UNCLASS insufficient for data classification SECRET",
  "metadata": {
    "classification": "SECRET",
    "clearance": "UNCLASS"
  }
}

Allow:

{
  "check_name": "classification_gate",
  "decision": "allow",
  "reason": "clearance TS cleared for SECRET",
  "metadata": {
    "classification": "SECRET",
    "clearance": "TS"
  }
}