CNML Documentation
This documentation is a proposal for OIML from the OIML SMART programme. Every specification, diagram, and operational description is a draft and may change without notice as the proposal evolves.
CNML is the Certificat Numérique de Métrologie Légale, the digital certificate format for OIML type approvals developed under the OIML SMART programme. The pages below cover what CNML is, why it exists, how it works, and how each audience participates.
Overview
Concepts
OIML, BIML, CIML, and OIML-CS
The institutional context: OIML, its bodies, the OIML-CS framework, the DoMC, and how CNML relates to the institutional hierarchy.
Threshold cryptography in CNML
The five-tier hierarchy, the algorithms at each tier, and the asynchronous coordinator model.
Alignment with NIST threshold cryptography research
How CNML adopts techniques surveyed by NIST IR 8214 and the NIST Multi-Party Threshold Schemes project, applied to legal metrology.
CNML and PTB DCC
How CNML complements PTB's Digital Calibration Certificate, which operates at the calibration tier while CNML operates at the type-approval tier.
FAIR principles and D-CoC
The FAIR principles applied to legal-metrology certificates, and the D-CoC framework described in the OIML Bulletin.
BIPM Digital SI and measurement units in CNML
The authority chain from BIPM Digital SI through UnitsDB and UnitsML into CNML XML.
Architecture
System architecture
The canonical description of CNML's system architecture: the five-tier hierarchy, the certificate model layers, and the data flow.
CNML and typical PKI compared
A neutral technical comparison of CNML PKI and web TLS PKI, framed as optimizations for different problem domains.
CNML architecture choices
CNML described on its own terms: air-gapped CA, scope governance, threshold signing, transparency log, hardware key tiers, post-quantum readiness.
Distributed management
How threshold cryptography distributes signing authority across geographies, directors, and officers.
Redundancy and continuity
How the system continues to operate when directors, officers, hardware keys, or facilities are lost.
Transparency and audit
The Merkle transparency log, gossip monitoring, OpenTimestamps anchoring, and hash-chained audit log.
Hardware key tiers
The three-tier hardware model: enterprise HSM at the root, personal hardware tokens at the IA, browser IndexedDB at the signer.
Confium integration
How the Ruby CA server and the TypeScript verifier invoke the Confium Rust threshold-cryptography framework.
Implementation
Schema-driven design
The principle that the schema is the specification, the per-Recommendation YAML model, and the open/closed extension patterns.
Verification pipeline
The multi-check pipeline, the Check registry pattern, and the scope check that binds the OIML-CS framework to the verifier.
D-CoC output and FAIR interchange
The implementation of D-CoC output, RDF/XML and JSON-LD serialization, and triple-store ingestion.
Internationalization
The xml:lang per-element language model, per-Recommendation language coverage, and the planned language tiers.
Guides
Getting started
Install the packages, run the web app, and try the certificate operations.
Signing a certificate
Key generation, certificate creation, XMLDSig signing, and composite signatures.
Verifying a certificate
The seven-check pipeline, how to run it, and how to add new checks.
QR code delivery
How instance certificates are delivered via QR codes and the passport endpoint.
Transparency operations
The operator runbook: publishing the log, running a mirror with fork rejection, the registry signing ceremony, and multi-log policy.
SMI integration
How CNML connects to the SMART Measuring Instrument ecosystem via the twin GraphQL interface.
Internationalization
The xml:lang model, locale switching, and the planned language tiers.
Roles
For IAs and BIML/CIML
The operational guide for IA officers and BIML/CIML staff: certificate creation, threshold signing, scope governance, ceremony participation.
For verifiers
The verification flow, offline trust-anchor distribution, CRL refresh, and library integration.
For developers
Repository layout, build and test commands, contribution workflow, and code quality rules.
Reference
Specifications
CNML profile of SIGNATIF
The conformance claims, hierarchy mapping, scope dimensions, and gap analysis of CNML as a domain profile of the SIGNATIF trust infrastructure framework.
SIGNATIF conformance plan
The phased implementation plan for full SIGNATIF framework conformance: coverage reports, co-signatures, transparency upgrades, and the closure of every declared gap.
SIGNATIF test mapping
The mapping from every CNML test suite to the SIGNATIF abstract test suite, per claimed conformance class.
Interoperability composition
How a CNML certificate composes with W3C Verifiable Credentials and the EU Digital Product Passport.
CNML format specification
The namespace, document structure, per-Recommendation schema model, and instance certificate format.
XMLDSig profile
The canonicalization, signature method, reference transforms, and KeyInfo conventions for CNML signatures.
Scope extension OID
The X.509 v3 extension that binds an Issuing Authority to its OIML-CS scope, and the four-layer enforcement model.
Deployment manifest
The confium.toml format: tier hierarchy, quorum definitions, transparency log endpoints, and validation rules.