ISO 20435

• Abstract:

  This document establishes a DLT agnostic architecture for physical assets using NFTs which includes:  An algorithmic data method for generating decentralized identifiers (DIDs) from physical assets with immutable unique identifiers, such as serial numbers.  Processes for utilizing off-chain trust anchors, to establish proof of real-world human and machine generated events and information, that tie a real-world asset to its digital representation.  A DID method scheme to enable DID Registry interoperability, so the Digital Representation can be stored, resolved, or transferred to any compliant DID Registry. This document is applicable to...  Serialized physical assets with unique immutable identifiers, such as serial numbers.  The systems, machines, organizations, and natural persons that process them. This document is not applicable to...  Fungible assets and non-serialized, non-fungible assets (unique assets without immutable identifiers).  Digital assets and identifiable bundles of assets  Any specific DID method, blockchain / DLT protocol, or NFT standard.

• Status: Not Published
• ICS: 35.240.99 - IT applications in other fields
• Technical Committee: ISO/TC 307 - Blockchain and distributed ledger technologies
• Drafting Committee: ISO/TC 307 - Blockchain and distributed ledger technologies
• Current Stage: 6000 - International Standard under publication
• Start Date: 18-Aug-2026
• Completion Date: 26-Sep-2026

Overview

ISO 20435: Framework for representing physical assets using tokens is an international standard developed by ISO to establish a Distributed Ledger Technology (DLT) agnostic architecture for representing serialized physical assets as non-fungible tokens (NFTs). This framework introduces algorithmic methods for generating decentralized identifiers (DIDs) from physical assets with immutable unique identifiers such as serial numbers. It also details processes for leveraging off-chain trust anchors to establish verifiable links between real-world events and a digital representation of assets, and a DID method scheme to promote interoperability across different DID registries.

This standard is intended for use with physical assets that possess unique, immutable identifiers. It provides guidance for systems, machines, organizations, and individuals who process these assets. ISO 20435 does not apply to fungible assets, non-serialized unique assets lacking immutable identifiers, digital-only assets, NFT standards, or specific blockchain/DLT protocols.

Key Topics

1. DLT-Agnostic Architecture

• Establishes a framework that is not tied to any single blockchain or distributed ledger protocol.
• Designed to allow the representation of physical assets across various technological ecosystems.

2. Decentralized Identifiers (DIDs)

• Offers a method for generating DIDs based on physical asset identifiers (e.g., serial numbers).
• Ensures immutability and uniqueness in asset representation.
• Enables resolving, storing, and transferring DIDs across compliant registries.

3. Off-Chain Trust Anchors

• Utilizes off-chain mechanisms to establish trust and verification, connecting real-world events to digital tokens.
• Supports both human and machine-generated information in linking physical assets to their NFT representations.

4. Tokenization of Physical Assets

• Provides methods for "wrapping" DIDs in NFTs, making unique, serialized assets digitally traceable and transferrable.
• Discusses models for asset data storage, encryption, and permanence.

5. Metadata and Data Methods

• Sets requirements for asset data objects, including schema, metadata, and traceability.
• Encourages the use of structured data for efficient asset lifecycle management.

6. Security, Privacy & Cybersecurity

• Addresses encryption, privacy, and best practices for integrating DIDs and NFTs securely.
• Supports quantum agility and compliance with current cybersecurity standards.

Applications

Supply Chain Management

• Enhanced traceability and provenance for goods with unique serial numbers.
• Automated lifecycle tracking via digital product passports and DID-linked tokens.

Asset Lifecycle Management

• Simplified documentation and management of serialized machinery, equipment, and high-value assets.
• Enables seamless asset transfer, leasing, and ownership tracking through interoperable digital records.

Regulatory Compliance

• Streamlines conformance to sector-specific traceability, anti-counterfeiting, and regulatory reporting requirements.
• Facilitates transparent audit trails for products from manufacturing to end-of-life events.

Interoperable Ecosystems

• Promotes interoperability between diverse DLT ecosystems and DID registries.
• Allows organizations to adopt NFT-based asset tracking without being locked into proprietary protocols.

Trust and Verification

• Integrates legal, human, and machine-generated trust anchors for thorough real-world event validation.

Related Standards

• ISO/TR 23644 - Pertains to decentralized identity reference architectures and provides context for trust anchor implementations.
• ISO/TC 307 Standards - Aims at blockchain and distributed ledger technologies, within which this standard is developed.
• Other DID Specifications - Such as W3C DID Core, for structuring and managing decentralized identifiers.
• Supply Chain Data Standards - That support serialized unique asset identification (e.g., GS1 identifiers).

Organizations looking to digitize the management of physical assets, improve traceability, and ensure compliance with global interoperability requirements will find ISO 20435 an essential resource as digital identity and tokenization technologies evolve.

International
Standard
First edition
Framework for representing
physical assets using tokens
Cadre pour la représentation des actifs physiques à l'aide de
jetons
PROOF/ÉPREUVE
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
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Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview . 4
4.1 Background .4
4.2 Problems to address .4
4.3 Objective of the standard .5
4.4 Use case - digital product passport (DPP) .5
5 DID registry framework or reference architecture . 7
5.1 Overview .7
5.2 DID registry framework .7
5.2.1 General .7
5.2.2 Data storage locations .8
5.3 Resolving the DID across multiple independent DID registries .8
5.3.1 General .8
5.3.2 Lookup registry.8
5.4 Tokenizing the DID data using NFTs .8
5.4.1 General .8
5.4.2 “Wrapping” the DID address in an NFT .8
5.4.3 NFT provides the DID registry encryption layer . .9
5.4.4 Benefit: Ability to leverage advanced NFT features .10
5.5 pNFT minting sequence diagram .10
5.5.1 General .10
5.5.2 User interaction with inventory system .11
5.5.3 Data handling through middleware .11
5.5.4 Off-chain storage system interaction .11
5.5.5 Verifiable data registry and universal "Lookup" . 12
5.5.6 Physical NFT (pNFT) creation . 12
5.6 Alternate tokenization implementations . 12
5.6.1 General . 12
5.6.2 Data model in DID registry only implementation . 12
5.6.3 Data model stored on-chain in the NFT layer . 12
5.7 Framework conclusion . 12
6 Physical asset identifier (PAI) generation method .12
6.1 Background and introduction . 12
6.1.1 General . 12
6.1.2 Rationale for hashing pre-existing universally unique identifiers . 13
6.1.3 Harmonization with existing supply chain standards . 13
6.2 DID generation method .14
6.2.1 General .14
6.2.2 DID generation method example .14
6.2.3 Use of alternate PAIs .14
6.3 Physical asset identifier (PAI) selection .14
6.4 PAI data object . 15
6.5 Universal serial number (USN): a “DID URL shortening” method . . 15
6.5.1 General . 15
6.5.2 USN shortening method .16
6.5.3 USN example .16
7 Asset data methods . 16
7.1 Overview & general requirements .16
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7.2 Types of asset data objects .17
7.3 Hashing method selection .17
7.3.1 Technical background . .17
7.3.2 SHA-256 is the default hashing algorithm .17
7.3.3 Storing asset data history .17
7.3.4 Use of a non-binary hash tree approach .18
7.4 Encryption of data objects .18
7.5 Data object metadata .18
7.6 Quantum agility .19
7.7 Hash tree method – details . .19
7.8 Snapshots and version identifiers . 20
7.9 Hash tree generation and updating example . . 20
7.9.1 Overview . 20
7.9.2 Initial minting of a pNFT . 20
7.9.3 Remove data object A and re-mint the pNFT .21
7.9.4 Replace data object B with D .21
7.9.5 Hash tree generation and updating example conclusion . 22
7.10 Hash tree explanation using a spreadsheet model . 22
7.10.1 General . 22
7.10.2 Snapshot 1: Initial minting . 22
7.10.3 Snapshot 2: Deletion of data object A . 22
7.10.4 Snapshot 3: deletion of B and addition of D . 23
7.10.5 Snapshot 4: modification of metadata for object D . 23
7.11 Justification for hash tree model .24
7.12 Hash tree storage location .24
7.13 Document size and computational considerations .24
7.14 Document management .24
7.15 Asset data permanence .24
8 Data objects and metadata.24
8.1 Overview .24
8.1.1 General .24
8.1.2 Schema and ontology . 25
8.1.3 Default minimum viable schema to enable the transport layer . 25
8.2 Alternative schema identification . 25
8.2.1 General . 25
8.2.2 Examples of schema identification . 26
8.3 Data object types, schemas, metadata, attributes . 26
8.3.1 General . 26
8.3.2 Global attributes . 26
8.3.3 System-level data object types . 26
8.3.4 Mandatory system-level data object types .27
8.3.5 Optional system-level data object types .27
8.3.6 Optional business-level data object types . 28
8.3.7 Traceability system integration . . 30
8.3.8 Designating permanent data objects .31
8.4 Metadata format .31
8.4.1 Ordering and required attributes .31
8.4.2 Use of structured data .31
8.5 Conclusion .31
9 Physical layer verification .32
9.1 Introduction .32
9.2 Resolving physical asset identifier (PAI) conflicts.32
9.2.1 General .32
9.2.2 Resolving ambiguity between “part number” vs “model” .32
9.2.3 Handling inconsistent identifiers for the same asset . 33
9.2.4 Handling missing identifiers . 34
9.2.5 Handling colliding identifiers . 34
9.3 Documenting data extraction methods. 36
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9.3.1 General . 36
9.3.2 Retrieval methods . 36
9.3.3 Manual data entry .37
10 DID method scheme .37
10.1 General .37
10.2 Overview of DID roles and components .37
10.3 DID document and metadata . 38
10.4 DID generation method requirements . 39
10.5 DID format and syntax . 39
10.6 Standardized DID and API operations . 39
10.6.1 General . 39
10.6.2 Resolve DID . 40
10.6.3 Register DID . . 40
10.6.4 Update DID .41
10.6.5 Deactivate DID .41
11 Trust anchors and legalities . 41
11.1 General .41
11.2 Natural person identification .42
11.2.1 Digital credential requirements .42
11.2.2 Trust anchor requirements .42
11.3 Machine/software identification requirements .42
11.3.1 Software interaction signing .42
11.3.2 Trust anchor validation .42
11.4 Issues and considerations . .42
11.4.1 Maturity of SSI/decentralized identity standards .42
11.4.2 Maturity of trust anchor standards .42
11.4.3 Legal ownership framework . . .42
11.5 Current domain-specific implementation .42
11.5.1 Role of trade and membership associations .42
11.5.2 Authority requests for device ownership .43
11.6 References to ISO/TR 23644 .43
12 Encryption, privacy and cybersecurity .43
12.1 Overview .43
12.2 DID authentication and encryption options .43
12.3 Data transfer methods for encrypted pNFTs . 44
12.3.1 General . 44
12.3.2 Off-chain re-encryption method . 44
12.3.3 Keystore transfer method . 44
12.3.4 Implementation considerations . 44
12.4 Encryption methods . 44
12.4.1 Data object encryption. 44
12.4.2 Optional individual encryption . 44
12.5 DID and USN generation security considerations . 44
12.6 Privacy considerations .45
12.6.1 Hashing and privacy .45
12.6.2 User responsibility .45
12.6.3 GDPR and privacy regulations .45
12.7 Cybersecurity best practices .45
12.8 Limitations and user responsibilities .45
12.8.1 Limitations of the standard .45
12.8.2 User responsibilities .45
12.9 References to DID method specification .45
12.10 Security conclusion .45
13 Conclusion .45
Bibliography . 47
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 307, Blockchain and distributed ledger
technologies.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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Introduction
This document outlines a framework for representing physical assets by means of tokens. The standard is
neutral on the choice of distributed ledger technology (DLT). This document introduces the universal serial
number (USN), which is a standardized identifier derived algorithmically from existing asset identifiers.
It also outlines methods for securely encoding physical asset data using decentralized identifiers (DIDs),
creating a standardized and verifiable framework that enables seamless transfers across different systems.
The framework enables comprehensive tracking of physical assets throughout their lifecycle, offering
significant environmental advantages. Additionally, this framework enables tokenization in initiatives such
as digital product passports (DPP).
The framework includes the following key components:
— A DID generation method: How to transform the existing identifiers of any physical asset that has a serial
number into a standard reproducible DID format called a USN.
— Physical asset data model: How to combine data objects about a physical asset into a standard provable
structure, using a hash tree format.
— DID method scheme with standardized application programming interface (API) endpoints: To allow
the digital representation to be transportable across independent DID registries.
— Business document classification: The minimum viable semantics that allow disparate systems to rec-
ognize the purpose (and legal requirements) of data objects.
— Physical layer verification: How to use trust anchors to verify and tie information about the real-world
object to its digital representation as per ISO/TR 23644.
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International Standard ISO 20435:2026(en)
Framework for representing physical assets using tokens
1 Scope
This document establishes a digital ledger technology (DLT) agnostic, decentralized identifier (DID)
framework for representing physical assets using tokens. This includes:
— A DID generation method: An algorithmic data method for generating DIDs from assets with immutable
unique identifiers, e.g. serial numbers.
— A cryptographic method to tie asset data objects to the DID: An algorithmic hash tree data method for
transferring a set of asset data objects that are cryptographically tied together, agnostic to any specific
DLT or blockchain system.
— A DID method scheme: A DID method scheme to enable DID registry interoperability, so the digital
representation can be stored, resolved or transferred to any compliant DID registry.
— Real world trust anchor processes: Processes for utilizing off-chain trust anchors to establish proof of
real-world human and machine generated events and information that tie a real-world asset to its digital
representation.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
W3C, Verifiable Credentials Data Model v2.0, W3C Recommendation 15 May 2025 https:// www .w3 .org/ TR/
vc -data -model/
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
asset
anything that has value to a stakeholder
[SOURCE: ISO 22739:2024, 3.1]
3.2
asset data object
data object (3.4) containing specific information about a physical asset
Note 1 to entry: Information may include documents, structured data, verified credentials or other information
representing attributes, events or states of the asset within a distributed ledger system.
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3.3
asset data set
collection of data objects (3.4) that comprehensively represent the information pertinent to a physical or
digital asset (3.1)
Note 1 to entry: This may include historical, operational and identification data.
3.4
data object
individual unit of data related to a physical asset (3.1) or its digital representation
Note 1 to entry: This data can be structured or unstructured and can include documents, images, structured data or
other digital content.
3.5
decentralized identifier
DID
identifier that is issued or managed in a decentralized system and designed to be unique within a context
Note 1 to entry: Decentralized identifiers are used in systems that do not rely on central registration authorities.
[SOURCE: ISO 22739:2024, 3.18]
3.6
DID registry
verifiable data registry (3.24) that provides the storage, resolution and management of decentralized
identifiers (DIDs) (3.5), ensuring that DIDs are accessible and verifiable across different systems and
platforms
3.7
digital asset
asset (3.1) that exists only in digital form or that is the digital representation of another asset
[SOURCE: ISO 22739:2024, 3.21]
3.8
digital product passport
DPP
digital document containing the lifecycle data of a product from manufacturing to end of life, to support
transparency, conformity and sustainability practices
3.9
digital representation of a physical asset
digital format encapsulating all essential data and attributes of a physical asset, enabling it to be uniquely
identified, managed and tracked within a digital ecosystem
3.10
DLT oracle
distributed ledger technology oracle
service that updates a distributed ledger using data from outside of a DLT system
Note 1 to entry: DLT oracles can be used by smart contracts to access data from sources external to the DLT system.
[SOURCE: ISO 22739:2024, 3.32]
3.11
lookup registry
decentralized system or service that stores and manages the resolution of digital identifiers across multiple
registries, ensuring the correct linking and retrieval of asset data and digital representations
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3.12
non-fungible
not capable of mutual substitution among individual units
Note 1 to entry: The individual units can be digital assets (3.7), e.g. tokens (3.20).
3.13
NFT
non-fungible token
token (3.20) that is non-fungible
[SOURCE: ISO 22739:2024, 3.64]
3.14
physical asset identifier
PAI
unique identifier for a physical asset, derived algorithmically, using identifiers affixed to the asset such as
serial numbers, model or manufacturer data
3.15
physical asset token
PAT
digital token that represents a physical asset within a blockchain or distributed ledger system
Note 1 to entry: PATs are designed to track ownership, authenticity and provenance of the physical asset throughout
its lifecycle. Depending on the implementation, a PAT is often realized as an NFT but can also be fungible or semi-
fungible based on the asset's characteristics and requirements.
3.16
physical NFT
pNFT
physical asset token (3.15) implemented as a non-fungible token (3.13), representing a unique physical asset
within a blockchain or distributed ledger system
Note 1 to entry: The pNFT purports to bind the digital representation of the asset to its physical counterpart, ensuring
traceability and authenticity.
3.17
root hash
single hash value at the top of the hash tree that results from consecutively hashing pairs of child node
hashes until a single hash remains
Note 1 to entry: This hash represents the entirety of the data stored in the tree. Any change in the data blocks at the
leaves of the tree causes a change in the root hash, thus providing a quick way to verify whether any data has been
altered.
3.18
semantic layer interoperability
ability of systems to use shared schema and ontologies to ensure that the content of exchanged data is
consistently understood and processed across different platforms in a verifiable manner
3.19
snapshot
unique historical version of an asset data set (3.3), minted into a physical non-fungible token (pNFT) (3.16) at
a point in time
Note 1 to entry: A snapshot serves as a single source of truth for the state of the asset at a point in time. Due to the gas
and storage costs of re-minting an NFT, off-chain systems typically make intermediate data changes to an off-chain
copy of the snapshot, only re-minting the pNFT as necessary for communication with external systems.
3.20
token
asset (3.1) that represents a collection of entitlements
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3.21
transport layer interoperability
capacity of systems to exchange data seamlessly and verifiably across a network, without interpreting or
modifying the content, regardless of differing underlying technologies or protocols
3.22
universal serial number
USN
shortened, universally unique identifier generated from the physical asset identifier (3.14) using
cryptographic hashing
Note 1 to entry: The USN is intended to simplify identification while maintaining uniqueness across systems.
3.23
verifiable credential
digital document issued by a trusted authority that contains claims about an individual, organization, or
object
Note 1 to entry: Verifiable credentials (VC) are cryptographically secure, tamper-evident and can be verified
electronically. VCs enable the holder to prove information to a verifier without revealing unnecessary personal details,
using a mechanism that ensures the integrity and authenticity of the claims presented.
[SOURCE: W3C Verifiable Credentials]
3.24
verifiable dat
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ISO #####-#:####(X/PRF 20435:2026(en)
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
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Header distance from edge: 1.27 cm, Footer distance
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
from edge: 0.5 cm
at the address below or ISO’s member body in the country of the requester.
Formatted: Widow/Orphan control
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Formatted: French (Switzerland)
EmailE-mail: [e-mail]
Formatted: French (Switzerland)
Website: www.iso.orgwww.iso.org
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Published in Switzerland
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ISO/DISPRF 20435:20252026(en)
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Foreword . ix
Introduction . x
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview . 5
4.1 Background . 5
4.2 Problems to address . 5
4.3 Objective of the standard . 5
4.4 Use case - digital product passport (DPP) . 5
5 DID registry framework or reference architecture . 8
5.1 Overview . 8
5.2 DID registry framework . 8
5.3 Resolving the DID across multiple independent DID registries . 10
5.4 Tokenizing the DID data using NFTs . 11
5.5 pNFT minting sequence diagram . 13
5.6 Alternate tokenization implementations. 16
5.7 Framework conclusion . 16
6 Physical asset identifier (PAI) generation method . 16
6.1 Background and introduction . 16
6.2 DID generation method . 18
6.3 Physical asset identifier (PAI) selection . 19
6.4 PAI data object . 19
6.5 Universal serial number (USN): a “DID URL shortening” method . 20
7 Asset data methods . 21
7.1 Overview & general requirements . 21
7.2 Types of asset data objects . 21
7.3 Hashing method selection . 22
7.4 Encryption of data objects . 23
7.5 Data object metadata . 23
7.6 Quantum agility . 23
7.7 Hash tree method – details . 23
7.8 Snapshots and version identifiers . 24
7.9 Hash tree generation and updating example . 25
7.10 Hash tree explanation using a spreadsheet model . 27
7.11 Justification for hash tree model . 30
7.12 Hash tree storage location . 30
7.13 Document size and computational considerations . 30
7.14 Document management. 30
7.15 Asset data permanence . 30
8 Data objects and metadata . 30
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8.2 Alternative schema identification . 31
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9.1 Introduction . 39
9.2 Resolving physical asset identifier (PAI) conflicts . 39
9.3 Documenting data extraction methods . 44
10 DID method scheme . 45
10.1 General. 45
10.2 Overview of DID roles and components . 45
10.3 DID document and metadata . 47
10.4 DID generation method requirements . 47
10.5 DID format and syntax . 47
10.6 Standardized DID and API operations . 48
11 Trust anchors and legalities . 50
11.1 General. 50
11.2 Natural person identification . 50
11.3 Machine/software identification requirements . 51
11.4 Issues and considerations . 51
11.5 Current domain-specific implementation . 51
11.6 References to ISO/TR 23644 . 51
12 Encryption, privacy and cybersecurity . 52
12.1 Overview . 52
12.2 DID authentication and encryption options . 52
12.3 Data transfer methods for encrypted pNFTs . 52
12.4 Encryption methods . 53
12.5 DID and USN generation security considerations . 53
12.6 Privacy considerations . 53
12.7 Cybersecurity best practices . 54
12.8 Limitations and user responsibilities . 54
12.9 References to DID method specification . 54
12.10 Security conclusion . 54
13 Conclusion . 54
Bibliography . 55

Contents . 3
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Terminology specific to this document: . 2
3.2 General terminology applicable to this document: . 3
4 Overview . 6
4.1 Background . 6
4.2 Problems to address . 6
4.3 Objective of the standard . 7
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4.4 Use case - digital product passport (DPP) . 7
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Figure 1 – Use case diagram: digital product passport (DPP) for tracking asset lifecycle . 8
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5 DID registry framework / reference architecture . 9
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5.2 DID registry framework / reference architecture . 9
Figure 2 – DID registry reference framework for supply chain implementations . 9
5.2.1 Data storage limitations . 10
5.3 Resolving the DID across multiple independent DID registries . 10
Figure 3 – DID Resolver / decentralized lookup . 11
5.3.1 Lookup registry . 11
5.4 Tokenizing the DID data using NFTs . 11
5.4.1 “Wrapping” the DID address in an NFT . 11
Figure 4 – Tokenizing the DID using an NFT (ERC-721 used as one example). 12
5.4.2 NFT provides the DID registry encryption layer . 12
5.4.3 Benefit: ability to leverage advanced NFT features . 13
5.5 pNFT minting sequence diagram . 13
Figure 5 – Sequence diagram showing pNFT minting/re-minting . 13
5.6 Alternate tokenization implementations . 14
5.6.1 Data model in DID registry only implementation . 14
5.6.2 Data model stored on-chain in the NFT layer . 14
5.7 Framework conclusion . 15
6 Physical asset identifier (PAI) generation method . 15
6.1 Background and introduction . 15
6.1.1 Rationale for hashing pre-existing universally unique identifiers . 15
6.1.2 Harmonization with existing supply chain standards . 16
6.2 DID generation method . 16
6.2.1 DID generation method example . 16
6.2.2 Use of alternate PAIs . 17
6.3 Physical asset identifier selection. 17
6.4 PAI data object . 17
6.5 Universal serial number (USN) - a “DID URL shortening” method . 18
6.5.1 USN shortening method . 18
6.5.2 USN example . 18
7 Asset data methods . 19
7.1 Overview & general requirements . 19
7.2 Types of asset data objects . 19
7.3 Hashing method selection . 19
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7.3.1 Technical background . 19
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7.3.2 SHA-256 is the default hashing algorithm . 20
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7.3.3 Storing asset data history . 20
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7.3.4 Use of a non-binary hash tree approach . 20
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7.4 Encryption of data objects . 21
7.5 Data object metadata . 21
7.6 Quantum agility . 21
7.7 Hash tree method – details . 21
7.8 Snapshots and version identifiers . 22
7.9 Hash tree generation and updating example . 23
7.9.1 Overview . 23
7.9.2 Initial minting of a pNFT . 23
Figure 6 –Root hash example, version 1 . 24
7.9.3 Remove data object A and re-mint the pNFT . 24
Figure 7 – Root hash example, document A removed . 24
7.9.4 Replace data object B with D . 24
Figure 8 – Root hash example, document B replaced by D. 25
7.9.5 Hash tree generation and updating example conclusion . 25
7.10 Hash tree explanation using a spreadsheet model . 25
7.10.1 Snapshot 1: initial minting . 25
Figure 9 – Hash tree snapshot 1 . 25
7.10.2 Snapshot 2: deletion of data object A. 25
Figure 10 – Hash tree snapshot 2 . 26
7.10.3 Snapshot 3: deletion of B and addition of D . 26
Figure 11 – Hash tree snapshot 3 . 26
7.10.4 Snapshot 4: modification of metadata for object D . 26
Figure 12 – Hash tree snapshot 4 . 26
7.11 Justification for hash tree model . 26
7.12 Hash tree storage location . 27
7.13 Document size and computational considerations . 27
7.14 Scope clarification: this is not a document management standard . 27
7.15 Asset data permanence . 27
8 Data objects and metadata . 27
8.1 Overview . 27
8.1.1 Scope of schema and ontology . 28
8.1.2 Default minimum viable schema to enable the transport layer . 28
8.2 Alternative schema identification . 28
Figure 13 – Metadata analogy . 29
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8.3 Data objects, schemas, metadata, attributes . 29
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8.3.1 System-level data objects and metadata . 29
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8.3.2 Mandatory system-level data objects. 30
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8.3.3 Optional system-level data objects . 30
8.3.4 Business-level data objects and metadata . 32
8.3.5 Traceability system integration . 33
8.3.6 Designating permanent data objects. 33
8.4 Metadata format . 34
8.4.1 Ordering and required attributes . 34
8.4.2 Use of structured data . 34
8.5 Conclusion . 34
9 Physical layer verification . 34
9.1 Introduction . 34
9.2 Resolving physical asset identifier conflicts . 35
9.2.1 Resolving ambiguity between “part number” vs “model” . 35
9.2.2 Handling inconsistent identifiers for the same asset . 35
9.2.3 Handling missing identifiers . 36
9.2.4 Handling colliding identifiers . 37
9.3 Documenting data extraction methods . 39
9.3.1 Retrieval methods . 39
9.3.2 Manual data entry . 39
10 DID method scheme . 40
10.1 Overview of DID roles and components . 40
Figure 14 – DID ecosystem . 40
10.2 DID document and metadata . 41
10.3 DID generation method requirements . 41
10.4 DID format and syntax . 42
Figure 15 – Structure of DID . 42
10.5 Standardized DID and API operations . 42
10.5.1 Resolve DID . 43
10.5.2 Register DID . 43
10.5.3 Update DID . 43
10.5.4 Deactivate DID . 44
11 Trust anchors and legalities . 44
11.1 Natural person identification . 44
11.1.1 Digital credential requirements:. 44
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11.1.2 Trust anchor requirements: . 45
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11.2 Machine/software identification requirements . 45
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11.2.1 Software interaction signing. 45
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11.2.2 Trust anchor validation . 45
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11.3 Issues and considerations . 45
11.3.1 Maturity of SSI/decentralized identity standards . 45
11.3.2 Maturity of trust anchor standards . 45
11.3.3 Legal ownership framework . 45
11.4 Current domain-specific implementation . 45
11.4.1 Role of trade and membership associations . 46
11.4.2 Authority requests for device ownership . 46
11.5 References to ISO/TR 23644:2021 . 46
12 Encryption, privacy and cybersecurity . 46
12.1 Overview . 46
12.2 Security model . 46
12.3 Data transfer methods for encrypted pNFTs . 47
12.3.1 Off-chain re-encryption method . 47
12.3.2 Keystore transfer method . 47
12.3.3 Implementation considerations . 47
12.4 Encryption methods . 47
12.5 DID and USN generation security considerations. 48
12.6 Privacy considerations . 48
12.7 Cybersecurity best practices . 48
12.8 Limitations and user responsibilities . 48
12.9 References to DID method specification . 48
12.10 Security conclusion . 48
13 Conclusion . 49
Annex A . 49
General . 49
Bibliography . 50
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ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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The procedures used to develop this document and those intended for its further maintenance are described
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This document was prepared by Technical Committee ISO/TC 307, Blockchain and distributed ledger
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Introduction
This document outlines a framework for representing physical assets by means of tokens. While the
framework could be applied to all types of assets, the implementation methods described focus on non-
fungible tangible assets with unique identifiers such as serial numbers. The standard is neutral on the choice
of digitaldistributed ledger technology (DLT). This document introduces the universal serial number (USN),
which is a standardized identifier derived algorithmically from existing asset identifiers. It also outlines
methods for securely encoding physical asset data using decentralized identifiers (DIDs), creating a
standardized and verifiable framework that enables seamless transfers across different systems.
The framework enables comprehensive tracking of physical assets througho
...