ETSI GR PDL 006 V1.1.1 (2022-08)

Permissioned Distributed Ledger (PDL); Inter-Ledger interoperability

DGR/PDL-006_Interop

General Information

• Status: Not Published
• Technical Committee: PDL - Permissioned Distributed Ledger
• Current Stage: 12 - Completion
• Due Date: 25-Aug-2022
• Completion Date: 26-Aug-2022

Standards Content (Sample)

GROUP REPORT
Permissioned Distributed Ledger (PDL);
Inter-Ledger interoperability
Disclaimer
The present document has been produced and approved by the Permissioned Distributed Ledger (PDL) ETSI Industry
Specification Group (ISG) and represents the views of those members who participated in this ISG.
It does not necessarily represent the views of the entire ETSI membership.

2 ETSI GR PDL 006 V1.1.1 (2022-08)

Reference
DGR/PDL-006_Interop
Keywords
conformity, interoperability, security, trust

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3 ETSI GR PDL 006 V1.1.1 (2022-08)
Contents
Intellectual Property Rights . 4
Foreword . 4
Modal verbs terminology . 4
Introduction . 4
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definition of terms, symbols and abbreviations . 8
3.1 Terms . 8
3.2 Symbols . 8
3.3 Abbreviations . 8
4 Why Interoperability between PDLs . 8
5 What is not Interoperability between PDLs . 9
6 Types of PDL Interoperability . 9
6.1 Unidirectional . 9
6.1.1 Description . 9
6.1.2 Data Integrity . 10
6.1.3 Data Security . 10
6.1.4 Data Format . 10
6.1.5 Standard Fields for PDL Interoperability . 10
6.1.6 Security Considerations . 11
6.2 Bidirectional . 12
7 PDL interoperability tools . 13
7.1 APIs or Tooling: as depicted in EIRA . 13
7.2 Atomic swaps . 15
7.3 Sidechains. 15
7.4 Layered value transfer protocols . 16
7.5 Apps for interoperability . 16
7.6 Ledger-of-Ledger . 18
8 PDL interoperability solutions . 18
8.1 Direct interoperability (OOP (The Once and Only Principle) . 18
8.2 Auxiliary PDL . 18
9 PDL interoperability goals/needs and recommendations . 19
9.1 Who will interoperate with (checklist from WEF) . 19
9.2 What information is exchanged . 19
9.3 Which operations are allowed . 19
9.4 Traceability and auditability . 19
9.5 Future-proof . 20
9.6 Minimal viable governance . 20
History . 21

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4 ETSI GR PDL 006 V1.1.1 (2022-08)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The declarations
pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
ETSI Web server (https://ipr.etsi.org/).
Pursuant to the ETSI Directives including the ETSI IPR Policy, no investigation regarding the essentiality of IPRs,
including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not
referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become,
essential to the present document.
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Foreword
This Group Report (GR) has been produced by ETSI Industry Specification Group (ISG) Permissioned Distributed
Ledger (PDL).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
Enabling communication between different DLT is a challenge that can be resolved in favour of scalability if
interoperability is implemented with security, however the architecture, taxonomy and ontology of the DLT landscape
is certainly very diverse and with a variety of technical issues and challenges that a lot of time and efforts are being
invested in deploying approaches and solutions. This is in favour of the ecosystem as a whole. Priorities for
multi-stakeholders are based on interoperability and cross-chain solutions for connecting the new era of internet.
The baseline for the present document is aligned with the definition of ISO/IEC 17788:2014 [i.19] whereby
Interoperability is "the ability of two or more systems or applications to exchange information and to mutually use the
information that has been exchanged".
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The European Interoperability Framework (EIF) [i.2] from the European Commission (EC) had the first version
adopted in 2010 between the new EU policies in the field of information technology with strong focus on openness and
information management, data portability, interoperability governance, and integrated service delivery. Furthermore,
National Interoperability Framework Observatory (NIFO) [i.13] produce a variety of documents with recommendations
for policy makers, researchers, and business stakeholders with the latest developments on digital government and
interoperability across Europe. On the other hand, the European Blockchain Services Infrastructure (EBSI) [i.1] is
officially established with which inter-ledger interoperability will be a key ingredient for scalable business and
connecting networks for cross-border communications. Actually, four use cases are applying on the top of EBSI and
one of them is related to trusted data sharing which is a value for considering interoperability as a priority within the
deployment of the European Digital Single Market.

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6 ETSI GR PDL 006 V1.1.1 (2022-08)
1 Scope
The present document describes the key elements of interoperability to exchange information between different ledgers
and to mutually use the information that has been exchanged.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] European Blockchain Services Infrastructure (EBSI).
NOTE: Available at https://ec.europa.eu/cefdigital/wiki/display/CEFDIGITAL/EBSI.
[i.2] European Interoperability Framework (EIF).
NOTE: Available at https://ec.europa.eu/isa2/isa2_en/.
[i.3] EU SOFIE project.
NOTE: Available at https://www.sofie-iot.eu/.
[i.4] SOFIE inter-ledger implementation.
NOTE: Available at https://github.com/SOFIE-project/Interledger.
[i.5] Inter-American Development Bank (IADB): "Quantum Resistance in Blockchain networks".
NOTE: Available at https://publications.iadb.org/publications/english/document/Quantum-Resistance-in-
Blockchain-Networks.pdf.
[i.6] ISO/TS 23635:2022: "Blockchain and distributed ledger technologies - Guidelines for
governance".
NOTE: Available at https://www.iso.org/standard/76480.html.
[i.7] D. Lagutin, F. Bellesini, T. Bragatto, A. Cavadenti, V. Croce, Y. Kortesniemi, H. C. Leligou, Y.
Oikonomidis, G. C. Polyzos, G. Raveduto, F. Santori, P. Trakadas, and M. Verber: "Secure Open
Federation of IoT Platforms Through Interledger Technologies" - The SOFIE Approach. In
Proceedings of European Conference on Networks and Communication (EuCNC) 2019. Valencia,
Spain, 2019.
[i.8] R. Neisse, J. L. Hernandez-Ramos, S. N. Matheu-Garcia, G. Baldini, A. Skarmeta, V. Siris, D.
Lagutin, P. Nikander: "An Interledger Blockchain Platform for cross-border Management of
Cybersecurity Information". IEEE Internet Computing, pp. 1-11. IEEE, June 2020.
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[i.9] D. Lagutin, Y. Kortesniemi, V. A. Siris, N. Fotiou, G. C. Polyzos and L. Wu.: "Leveraging
Interledger Technologies in IoT Security Risk Management". Chapter in: Security Risk
Management for the Internet of Things: Technologies and Techniques for IoT Security, Privacy
and Data Protection, pp. 229-246. now publishers, June 2020.
[i.10] European Interoperability Reference Architecture (EIRA).
NOTE: Available at https://joinup.ec.europa.eu/collection/european-interoperability-reference-architecture-
eira/about.
[i.11] European Solution Architecture Template (SAT) in EIRA.
NOTE: Available at https://joinup.ec.europa.eu/sites/default/files/document/2019-06/Detailed-
level%20Interoperability%20Requirements%20Solution%20Architecture%20Template%20%28DL%20S
AT%29%20Design%20Guidelines.pdf.
[i.12] European Library of Interoperability Specifications (ELIS).
NOTE: Available at https://joinup.ec.europa.eu/collection/common-assessment-method-standards-and-
specifications-camss/solution/elis/release/v110 and https://joinup.ec.europa.eu/collection/imaps-
interoperability-maturity-assessment-public-service.
[i.13] National Interoperability Framework Observatory (NIFO).
NOTE: Available at https://joinup.ec.europa.eu/collection/nifo-national-interoperability-framework-
observatory/3-interoperability-layers#3.1.
[i.14] V.A. Siris, P. Nikander, S. Voulgaris, N. Fotiou, D. Lagutin, G.C. Polyzos: "Interledger
Approaches", IEEE Access, vol. 7, 89948-89966, 2019. DOI: 10.1109/ACCESS.2019.2926880.
NOTE: Available at
https://acris.aalto.fi/ws/portalfiles/portal/35799505/ELEC_Siris_Interledger_approaches_IEEEAccess.pdf
[i.15] A. Back, M. Corallo, L. Dashjr, M. Friedenbach, G. Maxwell, A. Miller, A. Poelstra, J. Timón,
and P. Wuille: "Enabling Blockchain Innovations with Pegged Sidechains".
NOTE: Available at https://blockstream.com/sidechains.pdf.
nd
[i.16] Regulation (EU) 2018/1724 of the European Parliament and of the Council of 2 October 2018
establishing a single digital gateway to provide access to information, to procedures and to
assistance and problem-solving services and amending Regulation (EU) No 1024/2012.
NOTE: Available at https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex:32018R1724.
[i.17] EU Digital Single Market.
NOTE: Available at https://toop.eu/.
[i.18] WEF: "A Framework for blockchain Interoperability 2020".
NOTE: Available at
http://www3.weforum.org/docs/WEF_A_Framework_for_Blockchain_Interoperability_2020.pdf.
[i.19] ISO/IEC 17788:2014: "Information technology — Cloud computing — Overview and
vocabulary".
[i.20] barrywhiteHat's zkrollup.
NOTE: Available at https://github.com/barryWhiteHat/roll_up.
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3 Definition of terms, symbols and abbreviations
3.1 Terms
Void.
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ABBs Architecture Building Blocks
API Application Programming Interface
DL SAT Detailed Level interoperability requirements Solution Architecture Template
DLT Distributed Ledger Technology
EBSI European Blockchain Service Infrastructure
EC European Commission
EIF European Interoperability Framework
EIRA European Interoperability Reference Architecture
EIS European Interoperability Strategy
ID IDentifier
ILP Inter-Ledger Protocol
IoT Internet of Things
NIFO National Interoperability Framework Observatory
OOP Once and Only Principle
PDL Permissioned Distributed Ledger
SAT Solution Architecture Template
SLA Service Level Agreement
URL Uniform Resource Locator
V2X Vehicle-to-everything
4 Why Interoperability between PDLs
Combining two or more DLTs using inter-ledger mechanisms allows a different tradeoff in terms of trust and cost,
allows different levels of privacy, and can increase the overall scalability and functionality. A higher or wider-scale
trust requires a larger network with more nodes and/or a more demanding consensus model. This is the case of public
ledgers, which results in a higher computation cost, hence monetary transaction cost, and higher transaction delay
compared to permissioned DLTs. Hence, transactions requiring a higher level of trust can be recorded on a public
blockchain, whereas transactions which occur frequently but for which a lower level of trust is sufficient can be
recorded on a permissioned DLT. Utilizing permissioned DLTs can support higher privacy, since all transactions on a
public blockchain are public. Hence, data can be stored in permissioned DLTs for privacy, whereas hashes of the data
stored on permissioned DLTs can be periodically stored on public blockchains to ensure immutability of the data.
Finally, multiple permissioned DLTs can be combined with a public blockchain to exploit transaction locality, hence
achieve scalability, while also allowing the permissioned DLTs to support different consensus models and programming
functionality.
The present document envisions the scenarios for multiple ledgers and distinguishing from the present document
considerations intra-chain or inside the same PDL which allows interoperability between applications but do not
communicate with other PDL. Although it is a very important dimension of the interoperability which is part of the
intrinsic mechanism of the PDL, in this clause it is an introduction for a cross-chain or inter-ledger interoperability
scenario.
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5 What is not Interoperability between PDLs
user user
user
user user user
API API API
ledger
Figure 1: Example of non inter-ledger interoperability
Within the figure 1 the scenario represents a type of interoperability which is out of the scope of the present document.
With different components operating in the same ledger with which interoperates each others inside the PDL.
6 Types of PDL Interoperability
6.1 Unidirectional
6.1.1 Description
A PDL receives information from other(s) blockchains (PDLs or not) to update their status (i.e. an oracle blockchain
pushing information to a PDL).
A PDL sends information to others blockchain (PDLs or not) (i.e. a PDL updates the status of a delivery to
vendor/procurement PDLs).
user user
user
user user user
application
API API
API
ledger
SC ledger
SC SC SC
Figure 2: Example one of inter-ledger interoperability
In this basic scenario there are two ledgers whereby interoperate between them, one PDL is exchanging information
with other PDL to mutually use such information in a perfected and common interest. As per figure 2, the two ledgers
represent two different PDL which make via Gateway or API an interoperability approach, but there are a variety of
approaches. Independent ledgers into a same scenario can approach from a key-parameters which are recommended to
be in every ledger.
When one PDL takes information from another PDL or an external data source following considerations are
recommended:
1) Data Integrity: data feed to the ledger needs to be authenticated, guarantee from the source may be attached to
prove the integrity of the data.
2) Data Security: ensure the prevention of attacks such as eavesdropping and man-in-the-middle attack.
3) Data format: ensure the data is in the format compatible to the PDL.
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6.1.2 Data Integrity
When data is fed to the PDL, it is written to the PDL for eternity. Hence its integrity and authenticity is of prime
importance. Moreover, if this data is required to execute further Smart Contracts and invoke other chained transactions
this may result in wrong executions. For example, if a Smart Contract is programmed to pay to some customer, and
wrong recipient information is fed to the contract then the customer would be different and would not satisfy the
performance because of the integrity of the data. In another example, if a malicious party tampers a bid to be entered to
a PDL, and the bid value, can feed the wrong bid to the ledger.
6.1.3 Data Security
The data entered in a PDL needs to be secured from cyber attacks such as man-in-the-middle attack and eavesdropping.
For example, if a bid is placed by a PDL and to another PDL, it is essential to secure such information exchange.
6.1.4 Data Format
Two ledgers need to understand each other, that is to say that Data exchange between a PDL and another PDL or
storage follow a compatible format. Following a mutually agreed scheme for PDL may also help with automated
chained executions of the contracts where several Smart Contracts are involved in a chained execution process.
6.1.5 Standard Fields for PDL Interoperability
When interoperating between a PDL and another PDL (unidirectionally), the following fields may be considered as
essential.
1) PDL Identifier: Every PDL should have an Identifier - this will help in recording the identity of the ledger in
the Gateway (see next clause).
2) Node Identifier: A unique Node Identifier corresponding to their PDL. For example, a PDL Identifier XY can
have a Node with Identifier XY123.
3) Shareable Data Fields: Every PDL, when they want to share their data in the future should specify the fields
to the Gateway and the fields they do not intend to be shared may not be revealed to the Gateway at all for
security reasons.
Referenced architecture for Unidirectional PDL access:
1) The PDL, intending to access data from the other PDL/storage, makes a request to the Gateway. This Gateway
is a trusted entity by both PDLs and includes its own storage with Smart Contracts. This Gateway maintains all
the records of shareable data between the PDLs, for example, some PDLs may not prefer to share certain
details, will not reveal those fields to the Gateway. Smart Contracts stored by the Gateway, may be maintained
in another PDL or trusted data storage and depend on the resources available.
2) The PDL requesting for data may include the following details in the request:
a) Its own (PDL) Identity; may be public key.
b) PDL Identity they are requesting data from.
c) Data fields they require.
d) Duration for which need access.
3) The Gateway checks the requesting PDL credentials in their own records and verifies the access rights; if all
matches provide the keys and grants the access. A Smart Contract is executed at this stage and records the
details of requesting data and the requester.
NOTE: A Smart Contract will execute in both the cases (accepting or rejecting) the data request to keep record of
all the requests.
4) Using the keys PDL1 can access record from PDL2.
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Figure 3: Example with simple scenario of interoperability between two PDL (faster procedure)
6.1.6 Security Considerations
The major security consideration here is the single point of failure for a Gateway. This means that if the Gateway is
compromised, the malicious party can take over the system and issue the keys to themselves or possibly to other
malicious part
...