Gateway Identification and Discovery for Decentralized Ledger Networks

Document Type Active Internet-Draft (individual)
Authors Shiping Chen  , Thomas Hardjono 
Last updated 2021-06-07
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Internet Engineering Task Force                                  S. Chen
Internet-Draft                                                    Data61
Intended status: Informational                               T. Hardjono
Expires: December 10, 2021                                           MIT
                                                            June 8, 2021

 Gateway Identification and Discovery for Decentralized Ledger Networks


   Today there is a growth in the number of blockchain and decentralized
   ledger networks (DLN) around the world, and interoperability across
   different networks represents a challenge for the value proposition
   of these networks.

   One approach for blockchain interoperability to be achieved is to
   employ gateways that permit assets to flow across the relevant
   networks of blockchains.

   However, a core requirement for interoperability is the correct
   identification of computer systems that act as gateways and the
   correct validation of the ownership of the gateway.  A secondary
   requirement is for a gateway to inquire as to the existence of an
   entity address (public key) within a given decentralized ledger

   This memo discusses options with regards gateway identification and
   verification strategies.  It looks at addressing the problem from the
   application layer and from the network layer.  It also discusses
   other options, such as relying on a third-party blockchain-registered
   identifiers and resolver services

Status of This Memo

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   This Internet-Draft will expire on December 10, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Gateway Registration, Discovery and Validation  . . . . . . .   5
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Gateway Declaration and Registration  . . . . . . . . . .   5
     4.3.  Gateway Discovery and Validation  . . . . . . . . . . . .   6
     4.4.  Verification of Identities and Addresses  . . . . . . . .   6
   5.  Network Layer Gateway Discovery and Verification  . . . . . .   7
     5.1.  Prerequisites . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  DNS-based Gateway Discovery . . . . . . . . . . . . . . .   8
   6.  Application Layer Gateway Discovery and Verification  . . . .   9
   7.  Security Consideration  . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Currently there is a growth in the number of blockchain and
   distributed ledger technology (DLT) systems being deployed worldwide
   for different areas of applications (e.g. finance, supply chains, IoT
   devices, etc.).  One notable application is in the area of digital
   assets (or virtual assets) [FATF].

   As independent autonomous systems, each decentralized ledger network
   (DLN) employs its own interior protocols (e.g. consensus protocols)

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   that manages the resources (e.g. shared ledger) relevant to the
   assets and entities in that network.  Key to the success of the
   blockchain and DLT paradigm is the interoperability between DLNs,
   permitting digital assets to be moved across DLNs in an efficient and
   secure manner.

   For the purposes of asset transfers across DLNs, one or more nodes
   within a DLN can take-on the role of a gateway that peers with other
   gateways belonging to other DLNs [ARCH].  As a node participating in
   a blockchain, a gateway has access to the resources (e.g. ledger)
   located in the interior of that blockchain.  Facing outbound, the
   gateway has the ability to peer with matching gateways to facilitate
   asset transfers.

   A core requirement for the gateway-to-gateway protocol [ODAP]
   employed by peered gateways is the is the correct identification of
   the systems that act as gateways and the correct validation of the
   ownership of the gateway.  Gateway ownership is notably important in
   cases where a digital asset bearing economic value is to be
   transferred cross-border (cross regulatory jurisdictions).

   (a) Application layer: At the application layer a gateway
   identification scheme is needed that permits an organization who
   participate in a given DLN to declare (advertise) one or more
   gateways into that DLN.  This permits organizations to establish
   peering agreements (contracts) based on the asset type, DLN and
   jurisdictions, identifying (specifying) the gateways that will be
   used to connect to the DLN.

   (b) Network layer: In order for asset transfer services to scale-up,
   some degree of automation is needed for a gateway to discover peer
   gateways in remote DLN.  This discovery must be efficient in order to
   minimize the time required for a digital asset from an originator in
   an origin DLN to be transferred cross-chain to the beneficiary in the
   destination DLN (see [ODAP]).

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as carrying significance described in RFC 2119.

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3.  Terminology

   The following are some terminology used in the current document.
   Further terminology can be found in [NIST][OSI].

   o  Decentralized ledger network (DLN): A blockchain system or an
      implementation of a decentralized ledger technology (DLT)
      consisting nodes that shares a common set of resources.  This term
      is used generically to refer to the collection of nodes as an
      autonomous system.

   o  DLN identification number: This is the unique network
      identification for a DLN.  This is akin to the AS-number issued by
      ARIN in North America for autonomous systems operated by Internet
      Service Providers.

   o  Device identity: This is the unique public-private key pair that
      is bound to the device (e.g. hardware) of the gateway.  Examples
      include the IEEE 802.1AR Secure Device Identity [DevID] and the
      TPM EK/AIK key pair [TPM].  The device identity public key may be
      represented using an X.509 certificate.

   o  Gateway service endpoint: The URL or URI at the gateway device
      that provides gateway related services, such as asset transfer/
      migration services.  See [ODAP] for a definition of the ODAP

   o  Service endpoint identity: This is the unique public-private key
      pair bound to the protocol service end-point of the gateway
      function.  This key-pair is used in the establishment of a secure
      channel with a peer gateway (e.g.  TLS).  The endpoint identity
      public key should be represented using an X.509 certificate, which
      unambiguously states the purpose of the endpoint.

   o  Owner identity: This is the unique public-private key pair of the
      entity who legally owns and operates the gateway.  For clarity
      this entity is referred to as a virtual asset service provider
      (VASP).  The VASP identity public key should be represented using
      an X.509 certificate, possibly including extended fields such as
      those found in Extended Validation (EV) X.509 certificates [CAB].

   o  Blockchain gateway service provider (BGSP): The virtual asset
      service provider that owns and operates the gateway service.  The
      term provides distinction from a technical/protocol perspective,
      since a BGSP entity is a virtual asset service provider in the
      business and regulatory sense.

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4.  Gateway Registration, Discovery and Validation

4.1.  Overview

   In the context of a digital asset transfer, a gateway identification,
   discovery and verification solution consists of mechanisms that
   permit a local gateway to obtain assurance that a given remote device
   is a gateway with verifiable identity and ownership.  That is, it
   need to obtain assurance that (a) the device is operating as a
   gateway for a designated blockchain or decentralized ledger network
   and (b) is owned by an entity operating under the relevant
   jurisdiction in the context of the digital asset in question.

   (i) gateway identity authentication: verification that the device
   with a given identification truly functions as a gateway (and not a
   rouge server masquerading as a gateway);

   (ii) gateway ownership validation: verification that a remote gateway
   is owned by the organization (e.g.  VASP) that is operating within a
   given jurisdiction;

   (iii) asset type transferability: verification that a remote gateway
   for a destination DLN is mechanically capable to receive the type of
   asset and that legally permitted to receive the type of asset.

4.2.  Gateway Declaration and Registration

   A given asset service provider may possesses multiple nodes within
   one or more DLNs globally.  Depending on the specific technical
   constraints of a given DLN (e.g. consensus model), not every node
   within the DLN may be designated to be a gateway capable of
   participating in an asset transfer between two DLNs.  As such, the
   service provider must nominate its nodes or systems specifically as
   gateways.  As such, there must be some mechanism that permits the
   asset service provider to declare that a given device or system
   serves as a gateway into a given DLN.

   One possible approach is for the service provider to publish a signed
   list of the gateways and the endpoints that implement the cross-chain
   asset transfer protocol for a given asset type.  Extending this
   notion, a directory of gateways may be established by a group or
   consortium of asset service providers as a means to share a common
   location where gateway information can be found.

   This directory approach is currently already being develop by some
   asset service providers in the context originator/beneficiary data
   for compliance to the Travel Rule regulations [FATF] dealing with
   anti-money laundering (AML).  An example is the TRISA directory

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   [TRISA], which lists business information of virtual asset service
   providers (VASP) claiming compliance to the AML regulations.  Such a
   directory could be extended to include the gateways owned and
   operated by the VASPs.

4.3.  Gateway Discovery and Validation

   When an originator (sender) in an origin DLN1 seeks to transfer
   digital assets to a beneficiary (recipient) located in a remote
   destination DLN2, a gateway G1 in DLN1 must be able locate and
   validate one (or more) gateways G2 serving DLN2.

   This discovery process must be automated as far as possible, and
   discovery should not require human intervention.  If a directory of
   gateways is available, then it should be utilized by both gateways G1
   and G2.

   Discovery, therefore, covers a number of layers and functions:

   o  Gateway network device discovery: There must be a mechanism to
      discover the gateway at the IP network layer (e.g.  IP address,
      port number) and obtain the device identity of the gateway (e.g.
      LDevID or device public key).

   o  Gateway service endpoint discovery and validation: Following the
      device discovery, there must be a mechanism to discover and verify
      the endpoint at the gateway that provide services related to its
      role as a gateway.  These include the endpoint for asset transfers
      and the endpoint for crash recovery [Crash].

4.4.  Verification of Identities and Addresses

   In many cases, an originator (sender) in an origin DLN1 may be in
   possession only of the beneficiary?s name and blockchain-address.
   This means that the gateway G1 in DLN1 must ensure that the
   beneficiary?s address exists in the DLN2 and that it is bound to the
   beneficiary entity or user in DLN2.

   Although out scope for the current work, it is perhaps worth noting
   that the responsibility of verifying the identity and legal status of
   originators and beneficiaries lies with the virtual asset service
   providers who employ technical mechanism (including gateways and
   nodes) to transact the digital assets [FATF].

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5.  Network Layer Gateway Discovery and Verification

   Gateway discovery and verification at the network layer takes a
   bottom-up strategy, where a gateway discovers a peer remote gateway
   and initiates verifications.  This is part of Phase-1 of the gateway
   architecture [ARCH].  This approach mimics the client to MTA (Message
   Transfer Agent) interaction pattern in the classic SMTP mail transfer
   protocol [RFC2821].

5.1.  Prerequisites

   To ensure the safety of the transferred digital assets, blockchain
   gateway service providers (BGSP) must be trustworthy to clients who
   use the services.  As a result, they must meet a high standard to
   ensure security and trust at different levels, ranging from business
   to networking, from hardware device to software protocol.  In
   particular, the following basic prerequisites (but not limited to)
   must be met:

   o  They must be a legal business entity registered with local
      authority.  The registration should be certified in form of a
      verifiable digital certificate.

   o  They must apply for an Autonomous System (AS) number [RFC6996]
      from ARIN, or other region networking authorities (such as RIPE
      NCC for Europe and APNIC for East and South Asia), dedicated to
      their gateway IP addresses, e.g., 888.10.10.10

   o  The IP address should be bound to a meaningful domain name by
      registering in DNS [RCF1034, RFC1035], e.g.,

   o  To be better discovered, a number of canonical names are
      registered in DNS as CNAME record as shown in Table 1.

   o  In addition, BGSP(s) should also be issued with a license/
      certificate as authorized approval to provide blockchain gateway
      services from the corresponding blockchain foundation/authority,
      and register their services with well-known business directories
      and publish on the Internet.

   Based on the above prerequisites, blockchain gateways can discover
   each other to establish trust step by step for digital asset transfer
   using either bottom-up or top-down approach.

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          Domain/Name       Type       Host/Destination

       A          888.10.10.10
          DLT1              CNAME
       A          999.10.10.10
          DLT2              CNAME

                                 Figure 1

5.2.  DNS-based Gateway Discovery

   This is a bottom-up approach to blockchain gateway discovery as shown
   in the Figure below.

          (Figure TBD - DNS-based Gateway Discovery)

                                 Figure 2

   Client (Alice) wants to transfer a certain value of digital assets
   (v) from one blockchain (DLT1) to another client (Bob) on anther
   blockchain (DLT2), which can be represented in ERC20 as follows:

   transfer(Bob_PublicKey@DLT2, v)

   The following MTA-Style protocol is specified for gateway networking
   device discovery:

   o  Alice can send the transfer request to G1 directly if Alice trusts
      G1 and G1 is pre-configured in Alice wallet; Or Alice can discover
      G1 and establish trust with G1 by following the same protocol as
      described below.

   o  As a result of receiving Alice's request, G1 lookup a gateway for
      DLT2 via DNS and DNS returns G2's IP address, e.g., 999.10.10.10

   o  (Optional) G1 can verify the ownership of the received IP address
      with 3rd party service to ensure if G2 is trustworthy.

   o  G1 sends a request for exchanging business certificate (BC) by
      embedding its business certificate in the request, which can be
      specified in the json format (see Figure).

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   o  If G1's certificate is valid, G2 will reply by sending its
      business certificate as specified (see Figure).

   o  (Optional) G1 may request for verification of Bob's blockchain
      address (public key) and (optional) his living location (for tax
      purpose) with DLT2.

               "Request": {
               "CMD": "ExchangeBC",
                     "Certificate": {
                           . . .

                                 Figure 3

               "Response": {
                     "Certificate": {
                           . . .

                                 Figure 4

   Up to this point, G1 and G2 establish trust at both business and
   network levels enough and ready to start the transfer digital asset
   (v) via the asset transfer protocol [ODAP].

6.  Application Layer Gateway Discovery and Verification

   Another approach that is commonly adopted by a community of service
   providers is for the community to share information regarding
   standardized service endpoints (e.g.  REST APIs).  There are multiple
   ways for a community of consortium of entries to share endpoints
   information, including a centralized signed-list or database, a
   replicated distributed database and more recently listing mechanisms
   based on blockchains (e.g.  DIDs).  In the following, the term
   business directory is used generically to represent the list.  An
   example of this approach is the TRISA directory currently being
   developed for Travel Rule sharing [TRISA].  Depending on the
   community of consortium, the information in the directory may be

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   publicly readable or it may be accessible only to members of the

   Applying this approach to gateways, a business entities who
   participate in the directory must proactively register (publish) its
   gateways and the DLN for which each gateway speaks.  The information
   must include minimally the following: (a) the gateway device
   identity, (b) one of more blockchains (DLNs) served by the gateway,
   (c) the identity of the business entity (e.g. asset service
   provider), (d) expiration of the information in the directory.  This
   information must be source authentic (i.e. digitally signed) by
   entity registering it.

     (Figure TBD - Application Layer Gateway Discovery and Verification)

                                 Figure 5

   Suppose that BGSP-1 and BGSP-2 provide blockchain gateway services
   for DLT1 and DLT2 with G1 and G2, respectively and both register with
   business directories and publish their services on the Internet.  As
   a result, they should easily discover each other.

   o  BGSP-1 finds BGSP-2 via one of global business directories (or
      even Google), or vice versa.  Then, they negotiate each other with
      aim to establish a business collaboration via providing cross-
      chain asset transfer services between DLT1 and DLT2 offline.  As a
      result of successful negotiation, BGSP-1 and BGSP-2 both signs a
      legal business contract for the collaboration, including
      agreements about (but not limited to) the network configuration,
      security setting, and transfer protocols to be used.

   o  Up to the agreement signed, BGSP-1 and BGSP-2 can configure each
      network and gateway servers according to the agreed settings.

   o  At runtime, when receiving a transfer request from a client
      (Alice), G1 can send a handshaking request to G2 directly for
      establishing secure channel for transferring digital asset (v) via
      the asset transfer protocol [ODAP].

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7.  Security Consideration

   In addition to the basic security setting mentioned above, the
   following technologies can also be considered as either enhancement
   or alternatives of security settings:

   HTTPS/TLS: Whenever using HTTP [RFC2616] for the protocol execution,
   HTTPS/TLS [RFC2821] must be enabled by default against eavesdropping

   DNSSEC: is a set of extensions to DNS that uses asymmetric
   cryptography to provide origin authentication and integrity checking
   for DNS data [RFC 2535].  DNSSEC ensures not just the origin of the
   DNS record, but also its integrity, which thus enhances the security
   and trust of the blockchain gateway queries if adopting DNSSEC.

   Trusted hardware and attestations: Gateways may be implemented in
   computer systems possessing a secure processor (e.g.  TPM)[ISO/IEC
   11889] or secure enclave (e.g.  SGX).  For example, server machines
   can store security keys and conducts common security operations for
   hardware authentication and authorization.  The use of device-unique
   public key pairs boiund to these types of trusted hardware, copled
   with their attestations capabilities, may significantly enhance the
   security and trust between the gateways to conduct blockchain asset
   transfer services collaboratively.

8.  IANA Consideration


9.  References

9.1.  Normative References

   [FATF]     FATF, "International Standards on Combating Money
              Laundering and the Financing of Terrorism and
              Proliferation - FATF Revision of Recommendation 15",
              October 2018, <http://www.fatf-

   [ISO]      ISO, "Blockchain and distributed ledger technologies-
              Vocabulary (ISO:22739:2020)", July 2020,

   [NIST]     Yaga, D., Mell, P., Roby, N., and K. Scarfone, "NIST
              Blockchain Technology Overview (NISTR-8202)", October
              2018, <>.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, DOI 10.17487/RFC2234,
              November 1997, <>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,

9.2.  Informative References

   [ARCH]     Hardjono, T., Hargreaves, M., and N. Smith, "An
              Interoperability Architecture for Blockchain Gateways.
              draft-hardjono-blockchain-interop-arch-02", April 2021,

   [BCH21]    Belchior, R., Correia, M., and T. Hardjono, "DLT Gateway
              Crash Recovery Mechanism, IETF, draft-belchior-gateway-
              recovery-01.", March 2021,

   [ODAP]     Hargreaves, M. and T. Hardjono, "Open Digital Asset
              Protocol, IETF, draft-hargreaves-odap-01.", November 2020,

   [RFC5939]  Andreasen, F., "Session Description Protocol (SDP)
              Capability Negotiation", RFC 5939, DOI 10.17487/RFC5939,
              September 2010, <>.

   [TRISA]    TRISA, "Travel Rule Information Sharing Architecture for
              Virtual Asset Service Providers", August 2020,

Authors' Addresses

   Shiping Chen


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   Thomas Hardjono


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