Internet Engineering Task Force M. Hargreaves Internet-Draft Quant Network Intended status: Informational T. Hardjono Expires: May 5, 2021 MIT November 1, 2020 Open Digital Asset Protocol draft-hargreaves-odap-01 Abstract This memo describes the Open Digital Asset Protocol (ODAP). ODAP is an asset transfer protocol that operates between two gateway devices. The protocol includes a description of virtual or digital assets held on distributed ledgers in an open and interoperable format, a session negotiation part and message passing flows between gateways connecting disparate distributed ledger technologies (DLTs). Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 5, 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Hargreaves & Hardjono Expires May 5, 2021 [Page 1] Internet-Draft ODAP November 2020 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. The Open Digital Asset Protocol . . . . . . . . . . . . . . . 5 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. ODAP Model . . . . . . . . . . . . . . . . . . . . . . . 5 4.3. Types of APIs . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Types of Flows . . . . . . . . . . . . . . . . . . . . . 6 4.5. Resources and Identifiers . . . . . . . . . . . . . . . . 6 4.6. Access Modes . . . . . . . . . . . . . . . . . . . . . . 7 4.6.1. Direct Mode: Simple Client to Gateway . . . . . . . . 7 4.6.2. Direct Mode: Client to Multiple Gateway . . . . . . . 8 4.6.3. Relay Mode: Client-initiated Gateway to Gateway . . . 9 5. ODAP Message Format, identifiers and Descriptors . . . . . . 10 5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 10 5.2. ODAP Message Format . . . . . . . . . . . . . . . . . . . 10 5.3. Digital Asset Resource Descriptors . . . . . . . . . . . 11 5.3.1. Organisation Identifier . . . . . . . . . . . . . . . 11 5.3.2. DLT Gateway / Endpoint ID . . . . . . . . . . . . . . 11 5.3.3. DLT Identifier . . . . . . . . . . . . . . . . . . . 11 5.3.4. Resource . . . . . . . . . . . . . . . . . . . . . . 11 5.3.5. Examples . . . . . . . . . . . . . . . . . . . . . . 12 5.4. Digital Asset Resource Client Descriptors . . . . . . . . 12 5.4.1. Organization Identifier . . . . . . . . . . . . . . . 12 5.4.2. DLT Gateway / Endpoint ID . . . . . . . . . . . . . . 12 5.4.3. Organizational Unit . . . . . . . . . . . . . . . . . 12 5.4.4. Name . . . . . . . . . . . . . . . . . . . . . . . . 13 5.4.5. Examples . . . . . . . . . . . . . . . . . . . . . . 13 5.5. Gateway Level Access Control . . . . . . . . . . . . . . 13 5.6. Negotiation of Security Protocols and Parameters . . . . 14 5.6.1. TLS Established . . . . . . . . . . . . . . . . . . . 14 5.6.2. Client offers supported credential schemes . . . . . 14 5.6.3. Server selects supported credential scheme . . . . . 14 5.6.4. Client asserts of proves identity . . . . . . . . . . 14 5.6.5. Sequence numbers initialized . . . . . . . . . . . . 14 5.6.6. Messages can now be exchanged . . . . . . . . . . . . 15 5.7. Asset Profile Negotiation . . . . . . . . . . . . . . . . 15 5.8. Application Profile Negotiation . . . . . . . . . . . . . 15 5.9. Digital Asset Resource Discovery . . . . . . . . . . . . 15 5.10. Accessing Resources via a DLT Gateway . . . . . . . . . . 16 5.10.1. CREATE . . . . . . . . . . . . . . . . . . . . . . . 16 5.10.2. WRITE . . . . . . . . . . . . . . . . . . . . . . . 16 5.10.3. INVOKE . . . . . . . . . . . . . . . . . . . . . . . 16 Hargreaves & Hardjono Expires May 5, 2021 [Page 2] Internet-Draft ODAP November 2020 5.10.4. LOCK . . . . . . . . . . . . . . . . . . . . . . . . 16 5.10.5. UNLOCK . . . . . . . . . . . . . . . . . . . . . . . 16 5.10.6. TRANSFER . . . . . . . . . . . . . . . . . . . . . . 16 5.10.7. SUBSCRIBE . . . . . . . . . . . . . . . . . . . . . 16 5.10.8. DESTROY . . . . . . . . . . . . . . . . . . . . . . 16 5.10.9. READ . . . . . . . . . . . . . . . . . . . . . . . . 17 5.10.10. NATIVE_TXN . . . . . . . . . . . . . . . . . . . . . 17 5.11. Response Codes . . . . . . . . . . . . . . . . . . . . . 17 5.12. Backward Compatibility . . . . . . . . . . . . . . . . . 17 6. Transfer Initiation Flow (Phase 1) . . . . . . . . . . . . . 17 7. Lock-Evidence Verification Flow (Phase 2) . . . . . . . . . . 17 7.1. Transfer Commence Request . . . . . . . . . . . . . . . . 18 7.2. Transfer Commence Response . . . . . . . . . . . . . . . 19 7.3. Evidence Validation Request . . . . . . . . . . . . . . . 19 7.4. Evidence Validation Response . . . . . . . . . . . . . . 20 8. Commitment Establishment Flow (Phase 3) . . . . . . . . . . . 21 9. Security Consideration . . . . . . . . . . . . . . . . . . . 21 10. IANA Consideration . . . . . . . . . . . . . . . . . . . . . 21 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 11.1. Normative References . . . . . . . . . . . . . . . . . . 21 11.2. Informative References . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 1. Introduction There is a lack of interoperability between individual blockchains, but also a general difficulty building open DLT networks. Extant networks are custom built and relatively closed, usually limited to networks of a single DLT type. This memo proposes at DLT-agnostic protocol in order to allow the creation of business applications that use and modify multiple DLTs, through a single programmatic interface. The target DLTs can be of any type, operated by different owners and managed using different DLT interoperability / management platforms that implement ODAP interfaces. These platforms may act as gateways or relays for the application to interact with the hosted DLTs. They are referred to herein as DLT Gateways. When correctly implemented and deployed, the protocol should provide the basis for solutions involving asset migration between two DLT systems, as well as use-cases when one side is non-DLT system (e.g. legacy system). Hargreaves & Hardjono Expires May 5, 2021 [Page 3] Internet-Draft ODAP November 2020 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 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. 3. Terminology The following are some terminology used in the current document. Further terminology can be found in [Arch]. Client application: This is the application employed by a user to interact with a gateway node. Gateway: The node of the DLT system functionally capable of acting as a gateway in an asset transfer. Sender gateway: The gateway that initiates a unidirectional asset transfer. Recipient gateway: The gateway that is the recipient side of a unidirectional asset transfer. DLT resources: The various interior protocols, data structures and cryptographic constructs that are a core part of a DLT system. Off-DLT resources: The various resources that are outside a DLT system, and are not part of the operations of the DLT system. Role: As in the classic client-server roles. In the gateway-to- gateway interaction, one gateway will take the role of the client while the other takes the role of the server, depending on the type of interaction flow. Claim: An assertion made by an Entity [JWT]. Claim Type: Syntax used for representing a Claim Value [JWT]. DLT Claim: An assertion made by a Gateway regarding the status or condition of resources (e.g. asset, public keys, etc.) accessible to that gateway within its DLT system. Hargreaves & Hardjono Expires May 5, 2021 [Page 4] Internet-Draft ODAP November 2020 4. The Open Digital Asset Protocol 4.1. Overview The Open Digital Asset Protocol (ODAP) is a gateway-to-gateway protocol used by a sender gateway with a recipient gateway to perform a unidirectional transfer of a virtual asset [Arch]. The protocol defines a number of API endpoints, resources and identifier definitions, and message flows corresponding to the asset transfer between the two gateways. +----------+ +----------+ | Client | | Off-DLT | | (Applic) | | Resource | +----------+ +----------+ | |API Type-3| | +----------+ | ^ V | +----------+ | |API Type-1| | +------+ +----------+----+ +----+----------+ +------+ | | | | | | | | | | | DLT | | Gateway |API | |API | Gateway | | DLT | | L1 |---| G1 |Type|<------>|Type| G2 |---| L2 | | | | | 2 | | 2 | | | | +------+ +----------+----+ +----+----------+ +------+ Figure 1 4.2. ODAP Model Following the gateway interoperability architecture [Arch], the model for ODAP is shown in Figure 1. The Client (application) interacts with its local gateway (G1) over an interface (API Type-1) in order to provide instructions to the gateway with regards to actions related resources located in the local DLT system (L1) and resources located in remote DLT system (L2). Gateways interact with each other over a gateway interface (API Type- 2). A given gateway may be required to access resources that are not located in DLT system L1 or DLT system L2. Access to these types of resources are performed over an Off-DLT interface (API Type-3). Hargreaves & Hardjono Expires May 5, 2021 [Page 5] Internet-Draft ODAP November 2020 4.3. Types of APIs The following are the types of APIs in ODAP: o Gateway APIs for client (API Type-1): This the REST APIs that permit a Client (application) to interact with a local gateway, and issue instructions for actions pertaining to resources accessible to the gateway in the local DLT system. o Gateway APIs for peer gateways (API Type-2): This is the REST APIs employed by two (2) peer gateways in performing unidirectional asset transfers. o APIs for validation of off-DLT resources (API Type-3): This is the REST APIs made available by a resource server (resource owner) at which a gateway can access Off-DLT resources. The use of these APIs is dependent on the mode of access and the type of flow in question. 4.4. Types of Flows The ODAP protocol defines the following three (3) flows: o Transfer Initiation flow: This flow deals with the asset profile verification, asset ownership evidence verification and identities verification. o Lock-Evidence flow: This flow deals with the conveyance of evidence regarding the lock (escrow) status of an asset by one gateway, and the verification of the evidence by the other gateway. o Commitment Establishment flow: This flow deals with the asset transfer and commitment establishment between two gateways on behalf of their DLT systems. These flow will be discussed below. 4.5. Resources and Identifiers o (a) Resource addressing for DLTs, using the URL syntax. o (b) Client identification based on the URN format. These are for identifying clients (developers and applications) who access these resources, and which in some use-cases require access authorization. Hargreaves & Hardjono Expires May 5, 2021 [Page 6] Internet-Draft ODAP November 2020 o (c) Protocol message family for negotiating authentication, authorisation, and parameters for confidential channel establishment. o (d) Resource discovery mechanism for developers and applications to discover DLT-based resources hosted at a DLT gateway. The gateway response is subject to the level of access granted to that developer or application. 4.6. Access Modes This draft proposes three (3) distinct mode of operation for Clients when accessing resources recorded a DLT. These modes make use of a gateway, with the assumption that a gateway has full access to the DLT behind the gateway. +----------+ | Client | | (Applic) | +----------+ | | (1) | V +----------+ |API Type-1| +------+ +----------+----+ | | | | | | DLT | | Gateway |API | | L1 |<--(2)---| G1 |Type| | | | | 2 | +------+ +----------+----+ Figure 2 4.6.1. Direct Mode: Simple Client to Gateway In this mode, the client uses its local gateway known to the client in order to access (e.g. local transactions to) the local DLT. This is shown in Figure 2. In the direct mode, the simplest case, a client application interacts with a single DLT gateway in order to interact with the DLTs hosted behind the gateway. Hargreaves & Hardjono Expires May 5, 2021 [Page 7] Internet-Draft ODAP November 2020 The application must be recognized and authorized by the gateway. Asset transfers between the DLTs behind the gateway are possible, and the set of operations specified in section 5.10 MUST be supported by the DLT Gateway. Additional operations specific to DLT or Gateway implementations MAY also be available. +----------+ | Client | | (Applic) |------(1)--------- +----------+ | | | (1) | | | V V +----------+ +----------+ |API Type-1| |API Type-1| +------+ +----------+ +----------+ +------+ | | | | | | | | | DLT | | Gateway | | Gateway | | DLT | | L1 |<-(2)-| G1 | | G2 |-(2)->| L2 | | | | | | | | | +------+ +----------+ +----------+ +------+ Figure 3 4.6.2. Direct Mode: Client to Multiple Gateway In this mode, the client is interacting with multiple gateways simultaneously in order to access the DLTs behind each of those gateways. The client is assumed to be performing the synchronization of actions while interacting these gateways. This is illustrated in Figure 3. Direct mode can support connections from a single application to multiple DLT gateways. The applications may assert different identities with each gateway, provided it has the relevant credentials. The applications can interact with the DLTs behind each gateway according to the authorizations granted by the gateways. Asset transfers between/across DLTs hosted behind different gateways are not supported in this mode. Hargreaves & Hardjono Expires May 5, 2021 [Page 8] Internet-Draft ODAP November 2020 4.6.3. Relay Mode: Client-initiated Gateway to Gateway In this mode, the application interacts with a single Gateway, and that Gateway acts as an intermediary to other Gateways. Connection types and security methods used in the application to gateway connection can differ from those used in the gateway to gateway connection(s). The authorization method and credentials presented on behalf of the application must be acceptable to the final target gateway(s). In Relay Mode, additional functionality is available. Asset transfers, based on a two/three phase commit are available. These rely on evidence of locks on source DLTs, which can be passed from Gateway to Gateway, insulating the application from the additional complexity and keeping the lock data private from the application. Compliant Gateways MUST implement these operations, in order to support Relay Mode. Multi-hop connections between gateways are out of scope of this document. +----------+ | Client | | (Applic) | +----------+ | (1) | V +----------+ |API Type-1| +------+ +----------+----+ +----+-------+ +------+ | | | | | | | | | | | DLT | | Gateway |API |--(2)--->|API |Gateway| | DLT | | L1 |<-(4)-| G1 |Type| |Type| G2 |-(4)->| L2 | | | | | 2 |<---(3)--| 2 | | | | | | | | | | | | | | +------+ +----------+----+ +----+-------+ +------+ Figure 4 Hargreaves & Hardjono Expires May 5, 2021 [Page 9] Internet-Draft ODAP November 2020 5. ODAP Message Format, identifiers and Descriptors 5.1. Overview This section describes (i) the phases of the ODAP protocol; (ii) the format of ODAP messages; (iii) the format for resource descriptors; (iv) a method for gateways to implement access controls; (iv) protocol for negotiating security capabilities; (v) discovery and accessing resources and provisions for backward compatibility with existing systems. 5.2. ODAP Message Format ODAP messages are exchanged between applications (clients) and DLT gateways (servers). They consist of protocol negotiation and functional messages. Messages are JSON format, with protocol specific mandatory fields, support for arbitrary authentication and authorization schemes and support for a free format field for plaintext or encrypted payloads directed at the DLT gateway or an underlying DLT. JSON format message, mandatory fields are shown below: o Version: ODAP protocol Version (major, minor). o Resource URL: Location of Resource to be accessed. o Developer URN: Assertion of developer / application identity. o Action/Response: GET/POST and arguments (or Response Code) o Credential Profile: Specify type of auth (e.g. SAML, OAuth, X.509) o Credential Block: Credential token, certificate, string o Payload Profile: Asset Profile provenance and capabilities o Application Profile: Vendor or Application specific profile o Payload: Payload for POST, responses, and native DLT txns o Sequence Number: Sequence Number. Hargreaves & Hardjono Expires May 5, 2021 [Page 10] Internet-Draft ODAP November 2020 5.3. Digital Asset Resource Descriptors Resources are identified by URL [RFC 1738] as described below: o The type is new: application/odapres o The access protocol is ODAP. Data included in the URL includes the folowing: 5.3.1. Organisation Identifier This Legal Entity Identifier (LEI) or other identifier linking resource ownership to real world entity. Any scheme for identifying DLT Gateway owners may be implemented (e.g. LEI directory, closed user group membership, SWIFT BIC, etc.). The developer or application MAY validate the identity with the issuing authority. The identifier is not a trusted identity, but MAY be relied on where trust has been established between the two parties (e.g. in a closed user group). The mechanisms to determine organizations identifiers is out of scope for the current specification. 5.3.2. DLT Gateway / Endpoint ID FQDN of the ODAP compliant DLT gateway. Required to establish IP connectivity. This MUST resolve to a valid IP address. 5.3.3. DLT Identifier Specify to gateway behind which the target DLTs operates. This field is local to the DLT gateway and is used to direct ODAP interactions to the correct underlying DLT. For example: "Hyperledger1", "Bitcoin, "EU-supply-chain". 5.3.4. Resource Specifies a resource held on the underlying DLT. This field must be meaningful to the DLT in question but is otherwise an arbitrary string. The underlying object it points to may be a DLT address, block, transaction ID, alias, etc. or a future object type not yet defined. Hargreaves & Hardjono Expires May 5, 2021 [Page 11] Internet-Draft ODAP November 2020 5.3.5. Examples odapres://quant/api.gateway1.com/ripple odapres://quant/api.gateway1.com/bitcoin/xxxxxADDRESSxxxxx 5.4. Digital Asset Resource Client Descriptors Resources are identified by URN as described below: o The type is new: application/odapclient The URN format does not imply availability or access protocol. Data included in the URN includes the folowing: 5.4.1. Organization Identifier Legal Entity Identifier (LEI) or other identifier linking resource ownership to real world entity. Any scheme for identifying DLT Gateway owners may be implemented (e.g. LEI directory, closed user group membership, BIC, etc.). The DLT Gateway MAY validate the identity with the issuing authority. The identifier is not a trusted identity, but MAY be relied on where trust has been established between the two parties (e.g. in a closed user group). 5.4.2. DLT Gateway / Endpoint ID Multi-DLT applications can operate in a mode whereby the application connects to its local DLT gateway, which then forwards application traffic to local DLTs and to remote DLTs via other ODAP gateways. Where this is the case, this field identifies the "home" gateway for this application. This may be required to carry out Gateway to Gateway handshaking and protocol negotiation, or for the server to look up use case specific data relating to the client. 5.4.3. Organizational Unit The organization unit within the organization that the client (application or developer) belongs to. This assertion should be backed up with authentication via the negotiated protocol. The purpose of this field is to allow DLT gateways to maintain access control mapping between applications and resources that are independent of the authentication and authorization schemes used, Hargreaves & Hardjono Expires May 5, 2021 [Page 12] Internet-Draft ODAP November 2020 supporting future changes and supporting counterparties that operate different schemes. 5.4.4. Name A locally unique (within the OU) identifier, which can identify the application, project or individual developer responsible for this client connection. This is the most granular unit of access control, and DLT Gateways should ensure appropriate identifiers are used for the needs of the application or use case. 5.4.5. Examples odapclient:quant/api.overledger.quant.com/research/luke.riley 5.5. Gateway Level Access Control Gateways can enforce access rules based on standard naming conventions using novel or existing mechanisms such as AuthZ protocols using the resource identifiers above, for example: odapclient://hsbc/api.overledger.hsbc.com/lending/eric.devloper can READ/WRITE odapres://quant/api.gateway1.com/bitcoin AND odapres://quant/api.gateway1.com/ripple These rules would allow a client so identified to access resources directly, for example: odapres://quant/api.gateway1.com/bitcoin/xxxxxADDRESSxxxxx This example could be an client subscribing to or writing to an address associated with a smart contract as part of its functionality. This method allows resource owners to easily grant access to individuals, groups and organizations. Individual gateway implementations may implement access controls, including subsetting and supersetting or applications or resources according to their own requirements. Hargreaves & Hardjono Expires May 5, 2021 [Page 13] Internet-Draft ODAP November 2020 5.6. Negotiation of Security Protocols and Parameters 5.6.1. TLS Established TLS 1.2 or higher MUST be implemented to protect gateway communications. TLS 1.3 or higher SHOULD be implemented where both gateways support TLS 1.3 or higher. 5.6.2. Client offers supported credential schemes Capability negotiation prior to data exchange, follows a scheme similar to the Session Description Protocol [RFC 5939]. Initially the client (application) sends a JSON block containing acceptable credential schemes, e.g. OAuth2.0, SAML in the "Credential Scheme" field of the ODAP message. 5.6.3. Server selects supported credential scheme The server (DLT Gateway) selects one acceptable credential scheme from the offered schemes, returning the selection in the "Credential Scheme" field of the ODAP message. If no acceptable credential scheme was offered, an HTPP 511 "Network Authentication Required" error is returned in the Action/Response field of the ODAP message. 5.6.4. Client asserts of proves identity The details of the assertion / verification step are specific to the chosen credential scheme and are out of scope of this document. 5.6.5. Sequence numbers initialized Sequence numbers are used to allow the server to correctly order operations from the client, some of which may be asynchronous, synchronous, idempotent with duplicate requests handled in different ways according to the use case. The initial sequence number is proposed by the client (Application) after the finalization of credential verification. The server (DLT gateway) MUST respond with the same sequence number to indicate acceptance. The client (application) increments the sequence number with each new request. Sequence numbers can be reused for retries in the event of a gateway timeout. Hargreaves & Hardjono Expires May 5, 2021 [Page 14] Internet-Draft ODAP November 2020 5.6.6. Messages can now be exchanged Handshaking is complete at this point, and the client (application) can send ODAP messages to perform actions of DLT resources, which MAY reference the ODAP Payload field. 5.7. Asset Profile Negotiation TBD 5.8. Application Profile Negotiation Where an application relies on specific extensions for operation, these can be represented in an Application Profile. For example, a payments application tracks payments through the use of a cloud based API and will only interact with Gateways that log messages to that API, a resource profile can be established: Application Name: TRACKER X-Tracker_URL: https://api.tracker.com/updates X-Tracking-Policy: Always As Gateways implement this functionality, they support the TRACKER application profile, and the application is able to expand its reach by periodically polling for the availability of the profile. This is an intentionally generalized extension mechanism for application or vendor specific functionality. 5.9. Digital Asset Resource Discovery Applications MUST be able to discover which resources they are authorized to access to the level of individual DLTs. They MAY be able to discover lower level resources. Resource discovery is handled by the DLT gateway, for instance a GET request against the gateway URL with no DLT or resource could return a list of URLs available to the requester to DLT level. This list is subject to the access controls above. DLT Gateways MAY allow applications to discover resources they do not have access to, this should be indicated the free text field, and they should implement a process for applications to request access. Hargreaves & Hardjono Expires May 5, 2021 [Page 15] Internet-Draft ODAP November 2020 Formal specification of supported resource discovery methods is out of scope of this document. 5.10. Accessing Resources via a DLT Gateway The Action field is used to access resources via the gateway. We suggest these interactions use REST semantics however a detailed API specification is out of scope of this memo. In general, we suggest exposing a common subset of functionality via API using the Action field, augmented with DLT specific or smart contract specific functionality as needed. 5.10.1. CREATE Create an object on the target DLT. 5.10.2. WRITE Write to a location on the target DLT. 5.10.3. INVOKE Invoke code on the target DLT (typically a smart contract). 5.10.4. LOCK Lock an object on the target DLT. 5.10.5. UNLOCK Unlock an object on the target DLT. 5.10.6. TRANSFER Transfer an object from one DLT to another. 5.10.7. SUBSCRIBE Subscribe to be notified of transaction affecting an object on the target DLT. 5.10.8. DESTROY Destroy an object on the target DLT. Hargreaves & Hardjono Expires May 5, 2021 [Page 16] Internet-Draft ODAP November 2020 5.10.9. READ Read an object from the target DLT. 5.10.10. NATIVE_TXN Send a signed native transaction of any kind to the target DLT. Payload consists of the native transaction. 5.11. Response Codes The DLT Gateway MUST respond with return codes indicating the failure or success of the operation. For DLTs with slow consensus mechanism, the Gateway may return codes indicating the operation has been submitted. The application may carry out further operation in future to determine the ultimate status of the operation. For Non-native transactions, the Gateway is responsible for translating the request into the appropriate native format and ensuring correct signing takes place. 5.12. Backward Compatibility It is also possible to send a fully formatted native message to the underlying DLT in the Payload field using the NATIVE_TXN operation, directed to a resource URL. This allows existing DLT native code to be ported to ODAP infrastructures with minimal change. 6. Transfer Initiation Flow (Phase 1) TBD. 7. Lock-Evidence Verification Flow (Phase 2) This section describes the conveyance of claims regarding to the status of assets or resources from a sender gateway to a recipient gateway. In the following, the sender gateway takes the role of the client while the recipient gateway takes the role of the server. The client makes a request (POST) to the Transfer Request Endpoint (API Type-3) at the server gateway. Gateways as servers MUST support the use of the HTTP GET and POST methods defined in RFC 2616 [RFC2616] at the Transfer Request Endpoint and the Evidence Validation Endpoint. Hargreaves & Hardjono Expires May 5, 2021 [Page 17] Internet-Draft ODAP November 2020 Clients MAY use the HTTP GET or POST methods to send the Transfer Commence Request or the Evidence Validation Request to the Recipient Server. If using the HTTP GET method, the request parameters maybe serialized using URI Query String Serialization. The client and server may be required to sign certain messages in order to provide standalone proof (for non-repudiation) independent of the secure channel between the client and server. This proof maybe required for audit verifications post-event. (NOTE: nonces are not shown). 7.1. Transfer Commence Request This message is sent from the client (sender gateway) to the Transfer Request Endpoint at the server. It signals to the server that the client is ready to start the transfer of the digital asset. The message must contain claims related to the information from the previous flow (Phase 1). It must be signed by the client (sender gateway). The parameters of this message consists of the following: message_type REQUIRED. MUST be the value urn:ietf:odap:msgtype:transfer-commence-req originator_pubkey REQUIRED. This is the public key of the asset owner (originator) in the origin DLT system. beneficiary_pubkey REQUIRED. This is the public key of the beneficiary in the destination DLT system. sender_dlt_system REQUIRED. This is the identifier of the origin DLT system behind the client. recipient_dlt_system REQUIRED. This is the identifier of the destination DLT system behind the server. hash_asset_profile REQUIRED. This is the hash of the asset profile previously agreed upon. asset_unit REQUIRED. This is the unit amount of the asset being transferred, previously agreed upon. client_identity REQUIRED. This is the device identity of the client (sender gateway). Hargreaves & Hardjono Expires May 5, 2021 [Page 18] Internet-Draft ODAP November 2020 server_identity REQUIRED. This is the device identity of the server (recipient gateway). client_transfer_number OPTIONAL. This is the transfer identification number chosen by the client. This number is meaningful only the client. 7.2. Transfer Commence Response This message is sent from the server (recipient gateway) to client (sender gateway) in response to a Transfer Commence Request from the client. The message must be signed by the server (recipient gateway). The parameters of this message consists of the following: message_type REQUIRED. MUST be the value urn:ietf:odap:msgtype:transfer-commence-resp client_identity REQUIRED. This is the device identity of the client (sender gateway). server_identity REQUIRED. This is the device identity of the server (recipient gateway). hash_commence_request REQUIRED. This is the hash of the Transfer Commence Request received at the server from the previous message. client_transfer_number OPTIONAL. This is a replay of the client_transfer_number (if present) in the Transfer Commence Request received from the client. server_transfer_number OPTIONAL. This is the transfer identification number chosen by the server. This number is meaningful only the server. 7.3. Evidence Validation Request This message is used client (sender gateway) to convey lock/escrow evidence to the server (recipient gateway). This message is sent from the client to the Evidence Validation Endpoint at the server. The server must validate the lock evidence claims in this message. The message must be signed by the client (sender gateway). Hargreaves & Hardjono Expires May 5, 2021 [Page 19] Internet-Draft ODAP November 2020 The parameters of this message consists of the following: message_type REQUIRED. MUST be the value urn:ietf:odap:msgtype:evidence-validate-req client_identity REQUIRED. This is the device identity of the client (sender gateway). server_identity REQUIRED. This is the device identity of the server (recipient gateway). lock_evidence_claim REQUIRED. This is one or more claims signed by the client (sender gateway) that the asset in question has been locked or escrowed and under the control of the client. lock_claim_format OPTIONAL. lock_evidence_expiration REQUIRED. This is the duration of the lock or escrow, beyond which the evidence claim becomes stale or invalid. hash_commence_response REQUIRED. This is the hash of the Transfer Commence Response received by at the client in the previous message. client_transfer_number OPTIONAL. server_transfer_number OPTIONAL. 7.4. Evidence Validation Response This message is sent from the server (recipient gateway) to client (sender gateway) in response to Evidence Validation Request from the client. The message must be signed by the server (recipient gateway). A signed response indicates the server has validated the lock evidence claims and wishes to proceed with the transfer. The parameters of this message consists of the following: message_type REQUIRED. MUST be the value urn:ietf:odap:msgtype:evidence-validate-resp client_identity REQUIRED. This is the device identity of the client (sender gateway). server_identity REQUIRED. This is the device identity of the server (recipient gateway). Hargreaves & Hardjono Expires May 5, 2021 [Page 20] Internet-Draft ODAP November 2020 hash_evidence_validate_req REQUIRED. This is the hash of the Evidence Validation Request received by at the server in the previous message. client_transfer_number OPTIONAL. server_transfer_number OPTIONAL. 8. Commitment Establishment Flow (Phase 3) TBD. 9. Security Consideration Although the current interoperability architecture for blockchain gateways assumes the externalization of the value of assets, as a blockchain system holds an increasing number of virtual assets it becomes attractive to attackers seeking to obtain cryptographic keys of its nodes and its end-users. Gateway nodes are of particular interest to attackers because they enable the transferal of virtual assets to external blockchain systems, which may or may not be regulated. As such, hardening technologies and tamper-resistant crypto-processors (e.g. TPM, SGX) should be used for implementations of gateways [HS19]. Due to the consensus-based nature of the underlying DLT technologies, gateway responses may be conditional and require verification, for instance if the DLT is undergoing a byzantine attack at the time of the request. The application must evaluate the correctness of responses from the gateway in context and may need to perform further verification steps with later ODAP calls. The application may base this evaluation on the number of DLT nodes the gateway has interacted with in order to fulfil the request. 10. IANA Consideration (TBD) 11. References 11.1. Normative References Hargreaves & Hardjono Expires May 5, 2021 [Page 21] Internet-Draft ODAP November 2020 [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, . 11.2. Informative References [Arch] Hardjono, T., Hargreaves, M., and N. Smith, "An Interoperability Architecture for Blockchain Gateways. draft-hardjono-blockchain-interop-arch-01", October 2020, . [HS2019] Hardjono, T. and N. Smith, "Decentralized Trusted Computing Base for Blockchain Infrastructure Security, Frontiers Journal, Sepcial Issue on Blockchain Technology, Vol. 2, No. 24", December 2019, . [NIST] Yaga, D., Mell, P., Roby, N., and K. Scarfone, "NIST Blockchain Technology Overview (NISTR-8202)", October 2018, . [RFC5939] Andreasen, F., "Session Description Protocol (SDP) Capability Negotiation", RFC 5939, DOI 10.17487/RFC5939, September 2010, . Authors' Addresses Martin Hargreaves Quant Network Email: martin.hargreaves@quant.network Thomas Hardjono MIT Email: hardjono@mit.edu Hargreaves & Hardjono Expires May 5, 2021 [Page 22]