Internet DRAFT - draft-hargreaves-sat-core

draft-hargreaves-sat-core







Internet Engineering Task Force                            M. Hargreaves
Internet-Draft                                             Quant Network
Intended status: Informational                               T. Hardjono
Expires: 12 September 2023                                           MIT
                                                             R. Belchior
                                                         Technico Lisboa
                                                           11 March 2023


                 Secure Asset Transfer Protocol (SATP)
                      draft-hargreaves-sat-core-02

Abstract

   This memo This memo describes the Secure Asset Transfer (SAT)
   Protocol for digital assets.  SAT is a protocol operating between two
   gateways that conducts the transfer of a digital asset from one
   gateway to another.  The protocol establishes a secure channel
   between the endpoints and implements a 2-phase commit to ensure the
   properties of transfer atomicity, consistency, isolation and
   durability.

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 12 September 2023.

Copyright Notice

   Copyright (c) 2023 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



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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  The Secure Asset Transfer Protocol  . . . . . . . . . . . . .   5
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  SAT Model . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Types of APIs . . . . . . . . . . . . . . . . . . . . . .   6
     4.4.  Types of Flows  . . . . . . . . . . . . . . . . . . . . .   6
     4.5.  Resources and Identifiers . . . . . . . . . . . . . . . .   7
   5.  SATP Message Format, identifiers and Descriptors  . . . . . .   7
     5.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  SATP Message Format . . . . . . . . . . . . . . . . . . .   7
     5.3.  Digital Asset Resource Descriptors  . . . . . . . . . . .   8
       5.3.1.  Organization Identifier . . . . . . . . . . . . . . .   8
       5.3.2.  Gateway / Endpoint ID . . . . . . . . . . . . . . . .   9
       5.3.3.  Network or system Identifier  . . . . . . . . . . . .   9
       5.3.4.  Resource  . . . . . . . . . . . . . . . . . . . . . .   9
       5.3.5.  Examples  . . . . . . . . . . . . . . . . . . . . . .   9
     5.4.  Digital Asset Resource Client Descriptors . . . . . . . .   9
       5.4.1.  Organization Identifier . . . . . . . . . . . . . . .  10
       5.4.2.  Gateway / Endpoint ID . . . . . . . . . . . . . . . .  10
       5.4.3.  Organizational Unit . . . . . . . . . . . . . . . . .  10
       5.4.4.  Name  . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.4.5.  Examples  . . . . . . . . . . . . . . . . . . . . . .  10
     5.5.  Gateway Level Access Control  . . . . . . . . . . . . . .  11
     5.6.  Negotiation of Security Protocols and Parameters  . . . .  11
       5.6.1.  TLS Established . . . . . . . . . . . . . . . . . . .  11
       5.6.2.  Client offers supported credential schemes  . . . . .  11
       5.6.3.  Server selects supported credential scheme  . . . . .  11
       5.6.4.  Client asserts or proves identity . . . . . . . . . .  12
       5.6.5.  Sequence numbers initialized  . . . . . . . . . . . .  12
       5.6.6.  Messages can now be exchanged . . . . . . . . . . . .  12
     5.7.  Asset Profile Identification  . . . . . . . . . . . . . .  12
     5.8.  Application Profile Negotiation . . . . . . . . . . . . .  12
     5.9.  Discovery of Digital Asset Resources  . . . . . . . . . .  13
   6.  Identity and Asset Verification Flow (Stage 0)  . . . . . . .  13
   7.  Transfer Initiation Flows (Stage 1) . . . . . . . . . . . . .  14
     7.1.  Initialization Request Message (Stage 1)  . . . . . . . .  15
     7.2.  Initialization Request Message Response (Stage 1) . . . .  16
   8.  Lock-Assertion Flows (Stage 2)  . . . . . . . . . . . . . . .  17
     8.1.  Transfer Commence Message . . . . . . . . . . . . . . . .  18



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     8.2.  Commence Response Message (ACK-Commence)  . . . . . . . .  20
     8.3.  Lock Assertion Message  . . . . . . . . . . . . . . . . .  21
     8.4.  Lock Assertion Receipt Message (Assertion-Receipt)  . . .  22
   9.  Commitment Establishment Flow (Stage 3) . . . . . . . . . . .  23
     9.1.  Commit Preparation Message (Commit-Prepare) . . . . . . .  23
     9.2.  Commit Preparation Acknowledgement (ACK-Prepare)  . . . .  24
     9.3.  Commit Ready Message (Commit-Ready) . . . . . . . . . . .  25
     9.4.  Commit Final Message (Commit-Final) . . . . . . . . . . .  26
     9.5.  Commit-Final Acknowledgement Message (ACK-Final)  . . . .  26
     9.6.  Transfer Complete Message . . . . . . . . . . . . . . . .  27
   10. Security Consideration  . . . . . . . . . . . . . . . . . . .  28
   11. IANA Consideration  . . . . . . . . . . . . . . . . . . . . .  28
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     12.2.  Informative References . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   This memo proposes a secure asset transfer protocol (SATP) that is
   intended to be deployed between two gateway endpoints to transfer a
   digital asset from an origin network to a destination network.

   Both the origin and destination networks are assumed to be opaque in
   the sense that the interior constructs of a given network is not
   read/write accessible to unauthorized entities.

   The protocol utilizes the asset burn-and-mint paradigm whereby the
   asset to be transferred is permanently disabled or destroyed (burned)
   at the origin network and is re-generated (minted) at the destination
   network.  This is achieved through the coordinated actions of the
   peer gateways handling the unidirectional transfer at the respective
   networks.

   A gateway is assumed to be trusted to perform the tasks involved in
   the asset transfer.

   The overall aim of the protocol is to ensure that the state of assets
   in the origin and destination networks remain consistent, and that
   asset movements into (out of) networks via gateways can be accounted
   for.

   There are several desirable technical properties of the protocol.
   The protocol must ensure that the properties of atomicity,
   consistency, isolation, and durability (ACID) are satisfied.






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   The requirement of consistency implies that the asset transfer
   protocol always leaves both networks in a consistent state (that the
   asset is located in one system/network only at any time).

   Atomicity means that the protocol must guarantee that either the
   transfer commits (completes) or entirely fails, where failure is
   taken to mean there is no change to the state of the asset in the
   origin (sender) network.

   The property of isolation means that while a transfer is occurring to
   a digital asset from an origin network, no other state changes can
   occur to the asset.

   The property of durability means that once the transfer has been
   committed by both gateways, that this commitment must hold regardless
   of subsequent unavailability (e.g. crash) of the gateways
   implementing the SAT protocol.

   All messages exchanged between gateways are assumed to run over
   TLS1.2, and the endpoints at the respective gateways are associated
   with a certificate indicating the legal owner (or operator) of the
   gateway.

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:

   Client application: This is the application employed by a user to
   interact with a gateway.

   Gateway: The computer 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.



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   Claim: An assertion made by an Entity [JWT].

   Claim Type: Syntax used for representing a Claim Value [JWT].

   Gateway Claim: An assertion made by a Gateway regarding the status or
   condition of resources (e.g. assets, public keys, etc.) accessible to
   that gateway (e.g. within its network or system).

4.  The Secure Asset Transfer Protocol

4.1.  Overview

   The Secure Asset Transfer Protocol (SATP) is a gateway-to-gateway
   protocol used by a sender gateway with a recipient gateway to perform
   a unidirectional transfer of a digital asset.

   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-net  |
                |   (App)  |                | Resource |
                +----------+                +----------+
                     |                      |API Type-3|
                     |                      +----------+
                     |                           ^
                     V                           |
                +----------+                     |
                |API Type-1|                     |
     +------+   +----------+----+        +----+----------+   +------+
     |      |   |          |    |        |    |          |   |      |
     | Net. |   | Gateway  |API |        |API | Gateway  |   | Net. |
     | NW1  |---|    G1    |Type|<------>|Type|    G2    |---| NW2  |
     |      |   |          | 2  |        | 2  |          |   |      |
     +------+   +----------+----+        +----+----------+   +------+


                                  Figure 1

4.2.  SAT Model

   The model for SATP is shown in Figure 1.






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   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 to assets and related resources
   located in the local system or network (NW1).

   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 network NW1 or network NW2.  Access to these types of
   resources are performed over an off-network interface (API Type-3).

4.3.  Types of APIs

   The following are the types of APIs in SATP:

   *  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.

   *  Gateway APIs for peer gateways (API Type-2): This is the REST APIs
      employed by two (2) peer gateways in performing unidirectional
      asset transfers.

   *  APIs for validation of off-network resources (API Type-3): This is
      the REST APIs made available by a resource server (resource owner)
      at which a gateway can access 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 SAT protocol defines the following three (3) flows:

   *  Transfer Initiation flow: This flow deals with commencing a
      transfer from one gateway to another.  Several tasks are involved,
      including (but not limited to): (i) gateway identification and
      mutual authentication; (ii) exchange of asset type (definition)
      information; (iii) verification of the asset definition, and
      others.

   *  Lock-Assertion flow: This flow deals with the conveyance of signed
      assertions from the sender gateway to the receiver gateway
      regarding the locked status of an asset at the origin network.

   *  Commitment Establishment flow: This flow deals with the asset
      transfer and commitment establishment between two gateways.




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   These flow will be discussed below.

4.5.  Resources and Identifiers

   (a) Resource addressing for systems or networks, using the URL
   syntax.

   (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.

   (c) Protocol message family for negotiating authentication,
   authorisation, and parameters for confidential channel establishment.

   (d) Resource discovery mechanism for developers and applications to
   discover resources hosted at a gateway.  The gateway response is
   subject to the level of access granted to that developer or
   application.

5.  SATP Message Format, identifiers and Descriptors

5.1.  Overview

   This section describes (i) the phases of SATP; (ii) the format of
   SATP 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.  SATP Message Format

   SATP messages are exchanged between applications (clients) and
   gateways (servers).  They consist of protocol negotiation and
   functional messages.

   Messages are in JSON format, with protocol specific mandatory fields,
   support for several authentication and authorization schemes and
   support for a free format field for plaintext or encrypted payloads
   directed at the gateway.

   JSON format message, mandatory fields are shown below:

   *  Version: SATP protocol Version (major, minor).

   *  Message Type: This refers to the type of request or response to be
      conveyed in this message.




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   *  Session ID: unique identifier (UUIDv2) representing a session
      between two gateways handling a single unidirectional transfer.

   *  Sequence Number: Monotonically increasing counter that uniquely
      represents a message from a session.

   *  Resource URL: Location of Resource to be accessed.

   *  Developer URN: Assertion of developer / application identity.

   *  Action/Response: GET/POST and arguments (or Response Code)

   *  Credential Profile: Specify type of auth (e.g.  SAML, OAuth,
      X.509)

   *  Credential Block: Credential token, certificate, string

   *  Payload Profile: Asset profile and capabilities

   *  Application Profile: Vendor or Application specific profile

   *  Payload: Payload for POST, responses, and local networks.  The
      payload is specific to the current SAT phase.

   *  Payload Hash: hash of the current message payload.

   *  Message signature: Gateway EDCSA signature over the message

   Other relevant attributes may exists that need to be captured for
   logging purposes.

5.3.  Digital Asset Resource Descriptors

   Resources are identified by URL [RFC 1738] as described below:

   *  The type is new: application/satres

   *  The access protocol is SATP.

   Data included in the URL includes the folowing:

5.3.1.  Organization Identifier

   This MAY be a Legal Entity Identifier (LEI) or other identifier
   linking resource ownership to a real world entity.  Any scheme for
   identifying gateway owners may be implemented (e.g.  LEI directory,
   closed user group membership, SWIFT BIC, etc.).




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   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.  Gateway / Endpoint ID

   FQDN of the SATP compliant gateway.  Required to establish IP
   connectivity.  This MUST resolve to a valid IP address.

5.3.3.  Network or system Identifier

   Specific to the gateway behind which the target network operates.
   This field is local to the gateway and is used to direct SATP
   interactions to the correct underlying network.  This value maybe
   alphanumeric or a hexadecimal value.

   For example: "tradelens-network", "EU-supply-chain".

5.3.4.  Resource

   Specifies a resource held on the underlying network.  This field must
   be meaningful to the network in question but is otherwise an
   arbitrary string.  The underlying object it points to may be a
   network address, data block, transaction ID, alias, etc. or a future
   object type not yet defined.

5.3.5.  Examples

   satpres://quant/api.gateway1.com/swift

5.4.  Digital Asset Resource Client Descriptors

   Resources are identified by URN as described below:

   *  The type is new: application/satpclient

   The URN format does not imply availability of access protocol.

   Data included in the URN includes the following:








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5.4.1.  Organization Identifier

   Legal Entity Identifier (LEI) or other identifier linking resource
   ownership to a real-world entity.  Any scheme for identifying Gateway
   owners may be implemented (e.g.  LEI directory, closed user group
   membership, BIC, etc.).

   The 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.  Gateway / Endpoint ID

   Applications which interact with multiple networks can operate in a
   mode whereby the application connects to its local gateway, which
   then forwards application traffic to local networks and to remote
   networks via other SATP 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 gateways to maintain access
   control mapping between applications and resources that are
   independent of the authentication and authorization schemes used,
   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 gateways should ensure appropriate identifiers are used for the
   needs of the application or use case.

5.4.5.  Examples

   satclient:quant/api.overledger.quant.com/research/luke.riley




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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:

   satpclient://hsbc/api.overledger.hsbc.com/lending/eric.devloper

   can READ/WRITE

   satpres://quant/api.gateway1.com/tradelens

   AND

   satpres://quant/api.gateway1.com/ripple

   These rules would allow a client so identified to access resources
   directly, for example:

   satpres://quant/api.gateway1.com/tradelens/xxxxxADDRESSxxxxx

   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.

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 SATP message.

5.6.3.  Server selects supported credential scheme

   The server (recipient Gateway) selects one acceptable credential
   scheme from the offered schemes, returning the selection in the
   "Credential Scheme" field of the SATP message.



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   If no acceptable credential scheme was offered, an HTPP 511 "Network
   Authentication Required" error is returned in the Action/Response
   field of the SATP message.

5.6.4.  Client asserts or 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 (sender
   gateway) after the finalization of credential verification.  The
   server (recipient gateway) MUST respond with the same sequence number
   to indicate acceptance.

   The client (sender gateway) increments the sequence number with each
   new request.  Sequence numbers can be reused for retries in the event
   of a gateway timeout.

5.6.6.  Messages can now be exchanged

   Handshaking is complete at this point, and the client can send SAT
   messages to perform actions on resources, which MAY reference the SAT
   Payload field.

5.7.  Asset Profile Identification

   The client and server must mutually agree as to the asset type or
   profile that is the subject to the current transfer from the client
   and server.  The client must provide the server with the asset-
   identification number, or the server may provide the client with the
   asset-identification numbers for the digital asset supported by the
   server.

   Formal specification of asset identification is out of scope of this
   document.  Global numbering of digital asset types or profiles is
   expected to be performed by a legally recognized entity.

5.8.  Application Profile Negotiation

   Where an application relies on specific extensions for operation,
   these can be represented in an Application Profile.



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   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.  Discovery of Digital Asset Resources

   Applications located outside a network or system SHOULD be able to
   discover which resources they are authorized to access in a network
   or system.

   Resource discovery is handled by the gateway in front of the network.
   For instance using a GET request against the gateway URL with no
   resource identifier could return a list of URLs available to the
   requester.  This list is subject to the access controls above.

   Gateways MAY allow applications to discover resources they do not
   have access to.  This should be indicated in the free text field, and
   gateways SHOULD implement a process for applications to request
   access.

   Formal specification of supported resource discovery methods is out
   of scope of this document.

6.  Identity and Asset Verification Flow (Stage 0)

   Prior to commencing the asset transfer from the sender gateway
   (client) to the recipient gateway (server), both gateways must
   perform a number of verifications steps.  The types of information
   required by both the sender and recipient are use-case dependent and
   asset-type dependent.

   The verifications include, but not limited to, the following:






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   *  Gateway identity mutual verification: This is the identity of the
      gateway at the protocol and network layer.  This may include
      validating the X509 certificates of the gateways.

   *  Gateway owner verification: This is the verification of the
      identity (e.g.  LEI) of the owners of the gateways.

   *  Gateway device and state validation: This is the device
      attestation evidence [RATS] that a gateway must collect and convey
      to each other, where a verifier is assumed to be available to
      decode, parse and appraise the evidence.

   *  Originator and beneficiary identity verification: This is the
      identity and public-key of the entity (originator) in the origin
      network seeking to transfer the asset to another entity
      (beneficiary) in the destination network.

   These are considered out of scope in the current specifications, and
   are assumed to have been successfully completed prior to the
   commencement of the transfer initiation flow.

7.  Transfer Initiation Flows (Stage 1)

   This section describes the SATP initialization phase, where a sender
   gateway interacts with a recipient gateway, proposing a session.

   For this, several artifacts need to be validated: asset profile,
   asset ownership evidence, identities, and logging-related operations
   (log profile, access control profile).

   In this phase, gateways implement the Transfer Initiation Flows
   endpoint.

   In the following, the sender gateway takes instructions from an
   application, while the recipient gateway may act on behalf of its
   applications.

   The flow follows a request-response model.  The sender gateway makes
   a request (POST) to the Transfer Initiation endpoint at the recipient
   gateway.

   Gateways MUST support the use of the HTTP GET and POST methods
   defined in RFC 2616 [RFC2616] for the endpoint.

   Clients (sender gateway) MAY use the HTTP GET or POST methods to send
   messages in this phase to the server (recipient gateway).  If using
   the HTTP GET method, the request parameters may be serialized using
   URI Query String Serialization.



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   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 may
   be required for audit verifications (e.g. post-event).

   (NOTE: Flows occur over TLS.  Nonces are not shown).

7.1.  Initialization Request Message (Stage 1)

   This message is sent from the sender gateway (client) to the
   recipient gateway (server) to its Transfer Initiation Endpoint.

   The purpose of this message is for the client to initiate an asset
   transfer.  Depending on the proposal, multiple rounds of
   communication between the client and the server may happen.

   The parameters of this message consists of the following:

   *  Version: SAT protocol Version (major, minor).

   *  Message Type: The message type information indicating the current
      stage of the SATP flows.

   *  Session ID: A unique identifier (UUIDv2) chosen by the sender
      gateway representing a session.

   *  Developer URN: Assertion of developer / application identity.

   *  Credential Profile: Specify type of auth (e.g.  SAML, OAuth,
      X.509)

   *  Payload Profile: Asset Profile provenance and capabilities

   *  Application Profile: Vendor or Application specific profile

   *  logging_profile REQUIRED: contains the profile regarding the
      logging procedure.  Default is local store.

   *  Access_control_profile REQUIRED: the profile regarding the
      confidentiality of the log entries being stored.  Default is only
      the gateway that created the logs can access them.

   *  Initialization Request Message signature REQUIRED: Gateway EDCSA
      signature over the message

   *  Sender_gateway_pubkey REQUIRED: the public key of the gateway
      initiating a transfer




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   *  Sender_gateway_network_id REQUIRED: the ID of the source network

   *  Recipient_gateway_pubkey REQUIRED: the public key of the gateway
      involved in a transfer

   *  Recipient_gateway_network_id REQUIRED: the ID of the recipient
      network

   *  Lock_type REQUIRED: faucet, timelock, hashlock, hashtimelock,
      multi-claim PC, destroy/burn (escrowed cross-claim).

   *  Lock_expiration_time REQUIRED: when will the lock or escrow expire

   *  Multiple claims allowed: true/false

   *  Multiple cancels allowed: true/false

   *  Permissions: list of identities (public-keys or X.509
      certificates) that can perform operations on the escrow or lock on
      the asset in the origin network.

   *  Originator: along with the sender gateway identification, allows
      identifying from where are the asset is escrowed/provided

   *  Beneficiary: along with the recipient gateway identification,
      allows identifying to where are the escrowed asset is going

   *  Subsequent calls: details possible escrow actions

   *  History (optional): provides an history of the escrow, in case it
      has previously been initialized.

   The sender gateway makes the following HTTP request using TLS.

   Example: TBD.

7.2.  Initialization Request Message Response (Stage 1)

   After receiving an Initialization Request Message, the recipient
   gateway needs to validate the profiles.

   This validation could be performed automatically (using a defined set
   of rules), or by requiring approval by an application.

   If one of the profiles is rejected, the recipient gateway constructs
   a Initialization Denied Message, stating what was rejected, and
   proposing an alternative (if applicable).




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   Otherwise, if approved, the recipient gateway constructs an
   Initialization Request Message Response and sends it to the Transfer
   Initiation Endpoint at the sender gateway.

   The purpose of this message is for the server (recipient gateway) to
   indicate agreement to proceed with the proposed operations, under the
   proposed profiles.

   This message is sent from the recipient gateway to the sender gateway
   (client) in response to a Initialization Request from the sender
   gateway.

   The message must be signed by the server.

   The parameters of this message consists of the following:

   *  Message Type: The message type information indicating the current
      stage of the SATP flows.

   *  Session ID: A unique identifier (UUIDv2) chosen earlier by sender
      gateway in the Initialization Request Message.

   *  Sequence Number: monotonically increasing counter that uniquely
      represents a message from a session.

   *  Hash of the Initialization Request Message REQUIRED: the hash of
      the proposal.

   *  Destination: if the recipient gateway calculates the destination
      address dynamically.

   *  Timestamp REQUIRED: timestamp referring to when the Initialization
      Request Message was received.

   *  Processed Timestamp REQUIRED: timestamp referring to when the
      Initialization Response Message was constructed.

   Example: TBD.

8.  Lock-Assertion Flows (Stage 2)

   This section describes the conveyance of assertions (claims)
   regarding the status of the asset (or resource) from a sender gateway
   to a recipient gateway.

   In this phase, the gateways implement the Lock-Assertion Endpoint.





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   In the following, the sender gateway takes the role of the client
   while the recipient gateway takes the role of the server.

   The flow follows a request-response model.  The client makes a
   request (POST) to the Lock-Assertion Endpoint at the server.

   Gateways MUST support the use of the HTTP GET and POST methods
   defined in RFC 2616 [RFC2616] for the endpoint.

   Clients MAY use the HTTP GET or POST methods to send messages in this
   phase to the server.  If using the HTTP GET method, the request
   parameters may be 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 may
   be required for audit verifications post-event.

   (NOTE: Flows occur over TLS.  Nonces are not shown).

8.1.  Transfer Commence Message

   This message is sent from the client (sender gateway) to the Transfer
   Request Endpoint at the server (recipient gateway).  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.

   The parameters of this message consists of the following:

   *  message_type REQUIRED.  MUST be the value
      urn:ietf:satp:msgtype:transfer-commence-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  originator_pubkey REQUIRED.  This is the public key of the asset
      owner (originator) in the origin network or system.

   *  beneficiary_pubkey REQUIRED.  This is the public key of the
      beneficiary in the destination network.

   *  sender_gateway_network_id REQUIRED.  This is the identifier of the
      origin network or system behind the client.




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   *  recipient_gateway_network_id REQUIRED.  This is the identifier of
      the destination network or system behind the server.

   *  client_identity_pubkey REQUIRED.  The public key of client who
      sent this message.

   *  server_identity_pubkey REQUIRED.  The public key of server for
      whom this message is intended.

   *  hash_asset_profile REQUIRED.  This is the hash of the asset
      profile previously agreed upon in Stage 1.

   *  asset_unit OPTIONAL.  If applicable this is the unit amount of the
      asset being transferred, previously agreed upon.

   *  hash_prev_message REQUIRED.  The hash of the last message.

   *  client_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the client.  This number is
      meaningful only the client.

   *  client_signature REQUIRED.  The digital signature of the client.

   For example, the client makes the following HTTP request using TLS
   (with extra line breaks for display purposes only):


























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    POST /token HTTP/1.1
      Host: server.example.com
      Authorization: Basic awHCaGRSa3F0MzpnWDFmQmF0M2ZG
      Content-Type: application/x-www-form-urlencoded

          {
          "message_type": "urn:ietf:satp:msgtype:transfer-commence-msg",
          "session_id":"9097hkstgkjvVbNH",
          "originator_pubkey":"zGy89097hkbfgkjvVbNH",
          "beneficiary_pubkey": "mBGHJjjuijh67yghb",
          "sender_net_system": "originNETsystem",
          "recipient_net_system":"recipientNETsystem",
          "client_identity_pubkey":"fgH654tgeryuryuy",
          "server_identity_pubkey":"dFgdfgdfgt43tetr535teyrfge4t54334",
          "hash_asset_profile":"nbvcwertyhgfdsertyhgf2h3v4bd3v21",
          "asset_unit": "ghytredcfvbhfr",
          "hash_prev_message":"DRvfrb654vgreDerverv654nhRbvder4",
          "client_transfer_number":"ji9876543ewdfgh",
          "client_signature":"fdw34567uyhgfer45"
          }


                                Figure 2

8.2.  Commence Response Message (ACK-Commence)

   The purpose of this message is for the server to indicate agreement
   to proceed with the asset transfer.

   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.

   The parameters of this message consists of the following:

   *  message_type REQUIRED urn:ietf:satp:msgtype:ack-commence-msg

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client for whom this message
      is intended.

   *  server_identity_pubkey REQUIRED.  The server who sent this
      message.



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   *  hash_prev_message REQUIRED.  The hash of the last message.

   *  server_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the server.  This number is
      meaningful only to the server.

   *  server_signature REQUIRED.  The digital signature of the server.

   An example of a success response could be as follows:



   ```
        HTTP/1.1 200 OK
        Content-Type: application/json;charset=UTF-8
        Cache-Control: no-store
        Pragma: no-cache

        {
          "message_type":"urn:ietf:satp:msgtype:ack-commence-msg",
          "session_id":"9097hkbfgkjvVbNH",
          "client_identity_pubkey":"fgH654tgeryuryuy",
          "server_identity_pubkey":"dFgdfgdfgt43tetr535teyrfge4t54334",
          "hash_prev_message":"DRvfrb654vgreDerverv654nhRbvder4",
          "server_transfer_number":"ji9876543ewdfgh",
          "server_signature":"aaw34567uyhgfer66"
        }
   ```

                                  Figure 3

8.3.  Lock Assertion Message

   The purpose of this message is for the client (sender gateway) to
   convey a signed statement to the server declaring that the asset in
   question has been locked or escrowed by the sender in the origin
   network (e.g. to prevent double spending).

   The format of the evidence is dependent on the network or system of
   the client and is outside the scope of this specification.

   This message is sent from the client to the Lock Assertion Endpoint
   at the server.

   The server must validate the claims (payload) in this message prior
   to the next step.

   The message must be signed by the client (sender gateway).



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   The parameters of this message consists of the following:

   *  message_type REQUIRED urn:ietf:satp:msgtype:lock-assert-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client who sent this
      message.

   *  server_identity_pubkey REQUIRED.  The server for whom this message
      is intended.

   *  lock_assertion_claims REQUIRED.  The lock assertion claim or
      statement by the client.

   *  lock_assertion_format OPTIONAL.  The format of the assertion.

   *  lock_assertion_expiration REQUIRED.  The duration of time of the
      lock on the asset.

   *  hash_prev_message REQUIRED.  The hash of the previous message.

   *  client_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the client.  This number is
      meaningful only to the client.

   *  client_signature REQUIRED.  The digital signature of the client.

8.4.  Lock Assertion Receipt Message (Assertion-Receipt)

   The purpose of this message is for the server (recipient gateway) to
   indicate acceptance of the claims in the lock-assertion message
   delivered by the client (sender gateway) in the previous message.

   The message must be signed by the server.

   The parameters of this message consists of the following:

   *  message_type REQUIRED urn:ietf:satp:msgtype:assertion-receipt-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client for whom this message
      is intended.



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   *  server_identity_pubkey REQUIRED.  The server who sent this
      message.

   *  hash_prev_message REQUIRED.  The hash of previous message.

   *  server_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the server.  This number is
      meaningful only to the server.

   *  server_signature REQUIRED.  The digital signature of the server.

9.  Commitment Establishment Flow (Stage 3)

   This section describes the transfer commitment agreement between the
   sender gateway to a recipient gateway.

   This phase must be completed within the time specified in the
   lock_assertion_expiration value in the lock-assertion message.

   In this phase gateways implement the Transfer Commitment Endpoint.

   In the following, the sender gateway takes the role of the client
   while the recipient gateway takes the role of the server.

   The flow follows a request-response model.  The client makes a
   request (POST) to the Transfer Commitment endpoint at the server.

   Gateways MUST support the use of the HTTP GET and POST methods
   defined in RFC 2616 [RFC2616] for the endpoint.

   Clients MAY use the HTTP GET or POST methods to send messages in this
   phase to the 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: Flows occur over TLS.  Nonces are not shown).

9.1.  Commit Preparation Message (Commit-Prepare)

   The purpose of this message is for the client to indicate its
   readiness to begin the commitment of the transfer.

   The message must be signed by the client.




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   The parameters of this message consists of the following:

   *  message_type REQUIRED.  It MUST be the value
      urn:ietf:satp:msgtype:commit-prepare-msg

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client who sent this
      message.

   *  server_identity_pubkey REQUIRED.  The server for whom this message
      is intended.

   *  hash_prev_message REQUIRED.  The hash of previous message.

   *  client_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the client.  This number is
      meaningful only the client.

   *  client_signature REQUIRED.  The digital signature of the client.

9.2.  Commit Preparation Acknowledgement (ACK-Prepare)

   The purpose of this message is for the server to indicate to the
   client its readiness to proceed with the commitment finalization
   step.

   The message must be signed by the server.

   The parameters of this message consists of the following:

   *  message_type REQUIRED.  It MUST be the value
      urn:ietf:satp:msgtype:ack-prepare-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client for whom this message
      is intended.

   *  server_identity_pubkey REQUIRED.  The server who sent this
      message.

   *  hash_prev_message REQUIRED.  The hash of previous message.




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   *  server_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the server.  This number is
      meaningful only the server.

   *  server_signature REQUIRED.  The digital signature of the server.

9.3.  Commit Ready Message (Commit-Ready)

   The purpose The purpose of this message is for the server to indicate
   to the client that: (i) the server has created (minted) an equivalent
   asset in the destination network assigned to the server (gateway),
   and (ii) that the server is ready to transfer ownership of the newly
   minted asset to the intended beneficiary.

   The message must be signed by the server.

   The parameters of this message consists of the following:

   *  message_type REQUIRED.  It MUST be the value
      urn:ietf:satp:msgtype:commit-ready-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client for whom this message
      is intended.

   *  server_identity_pubkey REQUIRED.  The server who sent this
      message.

   *  mint_assertion_claims REQUIRED.  The mint assertion claim or
      statement by the server.

   *  mint_assertion_format OPTIONAL.  The format of the assertion
      payload.

   *  hash_prev_message REQUIRED.  The hash of previous message.

   *  server_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the server.  This number is
      meaningful only the server.

   *  server_signature REQUIRED.  The digital signature of the server.







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9.4.  Commit Final Message (Commit-Final)

   The purpose of this message is for the client to indicate to the
   server that the client (sender gateway) has completed the
   extinguishment (burn) of the asset in the origin network.

   The message must contain standalone claims related to the
   extinguishment of the asset by the client.  The claim must be signed
   by the client.

   The parameters of this message consists of the following:

   *  message_type REQUIRED.  It MUST be the value
      urn:ietf:satp:msgtype:commit-final-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client who sent this
      message.

   *  server_identity_pubkey REQUIRED.  The server for whom this message
      is intended.

   *  burn_assertion_claims REQUIRED.  The burn assertion claim or
      statement by the client.

   *  burn_assertion_format OPTIONAL.  The format of the assertion
      payload.

   *  hash_prev_message REQUIRED.  The hash of previous message.

   *  client_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the client.  This number is
      meaningful only the client.

   *  client_signature REQUIRED.  The digital signature of the client.

9.5.  Commit-Final Acknowledgement Message (ACK-Final)

   The purpose of this message is to indicate to the client that the
   server has completed the assignment of the newly minted asset to the
   intended beneficiary at the destination network.

   The parameters of this message consists of the following:





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   *  message_type REQUIRED.  It MUST be the value
      urn:ietf:satp:msgtype:ack-commit-final-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.

   *  client_identity_pubkey REQUIRED.  The client for whom this message
      is intended..

   *  server_identity_pubkey REQUIRED.  The server who sent this
      message.

   *  assignment_assertion_claims REQUIRED.  The assertion claim or
      statement by the server that the asset has been assigned by the
      server to the intended beneficiary.

   *  assignment_assertion_format OPTIONAL.  The format of the assertion
      payload.

   *  hash_prev_message REQUIRED.  The hash of previous message.

   *  server_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the server.  This number is
      meaningful only the server.

   *  server_signature REQUIRED.  The digital signature of the server.

9.6.  Transfer Complete Message

   The purpose of this message is for the client to indicate to the
   server that the asset transer session (identified by session_id) has
   been completed and that no further messages are to be expected from
   the client in regards to this transfer instance.

   The message closes the first message of Stage 2 (Transfer Commence
   Message).  It must be signed by the client.

   The parameters of this message consists of the following:

   *  message_type REQUIRED.  It MUST be the value
      urn:ietf:satp:msgtype:commit-transfer-complete-msg.

   *  session_id REQUIRED: 128-bit value identifying the current
      transfer-session between the client gateway and server gateway.
      This is the value from the Initialization Request Message.





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   *  client_identity_pubkey REQUIRED.  The client who sent this
      message.

   *  server_identity_pubkey REQUIRED.  The server for whom this message
      is intended.

   *  hash_prev_message REQUIRED.  The hash of previous message.

   *  hash_transfer_commence REQUIRED.  The hash of the Transfer
      Commence message at the start of Stage 2.

   *  client_transfer_number OPTIONAL.  This is the transfer
      identification number chosen by the client.  This number is
      meaningful only the client.

   *  client_signature REQUIRED.  The digital signature of the client.

10.  Security Consideration

   Gateways are of particular interest to attackers because they are a
   kind of end-to-end pipeline that enable the transferral of digital
   assets to external networks or systems.  Thus, attacking a gateway
   may be attractive to attackers instead of the network behind a
   gateway.

   As such, hardware hardening technologies and tamper-resistant crypto-
   processors (e.g.  TPM, Secure Enclaves, SGX) should be considered for
   implementations of gateways.

11.  IANA Consideration

   (TBD)

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, DOI 10.17487/RFC2234,
              November 1997, <https://www.rfc-editor.org/info/rfc2234>.






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   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

12.2.  Informative References

   [NIST]     Yaga, D., Mell, P., Roby, N., and K. Scarfone, "NIST
              Blockchain Technology Overview (NISTR-8202)", October
              2018, <https://doi.org/10.6028/NIST.IR.8202>.

   [RFC5939]  Andreasen, F., "Session Description Protocol (SDP)
              Capability Negotiation", RFC 5939, DOI 10.17487/RFC5939,
              September 2010, <https://www.rfc-editor.org/info/rfc5939>.

Authors' Addresses

   Martin Hargreaves
   Quant Network
   Email: martin.hargreaves@quant.network


   Thomas Hardjono
   MIT
   Email: hardjono@mit.edu


   Rafael Belchior
   Technico Lisboa
   Email: rafael.belchior@tecnico.ulisboa.pt






















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