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Secure Asset Transfer (SAT) Use Cases
draft-ietf-satp-usecases-03

Document Type Active Internet-Draft (satp WG)
Authors Venkatraman Ramakrishna , Thomas Hardjono
Last updated 2024-07-08
Replaces draft-ramakrishna-sat-use-cases
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draft-ietf-satp-usecases-03
Internet Engineering Task Force                           V. Ramakrishna
Internet-Draft                                              IBM Research
Intended status: Informational                               T. Hardjono
Expires: 8 January 2025                                              MIT
                                                             8 July 2024

                 Secure Asset Transfer (SAT) Use Cases
                      draft-ietf-satp-usecases-03

Abstract

   This document describes prominent scenarios where enterprise systems and
   networks maintaining digital assets require the ability to securely
   transfer assets or data to each other.

Status of This Memo

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   This Internet-Draft will expire on 8 January 2025.

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   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

 
1.  Introduction

   Business networks, built on both centralized and decentralized models,
   have emerged to manage cross-organization assets and workflows. The scope
   of such workflows and the assets they govern, as well as the set of
   participating organizations within a network, have been quite limited,
   partly for security, privacy, and scalability reasons, and partly because
   organizations have been reticent to moving large portions of their pre
   existing workflows to such networks. We see this especially in the areas
   of trade, finance, supply chain logistics, and property management. Yet
   the workflows managed by these networks are naturally interlinked in the
   real world, and therefore cannot afford to remain isolated from each
   other technologically, which would diminish the value of their assets. At
   the same time, a network, once built, has institutional staying power,
   and it is therefore impractical to assume that they will expand or merge.
   Interoperability is therefore an imperative in this fragmented business
   network ecosystem. This comes in different flavors, namely the ability to
   move an asset from one network to another, interlinking workflows to
   share asset state with proof of authenticity from one network to another,
   and swapping assets in different networks as part of a business
   transaction, as listed in the SAT Architecture Specification [SATA]. The
   purpose of this document is to describe prominent examples of these modes
   that have been encountered by enterprises and business consortiums and
   identified as challenges to be overcome. In particular, this document 
   describes scenarios where the Secure Asset Transfer Protocol (SATP) 
   [SATP] can be directly applied to solve the problem of moving digital 
   assets across networks, for which no other canonical protocol exists in 
   the literature. 

2.  Terminology

   There following are some terminology used in the current document.
   We borrow terminology from NIST and ISO as much as possible,
   introducing new terms only when needed:

   o  Asset network (system): The network or system where a digital
      asset is utilized.
   
   o  Asset Transfer Protocol: The protocol used to transfer (move) a
      digital asset from one network to another using gateways.

   o  Origin network: The current network where the digital asset is
      located.

   o  Destination network: The network to which a digital asset is to be
      transferred.

   o  Data sharing: The process, using the Asset Transfer Protocol, by which
      one or more units of verifiably authentic data are communicated from
      an Origin network to a Destination network, either voluntarily or upon
      request.

   o  Asset Transfer: A fail-safe process of moving an asset from one
      network to another, with the destruction of the asset in the Origin
      network and its recreation in the Destination network occurring as a
      single atomic action.

   o  Asset Exchange: A fail-safe process of exchanging (or swapping) assets
      held by a pair of owners, each asset being maintained in a different
      network, with the two in-network transfers occurring as a single
      atomic action.

   Further terminology definitions can be found in [NIST] and [ISO].

3.  International Trade and Supply Chains

3.1.  Trade Finance and Logistics

   There are several real-world examples of consortium networks managing
   different aspects of international trade. Networks like We.Trade [WET],
   built on Hyperledger Fabric [HLF], and Marco Polo [MP], built on R3 Corda
   [R3C], manage trade finance workflows by connecting exporters, importers,
   and financial institutions (primarily banks). Other networks like
   TradeLens [TL], built on Hyperledger Fabric, manage trade shipping and
   documentation logistics, by connecting exporters and shipping carriers.
   As an example, consider a system of two networks as illustrated in Figure
   1: (a) a trade finance network managing letters of credit business
   lifecycles from application to fulfilment, and (b) a trade logistics
   network managing shipping consignment creation and dispatch documents
   like bills of lading.

      +------------+
      | Exporter’s |  +----------+              +---------------------+
      |    Bank    |  | Exporter |              |       Exporter      |
      +------------+  +----------+              +---------------------+
            | |            |                       | |              |
       3    | |    5       |    4           1      | |      2       |   4
    Approve | | Request    | Upload       Book     | |   Create     | Accept
      L/C   | | Payment    |   B/L     Consignment | | Consignment  |  B/L
            | |            |                       | |              |
            V V            V                       V V              V
    +-------------------------------+     +-------------------------------+
    |     Trade Finance Network     |     |    Trade Logistics Network    |
    +-------------------------------+     +-------------------------------+
            ˄              ˄                           ˄     ˄
       2    |              |    1               5      |     |    3
    Propose |              | Request        Dispatch   |     | Upload
      L/C   |              |   L/C         Consignment |     |   B/L
            |              |                           |     |
      +------------+  +----------+                 +-------------+
      | Importer’s |  | Importer |                 |   Carrier   |
      |    Bank    |  +----------+                 +-------------+
      +------------+
                   (a)                                   (b)

                                 Figure 1

   An exporter who belongs to both systems must produce a valid bill of
   lading in the trade finance network to enforce a payment from the buyer
   to fulfil the terms of the letter of credit. But this bill, which serves
   as evidence of a shipping consignment’s dispatch via a carrier, lies in
   the other, i.e., trade logistics, network.  The two networks must
   therefore be interoperable in such a way that the logistics network can
   share a bill with the finance network along with independently verifiable
   proof of authenticity. Otherwise, the trade finance network’s workflow
   must trust that the exporter is acting in good faith and supplying
   genuine bills of lading, which adds insecurity. This interoperation,
   which involves sharing of network data, can be extrapolated to other
   scenarios involving the two networks. The trade logistics network can
   require an exporter to produce a valid letter of credit from the trade
   finance network before permitting a consignment record creation. Both
   these cross-network data sharing instances are illustrated in Figure 2.

               +----------+    1 Agree on      +----------+
               | Exporter |<------------------>| Importer |
               +----------+   Purchase Order   +----------+

      +------------+
      | Exporter’s |  +----------+              +---------------------+
      |    Bank    |  | Exporter |              |       Exporter      |
      +------------+  +----------+              +---------------------+
            | |                                    | |              |
       4    | |   12                        5      | |      7       |   9
    Approve | | Request                   Book     | |   Create     | Accept
      L/C   | |   L/C                  Consignment | | Consignment  |  B/L
            | |                                    | |              |
            | |                                    | |              |
            | |            |¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯|  | |              |
            | |            |    11 Share B/L    |  | |              |
            V V            V                    |  V V              V
    +-------------------------------+     +-------------------------------+
    |     Trade Finance Network     |     |    Trade Logistics Network    |
    +-------------------------------+     +-------------------------------+
            ˄              ˄    |               ˄      ˄     ˄
            |              |    |  6 Share L/C  |      |     |
            |              |    |_______________|      |     |
            |              |                           |     |
       3    |              |    2               10     |     |    8
    Propose |              | Request        Dispatch   |     | Upload
      L/C   |              |   L/C         Consignment |     |   B/L
            |              |                           |     |
      +------------+  +----------+                 +-------------+
      | Importer’s |  | Importer |                 |   Carrier   |
      |    Bank    |  +----------+                 +-------------+
      +------------+

                                 Figure 2

   Asset transfers among trade networks: In the preceding example, letters
   of credit and bills of lading represent portions of state of the larger
   export-import workflow. But these documents are also digital assets in
   their own rights.
   
   A bill of lading can serve as title to the consignment of goods being
   shipped, and hence can be traded as a security or used as collateral
   against debt obligations in the financial market. Hence, Step 11 in
   Figure 2 may well be embodied by the transfer rather than the sharing of
   state of a bill so that it ceases to remain on the Trade Logistics
   Network ledger and instead belongs to the Seller’s Bank on the Trade
   Finance Network’s ledger.

   A letter of credit may also assume the properties of a digital asset in
   certain situations. Consider the case of an importer who wishes to move
   their business to a different trade finance network and maintain their
   records on that network’s ledger. We can assume that the banks and the
   exporter participate in the second trade finance network as well, which
   exists to serve a different clientele. The importer needs to be able to
   move its letter of credit state to the other network and resume the trade
   workflow after migration. This requires the ability to transfer the
   letter in the form of a digital asset from one trade finance network to
   another.

3.2.  Tracking Food Shipments

   The use case linking a trade finance network with a trade logistics
   network can be augmented by adding a food tracking network like the IBM
   Food Trust [IFT] to the mix. Such a network connects producers,
   suppliers, manufactures, and retailers, who participate in food supply
   chains. Purchase orders, like those negotiated between producers and
   retailers, and which are illustrated as negotiated between exporter and
   importers in Figure 2, are recorded in this network’s ledger. For quality
   control, its business workflow will track at periodic intervals the state
   (e.g., temperature and humidity) of containers carrying, for example,
   produce from farm to source port and from destination port to warehouse.
   The trade logistics network handles documentation and dispatch but does
   not track the location or condition of a consignment outside of a
   carrier’s purview. Clearly, these networks play complementary roles in a
   supply chain. The logistics network should be able to get the state and
   history of a container before dispatch from the food tracking network, as
   should the latter from the former after the carrier has delivered a
   consignment. End-to-end supply chain visibility and effectiveness relies
   on the interoperability of these two networks, or to be precise, their
   ability to share verifiably authentic data with each other. Further, such
   interoperation also enables the trade finance network to allow the
   creation of a letter of credit only after verifying the existence of a
   valid purchase order in the food tracking network. Figure 3 illustrates
   the links between these networks.

                      +-------------------------------+
                 |¯¯¯¯|     Food Tracking Network     |¯¯¯¯¯¯¯¯¯¯|
                 |    +-------------------------------+          |
         Share   |                              ˄                |  Share
        Purchase |                              |  Share         | Shipment
         Order   |         |¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯|   | Shipment       |  State
                 |         |   Share B/L    |   |  State         |
                 V         V                |   |                V
    +-------------------------------+     +-------------------------------+
    |     Trade Finance Network     |     |    Trade Logistics Network    |
    +-------------------------------+     +-------------------------------+
                                |               ˄
                                |   Share L/C   |
                                |_______________|

                                 Figure 3

3.3.  Supply Chain Management

   To complete the picture, we can add a payments network to the mix, which
   maintains currency accounts for clients in different countries and
   enables cross-border payments, an example being the Stellar network
   [STN]. After goods have been dispatched, and optionally after
   verification of the delivery and proper condition of a shipment, payment
   is due from an importer to an exporter. The trade finance network can
   record a payment obligation on its ledger but it will rely on the
   payments network to process and confirm the actual transfer of funds. The
   former shares data about the obligation to the latter, which shares data
   about a successful (or otherwise) payment in return, as illustrated in
   Figure 4.

                      +-------------------------------+
                 |¯¯¯¯|     Food Tracking Network     |¯¯¯¯¯¯¯¯¯¯|
                 |    +-------------------------------+          |
         Share   |                              ˄                |  Share
        Purchase |                              |  Share         | Shipment
         Order   |         |¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯|   | Shipment       |  State
                 |         |   Share B/L    |   |  State         |
                 V         V                |   |                V
    +-------------------------------+     +-------------------------------+
    |     Trade Finance Network     |     |    Trade Logistics Network    |
    +-------------------------------+     +-------------------------------+
                | ˄               |               ˄
        Share   | |   Share       |   Share L/C   |
       Payment  | |  Payment      |_______________|
     Obligation | | Fulfilment
                | |
                V |
      +----------------------+
      |   Payments Network   |
      +----------------------+

                                 Figure 4

   Addendum: we can add yet another network to the mix, one that manages
   regulatory compliance. (E.g., proof-of-concept systems have been built to
   bring banks and corporations on a single distributed ledger and smart
   contract platform to share KYC information in privacy-preserving ways
   [BKYC] [SKYC].) Now issuances of letters of credit in the trade finance
   system will be dependent on valid KYC records being maintained as assets
   in the regulatory compliance system.

4.  Currency and Finance

   The emerging paradigm of Decentralized Finance (DeFi) and the emerging 
   application of Central Bank Digital Currency (CBDC) have opened up a 
   spectrum of scenarios that require management of financial digital assets 
   across multiple systems, typically built on distributed ledgers.

   DeFi is a “new financial paradigm that leverages distributed ledger 
   technologies to offer services such as lending, investing, or exchanging 
   cryptoassets without relying on a traditional centralized intermediary” 
   [BISDeFi]. Following the Web3 philosophy [Web3], scoped for the world of 
   finance, DeFi offers architecture and protocols built on smart contracts 
   deployed on blockchain or other distributed ledger technology. It thereby 
   obviates the need for centralized management and orchestration of 
   financial processes (e.g., currency transfers, exchanges, securities 
   settlements) by trusted authorities who can gain undue leverage.

   CBDC is a form of tokenized cryptocurrency that various central banks 
   around the world are experimenting with as the digital equivalent of 
   traditional central bank-issued money used by banks and other financial 
   institutions as well as end users for commercial transactions and 
   settlements. Central banks possess exclusive authority to mint and issue 
   money in physical cash form and in the form of electronic reserves. They 
   also support commercial bank money used in retail transactions by banks 
   and other users in their private capacities. Central banks have 
   traditionally used their control over these different forms of money to 
   enforce monetary policy in a way that promotes financial stability and 
   provides broad access to safe and efficient payments [BISCBDC]. CBDCs 
   would form a new, or alternative, type of central bank money, typically 
   (but not always) built on blockchain or other distributed ledger 
   technology. They have recently garnered significant interest in 
   government circles by promising increased access and inclusion, better 
   resilience, and increased scale and efficiency of currency transfers, 
   compared to traditional forms of central bank-issued or central bank-
   backed currency.

   CBDCs can broadly be classified into “wholesale” and “retail”. Wholesale 
   CBDC, which facilitates inter-bank and cross-border settlements, is 
   currency that is available only to banks and other financial 
   institutions. Retail CBDC is available to the public and can be used as a 
   digital form of cash, enabling fast transparent payments for goods and 
   services at high scale and volume; in effect, it can be used as a 
   substitute for legacy payment mechanisms.

   Different system architectures exist to manage CBDC for banks and end 
   users, from issuance to transfers to redemptions. A 2-tier model as 
   illustrated in Figure 5 has recently gained popularity, where wholesale 
   CBDC networks manage interactions between central and commercial banks, 
   and retail CBDC networks manage interactions between commercial banks and 
   end users. If we consider the role of the central bank as the defining 
   characteristic of a system architecture, this model can be referred to as 
   “indirect”, because commercial banks mediate claims between the central 
   bank and end users and also facilitate payments. Other architectures also 
   exist, including “direct CBDC”, where the central bank issues CBDC 
   directly to end users and facilitates payments, and “hybrid CBDC”, which 
   provides users the facility to make direct claims on the central bank 
   while allowing intermediaries to facilitate payments [BISRCBDC].

4.1.  Currency Transfers

   The 2-tier “indirect CBDC” model illustrated in Figure 5 presents unique 
   interoperability challenges that require protocols for asset transfers 
   and which SATP is well-suited to handle. In the higher tier lie
   wholesale CBDC networks, bringing together central or reserve banks and 
   various commercial banks. Following the DeFi logic, these networks are 
   typically built on distributed ledger and smart contract technologies. 
   Commercial banks hold reserve currency deposits with the reserve bank, 
   which has the special power to mint currency and issue CBDC and also 
   enforce regulatory compliance. In the lower tier lie retail CBDC networks 
   for commercial banks and their customers, built on similar technologies, 
   enabling seamless, efficient, and transparent payments using CBDCs. A 
   retail CBDC network may involve a single commercial bank or multiple 
   commercial banks, depending on the market caps of those banks and their 
   purposes for joining such a network.

                  +----------------------------------------+
                  |                                        |
                  |         Wholesale CBDC Network         |
                  |                                        |
                  |           +----------------+           |
                  |           |  Central Bank  |           |
                  |           +----------------+           |
                  |                                        |
                  |  +------------+  +------------+        |
                  |  | Commercial |  | Commercial |        |
                  |  |  Bank A’s  |  |  Bank B’s  | ...... |
                  |  |   Account  |  |   Account  |        |
                  |  +------------+  +------------+        |
                  |                                        |
                  +----------------------------------------+
                        ˄                      ˄
                        |                      |
                        |                      |
                        V                      V
   +----------------------------+  +----------------------------+
   |                            |  |                            |
   |    Retail CBDC Network     |  |    Retail CBDC Network     |
   |                            |  |                            |
   | +------------+ +---------+ |  | +------------+ +---------+ |
   | | Commercial | | Central | |  | | Commercial | | Central | |
   | |  Bank A’s  | |  Bank   | |  | |  Bank B’s  | |  Bank   | |
   | |   Account  | +---------+ |  | |   Account  | +---------+ |
   | +------------+             |  | +------------+             |
   |                            |  |                            | .......
   | +----------------+         |  | +------------+             |
   | | Client Account | ....... |  | | Commercial |             |
   | +----------------+         |  | |  Bank C’s  |             |
   |                            |  | |   Account  |             |
   +----------------------------+  | +------------+             |
                                   |                            |
                                   | +----------------+         |
                                   | | Client Account | ....... |
                                   | +----------------+         |
                                   |                            |
                                   +----------------------------+

                                 Figure 5

   Here we will encounter scenarios where a given commercial bank maintains
   digital currency accounts in a wholesale CBDC network as well as one or
   more retail CBDC networks. To inject liquidity into a retail CBDC
   network, this bank will need to transfer currency from its reserve
   account in the wholesale CBDC network. Or it may need to approve (or at 
   least audit) the transfer of currency from one retail CBDC network to 
   another bank in another retail CBDC network. In the world of 
   decentralized finance, or DeFi for short, currency cannot afford to 
   remain siloed in any single CBDC network. Hence, these networks must be 
   interoperable in order to facilitate secure transfers of currency among 
   themselves, as illustrated in Figure 5.

   We can identify two specific instances of currency transfer across 
   networks in this example: one from a wholesale CBDC network to a retail 
   CBDC network, and another from one retail CBDC network to another. Since 
   currency in tokenized form is a digital asset, these scenarios require 
   the direct application of a secure protocol for asset transfer. SATP 
   [SATP] fits the bill, is agnostic of the types of distributed ledger 
   technologies on which the respective networks are built, and simply 
   requires the networks to use SATP gateways. This is not just a 
   theoretical proposition; a candidate design for a bridge between 
   Hyperledger Fabric [HLF] and Hyperledger Besu [HLB] networks using SATP 
   and the Hyperledger Cacti interoperability platform [HLC] has been 
   proposed by distributed ledger researchers [Aug23].

4.2.  Multi-CBDC Economy

   Several governments, banks and financial communities have explored the 
   use of a shared ledger containing multiple CBDCs as way to potentially 
   obtain an economy of scale in the development and maintenance of their 
   own respective CBDCs. Such a Multi-CBDC approach has the potential 
   benefit to improve cross-border payments and protect monetary 
   sovereignty, without necessarily becoming a monetary union [BISMCBDC].

   However, even within a Multi-CBDC configuration, there must be a 
   mechanism to interconnect each respective national (sovereign) bank 
   network with the shared Multi-CBDC network. Gateways appear to be an 
   attractive means to permit the transfer of a CBDC from one national 
   network/ledger into the shared Multi-CBDC ledger, and vice versa.  One 
   major requirement is the assurance that consistency is maintained between 
   the CBDC counts on the national network with that on the Multi-CBDC 
   network (i.e. no counterfeiting; no double-spend).

   With or without a Multi-CBDC ledger, the existence of different national 
   networks managing different wholesale CBDC assets will necessitate inter-
   network transfers for cross-border payments and settlements [BISCBP] 
   [WBGCBP] [PUbin]. Whether directly between two wholesale CBDC networks or 
   between a wholesale CBDC network and the Multi-CBDC network, transfer of 
   currency assets is a problem for which SATP appears to be the most 
   suitable solution.

4.3.  Delivery vs Payment (DvP) of Securities

   In Decentralized Finance, or DeFi for short, investors and financial
   institutions will form networks to manage the creation and purchase of
   securities. As a simple example, we can consider a network consisting of
   the Treasury, which issues bonds, and commercial banks, which purchase
   and trade bonds. We can also consider a payments network of the kind we
   saw in Section 3.3 (or a retail CBDC network of the kind we saw in
   Section 4.1), which allows CBDC transfers between commercial banks’
   accounts. In the securities network, banks may wish to transfer bonds to
   each other but only in exchange for compensation. But such compensation
   can be made only on a payments network where the two maintain currency
   accounts (e.g., in CBDC). Therefore, the securities and payment networks
   must be able to interoperate in such a way that two banks can carry out a
   delivery-vs-payment transaction spanning these two independent networks.
   Such a transaction must be atomic, i.e., either both bond and CBDC tokens
   get transferred in their respective networks or neither gets transferred.
   Figure 6 illustrates this exchange.

   +-----------------------------------------------------------------------+
   |                             Bond Network                              |
   |                                                                       |
   |     +----------+      Issue        +---------------------------+      |
   |     | Treasury |------------------>|    Commercial Bank A’s    |      |
   |     +----------+       Bond        |         Portfolio         |      |
   |                                    +---------------------------+      |
   |                                                  |                    |
   |                                                  |  Transfer          |
   |                                                  |    Bond            |
   |                                                  V                    |
   |                                    +---------------------------+      |
   |                                    |    Commercial Bank B’s    |      |
   |                                    |         Portfolio         |      |
   |                                    +---------------------------+      |
   +-----------------------------------------------------------------------+
                                       ˄
                                       |
                                       |
                                       V
   +-----------------------------------------------------------------------+
   |                 Payment Network / Retail CBDC Network                 |
   |                                                                       |
   |     +-----------+                  +---------------------------+      |
   |     |  Central  |                  |    Commercial Bank A’s    |      |
   |     |    Bank   |                  |           Account         |      |
   |     +-----------+                  +---------------------------+      |
   |                                                  |                    |
   |                                                  |  Transfer          |
   |                                                  |  Currency          |
   |                                                  V                    |
   |                                    +---------------------------+      |
   |                                    |    Commercial Bank B’s    |      |
   |                                    |          Account          |      |
   |                                    +---------------------------+      |
   +-----------------------------------------------------------------------+

                                 Figure 6

   In a variation of this example, the two commercial banks may hold CBDC 
   accounts in two different Payment Networks. In that case, fulfilment of 
   the DvP would require transfer of CBDC from one network to another. An 
   instance of SATP between gateways representing those two networks would 
   handle that problem.

4.4.  Stock Options Contract Fulfilment

   Stock options are financial instruments that allow holders to buy or sell
   stock at predetermined prices until specific expiration dates [StOpt].
   Exercising an option, i.e., buying or selling a stock by paying a “strike
   price”, involves a more complex cross-network financial transaction than
   the securities DvP use case. Option contracts can be managed and enforced
   in a specific business network (which we can label as a “stock network”)
   to which entities like an Options Clearing Corporation (OCC), stock
   exchanges (e.g., the Chicago Board Options Exchange), and brokerage
   firms, belong. The OCC is the issuer and guarantor for all options and
   futures contracts traded on U.S. exchanges [cite]. It provides secured
   back-end clearing services, while exchanges provide front-end trading
   markets. Transfer and settlement of payments, just like in the DvP
   scenario, will typically occur in a dedicated payment network in which
   buyers and sellers of stock have currency accounts. Options contract
   fulfilment requires the stock and payment networks to work in concert,
   and hence need SATP to coordinate transactions across them.

   Figure 7 illustrates a simplified flow for the exercising of a “call”
   option, where a buyer acquires stock from a seller by paying it a strike
   price. First, the buyer informs its brokerage, which then notifies its
   exchange about the buyer's intent to exercise the option. The exchange in
   turn notifies the OCC in the Stock Network. (All these notifications
   typically occur via a smart contract). Steps 1-2 illustrate these
   notifications. The OCC then verifies the contract’s validity and the
   buyer’s right to exercise the option. If this is successful, the OCC
   triggers a payment request to the buyer through a contract-to-contract
   communication from the Stock Network to the Payment Network (step 3).
   (Alternatively, the buyer may trigger a payment request in the Payment
   Network, which then requests the Stock Network for proof of the
   contract’s validity from the OCC before approving the payment.) The buyer
   then pays the strike price to the seller (step 4). The payment receipt is
   now sent to the Stock Network for the OCC’s verification (or
   alternatively, the buyer can request the OCC to fetch and verify the
   receipt from the Payment Network) and fulfilment of the contract (step
   5). The OCC, via the exchange, requests the brokerage to transfer stock
   from the seller’s to the buyer’s account (steps 6-7).

   This cross-network transactions require SATP using gateways, either to
   communicate information of a contract’s validity (step 3) or a payment
   receipt (step 5) with authenticity proof (i.e., data sharing), or by
   ensuring that strike price payment (step 4) and contract fulfilment (step
   6-7) occur atomically as an exchange using a coordinated set of
   commitments.

   +-----------------------------------------------------------------------+
   | Stock Network                                                         |
   |                                                                       |
   | +-------------+          +--------------+           +---------------+ |
   | |  Brokerage  |          |   Exchange   | 2.        |      OCC      | |
   | |             |          |              | Request   |               | |
   | | +---------+ | 1.       | +----------+ | to        | +-----------+ | |
   | | | Buyer   | | Exercise | |          | | Clear     | |           | | |
   | | | Equity  |-|----------|>|          |-|-----------|>|           | | |
   | | | Account | |          | | Options  | |           | | Options   | | |
   | | +---------+ |          | | Contract | |           | | Contract  | | |
   | |             |          | | (Copy)   | |           | | (Primary) | | |
   | | +---------+ |          | |          | |           | |           | | |
   | | | Seller  |<|----------|-|          |<|-----------|-|           | | |
   | | | Equity  | | 7.       | +----------+ | 6.        | +-----------+ | |
   | | | Account | | Fulfil & |              | Fulfil &  |               | |
   | | +---------+ | Transfer |              | Transfer  |               | |
   | |             | Stock    |              | Stock     |               | |
   | +-------------+          +--------------+           +---------------+ |
   |                                                                       |
   +-----------------------------------------------------------------------+
                           |                    ˄
         3. Request to Pay |                    |
            Strike Price   |                    | 5. Send Payment Receipt
                           |                    |
                           V                    |
   +-----------------------------------------------------------------------+
   | Payment Network                                                       |
   |                                                                       |
   |      +--------------+                           +--------------+      |
   |      |   Buyer      |    4. Pay Strike Price    |   Seller     |      |
   |      |   Payment    |-------------------------->|   Payment    |      |
   |      |   Account    |                           |   Account    |      |
   |      +--------------+                           +--------------+      |
   |                                                                       |
   +-----------------------------------------------------------------------+
                                 Figure 7

5.  Decentralized Commerce: Payments for Goods and Services

   In the emerging Web3 world, undergirded by blockchain and DLT, goods and
   services are increasingly available on decentralized networks, either as
   purely digital objects or proxies of physical objects. The networks
   typically manage these assets in the form of non-fungible tokens (NFTs)
   using smart contracts and decentralized applications (DApps for short).
   DeFi in a Web3 ecosystem can create thriving online marketplaces where
   goods and services can be bought and sold across network boundaries if
   those networks are interoperable (i.e., assets and data can be
   moved or managed seamlessly across networks). SATP is a necessary
   requirement to enable and secure such a decentralized form of commerce.

5.1.  Transferal of Digital Art and Payments across National Borders

   There is currently growing interest within many artist communities of
   developing and selling digital-only artwork, in which the artwork
   consists of a file in a well-known (e.g. JPEG, MPEG) format that is
   created by an artist. The artists seek to sell copies of the digital-only
   artwork on the global marketplace, allowing anyone in the world to
   purchase a copy and consume (e.g. display offline) the artwork at the
   buyer’s discretion. Currently, the most popular technological vehicle to
   achieve this goal is through the tokenization of the copies of the
   artwork coupled with digital encryption/signature technologies to
   transfer control (and thereby legal ownership) of the digital-only
   artwork to the buyer.

   Although there are a number of technical and legal challenges (e.g.
   copyright enforcement) to completing such a sale, one key issue pertains
   to the sale and payment for digital-only artwork across national borders.
   Many nations enforce taxation upon the sale of any asset, including that
   of artwork generally both domestically and internationally. Thus, when
   the control/ownership of a tokenized digital-only artwork is transferred
   to a new owner in a foreign nation and payment is received, taxation must
   be obtained at the point-of-sale (which could be an online platform) and
   proof of delivery must be traceable to ensure that no taxation-avoidance
   occurs. A secure asset transfer protocol between systems that can be
   built on distributed or shared ledgers via gateways with designated legal
   authority is necessary to enforce governmental regulations and provide
   accountability.

5.2.  Payment for Streaming Services

   Streaming services like Netflix and IPTV can tap into the cryptocurrency
   and DeFi user market by offering content on distributed ledger networks
   using smart contracts. Instead of monthly subscriptions, they can offer
   pay-as-you-go streaming of arbitrarily low amounts to large numbers of
   users on such networks. Content transfer can be backed by NFTs, which the
   user can redeem on any video or audio playback app. Because there already
   exist several payment networks for unregulated (e.g., Bitcoin) and
   regulated (e.g., CBDC) currencies, the content networks are likely to
   remain independent and not involve any monetary transactions on their own
   ledgers, as that would create safety and regulatory issues. Content
   transfer in a content network can be backed by a corresponding payment in
   a payment network if there is a facility to transfer payment receipts
   from the latter to the former. This can be fulfilled through the data
   sharing mode of SATP, whereby knowledge of payment along with
   authenticity proof can be communicated across networks. Alternatively, an
   atomic swap of the content and the payment can occur across both networks
   using the asset exchange mode of SATP.

   In a related example, if the user wishes to obtain content that is not
   available currently with the streaming service provider, that provider
   may seek and purchase that content from another distributer that is
   offering it on a different content network. The copyright to that content
   can be backed by NFTs and the secure transfer of those NFTs from one
   network to another will require SATP.

6.  Trustworthy DNS Resource Record Migrations using an Augmented EPP

   We have seen several examples where SATP is indispensable for enabling
   cross-network asset and data transfer and transaction settlement. But
   SATP can also be used to augment an existing protocol by making it more
   secure, trustworthy, and efficient rather than creating an altogether new
   feature that preexisting technology was unable to provide. Conventional
   Internet architecture offers scope for such augmentation. Though highly
   decentralized, the Internet consists of nodes (or actors) that play
   critical roles in various protocols. Such protocols would benefit if the
   actions of these actors can be recorded and tracked on blockchain or
   other decentralized ledger networks. (It must be noted that the
   performance implications of these augmentations ought to be studied
   before firm recommendations are made.)

   We consider the DNS architecture [RFC1034] [RFC1035], where multiple
   registries and registrars may co-exist, managing DNS records for owners
   (registrants). For example, Verisign [VSign] acts as a TLD (top-level
   domain) registry for the “.com” namespace, and GoDaddy [GoDaddy] and
   Squarespace [SSpace] are registrars that can issue and sell SLDs (second-
   level domains) to customers (say Alice and Bob). The Extensible
   Provisioning Protocol (EPP) allows registrars to communicate with
   registries for resource record updates, including changes in domain
   ownership [RFC5730]. Consider a scenario in which Alice, who owns an SLD
   (say alice.com) issued by GoDaddy, wishes to transfer that SLD to
   Squarespace. She can submit a request to Squarespace for this purpose,
   following which the respective registrars (GoDaddy and Squarespace) can
   communicate with the registry (Verisign) using EPP to transfer the SLD
   between themselves. Squarespace will then reissue the domain to Alice. In
   a related scenario, Alice can transfer (or sell) her GoDaddy-issued
   domain to Bob, who uses Squarespace as a registrant.

   Though EPP facilitates these resource updates and transfers, and reputed
   registrars offer customers these features in a usable manner, we can see
   that such scenarios face safety issues as they require trust and proper
   coordination among the participants. These issues can be mitigated by
   distributed ledger networks, smart contracts, and NFTs, which
   collectively provide a platform for safe and transparent DNS resource
   transfers with easy detection of non-compliance.

   In such a scheme, domains (or domain names) can be monetized as NFTs or
   digital assets, e.g., in the form of ERC-721 [ERC721] tokens, a popular
   NFT standard in the Ethereum ecosystem [Ethereum]. The creation of a
   domain is represented by minting of an NFT and the deletion of a domain
   by the burning of the NFT using smart contracts whose transactions are
   tracked on a distributed ledger maintained by a network of entities.
   Registrants Alice and Bob also participate in the smart contracts and
   hold wallet identities, allowing them to trade assets by submitting
   transactions to the ledger. Registrants, registrars, and registries can
   engage in commercial transactions using contracts governing tokenized
   (and monetized) domains for the purposes of issuing and transferring
   domains (among owners and registrars). This provides more safety where
   registrars are not reputed, and allows new registrar services to emerge
   and build reputations. It also enables customers like Alice and Bob to
   sell domains to each other safely and seamlessly.

   SATP is crucial to enabling this scheme where registrars belong to, and
   issue, NFT-backed domains in different ledgers maintained by different
   networks. Ensuring that tokens are securely and atomically transferred
   between the ledgers will be a necessary prerequisite for an EPP resource
   record update operation. Further, non-compliance, or non-fulfilment of
   EPP, by either registrar, can be easily detected by examining the SATP
   logs from the respective networks’ gateways, thereby safeguarding the
   process. In future, reputed registrars may require their counterparties
   to comply with SATP-based transfers across ledgers as a prerequisite to
   engaging in a domain transfer with them.

   This scenario additionally illustrates an example of what typically
   occurs in Stage 0 of a SATP instance [SATP], which is where negotiation
   and agreement-building occurs between gateways. EPP instances among
   registrars and registries will occur in this stage, both prior to the
   start of an SATP instance and after its conclusion. EPP will produce the
   transaction context the gateways need to transfer an asset (in this case,
   a tokenized domain) using SATP. Many other applications of SATP for asset
   transfers may similarly augment or bolster pre-existing business
   workflows, which (like EPP here) will produce transactions contexts for
   SATP instances.

7.  Interoperation Protocol Considerations

   The use cases provided as examples serve to illustrate instances of
   general phenomena that the Secure Asset Transfer Protocol [SATP],
   with a limited number of variations, is designed to handle. The data
   sharing examples in Section 3 can be extrapolated to any kinds of data
   that need to be shared between networks running arbitrary workflows. The
   asset transfer example in Section 4.1 and the asset exchange example in
   Section 4.2 similarly can be extrapolated to any kinds of digital assets
   lying within any kind of network. Considerations for the interoperability
   protocol, or SATP, can therefore be limited to standard distributed
   systems issues like integrity, fault tolerance, and liveness, while
   completely disregarding the nature of the assets, networks, and
   workflows, which can all remain opaque to the protocol.

8.  References

8.1.  Normative References

   [Aug23]    A. Augusto, R. Belchior, I. Kocsis, L. Gönczy, A. Vasconcelos, 
              and M. Correia, "CBDC Bridging between Hyperledger Fabric and 
              Permissioned EVM-based Blockchains." 2023 IEEE International 
              Conference on Blockchain and Cryptocurrency (ICBC), Dubai, 
              United Arab Emirates, 2023, pp. 1-9,
              doi: 10.1109/ICBC56567.2023.10174953, 
              <https://www.techrxiv.org/articles/preprint/CBDC_bridging_
              between_Hyperledger_Fabric_and_permissioned_EVM-based_
              blockchains/21809430>.

   [BISCBDC]  Bank of Canada, European Central Bank, Bank of Japan, Sveriges 
              Riksbank, Swiss National Bank, Bank of England, Board of 
              Governors of the Federal Reserve, and Bank for International 
              Settlements, “Central bank digital currencies: foundational 
              principles and core features.” Bank for International 
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   [BISCBP]   Bank for International Settlements, Committee on Payments and 
              Market Infrastructures, Innovation Hub, International Monetary 
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              for cross-border payments.” Bank for International 
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   [BISDeFi]  R. Auer, B. Haslhofer, S. Kitzler, P. Saggese, and F. Victor, 
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   [BISMCBDC] R. Auer, P. Haene, and H. Holden, “Multi-CBDC arrangements and 
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   [BISRCBDC] R. Auer and R. Boehme, “The technology of retail central bank 
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   [BKYC]     Kumar Bhaskaran, Peter Ilfrich, Dain Liffman, Christian
              Vecchiola, Praveen Jayachandran, Apurva Kumar, Fabian Lim,
              Karthik Nandakumar, Zhengquan Qin, Venkatraman Ramakrishna,
              Ernie GS Teo, and Chun Hui Suen, "Double-Blind Consent-Driven
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   [HLF]      Elli Androulaki, Artem Barger, Vita Bortnikov, Christian
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              Suisse, DBS Bank, HSBC, J.P. Morgan, Mitsubishi UFJ Financial 
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   [RFC1035]  Mockapetris, P., "RFC 1035: Domain names - Implementation and
              Specification", November 1987,
              <https://datatracker.ietf.org/doc/html/rfc1035>.

   [RFC5730]  Hollenbeck, S., "RFC 5730: Extensible Provisioning Protocol
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   [SATA]     Hardjono, T., Hargreaves, M., Smith, N., and V. Ramakrishna,
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8.2.  Informative References

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Contributors

   The authors would like to thank André Augusto of INESC-ID and Técnico
   Lisboa (Portugal), Zainan Victor Zhou of Namefi by D3Serve Labs, and Dr.
   Chunchi (Peter) Liu of Huawei Research, for reviewing this draft and
   suggesting (and inspiring) use cases in the areas of CBDC, stock options
   trading, streaming media commerce, and DNS record maintenance, which
   augmented the existing use cases to show more applications for the
   interoperability modes listed in the SATP Architecture document.

Authors' Addresses

   Venkatraman Ramakrishna
   IBM Research - India

   Email: vramakr2@in.ibm.com

   Thomas Hardjono
   MIT

   Email: hardjono@mit.edu