Secure Asset Transfer (SAT) Interoperability Architecture
draft-ietf-satp-architecture-06
| Document | Type | Active Internet-Draft (satp WG) | |
|---|---|---|---|
| Authors | Thomas Hardjono , Martin Hargreaves , Ned Smith , Venkatraman Ramakrishna | ||
| Last updated | 2025-01-14 (Latest revision 2024-12-17) | ||
| Replaces | draft-hardjono-sat-architecture | ||
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draft-ietf-satp-architecture-06
Internet Engineering Task Force T. Hardjono
Internet-Draft MIT
Intended status: Informational M. Hargreaves
Expires: 21 June 2025 Quant Network
N. Smith
Intel
V. Ramakrishna
IBM
18 December 2024
Secure Asset Transfer (SAT) Interoperability Architecture
draft-ietf-satp-architecture-06
Abstract
This document proposes an interoperability architecture for the
secure transfer of assets between two networks or systems based on
the gateway model.
Status of This Memo
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This Internet-Draft will expire on 21 June 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Assumptions and Principles . . . . . . . . . . . . . . . . . 5
3.1. Design Principles . . . . . . . . . . . . . . . . . . . . 5
3.2. Operational Assumptions . . . . . . . . . . . . . . . . . 5
3.3. Assumptions Regarding Gateway Operators . . . . . . . . . 6
4. Gateway Interoperability Modes . . . . . . . . . . . . . . . 7
5. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Goal of Architecture . . . . . . . . . . . . . . . . . . 7
5.2. Overview of Asset Transfer . . . . . . . . . . . . . . . 8
5.3. Desirable Properties of Asset Transfer . . . . . . . . . 9
5.4. Event log-data, crash recovery and backup gateways . . . 11
5.5. Overview of the Stages in Asset Transfer . . . . . . . . 11
6. Pre-transfer Verification and Context Establishment
(Stage-0) . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Transfer Initiation and Commencement (Stage-1) . . . . . . . 15
8. Asset Lock Assertion and Receipt (Stage 2) . . . . . . . . . 16
9. Commitment Preparation and Finalization (Stage 3) . . . . . . 18
10. The Commitment sub-protocol . . . . . . . . . . . . . . . . . 20
11. Security Considerations . . . . . . . . . . . . . . . . . . . 21
12. Policy Considerations . . . . . . . . . . . . . . . . . . . . 21
13. Threat Analysis Considerations . . . . . . . . . . . . . . . 22
13.1. Multiple intentional aborts by the sender gateway . . . 22
13.2. Multiple intentional aborts by the receiver gateway . . 22
13.3. Failure to transmit ACK-Final Receipt . . . . . . . . . 23
13.4. Failure to extinguish asset . . . . . . . . . . . . . . 23
13.5. Identity impersonations . . . . . . . . . . . . . . . . 23
14. Compatibility Considerations . . . . . . . . . . . . . . . . 24
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
15.1. Normative References . . . . . . . . . . . . . . . . . . 24
15.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
This document proposes an interoperability architecture based on
gateways, which are points of interconnection between networks or
systems.
There are several services that may be offered by a gateway, one of
which being the direct transfer of a digital asset from one network
to another via pairs of gateways without a mediating third party.
A given network or system may have one or more gateways to perform a
unidirectional direct transfer of digital assets to another network
possessing one or more compatible gateway.
The peer gateways must implement a secure asset transfer protocol
that must satisfy certain security, privacy, atomicity and liveliness
requirements.
The purpose of this architecture document is to provide technical
framework within which to define the required properties of a gateway
that supports the secure asset transfer protocol.
2. Terminology
The current architecture specification borrows existing terminology
from NIST and ISO. New terms have been introduced notably in
relation to the use of the gateways paradigm and commitment
subprotocols.
* Asset network (system): The network or system where a digital
asset is utilized.
* Asset Transfer Protocol: The protocol used to transfer (move) a
digital asset from one network to another using gateways.
* Origin network: The current asset network where the digital asset
is located.
* Destination network: The asset network to which a digital asset is
to be transferred.
* Resource Domain: The collection of resources and entities
participating within an asset network. The domain denotes a
boundary for permissible or authorized actions on resources.
* Interior Resources: The various interior protocols, data
structures and cryptographic constructs that are a core part of an
asset network or system.
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* Exterior Resources: The various protocols, data structures and
cryptographic constructs that are outside of (external to) the
network or system.
* Gateway: The collection of services which connects to a minimum of
one network or system, and which implements the secure asset
transfer protocol.
* Entity public-key pair: This the private-public key pairs of an
entity, where the public-key is available and verifiable outside
the network. Among others, it may be utilized for interactions
other entities (e.g. sign messages) from outside the network. The
term is used to distinguish this public-key from other key-pairs
belonging to the same entity, but which is only available within
the (private) network.
* Originator: Person or organization in an origin network seeking
the transfer of a digital asset to a beneficiary located in a
remote network.
* Beneficiary: Person or organization in an destination network
seeking to receive the transfer of a digital asset to from an
originator located in a remote network.
* Gateway device identity: The identity of the device implementing
the gateway functions. The term is used in the sense of the DevID
(IEEE 802.1AR) [DevID] or the EK/AIK keys (in TPM1.2 and TPM2.0)
[TPMdevID].
* Gateway owner: The entity that owns and operates a gateway within
a network.
* Application Context-ID: The relevant identifier used by
originator's application and the beneficiary's application to
identify the context of the asset transfer at the gateway level.
The context identifier may also be used to bind the application to
selected gateway for the given transfer instance, identified by a
Session-ID.
* Gateway Session-ID: This is the identifier used between the sender
gateway G1 and the recipient gateway G2 to identify the specific
transfer instance between them. The Session-ID must be included
in all messages between the peer gateways.
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3. Assumptions and Principles
The following assumptions and principles underlie the design of the
current gateway architecture, and correspond to the design principles
of the Internet architecture.
3.1. Design Principles
* Opaque network resources: The interior resources of each network
is assumed to be opaque to (hidden from) external entities. Any
resources to be made accessible to an external entity must be made
explicitly accessible by a gateway with proper authorization.
* Externalization of value: The asset transfer protocol is agnostic
(oblivious) to the economic or monetary value (if any) of the
digital asset being transferred.
The opaque resources principle permits the architecture to be applied
in cases where one (or both) networks are private (closed
membership). It is the analog of the autonomous systems principle in
IP networking [Clar88], where interior routes in local subnets are
not visible to other external networks.
The value-externalization principle permits an asset transfer
protocol to be designed for efficiency, security and reliability --
independent of the changes in the perceived economic value of the
digital asset. It is the analog of the end-to-end principle in the
Internet architecture [SRC84], where contextual information is placed
at the endpoints of the transfer.
3.2. Operational Assumptions
The following conditions are assumed to have occurred, leading to the
invocation of the asset transfer protocol between two gateways:
* Application level context establishment: The transfer request from
an Originator utilizing an application (App1) in the origin
network is assumed to have occurred, and that some context-
identifier has subsequently been derived by the respective
applications (App1 and App2). Furthermore, this context-
identifier is assumed to have been delivered by the each
application to its corresponding gateway, permitting each gateway
to internally bind the transfer session-identifier to that
context-identifier.
* Identification of asset to be transferred: The applications at the
originator and the beneficiary are assumed to have identified the
digital asset to be transferred.
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* Identification of originator and beneficiary: The originator and
beneficiary are assumed to have been identified and that consent
has been obtained from both parties regarding the asset transfer.
* Identification of origin and destination asset networks: The
origin and destination networks is assumed to have been
identified.
* Selection of gateway: The two corresponding gateways at the origin
and destination networks is assumed to have been identified and
selected.
3.3. Assumptions Regarding Gateway Operators
The following conditions are assumed to have occurred, leading to the
invocation of the asset transfer protocol between two gateways:
* Identification of gateway-owners: The owners of the two
corresponding gateways are assumed to have been identified and
their ownership status verified.
* Gateway liabilities: Gateways and gateway-operators are assumed to
take on legal and financial liability for their transactions, and
gateways are assumed to operate under a well-defined legal
framework (e.g. contractual relationship). Furthermore, the legal
framework is assumed to be supported by compatible legislation in
the relevant jurisdictions where the gateways are operating.
* Gateway message signatures: All messages between gateways are
assumed to be signed and verified (e.g. X.509).
* Transitory control of asset by gateway: An asset being transferred
via SAT will technically be controlled by gateway throughout the
transfer duration to ensure the state of the asset is not modified
by another entity. Gateway owners are liable for the asset
throughout this duration.
* Network data: Gateways are assumed to have mechanisms in place to
trust data returned from their local networks. This will depend
on the technical architecture and capabilities of each specific
network.
* Gateways are trusted: The gateways are assumed to be trusted to
carry-out all the stages of the protocol described in this
architecture.
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4. Gateway Interoperability Modes
The current interoperability architecture based on gateways
recognizes several types of transfer flows:
* Asset transfer: This refers to the transfer of a digital asset
from the origin network to a destination network, where a
successful asset transfer causes the asset to be extinguished
(burned) in the origin network and be regenerated (minted) at the
destination network.
* Data transfer: This refers to the transfer of data only under
authorization, in such a way that the data can be verified by a
third party. The data transfer mode addresses the use-cases where
the state update in one network or system depends on the existence
of state information recorded in a different network or system.
* Asset exchange (swap): This refers to the case where two users are
present in two networks, and they perform concurrent and atomic
swaps of two assets in the two corresponding networks, without
transferring the assets outside (i.e. across) the networks. The
gateways aid in coordinating the messages pertaining to the swap.
The remainder of this architecture document will focus on the asset
transfer flows.
5. Architecture
5.1. Goal of Architecture
The goal of the interoperability architecture is to permit two (2)
gateways belonging to distinct networks to conduct a transfer of
digital assets transfer between them, in a secure, atomic and
verifiable manner.
The asset as understood by the two gateways is expressed in an
standard digital format in a way meaningful to the gateway
syntactically and semantically.
The architecture recognizes that there are different networks
currently in operation and evolving, and that in many cases the
interior technical constructs in these networks maybe incompatible
with one another.
The architecture therefore assumes that in addition to implementing
the bilateral secure asset transfer protocol, a gateway has the role
of making opaque (i.e. hiding) the constructs that are local and
specific to its network.
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Overall this approach ensures a high degree of interoperability
across these networks, where each network can operate as a true
autonomous system. Additionally, this approach permits each network
to evolve its interior technology implementations without affecting
other (external) networks.
The current architecture focuses on unidirectional asset transfers,
although the building blocks in this architecture can be used to
support protocols for bidirectional transfers.
For simplicity the current architecture employs two (2) gateways per
transfer as the basic building block, with one gateway in the origin
and destination networks respectively. However, the architecture
seeks to be extensible to address future cases involving multiple
gateways at both sides.
The abstract construct of the gateway is used to represent endpoints
that implement the asset transfer protocol interactions and the
business logic that coordinates the transfer protocol steps until
completion satisfying the ACID properties and ensuring liveliness of
the protocol interactions. In classical distributed databases, this
business logic is often referred to as the transaction manager or the
transaction coordinator. This architecture specification does not
prescribe any implementations of gateways.
5.2. Overview of Asset Transfer
An asset transfer between two networks is performed using a secure
asset transfer protocol implemented by the gateways in the respective
networks. The two gateways implement the protocol in a direct
interaction (unmediated).
A successful transfer results in the asset being extinguished
(burned) at the origin network, and for the asset to be regenerated
(minted) at the destination network.
The secure asset transfer protocol provides a coordination between
the two gateways through the various message flows in the protocol
that is communicated over a secure channel.
The protocol implements a commitment mechanism between the two
gateways to ensure that the relevant properties atomicity,
consistency, isolation, and durability (ACID) are achieved in the
transfer.
The mechanism to extinguish (burn) or regenerate (mint) an asset
from/into a network by its gateway is dependent on the specific
network and is outside the scope of the current architecture
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specification. The mechanisms used to provide cryptographic proofs
that an asset has been burned or minted in a given network is also
out of scope.
As part of the commitment mechanism, the sender gateway in the origin
network must deliver a signed assertion to the receiver gateway at
the destination network which states that asset in question has been
extinguished (burned) from the origin network.
Similarly, the receiver gateway at the destination network must in
return deliver a signed assertion to the sender gateway at the origin
network which states that the asset has been regenerated (minted) in
the destination network.
These two tasks must be performed in a synchronized fashion between
the two gateways, and the commitment mechanism must provide
sufficient evidence of the asset transfer that is verifiable by an
authorized third party.
5.3. Desirable Properties of Asset Transfer
The desirable features of asset transfers between two gateways
include, but not limited, to the following:
* Atomicity: A transfer must either commit or entirely fail (failure
means no change to asset state).
* Consistency: A transfer (commit or fail) always leaves the
networks in a consistent state (i.e. the asset is located in one
network only at any time).
* Isolation: While the transfer is occurring, the asset state cannot
be modified in the origin network.
* Durability: Once a transfer has been committed by both gateways,
it must remain so regardless of subsequent gateway crashes.
* Liveliness and safety: The asset transfer protocol results in both
gateways reaching a non-blocking state (commits or aborts)
satisfying the above ACID properties.
* Verifiable by authorized third parties: The proof that the asset
has been extinguished in the origin network, and the proof that
the asset has been generated in the destination network must be
verifiable by an authorized third party.
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An implementation of the asset transfer protocol should satisfy these
properties, independent of whether the implementation employs
stateful messaging or stateless messaging between the two gateways.
Performing an asset transfer safely and securely is not simply a
matter of communicating desire or intent between two systems
represented by gateways, though such communication is a necessary
part of asset transfer. The systems, or at least their gateway
proxies, must be interoperable in order to transfer assets among
themselves, but such interoperability imposes strictly more demands
on systems managing digital assets, especially systems that are built
on distributed ledgers, compared to conventional communication
interoperability.
Communication interoperability, which is concerned with syntax and
semantics of information geared towards producing a common
understanding (or knowledge reconciliation) among systems, is
insufficient to fulfill an asset transfer that requires systems to
carry out state updates in concert with each other. But
communication, or messaging standards, play a necessary and
complementary role to asset transfer protocols. An exemplar of this
is ISO 20022, which is a comprehensive global standard for financial
messaging that specifies message syntax for common actions occurring
in financial business processes, including payments, credit card
transactions, securities settlements, funds, and trade [ISO20022].
This standard provides the tools to model business processes from
basic logical building blocks and schemas to construct messages using
common formats like XML, JSON, and ASN.1.
As discussed later, such messaging standards are useful to
communicate information about the states of processes and digital
assets across systems, to make requests, and to convey intent. They
therefore play a necessary and complementary role in asset transfer
protocols. However they are by themselves insufficient to ensure the
ACID and verifiability properties described earlier. Another way to
think about the relationship between messaging standards like ISO
20022 and asset transfer protocols is that the former is concerned
with the "what" of cross-system interoperability whereas the latter
is concerned with the "how". Both kinds of protocols treat systems
as black boxes, but asset transfer protocols must place some
responsibility, and depend, on systems to drive a protocol instance
to successful conclusion.
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5.4. Event log-data, crash recovery and backup gateways
Implementations of a gateway should maintain event logs and
checkpoints for the purpose of gateway crash recovery. The log-data
generated by a gateway should be considered as an interior resource
accessible to other authorized gateways within the same network.
The mechanism used to provide gateway crash-recovery is dependent on
the specific network. For interoperability purposes the information
contained in the log and the format of the log-data should be
standardized.
The resumption of an interrupted transfer session (e.g. due to
gateway crash, network failure, etc.) should take into consideration
the aspects of secure channel establishment and the aspects of the
transfer protocol resumption. In some cases, a new secure channel
(e.g. TLS session) may need to be established between the two
gateways, before a resumption of the transfer can begin.
The log-data collected by a gateway acts also as a checkpoint
mechanism to assist the recovered (or backup) gateway in continuing
the transfer. The point at which to re-start the transfer protocol
flow is dependent on the implementation of the gateway recovery
strategy.
5.5. Overview of the Stages in Asset Transfer
The interaction between two gateways in the secure asset transfer
protocol is summarized in Figure 1, where the origin network is NW1
and the destination network is NW2. The gateways are denoted as G1
and G2 respectively.
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Originator Beneficiary
| |
+-------------+ +-------------+
| Client | | Client |
| Application | | Application |
| (App1) | | (App2) |
+-------------+ +-------------+
| |
| |
|-----------+ +-----------|
| | |<--(Stage 0)-->| | |
V | | | | V
+-------------+ V | | V +-------------+
| Network | +----+<-- Stage 1 -->+----+ | Network |
| NW1 | |Gate| |Gate| | NW2 |
| |--|way | |way |--| |
| +---------+ | | G1 |<-- Stage 2 -->| G2 | | +---------+ |
| | State | | +----+ +----+ | | State | |
| | Data DB1| | | | | | Data DB2| |
| +---------+ | |<-- Stage 3--->| | +---------+ |
+-------------+ +-------------+
Figure 1
The stages are summarized as follows.
* Stage 0: Pre-transfer Verification and Context Establishment. The
two applications utilized by the originator and beneficiary are
assumed to interact as part of the asset transfer. In this stage,
the applications App1 and App2 may establish some shared transfer
context information (e.g. Context-ID) at the application level
that will be made available to their respective gateways G1 and
G2. The legal verification of the identities of the Originator
and Beneficiary may occur in this stages [FATF]. This stage is
outside the scope of the current architecture specification.
* Stage 1: Transfer Initiation and Commencement. In this stage
gateways G1 and G2 must exchange information (claims) regarding
the asset to be transferred, the identity information of the
Originator and Beneficiary and other information regarding
relevant actors (e.g. gateway owner/operator). The main task in
this stage is for both gateways to finalize the parameters
previously negotiated in Stage 0 and to agree to commence the
transfer.
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* Stage 2: Lock Assertion and Receipt. In this stage, gateway G1
must provide gateway G2 with a signed assertion that the asset in
NW1 has been immobilized and under the control on G1. A signed
assertion is needed because NW1 may be a private or closed
network, and therefore the state-database (ledger) in NW1 is not
readable by external entities including by G2. This means that
gateway G1 must make an explicit signed assertion about the state
in NW1. Note that the owner/operator of G1 takes on liability in
signing this assertion.
* Stage 3: Commitment Preparation and Finalization. In this stage
gateways G1 and G2 commit to the unidirectional asset transfer
using a 3PC (3-phase commit) subprotocol.
These stages will be further discussed below.
6. Pre-transfer Verification and Context Establishment (Stage-0)
Although Stage 0 is out of scope for the current architecture, it is
discussed here in order to provide background with the regards to the
various asset verification requirements prior to commencing the
transfer in Stage 1.
Several tasks need to be conducted as part of the pre-transfer:
* Application level ContextID establishment: The application (App1)
used by the originator and the application (App2) used by the
beneficiary may need to establish a transfer context identifier
(contextID) to uniquely identity the transfer at the application
level.
* Identification of the asset in the origin network: The specific
asset in the origin network NW1 must be located and identified,
and its legal ownership be verified by gateway G1. A gateway
should not transfer assets whose ownership is unverified. An
asset may be identified by way of a combination of the network-
identifier and a cryptographic hash of the ledger data
representing the asset. Other syntax may also be used, such as
[ISO20022] or ITIN [ITIN].
* Verification of the class or type of asset: The receiving gateway
G2 may need to verify the class or type of asset that is to be
transferred by gateway G1 in network NW1. This is to ensure that
the asset type/class conforms to the governing policies in the
destination network NW2. Additionally, gateway G2 must ensure
that network NW2 can technologically receive (mint) the asset of
that given type/class. Asset schema definitions and asset profiles
may assist in this verification process.
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* Validation of asset ownership status: The gateway G1 in the origin
network NW1 must ensure that an asset to be transferred to an
external network is legally owned by the originator who is
requesting the transfer.
* Authorization to transfer: The gateway G1 must obtain
authorization from the owner of the asset (originator) to perform
the transfer to the beneficiary in network NW2. Similarly, the
gateway G2 serving network NW2 must obtain authorization from the
beneficiary to receive the transfer and assign the asset to the
beneficiary in NW2.
* Exchange of Travel Rule information and validation: In
jurisdictions where the Travel Rule policies regarding originator
and beneficiary information is enforced [FATF], the owners of
gateways G1 and G2 must comply to the Travel Rule. Mechanisms
must be used to permit gateways G1 and G2 to make available
originator/beneficiary information to one another in such a away
that the Travel Rule information can be logged as part of the
asset transfer history.
* Validation of the gateway ownership: There must be a means for
gateway G1 and G2 to verify their respective ownerships (i.e.
entities owning G1 and G2 respectively). Examples of ownership
verification mechanism include X.509 certificates, directories of
gateways and owners, and others.
* Mutual device attestations: In cases where device attestation
[RATS] is required, each gateway must yield attestation evidence
to the other regarding its configuration. A gateway may take on
the role as a attestation verifier, or it may rely on an external
verifier to appraise the received evidence.
* Negotiation of transfer protocol and network parameters: Gateway
G1 and G2 must agree on the parameters to be employed within the
asset transfer protocol. Examples include endpoints definitions
for resources, duration of time-outs of messages, type of
commitment flows (e.g. 2PC or 3PC), signature algorithms, average
lock-time durations in their respective networks, and others.
The current specification seeks to reuse as much as possible the
existing standards related to digital assets. We seek to rely on
existing messaging standards like ISO 20022 [ISO20022] or ITIN [ITIN]
for gateway ownership validation, owner status validation, asset
profile identification, and communication of travel rule and transfer
context information. For identification of digital assets maintained
by distributed ledgers or blockchain systems, we can also rely on
standards like ITIN [ITIN].
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7. Transfer Initiation and Commencement (Stage-1)
In Stage 1 the sender gateway (G1) and the receiver gateway (G2) must
explicitly accept the parameters of the transfer which were
negotiated in the pre-transfer stage (Stage 0).
This explicit acceptance of the parameters takes the form of gateway
G1 sending a signed Transfer Proposal message containing a Transfer
Initiation Claims set (namely the parameters agreed upon in Stage 0),
and for the gateway G2 to respond with a signed Proposal Receipt
message which carries a hash of the proposal message.
App1 DB1 G1 G2 DB2 App2
| | | | | |
| | | (Stage 0) | | |
| | | | | |
|<------------ (transfer context establishment) ------------>|
| | | | | |
|---request------->| |<------request----|
| | | | | |
| | |<-Param Negotiation-->| | |
| | | | | |
..|.....|............|......................|............|.....|..
| | | Stage 1 | | |
| | | | | |
| | (1.1)|---Transf. Proposal-->| | |
| | | | | |
| | | | | |
| | (1.2)|<--Proposal Receipt---| | |
| | | | | |
| | | | | |
| | (1.3)|---Transf. Commence-->| | |
| | | | | |
| | | | | |
| | (1.4)|<--- ACK Commence ----| | |
| | | | | |
..|.....|............|......................|............|.....|..
| | | | | |
Figure 2
There are several steps that may occur in Stage 1:
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* Secure channel establishment between G1 and G2: This includes the
mutual verification of the gateway device identities and the
exchange of the relevant parameters for secure channel
establishment.
* Transfer Proposal message (1.1): Gateway G1 sends a signed
transfer proposal message that contains the Transfer Initiation
Claims to gateway G2. The claims carry the parameters negotiated
in Stage 0 (pre-transfer negotiations).
* Proposal Receipt (1.2): The gateway G2 indicates acceptance of the
parameters in the Transfer Initiation Claims by way of sending a
signed Proposal Receipt message to G1. If gateway G2 decides not
to accept parameters in the Transfer Initiation Claims, then G2
can send an abort message to G1 ignore the message (time-out).
* Transfer Commence message (1.3): Once gateway G1 receives the
signed Proposal Receipt from gateway G2, gateway G1 is ready to
signal the commencement of the asset transfer. This is done by
gateway G1 sending a signed Transfer Commence message to G2.
* Commence Acknowledgement message (1.4): Gateway G2 accepts the
formal commencement of the transfer by responding with a signed
Commence ACK message.
It is important to note the logical separation between the transfer
proposal/receipt messages from the commencement messages. This
separation allows the gateways to decline to proceed during the
proposal finalization (1.1 and 1.2), prior to starting the 2PC
subprotocol which formally begins at the Commence messages (1.3 and
1.4).
This logical separation is useful because in some implementations the
decision to start the commencement (1.3 and 1.4) implies that the
gateways and network have sufficient resource to complete the
transfer. Gateways that experience extreme loads may use this
separation to slightly delay the commencement until their loads
subsides.
Note that some implementations may choose to enable a multi-round
interactions for steps 1.1 and 1.2.
8. Asset Lock Assertion and Receipt (Stage 2)
In this stage, gateway G1 must issue a signed assertion that the
asset in origin network NW1 has been immobilized and under the
control of G1.
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The steps of Stage 2 are summarized in Figure 4, and broadly consists
of the following:
* G1 lock/escrow asset (2.1): Gateway G1 proceeds to establish a
lock or escrow the asset belonging to the originator. This
prevents other local transactions in NW1 from changing the state
of the asset until such time the lock by G1 is finalized or
released. A time-lock or escrow may also be employed.
* Lock Assertion (2.2): Gateway G1 sends a digitally signed
assertion regarding the locked (escrowed or immobilized) state on
the asset in network NW1. The signature by G1 is performed using
its entity public-key pair. This signature signifies that G1
(i.e. its owner/operator) is legally standing behind its statement
regarding the locked/escrowed state on the asset. The mechanism
to lock or immobilize the asset is outside the scope of secure
asset transfer protocol.
* G2 Logs lock-assertion information (2.3): Gateway G2 logs/records
a copy of the signed lock-assertion message received in Step 2.4
to its local state data DB2. G2 may also notify the fact of the
lock-assertion to all members of network NW2. The mechanism to
log and to notify is also out of scope.
* Lock-Assertion Receipt (2.4): If gateway G2 accepts the signed
assertion from G1, then G2 responds with a digitally signed
receipt message which includes a hash of the previous lock-
assertion message. The signature by G2 is performed using its
entity public-key pair. Otherwise, if G2 declines accepting the
assertion then G2 can simply ignore the transfer and let the
session time-out (i.e. transfer attempt has failed).
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Orig DB1 G1 G2 DB2 Benef
| | | (Stage 1) | | |
| | | | | |
..|.....|............|....................|..............|.....|..
| | | Stage 2 | | |
| | | | | |
| |<---Lock----|(2.1) | | |
| | | | | |
| | (2.2)|--Lock-Assertion--->| | |
| | | | | |
| | | (2.3)|---Record---->| |
| | | | | |
| | | | | |
| | |<-----Receipt-------|(2.4) | |
| | | | | |
..|.....|............|....................|..............|.....|..
| | | | | |
Figure 3
The purpose of the signed lock-assertion is for dispute resolution
between G1 and G2 (i.e. the entities who own and operate G1 and G2
respectively) in the case that asset state inconsistencies in NW1 and
NW2 are discovered later.
The gateway G2 must return a digitally signed receipt to G1 regarding
the earlier signed lock-assertion in order to cover G1 (exculpatory
proof) in the case of later denial by G2.
9. Commitment Preparation and Finalization (Stage 3)
In Stage 3 the gateways G1 and G2 commit to the asset transfer by
making permanent the changes they made to the respective networks
(ledgers). The previous signed receipt message (2.4) from gateway G2
to gateway G1 signals the start of the commitment subprotocol in
Stage 3.
Upon receiving the signed receipt message from G2 in the previous
stage, G1 begins the commitment (see Figure 5):
* Commit-prepare (3.1): Gateway G1 indicates to G2 to prepare for
the commitment of the transfer. This message should include
hashes of the previous messages (message 2.2 and 2.4).
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* Temporary asset mint (3.2): Gateway G2 creates (mints) an
equivalent asset in NW2 assigned to itself as the owner. This
step can be reversed (i.e. asset destroyed) in the case of the
failure in the commitment steps because G2 is still the owner of
the asset in NW2.
* Commit-ready (3.3): Gateway G2 sends a commit-ready message to G1
indicating that it is ready to carry-out the last steps of the
commitment subprotocol. Note that that the entire asset transfer
session can be aborted before this step without affecting the
asset state in the respective networks.
* Asset burn (3.4): Gateway G1 extinguishes (burns) the asset in
network NW1 which it has locked since Step 2.3.
* Commit-final assertion (3.5): Gateway G1 indicates to G2 that G1
has performed the extinguishment of the asset in NW1. This
message must be digitally signed by G1.
* Asset-assignment (3.6): Gateway G2 assigns the minted asset (which
it has been self-holding since Step 3.2) to the Beneficiary.
* ACK-final receipt (3.7): Gateway G2 sends a signed assertion that
it has assigned the asset to the intended Beneficiary.
* Record receipt (3.8): Gateway G1 logs/records a copy of the signed
receipt message to its local state data DB1. G1 may also notify
the fact of the signed receipt to all members of network NW1. The
mechanism to log and notify is out of scope.
* Transfer complete (3.9): Gateway G1 must explicitly close the
asset transfer session with gateway G2. This allows both sides to
close down the secure channel established earlier in Stage 1.
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Orig DB1 G1 G2 DB2 Benef
| | | (Stage 2) | | |
| | | | | |
..|.....|.............|....................|............|.....|..
| | | Stage 3 | | |
| | | | | |
| | (3.1)|--Commit Prepare--->| | |
| | | | | |
| | | (3.2)|----Mint--->| |
| | | | | |
| | |<--Commit Ready ----|(3.3) | |
| | | | | |
| | | | | |
| |<---Burn-----|(3.4) | | |
| | | | | |
| | (3.5)|-Commit Final Asrt->| | |
| | | | | |
| | | | | |
| | | (3.6)|---Assign-->| |
| | | | | |
| | |<-----ACK Final-----|(3.7) | |
| | | | | |
| | | | | |
| |<---Record---|(3.8) | | |
| | | | | |
| | (3.9)|-----Completed----->| | |
| | | | | |
..|.....|.............|....................|............|.....|..
| | | | | |
Figure 4
10. The Commitment sub-protocol
Within Stage 3, the gateways must implement one (or more)
transactional commitment sub-protocols that permit the coordination
between two gateways, and the final commitment of the asset transfer.
In the case that there are multiple commitment subprotocols supported
by the gateways, the choice of the sub-protocol (type/version) and
the corresponding commitment evidence must be negotiated between the
gateways during Stage 0.
For example, in Stage 2 and Stage 3 discussed above the gateways G1
and G2 may implement the classic 2-Phase or 3-Phase Commit (2PC or
3PC) sub-protocol [Gray81] as a means to ensure efficient and non-
disputable commitments to the asset transfer.
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Historically, transactional commitment protocols employ locking
mechanisms to prevent update conflicts on the data item in question.
When used within the context of digital asset transfers across
networks, the fact that an asset has been locked in NW1 must be
communicated via an assertion to G2 (as the 3PC participant) in an
indisputable manner.
Similarly, G2 must return a signed assertion to G1 that the asset has
been regenerated (minted) in NW2.
These signed assertions must be verifiable by an authorized third
party, in the case that disputes occur (post event) or where legal
audit is required on the asset transfer.
The precise form of these assertions must be standardized (for the
given transactional commitment protocol) to eliminate any ambiguity.
11. Security Considerations
As an asset network holds an increasing number of digital assets, it
may become attractive to attackers seeking to compromise the
cryptographic keys of the entities, services and its end-users.
Gateways are of particular interest to attackers because they enable
the transferal of digital assets to external networks, which may or
may not be regulated. As such, hardening technologies and tamper-
resistant crypto-processors (e.g. TPM, SGX) should be used for
implementations of gateways [HS19].
12. Policy Considerations
Digital asset transfers must be policy-driven in the sense that it
must observe and enforce the policies defined for the network.
Resources that make-up a network are owned and operated by entities
(e.g. legal persons or organizations), and these entities typically
operate within regulatory jurisdictions [FATF]. It is the
responsibility of these entities to translate regulatory policies
into functions on networks that comply to the relevant regulatory
policies.
At the application layer, asset transfers must take into
consideration the legal status of assets and incorporate relevant
asset-related policies into their business logic. These policies
must permeate down to the gateways that implement the functions of
asset transaction processing.
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13. Threat Analysis Considerations
The SAT protocol faces challenges with regards to the confidentiality
of a transfer between gateways, and the potential issue related to a
denial-of-service (and resource waste) when either gateway is not
compliant with the protocol.
For confidentiality of a transfer, the secure asset transfer protocol
must utilize a TLS1.2 (TLS1.3) secure channel that must be
established between the sender gateway (G1) and the receiver gateway
(G2). The two gateways must first establish this secure channel at
the start of Stage 1 before they can proceed to execute the asset
transfer protocol. This includes both gateways verifying all the
relevant parameters required for their TLS1.2 session (e.g. correct
TLS endpoints, certificate validation, identity validation, etc.).
There are several challenges that may arise when gateways are not
compliant with the SAT protocol. Some of these are described below.
13.1. Multiple intentional aborts by the sender gateway
A dishonest sender gateway G1 may purposely fail to continue the
protocol run at certain crucial points. One such crucial point is in
Stage-3, where the gateway G1 is expected to transmit the Commit-
Final Assertion message (3.5). If the gateway G1 intentionally fails
to transmit this message, gateway G2 may conclude that the message
has been lost and may proceed to reverse the temporary hold it has
previously created (temporary asset mint in message 3.2). Although
this dishonest behavior by G1 does not cause asset damage to G2 or
NW2, it may exhaust computing resources at gateway G2. If network
NW2 incurs transaction fees, such a reversal may be costly for
gateway G2.
13.2. Multiple intentional aborts by the receiver gateway
In a similar manner, a receiver gateway G2 may also purposely fail to
continue the protocol run at certain crucial points. One such point
is the Commit-Ready message (3.3) that it should transmit to G1 after
receiving the commit prepare message (3.1) from G1. In this case,
gateway G1 may conclude that the message is lost and simply abort the
protocol run.
Another possible denial-of-service attack could arise when G2
purposefully fails to send a Lock-Assertion-Receipt (2.4), thereby
forcing G1 to reverse its lock that was performed earlier (2.1).
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13.3. Failure to transmit ACK-Final Receipt
Another possible point of attack by a dishonest gateway G2 may occur
by the gateway intentionally failing to transmit the ACK-Final-
Receipt (3.7) in response to the Commit-Final Assertion message (3.5)
from gateway G1. Here, the sender gateway G1 may conclude that the
message is lost and will assume that the transaction has reach
completion in network NW2. The sender gateway G1 has retained the
previous Lock-Assertion Receipt (2.4) in Stage-2 that was signed by
G2, indicating that the gateway G2 has accepted the responsibility of
ensuring that the asset-assignment (3.6) by G2 will be correctly
executed. Failure by G2 to complete this task becomes a financial
and legal liability for the owner of gateway G2.
In general, it is recommended that multiple redundant gateways be
utilized within a network to mitigate a single gateway's malicious
behavior. Furthermore, there are gateway recovery and failover
mechanisms that have been defined in [BCH21].
13.4. Failure to extinguish asset
Another potential attack may come from a dishonest gateway G1 who
intentionally fails to extinguish the asset in network NW1 (in step
3.4). This means G1 is henceforth in control of the asset. This
type of denial-of-service is network specific because it implies that
G1 was able to perform a lock on the asset on behalf of the asset-
owner (i.e. originator) through one or more mechanisms supported by
network NW1 independent of (and prior to) the secure asset transfer
protocol.
This denial-of-service is out of scope for the current architecture
specification because it represents a weakness on the part of the
network NW1.
13.5. Identity impersonations
Another vector of attack may involve a gateway that impersonates an
asset holder in a given network. For example, a gateway G1 may
pretend to be the owner of an asset (originator) in network NW1 and
proceed to transfer it to a beneficiary located in network NW2.
The verification of the identity of the originator and beneficiary
must be performed as part of the set-up stage (Stage 0) as described
in Section 6, which is currently out-of-scope for the secure asset
transfer protocol.
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The identity verification includes that of the owner of gateways G1
and G2 respectively. Standard protocols for federated identity
management already exist and have wide deployment.
14. Compatibility Considerations
As the asset transfer protocol must be agnostic to the anatomy of a
digital asset and to the type of ledger technology underlying a
system maintaining digital assets, it must be compatible with
different asset identification standards like ISO 20022 and ITIN, and
with standards for communicating information about business processes
(like ISO 20022). Keeping the Stage-0 specification open and not
tied to a specific messaging or identification standard allows the
Secure Asset Transfer architecture to be flexible and inclusive, and
thereby meet compatibility goals.
15. References
15.1. Normative References
[FATF] FATF, "International Standards on Combating Money
Laundering and the Financing of Terrorism and
Proliferation - FATF Revision of Recommendation 15
(Updated June 2021)", October 2018, <http://www.fatf-
gafi.org/publications/fatfrecommendations/documents/fatf-
recommendations.html>.
[ISO] ISO, "Blockchain and distributed ledger technologies-
Vocabulary (ISO:22739:2020)", July 2020,
<https://www.iso.org>.
[ISO20022] ISO, "Universal Financial Industry Message Scheme (ISO
20022).", July 2023, <https://www.iso20022.org>.
[ITIN] ITSA, "International Token Identification Number.", July
2023, <https://my.itsa.global/what-we-do>.
[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>.
[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>.
15.2. Informative References
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[ABCH20] Ankenbrand, T., Bieri, D., Cortivo, R., Hoehener, J., and
T. Hardjono, "Proposal for a Comprehensive Crypto Asset
Taxonomy", May 2020, <https://arxiv.org/abs/2007.11877>.
[Abebe19] Abebe, E., Behl, D., Govindarajan, C., Hu, Y.,
Karunamoorthy, D., Novotny, P., Pandit, V., Ramakrishna,
V., and C. Vecchiola, "Enabling Enterprise Blockchain
Interoperability with Trusted Data Transfer (Middleware
2019, Industry Track)", December 2019,
<https://arxiv.org/abs/1911.01064>.
[Abebe21] Abebe, E., Hu, Y., Irvin, A., Karunamoorthy, D., Pandit,
V., Ramakrishna, V., and J. Yu, "Verifiable Observation of
Permissioned Ledgers (ICBC2021)", May 2021,
<https://arxiv.org/abs/2012.07339>.
[BCH21] Belchior, R., Correia, M., and T. Hardjono, "DLT Gateway
Crash Recovery Mechanism, IETF, draft-belchior-gateway-
recovery-01.", March 2021,
<https://datatracker.ietf.org/doc/draft-belchior-gateway-
recovery/>.
[BVGC20] Belchior, R., Vasconcelos, A., Guerreiro, S., and M.
Correia, "A Survey on Blockchain Interoperability: Past,
Present, and Future Trends", May 2020,
<https://arxiv.org/abs/2005.14282v2>.
[Clar88] Clark, D., "The Design Philosophy of the DARPA Internet
Protocols, ACM Computer Communication Review, Proc SIGCOMM
88, vol. 18, no. 4, pp. 106-114", August 1988.
[DevID] IEEE, "802.1AR: Secure Device Identity", August 2018,
<https://doi.org/10.1109/IEEESTD.2018.8423794>.
[DLVIEW] Ramakrishna, V., Pandit, V., Nishad, S., Narayanam, K.,
and D. Vinayagamurthy, "Views and View Addresses for
Blockchain/DLT Interoperability, IETF Draft", November
2021.
[Gray81] Gray, J., "The Transaction Concept: Virtues and
Limitations, in VLDB Proceedings of the 7th International
Conference, Cannes, France, September 1981, pp. 144-154",
September 1981.
[Herl19] Herlihy, M., "Blockchains From a Distributed Computing
Perspective, Communications of the ACM, vol. 62, no. 2,
pp. 78-85", February 2019,
<https://doi.org/10.1145/3209623>.
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[HLP19] Hardjono, T., Lipton, A., and A. Pentland, "Towards and
Interoperability Architecture for Blockchain Autonomous
Systems, IEEE Transactions on Engineering Management",
June 2019, <https://doi:10.1109/TEM.2019.2920154>.
[HS2019] Hardjono, T. and N. Smith, "Decentralized Trusted
Computing Base for Blockchain Infrastructure Security,
Frontiers Journal, Special Issue on Blockchain Technology,
Vol. 2, No. 24", December 2019,
<https://doi.org/10.3389/fbloc.2019.00024>.
[RATS] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", January 2023,
<https://datatracker.ietf.org/doc/rfc9334/>.
[SATcore] Hargreaves, M., Hardjono, T., and R. Belchior, "IETF
Secure Asset Transfer Protocol (SATP)", 9 July 2023,
<https://datatracker.ietf.org/doc/draft-ietf-satp-
core/>.>.
[SRC84] Saltzer, J., Reed, D., and D. Clark, "End-to-End Arguments
in System Design, ACM Transactions on Computer Systems,
vol. 2, no. 4, pp. 277-288", November 1984.
[TPMdevID] TCG, "TPM 2.0 Keys for Device Identity and Attestation", 8
October 2021, <https://trustedcomputinggroup.org/resource/
tpm-2-0-keys-for-device-identity-and-attestation/>.
Appendix A. Acknowledgments
The authors would like to thank the following people for their input
and support:
Andre Augusto, Denis Avrilionis, Rafael Belchior, Carsten Bormann,
Sandip Chakraborty, Shiping Chen, Alexandru Chiriac, Claire Facer,
Martin Gfeller, Bishakh Ghosh, Wes Hardaker, Paul Hoffman, Russ
Housley, Nick Kerrigan, Krishnasuri Narayanam, Chris Ostrowski,
Vinayaka Pandit, Luke Riley, John Robotham, Orie Steele, Peter
Somogyvari, Mike Trutter, Gilbert Verdian, Dhinakaran Vinayagamurthy,
Paul Wouters, Qin Wang, Weijia Zhang.
Authors' Addresses
Thomas Hardjono
MIT
Email: hardjono@mit.edu
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Martin Hargreaves
Quant Network
Email: martin.hargreaves@quant.network
Ned Smith
Intel
Email: ned.smith@intel.com
Venkatraman Ramakrishna
IBM
Email: vramakr2@in.ibm.com
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