Internet DRAFT - draft-pouwelse-trustchain
draft-pouwelse-trustchain
Internet Engineering Task Force J. Pouwelse, Ed.
Internet-Draft Delft University of Technology
Intended status: Informational June 5, 2018
Expires: December 7, 2018
Trustchain protocol
draft-pouwelse-trustchain-01
Abstract
Trustchain is a protocol for a networked datastructure, designed to
act as a trust ledger. This protocol acts as a decentralized
alternative to platforms like eBay, Airbnb, and Uber. It is
specifically designed to record transactions among strangers without
central control, support high transaction volumes, be application
neutral, and avoid vendor lock-in. The protocol defines recording
transactions in an ordered list using an append-only datastructure, a
new communication overlay, and a horizontally scalable consensus
protocol based on checkpoint consensus, called CHECO. Trustchain has
resistance to traditional blockchain attacks, such as the 51 percent
majority attack. This is achieved by using a graph-based append-only
datastructure combined with a personal blockchain for each
participant with their own genesis block.
Status of This Memo
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This Internet-Draft will expire on December 7, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Trustchain Stack: Engineering trust . . . . . . . . . . . . . 5
3. Trustchain Fabric: internal data structure . . . . . . . . . 7
3.1. Architecture . . . . . . . . . . . . . . . . . . . . . . 7
3.2. TxBlock specification . . . . . . . . . . . . . . . . . . 9
3.3. Asynchronicity . . . . . . . . . . . . . . . . . . . . . 10
3.4. CHECO: Consensus protocol and block format . . . . . . . 11
4. IPv8: Overlay for identity, discovery and trust . . . . . . . 11
4.1. Identity establishment and discovery . . . . . . . . . . 12
4.2. Attestations and trust . . . . . . . . . . . . . . . . . 12
4.3. Peer-to-peer cryptographically signed messaging . . . . . 25
4.4. NAT traversal . . . . . . . . . . . . . . . . . . . . . . 25
5. Attack resistances . . . . . . . . . . . . . . . . . . . . . 26
5.1. Sybil attacks . . . . . . . . . . . . . . . . . . . . . . 26
5.2. Double spending attack . . . . . . . . . . . . . . . . . 26
5.3. Replay attack . . . . . . . . . . . . . . . . . . . . . . 27
5.4. Whitewashing attack . . . . . . . . . . . . . . . . . . . 27
5.5. Spam attack . . . . . . . . . . . . . . . . . . . . . . . 27
5.6. DDoS . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 28
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
For the past 10 years various distributed ledgers have been deployed
and used. This protocol aims to establish some form of trust using
software.
Creating trust between strangers is at the core of numerous
successful Internet companies. Starting 22 years ago, Craigslist
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offered an unmoderated mailing list of advertisements and gossip on
which buyer and seller could be trusted. eBay formalised this in
1997 and introduced a star-based rating system that enables traders
to build a trustworthy profile [resnick2002trust]. The e-commerce
platform was launched at a time when people were still hesitant to
use their credit card on a technology called The Internet. Nowadays,
people let strangers sleep in their houses using Airbnb (since 2008).
We trust Uber (since 2009) with our physical security and get into
cars late at night with a driver that has not undergone a criminal
background check or given a government license.
The Trustchain protocol aims to create a generic approach and
continues this evolution of building trust. Compared to successful
central platforms, we propose a distributed open underlying
infrastructure, based on blockchain inspired technology. Bitcoin
created money without the need for banks [nakamoto2008bitcoin]. In
the past, people were required to trust a central bank and a host of
other intermediaries when making payments [kokkola2011payment]. The
fundamental technology of Bitcoin, blockchain, radically reduced the
need to trust financial middlemen. It bootstrapped an economy where
no one can be stopped from spending their money. Despite widespread
speculation and ecosystems being worth billions, blockchain in
general suffers from scalability issues due to inefficient mechanisms
for fraud prevention. Bitcoin is theoretically limited to seven
transactions per second and Ethereum has a throughput of around 20
transactions per second [vukolic2015quest]. Despite various
scalability efforts like proof-of-stake and sharding, broader
adoption of blockchain stays out. Mt. Gox was at one point the
largest Bitcoin exchange worldwide. While a majority of Internet
users trust the company behind popular platforms, the events
involving Mt. Gox highlighted how digital trust can be established
and compromised[mcmillan2014inside]. In 2014, hackers stole Bitcoin,
worth around $460 million at that time. This event, together with
major data breaches in 2017 at high-profile companies like Uber and
Equifax, exposed the weakness of centralized architectures
[apostle2017uber]. These events motivated this proposed protocol
around decentralised infrastructures, not owned or operated by a
single authority. The generic problem of building trust between
strangers resides on the edge of technology, sociology and
behavioural science [yan2008trust]. The question whether someone can
be trusted, depends on properties like personality, level of
authority, culture and past behaviour. In this protocol, we address
the trust problem from a technological perspective, using tamper-
proof interactions on a scalable blockchain. This structure is built
to help ease the detection of fraudulent behaviour and
misrepresentation. Trust calculations are out of scope of this work,
we provide the enabling mechanisms.
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1.1. Purpose
This draft describes the Trustchain architecture, protocols and the
used technologies, designed to model application neutral trust
between interacting parties. Trustchain relies on a new
communication layer on top of existing communication networks, which
is designed with carrier-grade NAT infrastructure in mind, as well as
the network protocol based on the CrawlRequest and TxBlock message
types. A consensus protocol called CHECO (Cong et al, 2017
[cong2017blockchain]) is incorporated into Trustchain, which will be
discussed but not elaborated in this draft. It is based on the
blockchain paradigm where the complete network represents a ledger
where agents' transactions infer an amount of trust between the
involved parties, as is described by pouwelse, 2017
[pouwelse2017trustlaws].
As protocols have slowly been moving towards the business layer in
the past decade, Trustchain is implemented on top of a networking
overlay and as such is network agnostic. Other examples of moving
networking to the business layer are: R3 Corda (Brown, 2017
[brown2017introducing]) and IOTA (Atzori, 2016
[atzori2016blockchain]). The overlay, audaciously called IPv8,
provides encrypted communication between public keys. This overlay
has integrated NAT puncturing to support, for instance, Android-to-
Android overlay communication, does not require any central server,
lacks central authorities, and can run directly on top of UDP, TCP,
or other protocols. As such, IPv8 provides a set of communication
methods and messages that provide the required functionality to let
Trustchain function properly on both PC networks or smartphone-only
networks.
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.3. Terminology
Identity
The actual user representation, but can not be directly used,
since all information is identifier based.
Identifier
A reference that is owned by a given identity, referring to this
identity. Any identity can have multiple identifiers, whilst
staying anonymous.
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Agent
A node in the Trustchain network representing an identifier for a
given identity.
Message
The basic unit of Trustchain communication. A message will have
different representations on the wire depending on the transport
protocol used. Messages are typically multiplexed into a
datagram for transmission.
Datagram
A sequence of messages that is offered as a unit to the
underlying transport protocol (UDP, etc.).
Transaction
An interaction between two agents containing information on both
parties and what has been transacted. This is application
agnostic, meaning that any given application can infer what type
of information it needs based on a collection of transactions.
Signature
A cryptographic function that used the private key to create a
representing string, which can be verified by any other party
using the signer's public key.
Hash
The result of applying a cryptographic hash function, more
specifically SHA-256 [FIPS180-4], to a piece of data.
2. Trustchain Stack: Engineering trust
Our principal mechanism to establish some form of trust is: if
everyone keeps their secret keys secure, then no signed transaction
can be spoofed on the overlay by any significant likelihood. We
refer to the Trustchain protocol when discussing the mechanism to
record interactions which are cryptographically signed by multiple
parties. We explicitly do not support transactions signed by only a
single party, which is the foundation of Bitcoin. Our foundation is
a multi-signature agreement, without mono-signature support. The
Trustchain stack refers to the full system which also includes the
upper application layer, the network overlay and self-sovereign
identity layer. Together they form a complete solution stack.
The concept of a Self-Sovereign Identity (SSI) (Abraham, 2017
[abrahamself]) means that agents have full control over their
identity data, and provide it to those who need to validate it,
without relying on a central repository of identity data of any kind.
A large part of any SSI based system is rooted in the problem of
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proofs and attestations: proof can be anything, such as a secret
message that is re-encrypted with a shared secret. But the most
challenging part is working with attestations. An Attestation refers
to the process wherein a third party validates that according to
their records, the claims are true, that is, a more transitive
property of trust: C attests to B that A is who it claims to be,
Azouvi et al, 2017 [azouvi2017secure]. As such, an attestation from
the right authority could be more trustworthy than a proof, which
might have been forged. However, attestations can be a burden on the
agent as the information can be sensitive, hence, the information
needs to be maintained so that only specific agents can access it.
Our stack does not constrain the choice of SSI system, but our
implementation is focused on the Boneh-Franklin [boneh2004secure]
2-DNF scheme ("Evaluating 2-DNF Formulas on Ciphertexts").
Based upon the assumption that these identities are persistent and
secure, the new architecture (or Fabric) is designed to use Peer-to-
Peer communication to increase the transaction throughput. This
communication is based on the new networking overlay: IPv8, which
handles peer discovery, making connections with them across NAT boxes
and peer-to-peer cryptographically signed messaging. As IPv8 is
transport and application agnostic, it can run over any transport
protocol: it does not depend on IP and may run on top of NDN, XIA,
and other new Internet architectures.
To ensure that the blockchain is always in a valid state, a new
horizontal scaling consensus protocol is proposed: CHECO. CHECO is
specifically designed to counter the vulnerabilities that a
distributed, permissionless, multi-chain architecture will have to
cope with (although this also creates innate vulnerabilities to other
kinds of attacks). By creating an indication of the state of
validity for each agent, the responsibility of verification lies with
the agent itself. A malicious agent in an invalid state can easily
be detected, and should be avoided for interactions.
We do not constrain or limit the applications utilising this
blockchain, as each transaction block can contain information of
arbitrary content and length. Currently, there is a basic
decentralised market implemented. More specialised markets have to
also be implemented and emulated such as an open Taxi service market
and a mortgage investment market. Multiple applications can be used
at the same time, next to the decentralised market, for instance: it
could be used for byte accounting in an ad-hoc Manet
[jethanandani2017accounting].
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+--------------------------+
| |
| <Application layer> |
| |
+--------------------------+
| |
| CHECO |
| |
+--------------------------+
| |
| Trustchain Fabric |
| |
+--------------------------+
| |
| IPv8 |
| |
+--------------------------+
| |
| Self-Souvereign Identity |
| |
+--------------------------+
Figure 1
3. Trustchain Fabric: internal data structure
Trustchain is designed to be a non-blocking format for agents that
supports simultaneous interactions with other agents. Non-blocking
is a requirement rooted in the immutability of the chain and the
strict ordering of the blocks. To support this, the blocks are
designed to be dependent on signing by all participating agents, and
will be called TxBlocks henceforth, as is described in this section,
along with the macro data structure in which these blocks are used.
3.1. Architecture
In contrast to traditional blockchains, in Trustchain every agent in
the network has its own genesis node, in essence creating a personal
blockchain for each agent. Each interaction creates a new
transaction block, which is based on the last block of the two (or
more) concerned parties. This does not only influence the block-
creation speed, but also the amount of effort needed to verify a
chain. Along with some other security properties, this is one of the
implicit capabilities of this protocol.
By removing the proof-of-work mechanism needed for classic blockchain
implementations, Trustchain yields inherent horizontal scalability.
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However the cost of scalability is that each application requires a
mechanism to guard against transaction spam and abuse. Trustchain is
based on the assumption that both parties agree on the transaction
before signing it, making tampering inherently easy to detect. One
of the aspects that supports this is the fact that Trustchain is
organised as a set of temporally ordered, intertwining chains, which
form a Directed Acyclic Graph (DAG). This is called a "bottom-up
consensus model", giving the participants the responsibility to
verify the correctness of the transaction instead of a central
(sometimes randomly chosen) elected leadership.
Trustchain depends on signatures from all participants in a
transaction, creating an n-to-n node. This system is extendable, as
mentioned before, by extending the transaction description to provide
specific properties. Each transaction is stored in a block, in
agreement-block format, each block has parts that are signed and
submitted by all participating parties, where the initial request is
called the block-proposal and a completely signed and validated block
is called an agreement-block (where a pair indicates the cooperation,
not the limitation to two participating parties). These are signed
and sequenced so that each sequence number is unique in its accessory
chain, as can be seen below in the general structure diagram.
+---------+--+---------+
| |
| Transaction A with D |
| |
| |
+----------------------+
| sequence number A: 3 |
+----------------------+
| signed by A |
+----------------------+
| sequence number D: 49|
+----------------------+
| signed by D |
+---------+--+---------+
| |
| +----------------------+
| | |
+---------+--+---------+ +---------+--+---------+
| | | |
| Transaction A with C | | Transaction D with B |
| | | |
| | | |
+----------------------+ +----------------------+
| sequence number A: 2 | | sequence number D: 48|
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+----------------------+ +----------------------+
| signed by A | | signed by D |
+----------------------+ +----------------------+
| sequence number C: 4 | | sequence number B: 12|
+----------------------+ +----------------------+
| signed by C | | signed by B |
+---------+--+---------+ +---------+--+---------+
| | |
| +----------------------+
| |
+---------+--+---------+
| |
| Transaction A with B |
| |
| |
+----------------------+
| sequence number A: 1 |
+----------------------+
| signed by A |
+----------------------+
| sequence number B: 11|
+----------------------+
| signed by B |
+---------+--+---------+
Figure 2
3.2. TxBlock specification
Using the proposal-block and agreement-block formats means singing
the blocks on the current views of the respective parties: the
requester and the responder(s). Each party signs and fills the block
with the information that it has at that specific point in time. The
requester fills the structure with its own previous hash and its own
part of the transaction data, signs it and sends it to the
responder(s), which in turn construct the other sections of the
block, if it agrees with the content before sending it back. This
nullifies any ordering and asynchronicity issues, since the requester
constructs the block with the information that it has, and keeps it
in memory while it waits on the responder to send the finished block
back.
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+--------+----------------------------+--------------+--------------+
| Number | Description | Type | Size (bytes) |
+--------+----------------------------+--------------+--------------+
| 1 | Requester public key | Char array | 74 |
| 2 | Requester sequence number | Unsigned int | 4 |
| 3 | Responder public key | Char array | 74 |
| 4 | Responder sequence number | Unsigned int | 4 |
| 5 | Requester previous hash | Char array | 32 |
| 6 | Signature | Char array | 64 |
| 7 | Transaction block size (n) | Unsigned int | 4 |
| 8 | Transaction block | Char array | n |
| | *Total:* | | 256 + n |
+--------+----------------------------+--------------+--------------+
Table 1: TxBlock fields description
3.3. Asynchronicity
Because there is the need to communicate between the requester and
responder(s), there will be a delay which may be significant. To
have a high level of asynchronicity and enable multiple peers
interacting simultaneously, extending the chain should be possible
while waiting for a response. In order to do this, the block refers
to the previous block using the hash of the requester's part, since
this is the only stable reference at that point. The other hash
reference (the "previous hash responder") can then either be the
"hash requester" or "hash responder" part of the head-block of the
responder chain. Which one is used depends on whether the responder
was the requester or responder in its previous interaction. This
mechanic is also used for the "previous hash requester" field, but
this reference is known when the block is created. In effect, this
results to theoretically unlimited horizontal scalability: the more
actors are active on the chain, the more throughput can be achieved.
Though this is in fact limited by the memory speed, or database
slowdown when the chain grows.
One of the drawbacks of this mechanic is when the responder does not
sign and respond, whether because it will/can not. In such cases,
there will be an orphan block. While this is not a vulnerability in
itself, it might be the starting point of a certain type of attack
(the other "normal" types of attacks used for blockchains can be
mitigated, at least to a certain level, as is described in
resistances (Section 5).). The adversary might let someone initiate
a transaction, i.e. a block creation, after which it will create an
orphan. Doing this multiple times in a short time span will force
the requester to use a considerable amount of processing power and
memory, all the while injecting orphan blocks into its chain. As
mentioned before, this is not a vulnerability in itself, but might be
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a launchpad for a more elaborate attack. Although, one coping method
could be to split larger, more vulnerable transactions up into
multiple smaller transactions. This way, the consequences stay the
same for the malicious actor, but the losses are smaller.
3.4. CHECO: Consensus protocol and block format
The final part of the Trustchain Fabric is CHECO, a horizontally
scaling consensus protocol specifically designed for multi-chain
implementation and completely application agnostic. CHECO is based
on three separate protocols: A consensus protocol, a transaction
protocol and a validation protocol, as well as an extension of the
architecture by introducing a new type of block next to the TxBlock:
CpBlock. Every round a set of so-called facilitators is selected at
random, which collect the CP and TX blocks, to feed to the validation
protocol, after which, the results are broadcast before a new round
starts.
CHECO is designed to create an internal state ledger for each chain,
without having to rely on separate methods or instances. This is
achieved by introducing a new block: the Checkpoint block (CpBlock),
which contains a hash pointer to the previous block, along with a
hash of the consensus result, round and sequence number and, lastly,
a signature. The consensus result is defined as a tuple containing
the validity states of the blocks agreed on by the facilitators of
that round and the round number. If your chain is deemed valid, a
CpBlock is injected, thus validating the state of the chain. While
the content of the injected CpBlock differs from the TxBlock, these
blocks do not interfere with the transaction protocol, since they fit
in the architecture without modifying it.
Instead of requiring a proof-of-work (as seen in more conventional
blockchain implementations), CHECO is round based, creating a
consensus state every so often, thus enabling a fully asynchronous
and horizontally scaling protocol. These facilitators are chosen
randomly each round, and will collect the CpBlocks from all other
nodes since their last CpBlock. Validation is done using the
Asynchronous Common Subset (ACS) algorithm based on HoneyBadgerBFT
(Miller et al, 2016 [miller2016honey]), a byzantine consensus
algorithm.
4. IPv8: Overlay for identity, discovery and trust
To enable this new platform to function properly, a new method to
find, connect to and manage agents was needed. Additionally, new
models for identity verification, network discovery and inter-peer
trust were required to enable these agent methods. IPv8 is a network
stack, a set of protocols and models, that separates concerns and
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enables applications (such as Trustchain) to use the needed methods
and protocols, without giving up interoperability and upgradeability.
On top of this interface lies the actual Trustchain overlay, which
uses the components and protocols of the IPv8 interface to create the
specific functionalities needed for Trustchain to function.
IPv8 is built by closely abiding to the Unix Philosophy of creating
small components that are easy to understand and test. This is
mainly why the complete networking system used in Tribler was re-
written as a generic networking interface, enabling modifications and
additions without losing any functionality. Although agents might
use different protocols based on their capabilities, IPv8 is a basic
layer over a multitude of networking components and subsystems,
creating a means to communicate with other agents regardless of
networking capabilities. An open source reference implementation
based on Python is available on Github, called py-ipv8.
Interoperable open implementations in Java and Kotlin are still only
partially functional.
4.1. Identity establishment and discovery
Identities are created, attested and distributed over the Trustchain
using IPv8 as the communication interface. These are all public and
self sovereign, leading to distribution when an agent creates a new
identity, and are organised using a Public Key Infrastructure (PKI).
This distribution is done to agents who have (or might have) an
interest in obtaining the identity of this agent, since they are in
the same cluster or due to other factors. Spreading information this
way is called Gossiping, since agents learn of new identities, and
spreading them among directly connected agents like a gossip would
spread.
Discovering identities is done based on Distributed Hash Tables
(DHT), somewhat similar to the Domain Name System (DNS) currently
used for the web, using Random-Walk and Live-Edge-Walk: discovery
protocols for DHTs, respectively based on making random DHT queries
in order to learn about a large number of identities quickly and
making pseudo-randomised queries about the agents with the highest
trust scores in the network. The use of random-walks enables DHTs to
converge much faster, whilst having a small load at the very
beginning. Furthermore, by traversing the live edges, Trustchain is
more spam and Sybil attack resistant.
4.2. Attestations and trust
The primary problem with identities and proofs is falsification, and,
thus, these need to be verified to prevent this. However, even
proofs can be forged, leading to the problem of needing trust in a
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proving party, which can not be solved by having a more centralised
proving party. This is where attestations are used: a witness
reports that the identity in question is actually valid. This
requires some level of trust between the agents. Attestations are a
method to enable agents to validate interactive zero-knowledge proofs
(ZKPs) within a network of agents, a so-called web-of-trust
[azouvi2017secure], where the transitive property of trust is used to
prevent the need for every agent to verify an identity itself as is
noted in Section 2.
In this case, the probabilistic homomorphic asymmetrical encryption
scheme of Boneh-Franklin [boneh2004secure] is used to validate these
proofs, meaning that a form of randomness is used in the encryption,
and computations on the ciphertext result in a valid plaintext.
Using Boneh-Franklin leads to these ZKPs to be hardened against
chosen plaintext attacks (an attacker can encrypt the suspected
plaintext to see if the ciphertexts match) with the probabilistic
aspect. These attestations are tied to metadata, which can be
verified separately. The related identities are stored internally in
a database, and the aforementioned metadata attributes are gossiped
around the network using Trustchain.
4.2.1. Technical view of Attestations and Verifications
4.2.1.1. Attributes
Attributes are a generic term which can essentially refer to any
verifiable piece of information. For instance, an attribute may
define a peer's identity, the amount of cryptocurrency in one's
digital wallet, or perhaps, something as simple as one's previous
number of transactions. In the context of Trustchain, Attributes
mainly refer one's identity.
4.2.1.2. Attestations
In a truly distributed peer-to-peer system, where peers regularly
communicate and exchange information (hence they exchange attributes)
there is a need of verifying the veracity of attributes, without
relying on a well-known, well-trusted tertiary party / peer.
Attestations are a means which make this task possible. They allow
peers to verify the truthfulness of Attributes through a validation
process, using interactive zero-knowledge proofs. A system based on
Attestations is founded on the fact that, intrinsically, there exists
a degree of trust between the peers of a system. To this extent,
attestations are, generally speaking, a means through which peer C
vouches to peer B that A is indeed telling the truth. Unlike normal
centralized systems, where C is a well-known entity, in this case, C
may be any trustworthy fellow peer. This enforces the idea that
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trust is transitive, hence there is no need for a trusted central
peer to exist, since one can rely on other peers to attest for the
veracity of Attributes.
4.2.1.2.1. The Attestation process
As its name suggests, the Attestation Process is a mechanism through
which a peer (the Attestee) requests the attestation of one of its
Attributes from another fellow peer (the Attester). The process is
initiated by the Attestee. If the process is successful, and the
Attribute has indeed been attested, the Attester produces an
attestation as proof, which is returned to the Attestee. This should
complete the process. In the sections that follow, the messages
exchanged during the aforementioned process are detailed.
Additionally, a more detailed, high-level description of the peer
interaction is also presented.
4.2.1.2.2. Message types
The following sections present the different types of messages that
are exchanged between the Attestee and Attester peers during the
attestation process, namely the Attestation Request message and the
Attestation Response message. A section on the prefix field, which
is employed in all messages used towards peer communication, is also
presented in what follows.
4.2.1.2.2.1. Preamble field
The preamble field is present in all the messages employed in
Trustchain towards peer communication. Consequently, it plays an
important role in inter-peer communication. Figure 3 presents its
generic structure.
+-------------+-------------+---------------------+---------------+
| 0 (1B) | ver_nr (1B) | peer_key_hash (20B) | msg_type (1B) |
+-------------+-------------+---------------------+---------------+
Figure 3: The structure of the Preamble / Prefix field. The size of
each field is specified in parentheses in Bytes.
A description of the Preamble field's elements is presented in
Table 2.
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+---------------+--------+------------------------------------------+
| FIELD | OCTETS | DESCRIPTION |
+---------------+--------+------------------------------------------+
| 0 | 1 | The initial byte of any message is 0 |
| | | (0x00). |
| | | |
| ver_nr | 1 | The current implementation version. |
| | | |
| peer_key_hash | 20 | A hash of the key of the message |
| | | sender's master peer. |
| | | |
| msg_type | 1 | Indicates the nature of the message. For |
| | | instance, when 'msg_type = 5', the |
| | | message will be an ATTREQ. Similarly, |
| | | when 'msg_type = 2', the message is |
| | | either ATTRESP or VFRESP. Other types |
| | | are also available. |
+---------------+--------+------------------------------------------+
Table 2: Description of fields in the Preamble / Prefix field
4.2.1.2.2.2. The Attestation Request Message
The Attestation Request message (ATTREQ), is forwarded by the
Attestee towards the Attester, in order to indicate the Attestee's
desire to have one of its attributes attested by the Attester. The
structure of the ATTREQ message is presented in Figure 4.
+--------+---------------------------------+----------------------+----------------+
| Number | Description | Type | Size (bytes) |
+--------+---------------------------------+----------------------+----------------+
| 0 | Preamble / Prefix | Char Array | 23 |
+--------+---------------------------------+----------------------+----------------+
| 1 | Public Key in Binary Format | Unsigned Short Array | n |
+--------+---------------------------------+----------------------+----------------+
| 2 | Global Time (Lamport Timestamp) | Unsigned Long Long | 8 |
+--------+---------------------------------+----------------------+----------------+
| 3 | Attestation Metadata | Char Array (Raw) | 33 + m |
+--------+---------------------------------+----------------------+----------------+
| | *Total:* | | 64 + n + m |
+--------+---------------------------------+----------------------+----------------+
Figure 4: The structure of an ATTREQ message.
A description of the ATTREQ's fields is presented in Table 3.
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+-------------+--------+----------+---------------------------------+
| FIELD | OCTETS | TYPE | DESCRIPTION |
+-------------+--------+----------+---------------------------------+
| Preamble / | 23 | Char | Generic message preamble, as |
| Prefix | | Array | presented in Section |
| | | | 4.2.1.2.2.1, with msg_type = 5. |
| | | | |
| Public Key | n | Unsigned | The Attestee's public key in |
| | | Short | binary format. n = |
| | | Array | bin_public_key_char_length * 2, |
| | | | since each Unsigned Short |
| | | | element is 2 Bytes in size. |
| | | | |
| Global Time | 8 | Unsigned | A Lamport Timestamp (Scalar |
| | | Long | Clock) associated with the |
| | | Long | message. |
| | | | |
| Attestation | 33 + m | Char | Holds a string having the |
| Metadata | | Array | pattern: '{"attribute": |
| | | (Raw) | "attr_name", "public_key": |
| | | | pub_key}' (without the ' |
| | | | characters). The attr_name and |
| | | | pub_key tokens are replaced by |
| | | | actual values. The minimal size |
| | | | of the field is 33 Bytes (if |
| | | | both tokens would be omitted). |
| | | | m is the cumulative string |
| | | | length of the values in the |
| | | | attr_name and pub_key tokens. |
+-------------+--------+----------+---------------------------------+
Table 3: Description of the fields in an ATTREQ message
4.2.1.2.2.3. The Attestation Response Message
The Attestation Response message (ATTRESP), is forwarded by the
Attester towards the Attestee, in order to send the previously
requested attestation to the Attestee. It should be noted that
ATTRESP messages are sent only in case the attestation is successful.
If the attestation fails, no such messages are sent. Furthermore,
the attestation may be of arbitrary length, hence, it is impractical
to send it entirely at once. Consequently, the attestation is broken
up into smaller chunks (at most 800 Bytes) and each chunk is packed
as part of an ATTRESP message. The structure of an ATTRESP message
is presented in Figure 5
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+--------+---------------------------------+----------------------+--------------+
| Number | Description | Type | Size (Bytes) |
+--------+---------------------------------+----------------------+--------------+
| 0 | Preamble / Prefix | Char Array | 23 |
+--------+---------------------------------+----------------------+--------------+
| 1 | Public Key in Binary Format | Unsigned Short Array | n |
+--------+---------------------------------+----------------------+--------------+
| 2 | Global Time (Lamport Timestamp) | Unsigned Long Long | 8 |
+--------+---------------------------------+----------------------+--------------+
| 3 | Attestation Blob Hash | Char Array | 20 |
+--------+---------------------------------+----------------------+--------------+
| 4 | Sequence Number | Unsigned Short | 2 |
+--------+---------------------------------+----------------------+--------------+
| 5 | Attestation Blob Chunk | Char Array (Raw) | 800 |
+--------+---------------------------------+----------------------+--------------+
| | *Total:* | | 853 + n |
+--------+---------------------------------+----------------------+--------------+
Figure 5: The structure of an ATTRESP message.
A description of the ATTRESP's fields is presented in Table 4.
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+-------------+--------+----------+---------------------------------+
| FIELD | OCTETS | TYPE | DESCRIPTION |
+-------------+--------+----------+---------------------------------+
| Preamble / | 23 | Char | Generic message preamble, as |
| Prefix | | Array | presented in Section |
| | | | 4.2.1.2.2.1, with msg_type = 2. |
| | | | |
| Public Key | n | Unsigned | The Attester's public key in |
| | | Short | binary format. n = |
| | | Array | bin_public_key_char_length * 2, |
| | | | since each Unsigned Short |
| | | | element is 2 Bytes in size. |
| | | | |
| Global Time | 8 | Unsigned | A Lamport Timestamp (Scalar |
| | | Long | Clock) associated with the |
| | | Long | message. |
| | | | |
| Attestation | 20 | Char | A hash of the entire |
| Blob Hash | | Array | attestation blob. This can be |
| | | | used to check the integrity and |
| | | | completeness of the |
| | | | reconstructed blob on the |
| | | | Attestee's side. |
| | | | |
| Sequence | 2 | Unsigned | The message's sequence number |
| Number | | Short | in the sequence of ATTRESP |
| | | | messages sent for the |
| | | | particular attestation. |
| | | | |
| Attestation | 800 | Char | A chunk of the attestation |
| Blob Chunk | | Array | blob. |
| | | (Raw) | |
+-------------+--------+----------+---------------------------------+
Table 4: Description of the fields in an ATTRESP message
4.2.1.2.3. Attestee-Attester Interaction - Attestation Process
The following summary refers to the interaction between Attestee and
Attester during the attestation process. The timeline diagram in
Figure 6 shows the timing relationships in such an interaction.
Table 5 gives a brief reminder of the messages employed in the
attestation process.
The Attestee forwards an ATTREQ message to the Attester, with the
aim of requesting attestation for an Attribute, as indicated in
the ATTREQ message.
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After receiving the ATTREQ, and successfully completing the
attestation process, the Attester responds with a series of
ATTRESP messages. The message sequence may be of arbitrary
length. At a high-level, the sequence of ATTRESP message returns
the new attestation, hence, each message will contain a chunk of
the attestation blob. Additionally, each ATTRESP message also
contains a hash of the entire attestation blob, a message sequence
number, and additional message fields. If the attestation is
unsuccessful, no ATTRESP messages are returned.
The Attestee receives the sequence of ATTREQ messages from the
Attester, and puts them together. The Attestee will know it has
received the entire attestation blob, when the hash of the
attestation blob, present in the ATTREQ messages, matches a
locally computed hash of the reconstructed attestation blob.
Attestee Attester
v v
| |
| ATTREQ |
| +------------------> |
| |
| |
| Attest
| |
| |
| ATTRESP #1 |
| <------------------+ |
| . |
| . |
| . |
| ATTRESP #N |
| <------------------+ |
| |
| |
Attestation |
Complete |
| |
| |
v v
Figure 6: Timeline diagram of the messages exchanged between Attestee
and Attester during the attestation process.
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+---------+---------------------------------------------------------+
| MESSAGE | USE |
+---------+---------------------------------------------------------+
| ATTREQ | Attestee message to Attester requiring the attestation |
| | of an indicated Attribute. |
| | |
| ATTRESP | Attester message to Attestee provided that attestation |
| | was successful. Each ATTRESP carries a part of the |
| | successful attestation blob. |
+---------+---------------------------------------------------------+
Table 5: Attestation process message summary
4.2.1.3. Attestation Verification
Whilst Attestations are employed towards ensuring that peers are
truthful in regards to some of their Attributes, the Attestation
Verification request is employed towards ensuring that the
Attestations themselves are valid. The employed mechanism does not
stray far away from that which is employed in the case of
Attestations. In fact, they are structurally similar: during the
process of an Attestation Verification a peer C vouches to peer B
that A is indeed telling the truth regarding a supplied Attestation.
Once more, this enforces the idea that trust is transitive, hence
there is no need for a trusted central peer to exist, since one can
rely on other peers to attest for the veracity of an Attestation.
4.2.1.3.1. Attestation Verification Process
The Verification process defines an interaction between two peers,
the Requester peer, and the Verifier peer, wherein the Requester
demands that the Verifier verifies one of its attestations (that is,
an attestation of the Verifier). Intuitively, the Requester peer
initiates the process. If the verification is successful, the
Verifier should return the verified attestation. This should
complete the process. In the sections that follow, the messages
exchanged during the aforementioned process are detailed.
Additionally, a more detailed, high-level description of the peer
interaction is also presented.
4.2.1.3.1.1. Attestation Verification message types
The following sections present the different types of messages that
are exchanged between the Requester and Verifier peers during the
verification process, namely, the Verification Request message and
the Verification Response message. Incidentally, the Verification
Response message is identical to the Attestation Response message,
which was presented in Section 4.2.1.2.2.3.
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4.2.1.3.1.1.1. The Verification Request Message
The Verification Request message (VFREQ), is forwarded by the
Requester towards the Verifier, so as to demand that the Verifier
verifies one of its attestations, and then sends it back to the
Requester. The structure of the VFREQ message is presented in
Figure 7.
+--------+-----------------------------------+----------------------+--------------+
| Number | Description | Type | Size (Bytes) |
+--------+-----------------------------------+----------------------+--------------+
| 0 | Preamble / Prefix | Char Array | 23 |
+--------+-----------------------------------+----------------------+--------------+
| 1 | Public Key in Binary Format | Unsigned Short Array | n |
+--------+-----------------------------------+----------------------+--------------+
| 2 | Global Time (Lamport Timestamp) | Unsigned Long Long | 8 |
+--------+-----------------------------------+----------------------+--------------+
| 3 | Hash of the Verified Attestation | Char Array | 20 |
+--------+-----------------------------------+----------------------+--------------+
| | *Total:* | | 51 + n |
+--------+-----------------------------------+----------------------+--------------+
Figure 7: The structure of an VFREQ message.
A description of the VFREQ's fields is presented in Table 6.
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+-------------+--------+----------+---------------------------------+
| FIELD | OCTETS | TYPE | DESCRIPTION |
+-------------+--------+----------+---------------------------------+
| Preamble / | 23 | Char | Generic message preamble, as |
| Prefix | | Array | presented in Section |
| | | | 4.2.1.2.2.1, with msg_type = 1. |
| | | | |
| Public Key | n | Unsigned | The Requester's public key in |
| | | Short | binary format. n = |
| | | Array | bin_public_key_char_length * 2, |
| | | | since each Unsigned Short |
| | | | element is 2 Bytes in size. |
| | | | |
| Global Time | 8 | Unsigned | A Lamport Timestamp (Scalar |
| | | Long | Clock) associated with the |
| | | Long | message. |
| | | | |
| Verified | 20 | Char | A hash of the attestation which |
| Attestation | | Array | needs to be verified. |
| Hash | | | |
+-------------+--------+----------+---------------------------------+
Table 6: Description of the fields in an VFREQ message
4.2.1.3.1.1.2. The Verification Response Message
The Verification Response message (VFRESP) is identical in structure
to the Attestation Response message (ATTRESP), since both return an
attestation. For the VFRESP's structure please see section
Section 4.2.1.2.2.3. The two messages differ only slightly in terms
of semantics, since one is returned as a response to a successful
attestation request, thus returning a new attestation, while the
other (the verification) is returned upon a successful verification
request, thus returning the recently verified attestation. A
sequence of VFRESP messages should only be returned when the
verification was successful, i.e. the attestation could be verified.
As was the case in the ATTRESP messages, the verified attestation may
be of arbitrary length, hence, it is impractical to send it entirely
at once. Consequently, the attestation is broken up into smaller
chunks (at most 800 Bytes) and each chunk is packed as part of a
VFRESP message.
Since the semantics of some of the fields in the VFRESP messages
slightly differ than those in the ATTRESP messages, a description of
the VFRESP's fields is presented in Table 7.
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+-------------+--------+----------+---------------------------------+
| FIELD | OCTETS | TYPE | DESCRIPTION |
+-------------+--------+----------+---------------------------------+
| Preamble / | 23 | Char | Generic message preamble, as |
| Prefix | | Array | presented in Section |
| | | | 4.2.1.2.2.1, with msg_type = 2. |
| | | | |
| Public Key | n | Unsigned | The Verifier's public key in |
| | | Short | binary format. n = |
| | | Array | bin_public_key_char_length * 2, |
| | | | since each Unsigned Short |
| | | | element is 2 Bytes in size. |
| | | | |
| Global Time | 8 | Unsigned | A Lamport Timestamp (Scalar |
| | | Long | Clock) associated with the |
| | | Long | message. |
| | | | |
| Attestation | 20 | Char | A hash of the entire |
| Blob Hash | | Array | attestation blob. This can be |
| | | | used to check the integrity and |
| | | | completeness of the |
| | | | reconstructed blob on the |
| | | | Requester's side. |
| | | | |
| Sequence | 2 | Unsigned | The message's sequence number |
| Number | | Short | in the sequence of VFRESP |
| | | | messages sent for the |
| | | | verification. |
| | | | |
| Attestation | 800 | Char | A chunk of the attestation |
| Blob Chunk | | Array | blob. |
| | | (Raw) | |
+-------------+--------+----------+---------------------------------+
Table 7: Description of the fields in an VFRESP message
4.2.1.3.2. Requester-Verifier Interaction - Verification Process
The following summary refers to the interaction between Requester and
Verifier during the verification process. The timeline diagram in
Figure 8 shows the timing relationships in such an interaction.
Table 8 gives a brief reminder of the messages employed in the
verification process.
The Requester forwards a VFREQ message to the Verifier, with the
aim of requesting the verification of an Attribute's attestation,
as indicated by the attestation hash in the VFREQ message.
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After receiving the VFREQ, and successfully completing the
verification process, the Verifier responds with a series of
VFRESP messages. The message sequence may be of arbitrary length.
At a high-level, the sequence of VFRESP message returns the
recently verified attestation, hence, each message will contain a
chunk of the attestation blob. Additionally, each VFRESP message
also contains a hash of the entire attestation blob, a message
sequence number, and additional message fields. If the
verification is unsuccessful, no VFRESP messages are returned.
The Requester receives the sequence VFRESP messages from the
Verifier, and puts them together. The Requester will know it has
received the entire attestation blob, when the hash of the
attestation blob present in the VFRESP messages matches a locally
computed hash of the reconstructed attestation blob.
Requester Verifier
v v
| |
| VFREQ |
| +------------------> |
| |
| |
| Verify
| |
| |
| VFRESP #1 |
| <------------------+ |
| . |
| . |
| . |
| VFRESP #N |
| <------------------+ |
| |
| |
Verification |
Complete |
| |
| |
v v
Figure 8: Timeline diagram of the messages exchanged between
Requester and Verifier during the verification process.
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+---------+---------------------------------------------------------+
| MESSAGE | USE |
+---------+---------------------------------------------------------+
| VFREQ | Requester to Verifier requiring the verification of an |
| | attestation, as indicated in the VFREQ message. |
| | |
| VFRESP | Verifier to Requester provided that verification was |
| | successful. Each VFRESP carries a part of the recently |
| | verified attestation. |
+---------+---------------------------------------------------------+
Table 8: Verification process message summary
4.3. Peer-to-peer cryptographically signed messaging
Most messages that are sent between peers are encrypted, the keys are
retrieved from either the PKI, and verified based on the key
attestations, or from the internal database after verification has
already been done. Encryption is done using the ECDSA encryption
scheme [johnson2001elliptic], which is an Elliptic Curve based
cryptography system. This enables IPv8 to send messages effectively
to a multitude of agents when (at the least) their identities are
known, preferably also attested for. Having such a low bar to
encrypt messages discourages the use of unencrypted communication
channels, making interactions secure almost as early as the
handshake, since the first message sent to any agent can be already
encrypted with its respective key (which is retrieved from the
database, other agents or the initial bootstrapping list).
4.4. NAT traversal
Network Address Translation (NAT) is omnipresent in the modern
Internet, mostly due to networks being separated and the limited
amount of global IP addresses available. Most consumer devices are
behind a number of layers of NAT, but data center nodes can be behind
NAT for security or virtualisation reasons. Containerised
deployments are making things worse, as every peer based
communication scheme must have a way to traverse NATs, otherwise
operations will be affected. Even nodes meant to run with real IP
addresses must implement NAT traversal techniques, as they may need
to establish connections to peers behind NAT. Message puncturing
based on UDP is key to this overlay. It conducts a random network
walk to preserve connectivity under churn. Participants help each
other to puncture the NAT infrastructure. Each participant will
periodically introduce and connect some of its neighbors. When their
random neighbors do not yet know each other, a new participant is
discovered. Carefully timed concurrent UDP messages are used to
traverse carrier-grade NAT infrastructures. Implementation,
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deployment and measurements of smartphone users has shown that it is
possible to build a healthy overlay without servers, even if nearly
100 percent of users are behind a NAT (Android-to-android overlay
[TUDelft2018trustchain]).
5. Attack resistances
For blockchain implementations, attack resistance is an important
requirement, especially with horizontal scalability. Therefore,
Trustchain will have to cope with the same difficulties and attacks
that other blockchain implementations have to, but due to the novel
structure it introduces, these threats can be countered. With this
novel structure, validation, uncertainty, and tamper proofing can be
handled in a more intuitive manner while throughput does not need to
suffer.
5.1. Sybil attacks
One of the most difficult attacks to repel, for a blockchain
implementation, is the Sybil attack, where many agents are injected
into the chain (and authenticity cannot easily be verified) to
subvert a large portion of the system's voting power or trust (see
section 3.3). Usually peer verification is used to protect against
this kind of attacks (for instance: proof-of-work), usually resulting
in slow systems. But when the influence of the attacker is large
enough, even these methods will not be able to stop such an attack.
Trustchain deals with this problem by having an inherently different
structure, where each peer has its own origin. On top of that,
transaction injection can only be done with two valid signatures,
meaning a Sybil attacker can only create trust with itself. This
results in a network of disconnected agents that have no relation
outside of their own cluster, which can easily be identified. Even
when the Sybils acquire some degree of trust from outside of their
cluster, by using accounting mechanisms, the profit from such an
attack can only be weakly beneficial with bounded profit (using
Netflow, not discussed in this paper) (Otte et al, 2017
[otte2017trustchain]).
5.2. Double spending attack
Using control over the blockchain to create a fork and creating two
different transaction branches is called double spending. This kind
of attack can be applied with relative ease to single chain
implementations of the blockchain by injecting two conflicting
transactions at the same time. Trustchain deals with this kind of
attack by having the chain verified with each CHECO round, during
which the hidden transaction can be easily found. By broadcasting
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both blocks as a proof-of-fraud the malicious agent will have
decreased trust and can be blacklisted or refused service.
5.3. Replay attack
Using the transaction signature of the counterpart, a malicious agent
can try to replay a transaction on the blockchain, which results in
increased trust or may be used to gain credits. CHECO and the novel
structure make it trivial to find the conflicting blocks when
verifying the counterparty's chain. The two blocks with the same
outgoing pointer together make the proof-of-fraud, which then can
then be used to decrease the trust in the malicious party and can be
blacklisted or refused service.
5.4. Whitewashing attack
Abusing the permissionless structure of Trustchain to create
additional identities at any given point can negate the effect of
having trust, so this kind of attack differs from a Sybil attack.
When an agent suffers from reputation loss, it can simply discard its
current identity and take on a new one. Since refusing service to
agents with little trust will affect usability and willingness to
join the network, an adequate solution can be prioritising
strategies. One method for implementing this is described in the
paper discussing Netflow (not discussed in this paper) (Otte et al,
2017 [otte2017trustchain]).
5.5. Spam attack
Since the TxBlocks have dynamic size, spam (in the sense of useless
data in the transaction field) can be used to clog an agent's network
or database with excessively large messages, slowing down its
operations or bringing it to a complete halt due to memory/network
being full. This kind of attack can be coped with by having a
throttle per connection to keep some bandwidth available and a limit
on the size of the message. If large messages are to be expected, a
file based buffer will enable large message transfer without
exceeding the memory capacity.
Another type of spam can be identified as a collection of useless
messages, clogging the network and database with large amounts of
empty messages, which is possible since transactions do not require
an agent to pay transaction costs (as BitCoin does). Though this is
easily countered by not accepting those messages, leading to the
malicious agent having a lot of orphan blocks.
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5.6. DDoS
When massive quantities of useless or empty messages are sent over a
network, it might get congested, leading to dropped operations,
network congestion, unreachability of agents, or, in the most extreme
cases, even to system failure due to overload. Due to the
distributed, peer based communications architecture, this is not
feasible without flooding the network of the malicious agent itself,
as it has to send messages to each target individually.
6. Acknowledgements
We very much thank the European Union for providing us the required
funding for this work. Through EU FP6 and FP7 funding instruments we
have been developing and deploying our own distributed ledger fabric
since August 2007. An estimated 3.4 million Euro has been granted
through these specific projects and leading directly to this work
([P2P-Fusion], [P2P-Next],[QLectives]).
We thank master student Stijn for his help with writing of this
draft.
7. IANA Considerations
This memo includes no request to IANA.
All drafts are required to have an IANA considerations section (see
Guidelines for Writing an IANA Considerations Section in RFCs
[RFC5226] for a guide). If the draft does not require IANA to do
anything, the section contains an explicit statement that this is the
case (as above). If there are no requirements for IANA, the section
will be removed during conversion into an RFC by the RFC Editor.
8. Security Considerations
From a security perspective, the usage of novel structures such as
Trustchain might lead to new kinds of attacks. We consider this risk
of less importance for a private and consortium network, where all
participants are known to the operator and authentication mechanisms
are used to restrict access to the network.
For the public blockchain networks, the usage of Trustchain might
lead to new kinds of attacks. For instance, an attacker might be
able to pollute the chain with refusal to sign attacks to decrease
trust. The scope of such attacks and security violations needs to be
investigated and is not part of this draft.
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[jethanandani2017accounting]
Jethanandani, M., "Accounting in NETCONF and RESTCONF",
2017, <https://www.ietf.org/id/
draft-mahesh-netconf-accounting-03.txt>.
[johnson2001elliptic]
Johnson, D., Menezes, A., and S. Vanstone, "The elliptic
curve digital signature algorithm (ECDSA)", 2001,
<http://www.springerlink.com/index/0L7A1W9W38XL6W6R.pdf>.
[kokkola2011payment]
Kokkola, T., "The payment system: Payments, securities and
derivatives, and the role of the Eurosystem.", 2011,
<https://www.ecb.europa.eu/pub/pdf/other/
paymentsystem201009en.pdf>.
[mcmillan2014inside]
McMillan, R., "The inside story of Mt. Gox, Bitcoin's $460
million disaster.", 2014,
<https://www.wired.com/2014/03/bitcoin-exchange/>.
[miller2016honey]
Miller, A., Xia, Y., Croman, K., Shi, E., and D. Song,
"The honey badger of BFT protocols", 2016,
<http://dl.acm.org/citation.cfm?id=2978399>.
[nakamoto2008bitcoin]
Nakamoto, S., "Bitcoin: A peer-to-peer electronic cash
system", 2008, <http://www.academia.edu/download/32413652/
BitCoin_P2P_electronic_cash_system.pdf>.
[otte2017trustchain]
Otte, P., de Vos, M., and J. Pouwelse, "Trustchain: A
Sybil-resistant scalable blockchain", 2017,
<https://www.sciencedirect.com/science/article/pii/
S0167739X17318988>.
[P2P-Fusion]
"P2P-Fusion project", 2018,
<http://cordis.europa.eu/project/rcn/105290_en.html>.
[P2P-Next]
"Next Generation Peer-to-Peer Content Delivery Platform",
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[pouwelse2017trustlaws]
Pouwelse, J. and M. de Vos, "Laws for creating trust in
the blockchain age", 2017, <https://github.com/blockchain-
lab/shared_vision_towards_programmable_economy>.
[QLectives]
"QLectives project", 2018,
<http://cordis.europa.eu/project/rcn/89031_en.html>.
[resnick2002trust]
Resnick, P. and R. Zeckhauser, "Trust among strangers in
Internet transactions: Empirical analysis of eBay's
reputation system", 2002,
<http://www.emeraldinsight.com/doi/pdf/10.1016/
S0278-0984(02)11030-3>.
[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>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
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Pouwelse, J., "Trustchain - creating trust with software",
2018, <https://play.google.com/store/apps/
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Vukolic, M., "The quest for scalable blockchain fabric:
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Holtmanns, S. and Z. Yan, "Trust modeling and management:
from social trust to digital trust.", 2008,
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article1.pdf>.
Author's Address
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Dr. J.A. Pouwelse (editor)
Delft University of Technology
Delft
Netherlands
Phone: +31 15 2782539
Email: j.a.pouwelse@tudelft.nl
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