1) The document discusses adapting permissionless blockchain construction to user demand by allowing the number of blocks and block creation rate in a blockchain to self-adapt to transaction demand.
2) It proposes a system called Sycomore that moves from a chain of blocks to a directed acyclic graph (DAG) of blocks where the predecessor of a block is not predictable.
3) Sycomore aims to partition transactions over blocks in a way that is verifiable by anyone and allows the blockchain to scale to thousands of transactions per second while maintaining security properties like preventing double spending.
Simone Bronzini - Weaknesses of blockchain applications - Codemotion Milan 2018Codemotion
Due to the immutability of the ledger and the difficulty to update their consensus rules, Blockchain applications have many critical layers where a bug can cause huge, irreversible fund losses. This talk will shed some light on why and how Blockchain applications are so critical and will discuss past events that led to fund loss or consensus failures due to bugs in critical parts of the code of Bitcoin and Ethereum applications.
A basic overview of what blockchain is with step-by-step easy to follow explanation of its core concepts. It should be easy for anyone with zero knowledge of blockchain to follow through the slides
Intro to Blockchain - And, by the way, what the heck is proof-of-work?Jim Flynn
An overview of bitcoin and the blockchain with a more in-depth description of proof of work (POW). Conde samples used to demonstrate the concepts behind POW are available at http://jamespflynn.com.
Blockchain general presentation nov 2017 v engDavid Vangulick
These slides are used to introduce the concept of blockchain and how this technology can be used for peer to peer energy exchange linked with the wholesale energy market
Simone Bronzini - Weaknesses of blockchain applications - Codemotion Milan 2018Codemotion
Due to the immutability of the ledger and the difficulty to update their consensus rules, Blockchain applications have many critical layers where a bug can cause huge, irreversible fund losses. This talk will shed some light on why and how Blockchain applications are so critical and will discuss past events that led to fund loss or consensus failures due to bugs in critical parts of the code of Bitcoin and Ethereum applications.
A basic overview of what blockchain is with step-by-step easy to follow explanation of its core concepts. It should be easy for anyone with zero knowledge of blockchain to follow through the slides
Intro to Blockchain - And, by the way, what the heck is proof-of-work?Jim Flynn
An overview of bitcoin and the blockchain with a more in-depth description of proof of work (POW). Conde samples used to demonstrate the concepts behind POW are available at http://jamespflynn.com.
Blockchain general presentation nov 2017 v engDavid Vangulick
These slides are used to introduce the concept of blockchain and how this technology can be used for peer to peer energy exchange linked with the wholesale energy market
Talk for CodeMash 2018. Page to end for resources. Some more links (click to expand):
Bitcoin's Insane Energy Consumption Explained: https://arstechnica.com/tech-policy/2017/12/bitcoins-insane-energy-consumption-explained/
The Ethereum-blockchain size will not exceed 1TB anytime soon.
https://dev.to/5chdn/the-ethereum-blockchain-size-will-not-exceed-1tb-anytime-soon-58a
For use rights, please see license agreement below.
Consensus Algorithms - Nakov at CryptoBlockCon - Las Vegas (2018)Svetlin Nakov
Consensus Algorithms
Dr. Svetlin Nakov at CryptoBlockCon - Las Vegas (11 Dec 2018)
In this talk the speaker Svetlin Nakov explains very briefly the concepts of decentralized consensus and blockchain consensus algorithms, along with examples from popular blockchain networks and DLT ledgers:
The concept of Byzantine Fault Tolerance (BFT)
The role of consensus algorithms in decentralized systems and blockchains
Proof-of-work consensus (PoW), mining, pools, hash power, ASIC mining, etc.
Proof-of-stake (PoS) and its variants: DPoS (delegated PoS), RPoS (randomized PoS), LPoS (leased PoS), PoI (proof of importance)
Practical Byzantine Fault Tolerance (PBFT) and FBA (federated byzantine agreement)
Proof-of-Authority (POA)
Non-blockchain consensus, asynchronous byzantine fault tolerance (aBFT) and Hashgraph
Apart from Proof of Work there are many other Consensus Mechanisms being discussed. What are they and what are their pros and cons. (Proof of Stake, Proof of Elapsed Time, Proof of Authority, Proof of Burn, Proof of Authority, Byzantine Fault Tolerance, Proof of Importance)
At a very high level, the Blockchain is a decentralized ledger, or list, of all transactions across a peer-to-peer network. This is the technology underlying Bitcoin and other cryptocurrencies, and it has the potential to disrupt a wide variety of business processes.
Bitcoin, Blockchain and the Crypto Contracts - Part 2Prithwis Mukerjee
Where we explain how the cryptographic ideas are used to create a crypto asset on the block chain. This one part of a three part slide deck. For the full deck and the context please visit http://bit.ly/pm-bbc
Where we explain how the concept of a crypto currency can lead to the creation of a new kind of autonomous corporation. This one part of a three part slide deck. For the full deck and the context please visit http://bit.ly/pm-bbc
The presentation slides for a blockchain event - All About TenX Cryptopayment Technology, Lightning Network & Bitcoin Mining.
Presenter: Sun Sagong
Venue: Tenx (Singapore)
Date: 07Feb2018
Best practices to build secure smart contractsGautam Anand
- Quick update in blockchain tech space
- Comparision between tech
- Security in Blockchain (Focusing on ETH Solidity attack vectors)
- Design patterns
- 2 Popular hacks (Case study)
Presentation material for Quorum meetup in Singapore (1 June) for the purpose of circulating among attendees.
Presentation by Sai Valiveti, Quorum platform development lead for APAC
An introduction to Quorum that covers:
- What is Quorum
- Key features
- Technical deep-dive: privacy
- What can be done with Quorum
- Existing use-cases
- Getting started with Quorum
Connecting The Block Cointelligence Academy by Dr Vince MingCointelligence
This lecture is intended for konwledge sharing and educational purpose only in order to provide a comprehensive overview and helping people who wants to find out about the blockchain's core concept from a general technical standpoint with the intention to gain the right perception, the basic know-how and overall perspective on the emerging technology.
Bitcoin Lightning Network - Presentation Jim Brysland
Slides used for my talk on the Lightning Network @ Strathclyde for our Glasgow Bitcoin Meet-up: https://www.meetup.com/TheCryptograph-com-Cryptocurrency-Meetup/
An introduction to Ethereum, the peer to peer computing framework based on the blockchain design. It describes how Ethereum relates to earlier blockchain technologies and how it represents an evolution of these technologies
Talk for CodeMash 2018. Page to end for resources. Some more links (click to expand):
Bitcoin's Insane Energy Consumption Explained: https://arstechnica.com/tech-policy/2017/12/bitcoins-insane-energy-consumption-explained/
The Ethereum-blockchain size will not exceed 1TB anytime soon.
https://dev.to/5chdn/the-ethereum-blockchain-size-will-not-exceed-1tb-anytime-soon-58a
For use rights, please see license agreement below.
Consensus Algorithms - Nakov at CryptoBlockCon - Las Vegas (2018)Svetlin Nakov
Consensus Algorithms
Dr. Svetlin Nakov at CryptoBlockCon - Las Vegas (11 Dec 2018)
In this talk the speaker Svetlin Nakov explains very briefly the concepts of decentralized consensus and blockchain consensus algorithms, along with examples from popular blockchain networks and DLT ledgers:
The concept of Byzantine Fault Tolerance (BFT)
The role of consensus algorithms in decentralized systems and blockchains
Proof-of-work consensus (PoW), mining, pools, hash power, ASIC mining, etc.
Proof-of-stake (PoS) and its variants: DPoS (delegated PoS), RPoS (randomized PoS), LPoS (leased PoS), PoI (proof of importance)
Practical Byzantine Fault Tolerance (PBFT) and FBA (federated byzantine agreement)
Proof-of-Authority (POA)
Non-blockchain consensus, asynchronous byzantine fault tolerance (aBFT) and Hashgraph
Apart from Proof of Work there are many other Consensus Mechanisms being discussed. What are they and what are their pros and cons. (Proof of Stake, Proof of Elapsed Time, Proof of Authority, Proof of Burn, Proof of Authority, Byzantine Fault Tolerance, Proof of Importance)
At a very high level, the Blockchain is a decentralized ledger, or list, of all transactions across a peer-to-peer network. This is the technology underlying Bitcoin and other cryptocurrencies, and it has the potential to disrupt a wide variety of business processes.
Bitcoin, Blockchain and the Crypto Contracts - Part 2Prithwis Mukerjee
Where we explain how the cryptographic ideas are used to create a crypto asset on the block chain. This one part of a three part slide deck. For the full deck and the context please visit http://bit.ly/pm-bbc
Where we explain how the concept of a crypto currency can lead to the creation of a new kind of autonomous corporation. This one part of a three part slide deck. For the full deck and the context please visit http://bit.ly/pm-bbc
The presentation slides for a blockchain event - All About TenX Cryptopayment Technology, Lightning Network & Bitcoin Mining.
Presenter: Sun Sagong
Venue: Tenx (Singapore)
Date: 07Feb2018
Best practices to build secure smart contractsGautam Anand
- Quick update in blockchain tech space
- Comparision between tech
- Security in Blockchain (Focusing on ETH Solidity attack vectors)
- Design patterns
- 2 Popular hacks (Case study)
Presentation material for Quorum meetup in Singapore (1 June) for the purpose of circulating among attendees.
Presentation by Sai Valiveti, Quorum platform development lead for APAC
An introduction to Quorum that covers:
- What is Quorum
- Key features
- Technical deep-dive: privacy
- What can be done with Quorum
- Existing use-cases
- Getting started with Quorum
Connecting The Block Cointelligence Academy by Dr Vince MingCointelligence
This lecture is intended for konwledge sharing and educational purpose only in order to provide a comprehensive overview and helping people who wants to find out about the blockchain's core concept from a general technical standpoint with the intention to gain the right perception, the basic know-how and overall perspective on the emerging technology.
Bitcoin Lightning Network - Presentation Jim Brysland
Slides used for my talk on the Lightning Network @ Strathclyde for our Glasgow Bitcoin Meet-up: https://www.meetup.com/TheCryptograph-com-Cryptocurrency-Meetup/
An introduction to Ethereum, the peer to peer computing framework based on the blockchain design. It describes how Ethereum relates to earlier blockchain technologies and how it represents an evolution of these technologies
Understanding Blockchain: Distributed Ledger TechnologySuraj Kumar Jana
A complete introduction to Distributed Ledger Technology and Blockchain. Also, get introduced to Hyperledger, an open source permissioned blockchain framework by The Linux Foundation.
A brief introduction to Blockchain and the underlying technology of distributed computing, challenges and future scope.
Copyrights belong to the respective owners, intention is purely for informational/educational purpose
I would like to thank various blogs, technical tutorials, books, videos to help me understand the basics and collate this presentaion
A Primer on Blockchain and its Potential, with a Focus on the GCCZeyad T. Al Mudhaf
During my summer internship at BECO Capital, a technology-focused Venture Capital firm based in Dubai, I put together this primer on blockchain that demystifies this hyped up technology, covers key investment trends in the space both globally and regionally within the GCC*, and highlights both the barriers and enablers for wider blockchain adoption in the region. *The GCC is the Gulf Cooperation Council - comprised of the United Arab Emirates, Saudi Arabia, Kuwait, Bahrain, Qatar, and Oman.
An overview of blockchain and Distributed Ledger Technologies (DLT) including consensus, PoW, PoS, dBFT, DAG, smart contracts, Ethereum, Stellar, Ripple, Hashgraph Hedera, tokens, tokenomics, cryptocurrencies, ICO... taught during the ITU DLT seminar in Bangkok Thailand in September 2018
Blockchain Ecosystem and Cryptocurrency RegulationsAmir Rafati
A blockchain is a general digital ledger of transactions that are executed on the network, e.g. using Bitcoin to buy a cup of coffee is a transaction.
All users of the network, ‘Nodes’, have a copy of the transaction records and can access them freely, a role previously played by centralized institutions. Therefore, the blockchain network is ‘decentralized’.
Blockchain has gained lots of attention in recent years. Bitcoin and Ethereum are leading the race. Crypto currencies in spite of uncertainty and volatility are here to stay. Smart contract programming is the future for the Internet 3.0.
Virtual or digital currencies, with Bitcoin chief amongst them, have been gaining momentum and investment over the last couple of years. Offering an almost costless means of making payments around the globe, virtual currencies have the potential to bring significant disruption to the banking industry. This potential is not lost on either Bitcoin startups or banks themselves. But how does Bitcoin actually work? A peer-to-peer network maintains the “blockchain”, an innovative cryptographic protocol which securely mediates payments between parties without mutual trust. This session will step through the structure of the blockchain, showing how it solves the “double spend” problem and allows decentralised processing of financial transactions. Whether Bitcoin will become the currency of the internet or it’s a bubble that is doomed to burst sooner or later, the blockchain itself will change the face of transactional banking and perhaps other industries along the way.
Presentation to the Sydney Financial Mathematics Workshop (11 March 2015)
http://www.qgroup.org.au/content/bitcoin-banking-and-blockchain
Blockchain technology is a distributed ledger platform that provides open and transparent transaction information with integrity and non-repudiation based on modern cryptography. It is also the technology behind many cryptocurrencies. This presentation will give fundamental knowledge on how blockchain works, its cryptography implementation, cryptocurrency definition and related terms and also blockchain use cases.
An introductory presentation discussing the basics of technology behind blockchain, cryptocurrency mining, and an attempt to value a cryptocurrency. Further discussion on altcoins, and a preview on ICOs.
Exploring the tech and legal side of Blockchain. A peek behind the curtain of how it works. Presented by Susan Goldsmith and Ash Yadav at whartonclubnj event.
Similar to Can we safely adapt the construction of permissionless blockchain to user demand ? (20)
Colloque Healthcare 4.0 : "Accompagnement des troubles du sommeil : la recher...I MT
Colloque Healthcare 4.0 : "Accompagnement des troubles du sommeil : la recherche-projet Som'Health"
Plus d'infos : https://www.imt.fr/retour-sur-le-colloque-imt-healthcare-4-0-du-15-octobre-2019/
Colloque Healthcare 4.0 : « Vous ne devriez pas autant être sur les écrans ! » I MT
Colloque Healthcare 4.0 : « Vous ne devriez pas autant être sur les écrans ! »
Plus d'infos : https://www.imt.fr/retour-sur-le-colloque-imt-healthcare-4-0-du-15-octobre-2019/
Colloque Healthcare 4.0 : "NeuroLife : Interfaces Cerveau Machine pour la San...I MT
Colloque Healthcare 4.0 : "NeuroLife : Interfaces Cerveau Machine pour la Santé et l’Autonomie"
Plus d'infos : https://www.imt.fr/retour-sur-le-colloque-imt-healthcare-4-0-du-15-octobre-2019/
Colloque Healthcare 4.0 : "La protection de données en santé"I MT
Colloque Healthcare 4.0 : "La protection de données en santé"
Plus d'infos : https://www.imt.fr/retour-sur-le-colloque-imt-healthcare-4-0-du-15-octobre-2019/
Colloque IMT - 15/10/2019 - Healthcare 4.0 – « Modélisation semi-analytique personnalisée du port des ceintures lombaires. Application à des essais précliniques in vitro » -Présentation par Jérôme Molimard
Colloque IMT - 15/10/2019 - Healthcare 4.0 – « Développement de la caméra XE...I MT
Colloque IMT - 15/10/2019 - Healthcare 4.0 – « Développement de la caméra XEMIS2 pour l'imagerie médicale à 3 gammas » - Présentation par Dominique Thers
Colloque IMT - 15/10/2019 - Healthcare 4.0 – « Pilotage intelligent du service des urgences par une approche jumeau digital » - Présentation par Vincent Augusto
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - "Machine...I MT
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - "Machine Listening: L'intelligence artificielle pour les sons et la musique". Présentation par Gaël Richard
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - Contrôle...I MT
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - Session Robotique, Perception, Interaction: Contrôleurs neuronaux plastiques pour l'émergence de coordinations motrices dans l'interaction physique et sociale humain/robot. Présentation par Patrick Henaff (IMT Mines Nancy)
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - Interopé...I MT
Colloque IMT - L'IA au cœur des mutations industrielles - Session Données et connaissances: Interopérabilité sémantique et coordination décentralisée. Présentation par Maxime Lefrançois, Maître-assistant Mines
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - TeraLab,...I MT
Colloque IMT - L'IA au cœur des mutations industrielles - Session Données et connaissances: TeraLab, un accélérateur de l'industrie 4.0. Présentation par Anne-Sophie Taillandier, Directrice de projet TeraLab (IMT)
Colloque IMT -04/04/2019- L'IA au cœur des mutations industrielles - Session ...I MT
Colloque IMT - L'IA au cœur des mutations industrielles - Session: Contrôle dynamique des systèmes ou produits industriels : une intelligence artificielle ? Présentation par Philippe Chevrel
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
Courier management system project report.pdfKamal Acharya
It is now-a-days very important for the people to send or receive articles like imported furniture, electronic items, gifts, business goods and the like. People depend vastly on different transport systems which mostly use the manual way of receiving and delivering the articles. There is no way to track the articles till they are received and there is no way to let the customer know what happened in transit, once he booked some articles. In such a situation, we need a system which completely computerizes the cargo activities including time to time tracking of the articles sent. This need is fulfilled by Courier Management System software which is online software for the cargo management people that enables them to receive the goods from a source and send them to a required destination and track their status from time to time.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Can we safely adapt the construction of permissionless blockchain to user demand ?
1. 1
Can we safely adapt the construction of
permissionless blockchain to user demand?
Emmanuelle Anceaume (CNRS)
Joint work with
Antoine Durand (IRT SystemX), Romaric Ludinard
(IMT-Atlantique), Bruno Sericola (INRIA)
Journées Futur & Ruptures - January, 31st of January 2019
2. 2
Bitcoin is a cryptocurrency and payment system
• Fully decentralized
• No public key infrastructure
• Permissionless
Such constraints make the general problem of consensus
impossible to solve
• Relies on rational behavior and incentives mechanisms
To reach a consensus on the cryptocurrency state
4. 4
The state of the cryptocurrency system is represented by transactions
• Transfers currency from one user to another
• Does not contain any encrypted information nor confidential
information
Transaction 20ab3701i
Transaction 74201ab3c
UTXO
UTXO = Unspent Transaction Output
Output #2
account + ฿ + script
Output #1
account + ฿ + script
Output #1
account + ฿ + script
Output #1
account + ฿ + script
Input #1
Output ref. + script
Transaction 1206ac34e
Output #2
account + ฿ + script
Output #3
account + ฿ + script
Output #1
account + ฿ + script
Input #1
Output ref. + script
Input #2
Output ref. + script
Input #1
Output ref. + script
Input #2
Output ref. + script
Do not forget Tx fees, i.e., ฿ input ฿ output
UTXO
5. 5
Checking the ownership of an account
• How can anyone check that I am the legitimate owner of an
account since there are no identities in a transaction ?
• Using « public keys as identities » principle 1
• Ownership = knowing a private key that redeems an output
Account / address / UTXO = « single use » object
• debited once
• should be credited once
1. D. Chaum, « Untraceable Electronic Mail, Return Addresses, and Digital
Pseudonums », Communications of the ACM 24(2), pp :84–90,1981
6. 6
Signed transactions guarantee that only the owner of an
output can spend bitcoins
However signatures do not prevent double-spending attacks
• I.e., the fact that Alice spends an output twice
A publicly, immutable, and totally ordered sequence of transactions
7. 7
2. Nakamoto Consensus protocol : Adversary model 2
The Computational Threshold Adversary (CTA) model
• The adversary controls a minority of the total amount of
computational power
• The CTA model is also called the permissionless model
• There is no membership protocol
• Incorporates some degree of synchrony
The Stake Threshold Adversary (STA) model
• The adversary controls a minority stake in some limited
resource, i.e., the crypto-currency
• May allow to punish malicious parties via some stake deposit
2. Ittai Abraham and Dahlia Malkhi, « The blockchain consensus layer and
BFT », The distributed Computing Column, 2017
8. 8
2. Nakamoto Consensus protocol
Two ingredients : Leader Election Oracle + Heavier Fork Strategy
1 A leader election oracle by relying on the PoW mechanism
• Each party is elected independently
• The probability of electing each party is proportional to its
relative computational power
• Each party commits to a single block
→ Synchronize the creation of blocks
→ Prevent Sybil attacks
→ Incentivize correct behavior through currency creation
9. 9
2. Nakamoto Consensus protocol
Two ingredients : Leader Election Oracle + Heavier Fork Strategy
2 The simple and local Heavier Fork Strategy
• Select the chain which required the greatest among of work
• Random nature of the PoW + Non-faulty leaders always use
the chain which required the greatest among of work
→ One chain will be extended more than the others
→ The blockchain
B0 Bi
Bi+1
Bi+1
10. 10
2. Nakamoto Consensus protocol
The goal of the Consensus Nakamoto protocol is to implement a
blockchain replication protocol 3
• (Uniqueness) There is a unique chain of blocks (i.e., the
blockchain) extracted from the tree
• (Liveness) The blockchain is constantly growing
• (Safety) The deeper a block is buried in the blockchain the
harder it is to abort it
• (Fairness) The proportion of blocks of non-faulty parties in the
blockchain is proportional to their computation power
3. J. Garay and A. Kiayias, The Bitcoin Backbone Protocol : Analysis and
Application, Eurocrypt 2015
11. 11
3. Peer-to-Peer Network
• Topology formed through a randomized process
• No coordinating entity
• Broadcast is based on flooding/gossiping neighbors’ link
Tx d - e
Tx a - B
Tx a - B Tx a - B
Tx a - B
Tx a - B
Tx a - B
Tx a - B
Tx a - B
Tx a - B
Tx a - B
Tx d - e
Tx d - e
Tx d - e
Tx d - e
Tx d - e
Tx a - B
Tx d - e
Tx d - e
Tx a - B
Tx a - B
Tx d - e
12. 12
Required properties
1. Connectivity
• Each node should receive any broadcast information
2. Low latency 4
msg. transmission time
block time interval
1
Allows to keep the probability of fork small (i.e. 10−3)
PoW mechanism allows this ratio to continuously hold
Safety requires to wait one hour (i.e., no instant finality)
No more than 7 trans/s can be permanently confirmed in
average ! !
4. J. Garay and A. Kiayias, The Bitcoin Backbone Protocol : Analysis and
Application, Eurocrypt 2015
13. 13
Electing a leader in a permissionless setting
• Proof-of-work
Works in practice and this is true since 2009
Security analysis
Environmental issues
Diminishing returns
Distinction between miners and crypto-currency holders (i.e.,
miners control what is inside blocks)
• Proof-of-work with useful computation, proof-of-space,
proof-of-storage, . . .
Physical resources
• Proof-of-stake
Abstract but limited resource : coin itself
All the required information is already in the blockchain
Numerous attacks
14. 14
Proof-of-stake approaches
Proof-of-stake motto : « The probability for party p of winning the
leader election is proportional to the fraction of currency p owns »
• Eventual-consensus
• Protocols that apply some form of longest-chain rule to the
blockchain
• Immutability of a block increases gradually
• e.g. PPcoin, NXT, Ouroboros, . . .
• Blockwise-BA
• Immutability of a block is achieved by BA before working on
the next one
• e.g. Algorand
15. 15
Proof-of-stake approaches
PoS approaches are subject to attacks 5 essentially because it costs
nothing to create blocks and because of currency transfer from
transacting parties to the parties that maintain the ledger
• Checkpointing mechanisms
• Provide newcomers with a relatively recent block (trust issue)
• Prevent to adopt a new chain that originates to much in the
past (knowledge of the honest chain)
• Key-evolving cryptography : secret keys are evolving so that
past signatures cannot be forged (does not apply to UTXO
based model)
• Enforce strict chain density statistics (knowledge of the
number of parties at any time)
• Add context in each transaction (knowledge of the honest
chain)
5. P. Gazi, A. Kiayias, A. Russel, « Stake-Bleeding Attacks on Proof-of-Stake
Blockchains », IOHK
16. 16
Preventing conflicts as soon as possible
1. Valid blocks should never be confronted with any other
conflicting blocks
→ No fork !
→ 0-confirmation delay
2. Valid transactions should never be confronted with any other
conflicting transactions
→ No double spending attacks !
→ Fast payments feasible
17. 17
Preventing conflicts as soon as possible 6
1. Valid blocks should never be confronted with any other
conflicting blocks
How ? Agreement on the unique block that can reference an earlier
block in the blockchain
2. Valid transactions should never be confronted with any other
conflicting transactions
How ? Agreement on the unique transaction that can redeem unspent
transaction outputs (UTXOs)
6. Joint work with Antoine Durand (IRT SystemX), Romaric Ludinard (IMT),
Bruno Sericola (Inria)
E. Anceaume, A. Guellier, R. Ludinard, UTXO as a proof of membership for
Byzantine Agreements, IEEE Blockchain 2018.
18. 18
Model
• Permissionless system
• Partially synchronous environment
• Adversary : no more than 1/3 of the total amount of money is
held by the adversary
• Nodes have access to safe cryptographic functions (hash
function and signature scheme)
• Each object of the system (i.e., UTXO, transaction and block)
is assumed to be uniquely identified
• No public key infrastructure to establish node identities
19. 19
Properties
Most of the permissionless blockchain-based cryptosystems
guarantee that :
Property (Safety)
If a valid transaction T is deeply confirmed at some
non-compromised node then no transaction conflicting with T will
ever be deeply confirmed by any non-compromised nodes
Property (Liveness)
Any conflict-free and valid transaction will eventually be deeply
confirmed in the blockchain of all non-compromised nodes at the
same height in the blockchain
20. 20
Properties
We aim at strengthening both properties
Property (Strong safety)
If a valid transaction T is confirmed at some non-compromised
node then no transaction conflicting with T will ever be confirmed
by any non-compromised nodes
Property (Strong liveness)
Any valid transaction will eventually be confirmed in the blockchain
of all non-compromised nodes at the same height in the blockchain
21. 21
Transaction validation protocol
At most one transaction is allowed to use
all the UTXOs referenced in its input set
TRANSACTION
WITH BOB
VALID ??
YES !
ALICE
23. 23
Transaction validation protocol
At most one transaction is allowed to re-
deem all the UTXOs referenced in its input set
TRANSACTION
WITH BOB
VALID ??
YES !
ALICE
TRANSACTION
WITH EVE
VALID ??
NO!
24. 24
Block validation protocol
Any validated block has at most one
valid block as immediate successor
VALID ??
YES !
Pred=0001001
Block 0000111
25. 25
Block validation protocol
Any validated block has at most one
valid block as immediate successor
VALID ??
YES !
Pred=0001001
Block 0000111
Pred=0001001
Block 0000001
NO !
VALID ??
26. 26
A set of ingredients
1. Byzantine Agreement (BA)
• Primitive enabling a set of committee members to agree on a
single value, each member holding a possibly different initial
value.
• Tolerate the presence of a minority of malicious members
27. 27
2. « Public keys as identities » principle
• Users, i.e. owners of accounts (owners of UTXOs), participate
to BA 7
• Alternative to existing designs
• Rely on the unique association UTXO/identity as a proof of
membership for BA
7. E. Anceaume, A. Guellier, R. Ludinard, UTXO as a proof of membership
for Byzantine Agreements, IEEE Blockchain 2018.
28. 28
3. Clustered-based Distributed Hash Table (DHT)
• P2P overlay whose topology approximates a structured graph
• For resiliency reasons, each vertex of the graph is a set of
nodes
• Nodes logically close to each other belong to the same cluster
• e.g., PeerCube is a clustered-based overlay 8
resilient to
adversarial behavior and robust to high churn
8. E. Anceaume, R. Ludinard and B. Sericola. Performance evaluation of large-scale
dynamic systems. ACM Sigmetrics Performance Evaluation Review, 39(4), 2012.
29. 29
3. Clustered-based Distributed Hash Table (DHT) (cont’d)
By reaching an agreement around the objects to be validated
• Resistance to Eclipse attacks
• IDs are random, ephemeral and verifiable
• Resistance to Sybil attacks
• Participation to committees is weighted by UTXOs amount
• Resistance to Selfish attacks
• Miners cannot create a block without disclosing it
• No double-spending
• No forks
30. 30
Sycomore : from a chain of blocks to a DAG of blocks 9
9. E. Anceaume, A. Guellier, R. Ludinard, B. Sericola, Sycomore : a
Permissionless Distributed Ledger that self-adapts to Transactions Demand,
IEEE NCA, 2018
31. 31
Sycomore : from a chain of blocks to a DAG of blocks
• Transactions are partitioned over the blocks of the ledger -
verifiable by anyone
32. 32
Sycomore : from a chain of blocks to a DAG of blocks
• The number of blocks and their creation rate self-adapt to
transactions demand - verifiable by anyone
33. 33
Sycomore : from a chain of blocks to a DAG of blocks
• The predecessor of a block is not predictable - verifiable by
anyone
34. 34
0
100
200
300
400
500
600
1 5 10 15 20 25 30 35
Meaninter-blocktime(s)
c
1/(cλ0)
• With c = 30 leaf blocks,
a block is mined every
20s (7, 000 Tx/s) with a
proba of fork of 10−6
• Bitcoin : a block every 10
mns (7 Tx/s) with a
proba of fork of 10−3
• Could even go faster by
relying on our structured
DHT
Mean inter-block time as a function
of the number of leaf blocks c.
35. 35
Collaborations and financial support
Current collaborations
• Local : R. Ludinard (IMT Atlantique), B. Sericola and Y.
Mocquard (Dionysos), F. Tronel (Cidre).
• National : A. Durand (IRT SystemX), M. Potop-Butucaru
(LIP6), A. Del Pozzo and S. Tucci (CEA)
• International : P. Tzigas (Chalmers Univ), L. Querzoni (La
Sapienza Univ),
Financial support
• PEPS INS2I Securite 2016 and 2017 : BIPs
• Labex Cominlabs 2019 : Blockchain FM
36. 36
Collaborations and financial support
We are looking for students, engineers, researchers to join us in this
adventure to build a nice and secure infrastructure
Thanks for your attention