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Blockchain is a cutting-edge technology that is being used in a variety of applications these days, including smart healthcare, smart education, cryptocurrency, and many more. This technology and its applications consist of many topics which can be published and debated in a variety of generalized and well-respected conferences, journals, summits, and workshops. Crypto Valley Conference on Blockchain Technology, CVCBT
Link: https://www.cryptovalleyconference.com/ ICBC - IEEE International Conference on Blockchain and Cryptocurrency
Link: https://icbc2022.ieee-icbc.org/ IEEE International Conference on Blockchain, (Blockchain)
Link: http://www.blockchain-ieee.org/ International Conference on Cloud Computing, Big Data and Blockchain, ICCBB
Link: http://fzuconf.com/ICCBB-2018/index.htm Bitcoin Conference
Link: https://b.tc/conference/ CRYBLOCK  - Workshop on Cryptocurrencies and Blockchains for Distributed Systems Link: http://www.cryblock.org/ BCC - ACM Workshop on Blockchain, Cryptocurrencies and Contracts Link: https://www.isical.ac.in/\~bcc/bcc19/ IWBOSE  - IEEE  International Workshop on Blockchain Oriented Software Engineering Link: https://www.agile-group.org/iwbose2021/ IEEE/ACM International Workshop on Emerging Trends in Software Engineering for Blockchain, WETSEB. Link: https://www.agile-group.org/wetseb2022/ BlockSys - Workshop on Blockchain-Enabled Networked Sensor Systems Link: https://acmblocksys.github.io/blocksys2021/ BSCI ACM International Symposium on Blockchain and Secure Critical Infrastructure Link: http://www.cloud-conf.net/bsci/2022/ Paris Blockchain Week Summit Link: https://pbwsummit.com/ Blockchain Life Link: https://blockchain-life.com/europe/en/ World Blockchain Summit Link: https://tresconglobal.com/conferences/blockchain/dubai/ Blockchain Revolution Global Link: https://blockchainrevolutionglobal.com/ DC Blockchain Summit
Link: https://dcblockchainsummit.com/ Blockchain & Sustainable Economic Growth Link: https://gbaglobal.org/blockchain-sustainable-economic-growth/ European Blockchain Convention
Link: https://eblockchainconvention.com/ Blockchain and Internet of Things Conference Link: http://www.biotc.net/ International Congress on Blockchain and Applications
Link: https://www.blockchain-congress.net/ Government Blockchain Association (GBA) Events Link: https://gbaglobal.org/events/ Sustainable Energy: Blockchain and Cryptocurrency
Link: https://www.sebccon.com/ Blockchain in Oil & Gas Conference Link: https://blockchain-oilandgas.energyconferencenetwork.com/ Blockchain Tech Summit
Link: http://blockchaintechsummit.org/ Blockchain Economy Summit
Link: https://blockchaineconomy.global/ Future Blockchain Summit Link: https://www.futureblockchainsummit.com/ Blockchain for Governance Link: https://www.d4a.io/ Istanbul Blockchain Week
Link: https://istanbulblockchainweek.com/ Blockchain Summit Link: https://blockchainvsummit.com/ ELEV8CON PARABOLIC Link: https://elev8con.com/elev8con/ CRYPTOWORLDCON Link: https://cryptoworldcon.com/ Israel Crypto Conference Link: https://www.israelcrypto.io/events/israel-crypto-conference-2022 BlockchainUA Conference. Community. Trends. Link: https://blockchainua.com/en/ Permissionless Link: https://blockworks.co/events/permissionless/ Consensus Link: https://www.coindesk.com/consensus2022/ Blockchain Futurist Conference
Link: https://www.futuristconference.com/ India Blockchain Week (IBW)
Link: https://www.inblockchainweek.com/ The North American Bitcoin Conference Link: https://www.btcmiami.com/ The Science of Blockchain Conference (SBC) Link: https://cbr.stanford.edu/sbc22/ The Blockchain Event Link: https://www.theblockchainevent.com/east/ ETHDenver Link: https://www.ethdenver.com/ LendIt Fintech NEXUS Link: https://www.lendit.com/nexus/2022/ Bitcoin Day Sacramento
Link: https://bitcoinday.io/sacramento22 Crypto State Link: https://www.coindesk.com/static/2021/11/30/crypto-state-2021-events-page/ FinTech Festival India Link: https://www.fintechfestival.in/event/6cf223a8-3f97-45d0-a2d9-1e8c1cae49ba/summary Future Digital Finance Link: https://netfinance.wbresearch.com/ Crypto Clarity: A Behind-the-Scenes Look at Crypto and Financial Crime with Coinbase and Binance Link: https://www.unit21.ai/resources/events-webinars/register-for-crypto-clarity-webinar-with-coinbase-and-binance Shred the System: Driving the Crypto & Blockchain Revolution Link: https://summits.harrisburgu.edu/cryptocurrency-conference/ Blockchain Africa Conference
Link: https://blockchainafrica.co/ Dystopia Fest Link: https://dystopialabs.com/ New York FinTech Week Link: https://empirestartups.com/events/new-york-fintech-week/ Empire FinTech Conference Link: https://empirestartups.com/events/fintech-conference/ Open Banking & Instant Payments Summit Link: https://www.kinfos.events/ob-ips/ AIM Summit Link: https://www.aimsummit.com/ Reuters Events: Investment USA Link: <https://events.reutersevents.com/finance/investment-usa?        utm_source=bizzabo&utm_medium=eventlisting &utm_campaign=5530> LendIt Fintech USA Link: https://www.lendit.com/usa/2022/ DeFi Conf Link: https://deficonf.xyz/#/ MONEYCONF Link: https://websummit.com/tracks/moneyconf Money20/20 Europe Link: https://europe.money2020.com/ Reuters Events Renewable Finance and Investment North America Link: <https://events.reutersevents.com/renewable-energy/finance-investment-usa?utm_source=Media Partner%3A Bizzabo&utm_medium=Event Listing &utm_campaign=5536> Reuters Events: Payments Summit Europe Link: <https://events.reutersevents.com/finance/payments-europe?utm_source=bizzabo&utm_medium=eventlisting &utm_campaign=5565> Mallorca Blockchain Days Link: https://mallorcablockchaindays.com/ London FinTech Week 2022 Link: https://www.fintechweek.london/event/0d7c012f-8593-4b1a-a93d-0d4a22b5b9b9/summary Zebu Live Link: https://www.zebulive.xyz/ Money 20/20 USA Link: https://us.money2020.com/ TOKEN2409 Europe Link: https://www.europe.token2049.com/ Decentralized Link: https://www.decentralized.com/ Blockchain Finance Forum: Europe Link: https://www.blockchainfinanceforum.com/ Fintech connect Link: https://www.fintechconnect.com/events-london CrossTech Conferences/ Events
Link: https://imtconferences.com/ Blockchain Conference - Harvard CMSA Link: https://cmsa.fas.harvard.edu/blockchain/ BSV-DEVCON
Link: https://bsvdevcon.net/ Blockchain Technology Conference (Blockchainconf)
Link: https://blockchainconf.net/ Blockchain: Research and Applications (Journal)
Link: https://www.journals.elsevier.com/blockchain-research-and-applications Frontiers in Blockchain (Journal)
Link: https://www.frontiersin.org/journals/blockchain International Journal of Blockchains and Cryptocurrencies
Link: https://www.inderscience.com/jhome.php?jcode=ijbc IET Blockchain  (Journal)
Link: https://ietresearch.onlinelibrary.wiley.com/journal/26341573 Journal of Blockchain Research
Link: https://www.intlpress.com/site/pub/pages/journals/items/jbr/_home/_main/index.php Special Issue "Advances in Blockchain Technology and Applications"
Link: https://www.mdpi.com/journal/applsci/special_issues/Blockchain_2020 Special Issue "Blockchain and Cryptocurrencies"
Link: https://www.mdpi.com/journal/jrfm/special_issues/Blockchain Stanford Journal of Blockchain Law and Policy
Link: https://stanford-jblp.pubpub.org/ Call For Papers: Special Issue on Blockchain
Link: https://www.springer.com/journal/10619/updates/19089506 The Journal of The British Blockchain Association (The JBBA)
Link: https://jbba.scholasticahq.com/ Special Issue Call for Papers: Blockchain-based applications for enhancing cybersecurity in manufacturing and building supply chain resilience
Link: https://research.com/special-issue/blockchain-based-applications-for-enhancing-cybersecurity-in-manufacturing-and-building-supply-chain-resilience Blockchain in Healthcare Today(BHTY)
Link: https://blockchainhealthcaretoday.com/index.php/journal International Journal of Blockchain Applications and Secure Computing (IJBASC)
Link: [https://www.igi-global.com/journal/international-journal-blockchain-applications-secure/290373#:\~:text=provides a...-,The International Journal of Blockchain Applications and Secure Computing (IJBASC,blockchain technology and secure computing](https://www.igi-global.com/journal/international-journal-blockchain-applications-secure/290373#:%5C~:text=provides%20a...-,The%20International%20Journal%20of%20Blockchain%20Applications%20and%20Secure%20Computing%20(IJBASC,blockchain%20technology%20and%20secure%20computing) Special Issue on Fusing Blockchain and AI with Metaverse: Technologies, Trends, and Applications
Link: https://www.computer.org/digital-library/journals/oj/cfp-blockchain-ai-metaverse Recent Advances on Blockchain for Network and Service Management
Link: https://www.comsoc.org/publications/journals/ieee-tnsm/cfp/recent-advances-blockchain-network-and-service-management Blockchain Incubator Workshop
Link: https://blockchain.ieee.org/conferences/incubator-workshop Ledger journal
Link: https://ledgerjournal.org/ojs/index.php/ledger Blockchain Expo World Series
Link: https://www.blockchain-expo.com/ Call for Papers for Special Issue on "Blockchain and Electronic Commerce"
Link: https://www.springer.com/journal/12525/updates/20197204 BSV Bitcoin association (Conferances and Events)
Link: https://bitcoinassociation.net Dcentral Austin
Link: https://www.dcentralcon.com/ BlackSeaChain Link: https://www.blackseachain.com/ Blockchain Oracle Summit Link: https://blockchainoraclesummit.io/ Blockchain Technology Symposium Link: https://bts-2022.cpsc.ucalgary.ca/ Bitcoin Mining Conference Link: https://braiins.com/bitcoin-mining-conference-2022 The African Women in Technology- Blockchain/Crypto Conference Link: https://www.africanwomenintech.com/the-african-women-in-technology-host-the-blockchain-crypto-conference-july-6-8/ International Conference on Blockchain Technology and Information Security Link: http://www.bctis.net/ I've listed some of the venues here, but this list is likely to grow in the near future as new venues are added. Aside from this, there are a number of blockchain-related books where researchers can quickly publish their findings. Various groups, webcasts, podcasts, blogs, and lecture series relevant to blockchain research can also be used to discuss your ongoing work and receive suitable feedback. Please let me know if there is anything I've forgotten. Both I and this blog will be upgraded. Please contact me via any social media platform or email. kaur.3@iitj.ac.in https://twitter.com/Jaspreet173 https://www.linkedin.com/in/jaspreet-kaur-07726a123/ https://www.facebook.com/profile.php?id=100003792556320 https://www.researchgate.net/profile/Jaspreet-Kaur-107

100 Blockchain Conferences, Events,  and Workshops Everyone Should Know

Building mobile applications can be tasking sometimes. But C++Builder makes it easy to build mobile and desktop applications while writing code in C++. In this article, we will share a few steps you can take to build your first app using C++Builder. If you haven’t read: Building Your First App Using C++ Builder (Part 2) The app discussed here is a mini reminder application that will feature the SQLite database, some input fields, date/time pickers, and more components—a wide variety of functionality to give you an idea of what is easily possible. First Step: Setting Up C++Builder To start building your first application using C++Builder, you will need to set up the IDE on your device. After setting up , the next step is to design the UI by dragging and dropping components. C++Builder A component is a visual control like a button or a nonvisual bit of functionality like configurable database access. C++Builder is easy to use because it allows you to simply drag and drop components like buttons, text fields, time pickers, shapes, and so on to the design form (the form is what becomes your window or screen when the app runs); this makes the process of designing the UI and connecting other functionality simple and fast. Select the type of application you want to build and move to the next step. Note that the app we intend to build is a Windows application, so we recommend selecting the option that lets you create one. Second Step: Drag and Drop Once you have selected the type of application you want to build, you can begin the design process. The components are located at the bottom right of the page in the “Palette” section. Simply search for the component you are interested in using and drag it to the form panel. Or you can browse the list and see the visual controls and other functionality that’s available—there are over seven hundred components. Palette Section: Form panel: The design tab on the bottom right contains the form used to align components for your application. The Unit1.cpp tab right next to it provides the editor for writing your C++ code to control components and implement important functions. The Unit1.h tab contains the header for Unit1.cpp. The object inspector on the left-hand side is used to adjust properties of the components in the application. Select one or more, and their properties will be available to edit. It has an event list that contains event listeners that can be added to your code. This allows you to call code in response to something happening—for example, call a method when a button is clicked or something more complex, such as when the location of your device changes. In our mini reminder app, we will begin by using some basic label fields and buttons but will follow an iterative design approach (we will start with a simple design and further improvements will be made to the UI after we have made some progress). We will begin by dragging components such as the TLabel field, date/time pickers, fdconnection, a button, and a memo. The static text field allows us to display text. In the design form shown below, our static text field is displaying “Time.” We will also need to add a time picker and a date picker for the reminder app. Go to the Palette section and search for these two components. Drag and drop them into the form. Next we want a button to add reminders into our mini SQlite database so that we can retrieve and display them when the user requests them. Drag and drop the button onto the design form as well. Third Step: Code, Code, Code Next, we will write code to retrieve user input using the time picker and date picker, and we’ll display the code in our memo. For now, we will make use of the Add Reminder button to get the time and date input and display them in our memo. In the next part of this article, we will store the value directly to the SQLite database using the button. Double-click on the button in the design form, which will direct you to the fastcall function for the button. In this function, we will implement the code that will be executed in the OnClick event of the button—this event is just what it sounds like. It allows you to call a method when the button is clicked. Events are named “On” plus the event, such as , , or . OnDoubleClick OnKeyPress OnDataReceived __fastcall TForm1::Button1Click(TObject *Sender)
{
	TDateTime dateTime;
	ReplaceDate(dateTime, DateTimePicker1-> );
	ReplaceTime(dateTime, TimePicker1->Time);
Memo1->Text = dateTime.FormatString( );
} void Date "dd/mm/yyyy HH:mm" Run your code and click the “Add Reminder” button; your date and time should be displayed in the memo. Before Clicking The Button: After clicking the button: Congrats! We have discussed how to design forms and make use of some components using C++Builder, from . Embarcadero In the next part of this article, we will work on improving the application, including the user interface, and incorporating our database and some notifications.

Building Your First App Using C++ Builder (Part 1)

If you want to do anything interesting in Ethereum, you will have to interact with smart contracts. Whether you want to send ERC20 tokens like LINK or DAI, trade non fungible tokens like digital art, or earn interest on your crypto and interact with other DeFi products, a smart contract is always involved. However, smart contracts are becoming increasingly complex. From proxy contracts to allow for upgradeability, to multi-send contracts that allow for the batching of transactions, what we are seeing is a rapid evolution of features that allow for the movement of one's assets. You've also got DeFi transactions, they are often not generated by you or your code so you need to verify it's doing what you think it is. Additionally, understanding a method call is useful for: Seeing and knowing that the contract methods calls are what you expect Seeing the parameter types and values that allow you to understand how the contracts work Analysing a contract to produce stats on method calls Tracking interactions with key addresses Writing your own rules to decide on which transactions to sign (more on that later) Having fun, if you like that sort of thing In part one of our new DeFi blog series, we will demonstrate and introduce what goes on inside an Ethereum transaction and how you can use Trustology’s custodial wallet platform to interact with smart contracts in a much more secure way. This knowledge will provide you with a good foundation in subsequent posts when we talk about our Firewall, Webhooks, and other DeFi services that we offer. Let's dig in. We’re going to start with a Gnosis Safe contract and a transaction a user would send that the Gnosis safe Dapp would generate. Gnosis Safe is a popular wallet contract implemented by . A multi-user organisation that wants to use Gnosis Safe will first have to define a list of accounts and a required threshold of signatures needed to send a transaction. Users will submit the transaction to the Safe, which will authorise the execution of the transaction only when the threshold required is reached. This way, the users have tighter control of their funds. Gnosis The Gnosis safe has lots of features including offline-signing (which saves on gas fees) but for now, we’re going to take a look at the basic method for executing a transaction. First port of call: Start with Etherscan Let's start with a transaction as seen by Etherscan and see if we can get the output they do. The transaction above is from a user that has interacted with the Gnosis Safe smart contract on the Ethereum mainnet and we can see the details directly on Etherscan. Let’s start by looking at the “data” field. This is the field that Ethereum uses to decide what method to call on the “to” (or “Interacted with” in Etherscan) contract. Here’s the full data payload below. As you can see, a lot of hex values. This looks difficult to understand but with a little skill and knowledge we can break this up into the important parts. Start at the beginning All “data” fields on an Ethereum transaction contain the name of the method that is to be called. This is the first thing we should look at. Etherscan shows this for us in the “Input Data” section: In this section we can see what Etherscan has given us: Function: execTransaction(address to, uint256 value, bytes data, uint8 operation, uint256 safeTxGas, uint256 dataGas, uint256 gasPrice, address gasToken, address refundReceiver, bytes signatures) So, how did they get this? Well, the first thing we need is to use the first 4 bytes (first 8 hex characters) of the input data, which is: 6a761202 This hex value is derived from taking the method name and its argument types, removing any whitespace, taking the `keccak hash of the result, and then taking the first 4 bytes of it and displaying it in hex. With me so far? Note: The parameter names are not included in the hash, only the types. This means that different contracts can have the same methodId's but call their parameters differently and potentially have different logic. Thus it is sensible to keep track of the contract which the method belongs to. There is a handy website that tracks these. Check out and enter the hash 6a761202. At the time of writing, there is only 1 registered method. https://www.4byte.directory/ We have the source of the Gnosis contract so we know what the method name and the parameters are. We grab them from here. In JavaScript, the following will output the keccak hash of our method plus parameters: // import a keccak decoder or write your own import { keccak } from "../decoder/keccak"; const method = `execTransaction(address to, uint256 value, bytes data, uint8 operation, uint256 safeTxGas, uint256 dataGas, uint256 gasPrice, address gasToken, address refundReceiver, bytes signatures)` // regex pattern to remove the word before a comma or closing bracket export const removeArgsFromMethod = (method: string) => { return method.replace(/\s\w+(,|\))/g, (_, commaOrBracket) => commaOrBracket); }; // remove the argument names and remove any spaces const preparedMethod = removeArgsFromMethod(method).replace(/s/g, "") // keccak hash of the method const keccakHashOfMethod = keccak(Buffer.from(preparedMethod)) // first 4 bytes const methodId = keccakHashOfMethod.slice(0,4).toString("hex") // 6a761202 Note: If you don’t have the source code of the smart contract then you won’t be able to generate the hash to check and it will be more difficult calculate the exact parameter types. The output from that Javascript is 6a761202 which matches the first 4 bytes (8 hex characters) of the data payload. Great. We’ve identified that the method being called is in fact “execTransaction” with the 10 parameters. Now, if you go back to Etherscan and click on the `Decode Input Data button you can see how Etherscan has taken the data payload and broken it up into the 10 parameters including the types. Again, how have they done this? Get a handle on parameters Our next job is to break up all the parameters that have been passed to the execTransaction and see what they are. Before we do that a quick note on bytes to hex conversion. Very simply 1 byte of data = 2 characters of Hex. So, whenever you see a string of hex characters, you can divide the number of characters by 2 to get the size in bytes. Any "0x" at the beginning is ignored in the actual calculation. Now, on to decoding the method parameters. Let's have a look at the data again but this time we split it into 32 byte (64 Hex characters) strings. Why? Because ethereum uses 32 bytes blocks and nearly all primitive types are 32 bytes. There are a couple of exceptions though, such as the "bytes" type which we'll see later. : MethodID 0x6a761202 So, once we strip off the methodId (0x6a761202) and then break the remaining data into 32 bytes (or 64 characters) chunks we can start to see something more interesting. : MethodID 0x6a761202 These are the values of the input parameters of the execTransaction function. It's not quite straightforward so let's work through each 32 byte value in turn. Column 3 of the table above shows where each of the values maps to the parameters of the execTransaction function. For example, the first parameter (the `"to" parameter): 000000000000000000000000dac17f958d2ee523a2206206994597c13d831ec7 is of type address. Ethereum addresses are 20 byte values so it has been zero-padded to fit into a 32 byte value. To get the actual address, we just need to extract the last 20 bytes and prefix 0x. In this case, it becomes: `0xdac17f958d2ee523a2206206994597c13d831ec7` (Hmm...this is the Tether contract) In fact, removing the zero padding is how to decode most of the simple parameters like uint8, unit256, etc... The next parameter is the “value”. This, we assume, is how much value needs to be transferred from the Gnosis safe.  Its value is zero.  (This is the value of Ether remember) The next parameter is interesting, it's of types bytes. bytes is a variable-length so how long is it?  The value is: `0000000000000000000000000000000000000000000000000000000000000140` This value represents the offset in hex of bytes from the `methodId` of where the actual data begins. Think of it as a pointer, redirecting you to where you should look for this information. So we need to convert 0x140 bytes into hex characters. 0x140 (bytes in hex) = 320 bytes in decimal 320 bytes in decimal x 2 = 640 characters in hex so the data begins 320 bytes from the start, and thus it is 640 hex characters along, or 10 rows along. In JavaScript, it will look as follows: const numberOfBytesInHex = 140 const numberOfHexCharacters = parseInt(numberOfBytesInHex, 16) * 2; // = 640 Going to the 10th row the first 64 characters represent the length of the data (this requires the same conversion done above). `0000000000000000000000000000000000000000000000000000000000000044` is decoded into a length of 136 hex characters. So finally on the 11th row the data begins and ends after 136 characters. Which means our data field is the following: `a9059cbb000000000000000000000000ba339b8271afea713008314487dd98f8d941720f00000000000000000000000000000000000000000000000000000002540be400` So in summary, for a bytes field, the first 32 bytes is a pointer to where the data starts, once there, the next 32 bytes tells you how long the data is. Then you read that many bytes. If the data doesn’t end in a 32 byte block, it will be padded so whatever is next, will start in the next 32 byte block. Looking at the value again: `a9059cbb000000000000000000000000ba339b8271afea713008314487dd98f8d941720f00000000000000000000000000000000000000000000000000000002540be400` It looks a little familiar... It has a 4 byte methodId and then 2 x 32 byte chunks (2 lots of 64 hex characters). It’s another method call! In fact, we can recognise immediately that this transaction is in itself an ERC20 transfer transaction as it has the famous a9059cbb method signature. (Tip: go to https://emn178.github.io/online-tools/keccak_256.html and type in transfer(address,uint256) and you will see the first 8 characters are in fact a9059cbb`) So, we can see that this Gnosis transaction is to call another contract of address 0xdAC17F958D2ee523a2206206994597C13D831ec7 with the “data” of: `a9059cbb000000000000000000000000ba339b8271afea713008314487dd98f8d941720f00000000000000000000000000000000000000000000000000000002540be400` Which is an ERC20 “transfer” call. We could then use what we learnt above to recursively calculate the details of this data call by extracting the methodId bytes and breaking up the data and looking at the parameters. Take a look and see if you can work out the recipient and value of tokens sent to the Tether contract. Conclusion There was a lot of information here and we didn't go through every single parameter, but hopefully, you can see it was very useful to be able to break the transaction data down and by working through a data payload methodically you can always understand what's happening. We saw how for a Gnosis contract transaction we could break it down into the constituent parts and we saw the methodId and the parameter types and how to deconstruct them into useful arguments. We also saw how that, in this case, there was effectively a transaction within a transaction. The Gnosis safe transaction was just wrapping an ERC20 transfer. This was effectively moving USDT tokens from the Gnosis safe to somewhere else. In our next blog, we’ll see how we can take our understanding of Ethereum transactions to break down a Defi contract call to apply rules to decide if we want to sign/send the transaction. This is something that Trustology uses in its new Defi firewall to protect customers from signing/sending transactions that don’t meet certain criteria. The DeFi Firewall is the first in a suite of services Trustology aims to launch for institutional users looking to support new tokens in DeFi or explore yield-bearing opportunities. Notifications and flows are next on our list to complement our current firewall solution. Currently, we are the only custodial wallet to integrate with , which lets institutions tap DeFi innovation from the security of an insured custodial wallet platform. MetaMask To access the code demonstrated in this blog and more, please click here. To enquire about our DeFi services chat to us. About Trustology Backed by ConsenSys and Two Sigma Ventures, and founded in 2017, Trustology was established on the premise of enabling greater freedom to transact in a fair and efficient manner. By bringing the world of blockchain technology and cryptoassets to new market participants, we believe this will help make this happen. That’s why we built TrustVault — a fast, user-friendly, insured and highly-secure custodial wallet service for institutions and individuals designed to address the security and ownership shortcomings of existing solutions today. Learn more about us at . trustology.io Recommended reading: If you want to know more about Ethereum transactions there are some good articles, you start with: Understanding an Ethereum Transaction The transaction payload

Ethereum Transactions: Under The Hood

Introduction With the rise of based crypto currencies, smart contracts have become increasingly more popular. blockchain Crypto startups are utilizing smart contracts to create intelligent agreements that can be executed in a “ ” environment. Smart contracts take out the middleman and execute on contract terms automatically, based on rules put in place. Although smart contracts harbor a lot of promise, we have seen a worrying history of hacked smart contracts, where hundreds of millions of dollars worth of crypto currencies have been lost or stolen. trustless My growing interest in crypto currencies and blockchain based has led me to research and investigate these hacks, to gain a better understanding of technology how they were hacked. , where we will dive deep into the most infamous hacks. This article is part 1 of a 3 part series We will study how strokes of genius, or subtle mistakes caused earthquakes in the crypto world. Aside: This article is based on the amazing lecture of at I highly recommend watching this talk, and all other materials on the channel. Leonid Beder Blockchain Academy — How to Not Destroy Millions. Kin Ecosystem Foundation Youtube Smart Contracts A smart contract is a set of promises, specified in digital form, including protocols within which the parties perform on these promises — Nick Szabo, 1996 Let’s break down this definition term by term. Contract An example of a common contract is a . sales contract The seller to deliver the goods in exchange for the buyer. promises The buyer to pay the desired price. promises Digital form means that the contract has to be programmed in machine readable code. We want the contract to be Digital form deterministic in nature, thus providing the same outcome based on the same input, every single time. Protocols For example, say the parties agree that the purchased good is to be paid in Bitcoin. The obvious protocol of choice would then be the Bitcoin protocol. Smart this just sounds cool. Popular implementation of smart contract programming languages Ethereum Implements a nearly Turing-complete language on its blockchain, a prominent smart contract framework. We say nearly Turing-complete b/c in order to be completely Turing complete we need unlimited computational power. Bitcoin Implements a Turing-incomplete scripting language that allows the creation of limited smart contracts, such as: multisignature accounts payment channels escrows time locks atomic cross-chain trading oracles Solidity by Example Solidity is an OOP language for writing smart contracts (mostly?) on Ethereum. We’ll start with a simple example of a smart contract named Greeter, which will: Initialize with a greeting message (eg., “Hello World!”) Provide a method to read/query the greeting message. Provide a method to write/modify the greeting message. For these examples we will use the official online Remix IDE found @ https://remix.ethereum.org It is best practice at the moment to specify explicitly which version of solidity we are using, because we don’t know which bugs can be introduced in future releases. Solidity has a similar syntax to JS. We are defining a contract named Additionally, we have a public state variable of type string called greeting and two methods (constructor and setGreeting). Greeter. Fundamentals: Execution Model Every smart contracts needs to be compiled to byte code before it can be deployed to the network. Deployment means being stored on the Ethereum network. This can be a production, test or private network. Every transaction or message call in Ethereum is executed by the Etherum Virtual Machine (EVM) on every Ethereum node. (miner or just a full node). Since is running on the EVM, and is executed simultaneously by in the network — there should a mechanism to used by each contract. The mechanism that limits resources in Ethereum is gas. every smart contract every single operation every node limit the resources Every operation executed has a deterministic (yet sometimes hard to predict) cost measured in units of gas. It’s hard to determine gas costs because conditional control flows can change which operations get executed in run time. Image the following program if (condition is true) { // do something super simple which is very cheap in gas terms } else { // do something really complicated which will be very expensive! } Every gas unit consumed by a transaction must be paid for in Ether, based on a gas/Ether price which is set by the sender of the transaction. Each sender determines what he’s willing to pay. The idea is the more important or urgent it is to you, the more you’d be willing to spend. Transactions have also a on how much gas the transaction can consumer gas limit parameter that is an upper bound Why is the gas limit parameter needed? We have an upper bound b/c it isn’t always clear how much the execution of a transaction will cost, and we want to cap how much Ether we spend on it! Let’s upload the contract to the Remix IDE, create and deploy it. Remix can work against main net and test nets. It’s really convenient to work against an Ethereum simulation. When using the simulation we can pretend to have millions of Ether, and not wait on Ethereum transactions to be processed which make development a lot faster. Running smart contracts via Remix is completely free, so I recommend you give it a try at home :) Once the contract is deployed we see it in the Deployed Contracts section in the box (see the arrow!). Notice that we can easily change the constructor argument and redeploy to the network. Fundamentals: Special Variables and Functions There are special variables and functions which always exist in the global namespace. Here are the ones we’ll discuss today (Ethereum address): sender of the message (current call). Thsi belongs to the original caller of the transaction. This can either be a users account or the address of another smart contract. The Ethereum security model guarantees that msg.sender cannot be faked. msg.sender (unit): number of wei sent with the message. wei is the smallest unit of Ether (think cents to dollars.) So this specifies how much ether we are sending with the function for buying, transacting, etc... msg.value Fundamentals: Function and State Variables Visibility In Solidity, there are four types of visibilities: For functions: : can be called externally from other accounts / contracts. It is important to note that we cannot call this code from our script. We would need to create an additional transaction which would invoke this externally. This is very good for methods that need to be publicly accessible but you want to avoid using them in your own code. external (default) can be called by everyone. public : : can only be called internally from our smart contract or a smart contract that inherits from our smart contract. internal can only be called internally and only from the contract itself. private: For state variables: : can be accessed by everyone. Solidity automatically generates a getter for a public variable. public (default): can only be accessed internally and only from the contract itself. internal : can only be accessed internally and only from the contract itself. private Fundamentals: Function Modifiers Modifiers can be used to modify the behavior of functions. This lets us add functionality before, after or even around the invocation of the function. (Logging for example) Modifiers are very similar to before/after/around/hooks in other programming languages. For example, let’s augment our Greeter smart contract to: Have an owner (in our case, the deployer of the smart contract) Make sure that only the owner can further modify the greeting We’re going to see this pattern a lot, in the coming examples as well as in the wild. Additionally, let’s add a condition that says only the owner can change the greeting. It is important to note that require is a predicate in Solidity. If its evaluation returns false, then an exception is thrown, and all changes done in contract are completely rolled back. The underscore is equivalent to a yield. This basically means execute in this place the remaining code of the function. Fundamentals: Fallback Function A smart contract can have exactly one unnamed function. This function is invoked when a call to the contract is made and none of the other functions match the given function identifier. A common use for fallback functions is when Ether is being transferred to the contract. This triggers the invocation of the fallback function. So, in order to set up an account to be able to receive Ether the bare minimum (in most cases) is setting this function up. Fundamentals: Payable Modifier In order to receive Ether, . This is to protect us from accidentally sending ether to a contract that doesn’t expect it. every function must be marked as payable When sending Ether as part of a function call, the function must be marked as payable. When sending Ether directly to a contract, its fallback function must be marked as payable. If no such function exists, the contract receive Ether through regular transactions. cannot Events Example This is a fancy way to do some logging in Ethereum. Aside: We have a function called that logs returns and event. This could be useful for the case of having an off-chain client that reads the loggings and manages all the donations. Donate We have a function called which is (we added the payable modifier). We also have a function called which is , so sending Ether should fail in this case (payable modifier is missing). donate payable troll not payable Let’s deploy this contract to Remix so that we can verify the results of sending money via each of these methods. In the gif above we can see that invoking the method results in a transaction where a value of 5 wei is transferred, and when we invoke the method no money is transferred. donate troll Let’s Destroy Some Ether We can see in Reward that we have a mapping between We use an owner concept here so our owner can call the method, deciding that a specific address is supposed to get some amount of a magic token. Additionally, we have the method which is publicly accessible by everyone. This method gives you the reward that belongs to your address, and then emit an event for the reward. address and a uint. setReward claimReward Can anyone spot a problem with this? Notice that when we declare the mapping, it is a map from rewards address to unsigned integer. We are subtracting here without checking that the necessary funds are available! So any scenario where we reach a negative value in rewards will result in an underflow. Aside: A , will change what should be a negative value to an extremely large positive one. Check out the link, for a further explanation on how underflows work. n underflow Consider the following example. A reward claim of 500 units is made. Now, our hacker will try and claim 1000. In theory, this shouldn’t work because we only have 500 left. After running this transaction will have an infinite amount of coins! the claimer Bugs: Overflow / Underflow Solidity can handle up to 256 bit numbers is when a number gets incremented above its maximum value. So adding 1 to 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF results in 0. Overflow is the inverse case, when the number is unsigned, decrementing will underflow the number. This will work the other way around, where subtracting 1 from 0x00000000000000000000 results in 0xFFFFFFFFFFFFFFFFFFFFF. Underflow Mitigation #1: Test for Correctness Test for correctness before performing any operation. A quick fix for this is to implement a check to verify that the claim is smaller than the current account balance. Mitigation #2: SafeMath Always use the (de-facto) standard library. SafeMath Find nice, relatively stable, smart contracts in . OpenZeppelin’s Github repo What the library does is implement mathematical operations in a safe way, such that if an overflow occurs it rolls back the transaction. Assert is very similar to revert it rolls back bad transaction. In the example below we have imported SafeMath, injected it for use on , and therefore the library will revert any transactions that cause an underflow on line 30. unit256 Setting Function Visibility Can you spot an error in the Charity contract? Let’s break it down. We have a payable fallback function and a withdrawal function where the owner can withdraw his funds. You can imagine that at some point the owner may want to withdraw his funds so he can do something with them. Now, let’s take a look at the method. It’s using the owner paradigm. It has no privacy. Anyone can change the owner, thus transferring the funds to himself / herself. setOwner In Solidity functions are public by default! Hack Scenario: Alice deposits 1000 wei for this example. Bob tries to withdraw with but fails because he is not the owner of the charity. Now, Bob calls into setOwner, changing the owner to himself. Bob takes all the funds. All this because someone forgot to define visibility! Mitigation #3: Always Define Visibility! Always define visibility Limit function visibility when possible Conclusion This has been a primer on the Solidity language, and we have examined some of the simple, dangerous mistakes that can be made during smart contract development. The next post in this series will dive into infamous, genius and nuanced hacks, that have so far in the past several years. drained hundreds of millions of dollars worth of crypto If you’re looking for resources to ramp up on the blockchain world, I highly recommend (again) checking out the , as it has a wonderful inventory of high quality, technical discussions and lectures. Huge thanks to for building this lecture and teaching it at Blockchain Academy! Kin Ecosystem Youtube channel Leonid Beder If this post was helpful, please subscribe and click the clap 👏 button below to show your support! ⬇⬇ You can follow me on , and . Instagram Linkedin Medium

How to Not Destroy Millions in Smart Contracts (Pt. 1)

We live in exciting times where humankind is rapidly evolving and improving its standard of living through innovation. As says, All we need are committed individuals who envision a positive future and want to match their skills and passions with the biggest challenges that are blocking their country’s . Africa is about to create their own positive far away from the eyes and limited imaginations of other developed countries. Peter Diamandis “We live in an era where we have the tools to take on any challenge.” development future Last February in Ghana, and organized the largest hackathon to ever take place in Africa. At the time, I was struck by the potential and resilience of the new generation of entrepreneurs, and also by the sense of urgency they possess to tackle healthcare issues. Everyone needs access to . Hack For Big Choices Impact Hub Accra healthcare This is why we have recently launched with a Impact Hub Accr I Care 4 Africa , the biggest healthcare program to date that will empower entrepreneurs and medical professionals to use their first-hand experiences and talents to match business opportunities in the healthcare space. Universal healthcare is within our grasp and it can happen if we catalyze a new healthcare system. African entrepreneurs will help make this a reality. Sub-Saharan Africa, with just 13% of the world’s population, carries 24% of the world’s disease burden. Yet, it only has . It is common knowledge that Africa faces the largest healthcare challenges in the world, and that these issues may continue to worsen due to inadequate systems for prevention and care. As the population of Africa continues to boom, solving these health crises is imperative. 2% of the world’s doctors If we take a closer look at the reasons for lower mortality in the continent, we see that such as HIV/AIDS, hepatitis, malaria, tuberculosis, ebola, etc. amount to , while such as heart disease, various forms of cancer, diabetes, etc. account for in the continent. communicable diseases 61% for cause of death non-communicable diseases 28.6% of all deaths Epidemic diseases such as malaria, tuberculosis, and HIV have been contained or overcome in most countries because we possess the knowledge and medications to fight them. However, Africa still faces these preventable diseases mainly due to two factors. First, there isn’t a systematic approach and model in place. This means that every time there is a new pandemic, it is treated as an emergency and all the resources become dedicated to it. Instead, what needs to be built is a complete system that can avoid reaching critical mass. Second, this burden should not be the sole responsibility of only a few stakeholders. After the Ebola crisis, The World Bank acknowledged that “No country or organization has wanted to own the issue of pandemic preparedness and response.” They estimate that “we could face an annual funding gap of US$35 billion by 2031” if there is no proactive action taken. These trends are in stark contrast with the rest of the world. While the entirety of Africa is still working to contain and diminish pandemics and communicable diseases with existing cures, Policies and resources are mainly dedicated to fighting the infectious diseases of today. HIV, malaria and tuberculosis are the big targets. However, over the next 15 years, chronic diseases like cancer, heart disease, and kidney failure will become the major killers. According to the World Health Organization report in the Economist Intelligence Unit, by 2030, it is estimated that chronic non-communicable disease will account for 42% of all deaths in the region, up from 25% today. Sub-Saharan Africa is facing a healthcare tipping point. Africa has the opportunity to better manage and reduce the suffering of chronic diseases than current developed worlds by building early diagnostic systems and creating better healthcare education. African countries are not as heavily invested in a half-century old monopolistic system adverse to change, as developed countries are. Africa is a blank slate ready to adopt the best solutions Africans can imagine. India currently presents a strong case where the lack of traditional health-care infrastructure is being turned into tremendous business opportunity. General Electric has been behind this effort. They have developed breakthrough technologies for portable electrocardiogram machines that have had an impact in other developing countries as well. Vijay Govindarajan, first Professor in Residence and Chief Innovation Consultant at General Electric, explains that the initial obstacle that GE encountered was adopting a globalization strategy before recognizing that reverse innovation was the only way to address unique market needs. In 2005, GE offered in India “a version of its high-end product for $3,000, the low end of the premium price range. The results had been underwhelming. By then, the company saw that a more sophisticated approach was required, but it hadn’t yet entrusted its local talent with the challenge of designing breakthrough products for Indian consumers.” Today, GE healthcare is the leader in the ultrasound market and in 2014 they had 4.1 billion in revenue. African countries, therefore, don’t have the arduous task of adapting archaic healthcare systems centered on the doctor’s role of providing reactionary care rather than preventative care. There is a great opportunity within our grasp when we finally decide to approach the African healthcare system at a structural level and let local innovation enable solutions that fit the African market. Current local healthcare systems and international organizations are unprepared for a major health disaster and the emergence of non-communicable disease. Most of the reports about the status and future of healthcare in Africa don’t take into account entrepreneurship as a force that can contribute to the development of the continent. For example, the last healthcare report by the Economist Intelligent Unit1 mentions critical stakeholders, such as governments, NGOs (Unicef, American Red Cross, Save the Children, One Foundation), and international organizations (UN, USAID, The World Bank), without any mention of entrepreneurs. I believe entrepreneurs are the missing key element needed to create innovative, sustainable solutions. Entrepreneurship is recognized worldwide as the fuel of innovation. Africa is not following the same path of development as developed countries. This gives Africa the key advantage of being able to tackle old problems with new technology. What has been achieved in decades, can now be done in a few years. Educating medical professionals can be done through technologies like VR or online courses that are much cheaper, offered on demand, and are scalable. Also, patients can become “power-patients” who learn on their own about their health and interact with professionals to determine their next steps towards building healthier lives. Specifically, in the case of Sub- Saharan Africa, innovative business models can succeed because of the high number of entrepreneurs able to enter the market and the modern accessibility of tools. African entrepreneurs do not fear failure and are willing to take risks to discover ways to introduce high-impact innovations to the growing markets. Developing countries are the most ripe for adapting breakthrough technologies due to their lack of infrastructure and urgent need for innovative solutions. African entrepreneurs have the right mindset to adopt these tools to innovate at local levels. These local entrepreneurs are the ones who experience the world’s toughest issues first hand. They have a deep understanding of their cultures and present fresh perspectives that are unlimited by preconceived notions of conventional practices. This is the key advantage African entrepreneurs have, and it is core to having an innovative mindset. What’s next? After realizing what is happening and seeing the big opportunity of empowering entrepreneurs to leapfrog the current system, I’ve decided to take action and work together with Impact Hub Accra to design a program that can catalyze the healthcare system in Africa and provide access to healthcare for everyone. This is why we have created They, like us, see big opportunities where others see problems. Connecting problems to innovators can actively reshape markets by creating sustainable and inclusive businesses that translate to a higher quality of life for all. I Care 4 Africa , the biggest healthcare program to date that will empower entrepreneurs and medical professionals to use their first-hand experiences and talents to match business opportunities in the healthcare space. With the support of and , we will start , a 10 month program starting in March, 2016. The program will also include the Multi-stakeholder collaborations are necessary to address complex challenges. We are currently scouting organizations, institutions, universities, NGOs, and private companies that can bring funding, knowledge, expertise, and technologies that can add value to and catalyze the healthcare system in Africa. Merck Facebook I Care 4 Africa biggest hackathon of the continent taking place from June 24th — 26th, 2016. Until now African healthcare has depended heavily on international aid organizations that are not unified in their approach of creating sustainable innovation to solve healthcare issues. I believe that local entrepreneurs, who until now have been left out of the equation, are the trigger that can leapfrog the system. We intend to prove that, through collaboration with the world’s leaders and local stakeholders, it is possible to structure an innovative and sustainable healthcare system. As Vijay Govindarajan says “The new reality is that the future is far from home. If rich nations and established multinationals are to continue to thrive, the next generation of leaders and innovators must be just as curious about needs and opportunities in the developing world as they are about those in their own backyard.” We look forward to building a future together that provides access to healthcare for everyone. You can to be invited to the upcoming events. sign up here Aurora Chisté P.S. If you want to be part of I Care 4 Africa as amentor, sponsor or partner, email me at aurora@h4bc.org

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