School of Engineering Department of Computer Science and Engineering 112 Building a Blockchain and Smart Contract Application Supervisor: CHEUNG Shing Chi / CSE Student: NGUYEN Kha Nhat Long / COMP Course: UROP1100, Spring Blockchain has become very popular and outstanding technology in recent day. The technology helps us to deal with the trust problem that occur for many years. With a large amount of user, security becomes a big problem for blockchain since it directly relates to money. With the evolution of blockchain, people are able to do many thing on its and the we can write more complicated code by using smart contract. This lead to a problem that many bug has happened on the blockchain and cause lost of money. Example can see that the DAO attack lost 80 million dollar. The important is to find the bug on smart contract by using an general method. I will give some investigation on two popular attack on block chain: On chain off chain and front running. Building a Blockchain and Smart Contract Application Supervisor: CHEUNG Shing Chi / CSE Student: PHAM Thanh Lam / MATH-CS Course: UROP1100, Spring Smart contract auditing is critical because once a smart contract is published to the main network of the blockchain system, it cannot be modified and remains in effect indefinitely. All the contract's flaws and vulnerabilities will be exploited, resulting in massive financial and token losses. In our present work, developing a tool that can be utilized for several purposes, such as visualizing a transaction, analyzing a smart contract, and so on, necessitates the use of smart contract analysis tools. As a result, developing a parser to transform the output of such tools into the appropriate format is a critical effort. My current emphasis is on the ETHRACER tool, which detects Event-Ordering bugs (EO bugs). This report helps understanding EO bugs, front-running attack, how ETHRACER works in brief, and how I came up with a parser.