Technology and Research Articles
Although repricing opcodes can always break contracts, the EVM should be able to evolve too. Clearly, a decent number of contracts will be broken due to [EIP-1884], so care must be taken to lessen the impact on the overall ecosystem.
In a few hours, an attacker will claim the prize for the first Consensys Diligence Ethereum hacking challenge. Here’s how they’ll do it, why nobody else can perform the same attack (any longer), and why the attacker has to wait…
Trivial Exploits of Bad Randomness In Ethereum, and How To Do On-Chain Randomness (Reasonably) Well.
Ethereum has been used as a platform for a variety of applications of financial interest. Several of these have a need for randomness — e.g., to implement a lottery, a competitive game, or crypto-collectibles. Unfortunately, writing a random number generator on a public blockchain is hard: computation needs to be deterministic, so that it can be replayed in a decentralized way, and all data that can serve as sources of randomness are also available to an attacker. Several exploits of bad randomness have been discussed exhaustively in the past. Next, we discuss near-trivial exploits of bad randomness, as well as ways to obtain true randomness in Ethereum.
[Research article, at ICSE'19 conference]
The rise of smart contract—autonomous applications running on blockchains—has led to a growing number of threats, necessitating sophisticated program analysis. However, smart contracts, which transact valuable tokens and cryptocurrencies, are compiled to very low-level bytecode. This bytecode is the ultimate semantics and means of enforcement of the contract.
We present the Gigahorse toolchain. At its core is a reverse compiler (i.e., a decompiler) that decompiles smart contracts from Ethereum Virtual Machine (EVM) bytecode into a high- level 3-address code representation.
[Research Article, distinguished paper award at OOPSLA'18 conference]
Ethereum is a distributed blockchain platform, serving as an ecosystem for smart contracts: full-fledged inter- communicating programs that capture the transaction logic of an account. Unlike programs in mainstream languages, a gas limit restricts the execution of an Ethereum smart contract: execution proceeds as long as gas is available. Thus, gas is a valuable resource that can be manipulated by an attacker to provoke unwanted behavior in a victim’s smart contract (e.g., wasting or blocking funds of said victim). Gas-focused vulnerabilities exploit undesired behavior when a contract (directly or through other interacting contracts) runs out of gas. Such vulnerabilities are among the hardest for programmers to protect against, as out-of-gas behavior may be uncommon in non-attack scenarios and reasoning about it is far from trivial.