Out of the Ether. Matthew Leising

Чтение книги онлайн.

Two

      Like so many days in Seattle, Friday, June 17, 2016, was slightly overcast with the chance of rain. That afternoon on the edge of town, Dax Hansen left the city on the ferry for Bainbridge Island where he lives. Hansen was one of the earliest lawyers to get involved in blockchain technology and helped shape the early industry though his work as a partner at Perkins Coie. So news of the DAO hack had reached him. When he arrived on Bainbridge Island he saw his friend Peter Vessenes waiting to take the ferry back to Seattle. Vessenes had long been in the blockchain world, and Dax knew he'd have heard too.

      “Wow, big day, huh?” Dax said to Peter.

      “Yeah,” Vessenes said. “I'd already been looking into that and saw some vulnerabilities. I warned people this was going to happen.”

Bainbridge Island is about as idyllic a location as you are going to find in the US. If only the cars could be removed it would feel like Cabot Cove waiting for one of Jessica Fletcher's nieces to get murdered. There's wood everywhere. Evergreens come right up to the edge of steep cliffs with houses peeking from between the limbs. Sailboats and motorboats fill a small harbor just across from the ferry terminal. The ferry dock is made of dark V-shaped planks of wood. It all has the feel of another time. Just outside the main terminal, where the taxis line up, Dax and Peter chatted about the DAO.

      By 2016, Peter Vessenes had been around the crypto world for a long time. He cofounded the Bitcoin Foundation and started CoinLab, a Bitcoin project incubator that signed a deal in 2012 to handle the US and Canadian customers of Mt. Gox, the largest early Bitcoin exchange, according to Reuters. A year later, a string of lawsuits between the two companies began as CoinLab accused Mt. Gox of not handing over the customer accounts as promised, Reuters said. Vessenes later shut CoinLab down, according to the news agency.

      By 2016, Vessenes was a consultant to blockchain firms and did some security work on his own. He became interested in smart contracts and Ethereum and decided to look into why some smart contracts are so dumb. The first one he examined, Ethstick, was a “pyramid scheme which incentivizes participants (donkeys) to keep depositing money to get the payout (carrot),” he wrote in a blog post dated May 18, 2016. “As each payment comes in, a ‘lucky donkey’ is chosen for payout; the lucky one is chosen from a list of eligible donkeys.” But it was a scam; also, about 4,000–5,000 ether were trapped in the contract and he wanted to figure out what went wrong. He identified several major problems in the code that didn't allow the ether to be freed. More generally, he had taken a look at a cross-section of smart contracts that had been deployed on the Ethereum blockchain at that time. He estimated that more than 10 percent of the Ethereum smart contract code he examined had a bug in it. The title of his blog post: “Ethereum Contracts Are Going to Be Candy for Hackers.”

The write-up got a fair amount of notice and was picked up by Hacker News. Vessenes was intrigued, so he kept looking for security issues to highlight on his blog. A few weeks after his first smart contract post, he published one called “More Ethereum Attacks: Race-to-Empty Is Real.” Vessenes had noticed a comment online by Christian Reitwiessner, one of the creators of Solidity, the computer language used to write smart contracts. The bug allowed users to ask for money back from a smart contract and end up getting more than they had available to withdraw. While Peter called the bug “race-to-empty,” it would soon be known more widely as a “reentrancy bug.”

      In any event, he wrote this on his blog on June 9, 2016, eight days before the DAO attack, “Your smart contract is probably vulnerable to being emptied if you keep track of any sort of user balances and are not very, very careful.”

      Vessenes had seen plenty of controversy by then. He'd lost a battle to remake the board of directors of the Bitcoin Foundation and tangled with Mt. Gox in court for years. He said he's received death threats. In one sense, to him, the DAO was just another chapter in the unbelievable blockchain story.

      “It's always something in digital currency land,” he said. “This was a little bigger, but at the time it wasn't clear it was going to be bigger.” In any event, it was impossible to look away.

      “Kids get a bunch of money and flamethrowers, so every week, you tune in,” he said.

      Outside the ferry building on Bainbridge Island, the coincidental timing of meeting Peter Vessenes has stuck with Dax Hansen over the years. “I thought it was really interesting and kind of ironic that I ran into him on that day, and that he had been paying attention to it,” Hansen said. Afterwards, Vessenes got on the ferry and headed into Seattle.

      Three thousand miles away on the East Coast, another researcher had been looking at security flaws in the DAO. Emin Gün Sirer is an associate professor of computer science at Cornell University. In 2002, he devised a decentralized system for rewarding good behavior he called Karma. It was the first currency system to use proof of work to establish the validity of transactions. Cynthia Dwork and Moni Naor invented the idea of proof of work in 1993 as a means to reduce email spam. The concept was later adopted for cryptocurrencies by people such as Adam Back, and most famously by Satoshi Nakamoto in his design for Bitcoin.

So by the time Bitcoin came around in 2009, Gün – everyone calls him Gün (pronounced goon) – was well versed in digital currencies. And then, with its added complexity, Ethereum opened up a whole new vista of possibilities for blockchain applications. With the rise of the DAO, Gün found himself in computer scientist nerd heaven.

      “It's a fascinating story,” he said. “This is one of the best heist stories I know. It all happened out in the open.” He wears his dark hair short and appears years younger than he is thanks to his Turkish roots. He drives his BMW around Ithaca like he's still in Istanbul. There is an earned arrogance about Gün: he rubs some people the wrong way, but I've always found him to be extremely helpful and generous with his time. “People stole from a robot,” he said. “It's man versus robot. It's insane.”

      Every aspect of the DAO was prescribed. It's written in code. The amount of time it was open to collect money had been set to run from April 30 to May 28. This was the fundraising part of the DAO, the time when more money than anyone associated with it could have imagined came pouring in. It was during this period that Gün decided to take a look at its source code along with two friends, Dino Mark and Vlad Zamfir. From the very start they saw it was bad.

      “There are like nine different ways of getting money out of this thing,” Gün said. Based on the severity of what they found, the three researchers published “A Call for a Temporary Moratorium on the DAO” on May 27, a day before the crowdfunding was set to end.

      “These concerns motivate a moratorium on funding proposals to prevent losses due to poor mechanism design,” Mark, Zamfir, and Sirer wrote. “A moratorium would give the DAO time to make critical security upgrades.”

      They'd discovered seven potential flaws in the DAO code, such as inherent biases involved in how DAO token holders would vote on proposals. Another was termed a “stalking attack,” and would become important later. A stalking attack is done to someone who wants to withdraw their funds from the DAO. To withdraw their ether, they create a subcontract that's an exact copy of the DAO, known as a child DAO. Remember our underground bank? The bank is the DAO and the room you carved out is the child DAO.

And СКАЧАТЬ