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全文Blockchain with immutability, distributed consensus, established trust, distributed identity and eternal verifiable claims may sound like the ultimate security foolproof technology. But new age security attacks are emerging, which are very sophisticated and can cause huge irreparable damages. Understanding these attack vectors is very important for anyone developing and deploying blockchain solutions. Prevention is better than cure!
In this article, the emerging new age blockchain security attacks are grouped into four categories:
- Peer-to-peer network-based attacks
- 共识和基于分类帐的攻击
- Smart Contract-based attacks
- Wallet-based attacks
Peer-to-Peer Network-based Attacks
- Eclipse attack- 节点将取决于使用对等选择策略选择的“ X”数量的节点来具有分布式分类帐的视图。但是，如果攻击者能够设法从他的恶意节点中选择所有“ X”数量的节点，那么他就可以将原始分类帐的视图黯然失色，并将自己的操纵分类帐呈现给节点。
资料来源：http：//cs-people.bu.edu/heilman/eclipse/
- Sybil攻击- 日食攻击是关于将用户黯然失色的真实分类帐的视图，而Sybil攻击则针对整个网络。在SYBIL攻击中，攻击者会以具有化名身份的大量节点淹没网络，并尝试影响网络。这些节点虽然像无关的个体一样出现，但由单个操作员在后面操作。在这种情况下，目标不是针对一个用户，而是全部节点或网络，并在可能的情况下在分类帐中生成叉子，从而允许攻击者进行双重支出和其他攻击。
Consensus Mechanism and Mining-based Attacks
- Selfish mining attack: Many blockchains consider the longest chain to be the true latest version of the ledger. So a selfish miner can try to keep building blocks in stealth mode on top of the existing chain, and when he can build a lead of greater than two or more blocks than the current chain in the network, he can publish his private fork, which will be accepted as a new truth as it is the longest chain. He can do transactions in the public network just before publishing his longer stealth chain to reverse the transaction he just did. This effectively provides a small window for the attacker to do double spending based on this ability to build a stealth chain by building sufficient block lead (Finney attack).
- Mining malware：恶意软件使用毫无戒心的受害者计算机的计算能力来开采黑客的加密货币。中国报告说，超过一百万台计算机被该恶意软件感染，并帮助攻击者挖掘了超过2600万个代币的各种加密货币。
- 51% attack：当矿工或一组矿工控制区块链网络的51％或更多的矿业能力时，可能会发生这种攻击。尽管大型网络很难发生，但在小型网络中，攻击的可能性更高。一旦一组对区块链网络上交易的多数控制，它就可以防止特定的交易甚至逆转旧交易。
- Timejack attack像Bitcoi:在某些区块链节点网络n depend on internal timing derived from median time reported by its peer nodes. For example, you depend on your friends to know the time. Let us say an attacker manages to put a lot of malicious people in your friends’ list, then he can manipulate your time. The first step to this attack can be an Eclipse attack on the target node. Once this attack is complete on a target node, then the target node will not accept blocks from the actual network as the timestamp of the blocks will not be in line with its timestamp. This provides an opportunity for the attacker to be double spending or do transactions with the targeted node as these transactions can’t be submitted to the actual blockchain network.
- Finney attack: If you can mine a block with one of your transactions in it and keep it in stealth, there is an opportunity for you to double spend the money. If a merchant accepts the unconfirmed transaction, you can transfer him this earlier transacted currency. Next you publish the earlier mined block, which was kept in stealth, before your new transaction is confirmed on network.
- 种族攻击: This attack is minor variation of the Finney attack. The difference is that the attacker need not pre-mine the block with his transaction, which he intends to double spend. During the attack, the attacker submits an unconfirmed transaction to a merchant (victim) and simultaneously does another transaction which he broadcasts to the network. It is easier for the attacker to launch the attack if he is directly connected to the merchant’s node. This would give the merchant an illusion that his transaction is the first, but that is never submitted to the blockchain network by the attacker.
Smart Contract-based Attacks
智能合约是完全自动化的合同，这些合同以参与者之间的约定方式执行交易，现实世界的意见以及任何中间商的干预。因此，一旦开始，就无法停止智能合同。一旦完成并写入区块链的交易变得不可变。这为参与者的收益提供了根据其绩效的保证，如签订合同时的同意。但是，请考虑一下如果智能合约有错误，会发生什么：数百万美元被危险，没有人可以改变它。我们将研究与智能合约有关的此类攻击或攻击向量。
- DAO攻击：加密货币历史上最大的剥削是“ dao” hack。分散的自治组织是以太坊的雄心勃勃的特征。一家名为Slock的公司开始为一个名为“ The Dao”的项目进行众筹。众筹获得了压倒性的回应，收集了1,270万以太，价值1.5亿美元（今天20亿美元）。但是，攻击者确定了代码中的漏洞，可以通过递归提取功能执行无需检查当前交易的结算。因此，攻击者通过少量贡献并要求使用递归功能提取攻击开始攻击。这使他从众筹中筹集了近7000万美元。这次事件发生了一个有趣的转变。以太坊基金会威胁攻击者停止攻击并冻结帐户。袭击者回答说，他正在按照商定的合同进行比赛，通过软叉或硬叉进行干预将是违反合同的行为，他可以将其告上法庭（阅读攻击者的公开信。）But he stopped the attack. Later the Ethereum Foundation went with a hard fork to recover the money, though this decision raised many concerns of autonomy of smart contracts. This hard folk resulted in two Ethereum currencies – Ethereum & Ethereum classic and a lot of controversy.
Wallet-based Attack
- Parity Multisig Wallet Attack：就是这样一个脆弱性的情况，即派式客户钱包被攻击者入侵，导致500,000以太币（今天为7700万美元）。钱包合同比在用户钱包上构建的逻辑还要多，以进行常规自动付款。为了减少气体或交易费用，奇偶校验的多西格钱包功能（Multisig Wallet就像与多个所有者的银行中的联合帐户一样）使用了集中的图书馆合同。但是他们打开了一些关键功能，从而导致脆弱性，这是由攻击者利用的。攻击者在图书馆合同中添加了他作为所有者的帐户，因此，对于特定日期后实施的所有钱包，攻击者成为联合所有者。然后他触发了杀戮功能，这使钱包中的货币冻结了。截至当天，他基本上锁定了1.55亿美元，永远在密码不可访问的钱包上。
Conclusion
区块链部署中的错误可能非常昂贵，尤其是在无许可的网络中，因为任何人都可以参与，他们的身份是匿名的，而恢复错误是不可能的。本文中讨论的大多数攻击向量和漏洞在部署前都有解决方案。但是，考虑区块链和硬叉或软叉的不变性并不是一个实际选择，通过理解概念，安全审核和详细测试在部署前非常重要。
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