56 research outputs found
Sereum: Protecting Existing Smart Contracts Against Re-Entrancy Attacks
Recently, a number of existing blockchain systems have witnessed major bugs
and vulnerabilities within smart contracts. Although the literature features a
number of proposals for securing smart contracts, these proposals mostly focus
on proving the correctness or absence of a certain type of vulnerability within
a contract, but cannot protect deployed (legacy) contracts from being
exploited. In this paper, we address this problem in the context of re-entrancy
exploits and propose a novel smart contract security technology, dubbed Sereum
(Secure Ethereum), which protects existing, deployed contracts against
re-entrancy attacks in a backwards compatible way based on run-time monitoring
and validation. Sereum does neither require any modification nor any semantic
knowledge of existing contracts. By means of implementation and evaluation
using the Ethereum blockchain, we show that Sereum covers the actual execution
flow of a smart contract to accurately detect and prevent attacks with a false
positive rate as small as 0.06% and with negligible run-time overhead. As a
by-product, we develop three advanced re-entrancy attacks to demonstrate the
limitations of existing offline vulnerability analysis tools
EVMPatch: Timely and Automated Patching of Ethereum Smart Contracts
Recent attacks exploiting errors in smart contract code had devastating
consequences thereby questioning the benefits of this technology. It is
currently highly challenging to fix errors and deploy a patched contract in
time. Instant patching is especially important since smart contracts are always
online due to the distributed nature of blockchain systems. They also manage
considerable amounts of assets, which are at risk and often beyond recovery
after an attack. Existing solutions to upgrade smart contracts depend on manual
and error-prone processes. This paper presents a framework, called EVMPatch, to
instantly and automatically patch faulty smart contracts. EVMPatch features a
bytecode rewriting engine for the popular Ethereum blockchain, and
transparently/automatically rewrites common off-the-shelf contracts to
upgradable contracts. The proof-of-concept implementation of EVMPatch
automatically hardens smart contracts that are vulnerable to integer
over/underflows and access control errors, but can be easily extended to cover
more bug classes. Our extensive evaluation on 14,000 real-world (vulnerable)
contracts demonstrate that our approach successfully blocks attack transactions
launched on these contracts, while keeping the intended functionality of the
contract intact. We perform a study with experienced software developers,
showing that EVMPatch is practical, and reduces the time for converting a given
Solidity smart contract to an upgradable contract by 97.6 %, while ensuring
functional equivalence to the original contract.Comment: A slightly shorter version of this paper will be published at USENIX
Security Symposium 202
Censorship-Resilient and Confidential Collateralized Second-Layer Payments
Permissionless blockchains are too slow for applications like
point-of-sale payments. While several techniques have been proposed to
speed up blockchain payments, none of them are satisfactory for application
scenarios like retail shopping. In particular, existing solutions like
payment channels require users to lock up significant funds and schemes
based on pre-defined validators enable easy transaction censoring. In this
paper, we develop Quicksilver, the first blockchain payment scheme that
works with practical collaterals and is fast, censorship-resilient, and confidential
at the same time.We implement Quicksilver for EVM-compatible
chains and show that censoring-resilient payments are fast and affordable
on currently popular blockchains platforms like Ethereum and Polygon
Two Bitcoins at the Price of One? Double-Spending Attacks on Fast Payments in Bitcoin
Bitcoin is a decentralized payment system that is based on Proof-of-Work. Bitcoin is currently gaining popularity as a digital currency; several businesses are starting to accept Bitcoin transactions. An example case of the growing use of Bitcoin was recently reported in the media; here, Bitcoins were used as a form of fast payment in a local fast-food restaurant.
In this paper, we analyze the security of using Bitcoin for fast payments, where the time between the exchange of currency and goods is short (i.e., in the order of few seconds). We focus on double-
spending attacks on fast payments and demonstrate that these attacks can be mounted at low cost on currently deployed versions of Bitcoin. We further show that the measures recommended by Bitcoin developers for the use of Bitcoin in fast transactions are not always effective in resisting double-spending; we show that if those recommendations are integrated in future Bitcoin implementations, double-spending
attacks on Bitcoin will still be possible. Finally, we leverage on our findings and propose a lightweight countermeasure that enables the detection of double-spending attacks in fast transactions
Tampering with the Delivery of Blocks and Transactions in Bitcoin
Given the increasing adoption of Bitcoin, the number of transactions and the block sizes within the system are only expected to increase. To sustain its correct operation in spite of its ever-increasing use, Bitcoin implements a number of necessary optimizations and scalability measures. These measures limit the amount of information broadcast in the system to the minimum necessary.
In this paper, we show that current scalability measures adopted by Bitcoin come at odds with the security of the system. More specifically, we show that an adversary can exploit these measures in order to effectively delay the propagation of transactions and blocks to specific nodes—without causing a network partitioning in the system. We show that this allows the adversary to easily mount Denial-of-Service attacks, considerably increase its mining advantage in the network, and double-spend transactions in spite of the current countermeasures adopted by Bitcoin. Based on our results, we propose a number of countermeasures in order to enhance the security of Bitcoin without deteriorating its scalability
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