SmartCheck: Static Analysis of Ethereum Smart Contracts · SmartCheck: Static Analysis of Ethereum Smart Contracts Tikhomirov, Voskresenskaya, Ivanitskiy, Takhaviev, Marchenko, Alexandrov

SmartCheck:Static Analysis ofEthereum Smart

Contracts

Tikhomirov,Voskresenskaya,

Ivanitskiy,Takhaviev,Marchenko,Alexandrov

Introduction

Classification ofissues in Soliditycode

SmartCheck:smart contractanalyzer

Future work andstate of the project

1/23

SmartCheck: Static Analysis of EthereumSmart Contracts

Sergei Tikhomirov, Ekaterina Voskresenskaya,Ivan Ivanitskiy, Ramil Takhaviev, Evgeny Marchenko,

Yaroslav Alexandrov

SnT, University of Luxembourg / SmartDec

27 May 2018WETSEB, Gothenburg, Sweden


Contracts



Introduction




2/23

Outline

Introduction

Classification of issues in Solidity code

SmartCheck: smart contract analyzer

Future work and state of the project


Contracts



Introduction




3/23

Outline

Introduction





Contracts



Introduction




4/23

Goal: finding bugs that can cost you millions

I Smart contracts: a decentralized way to enforce digitalagreements

I Ethereum: a blockchain-based Turing completeapplication platform

I Bugs can be (and have been) exploited: hundredsmillion USD lost

I We present SmartCheck – a static analyzer forEthereum contracts


Contracts



Introduction




5/23

What Ethereum nodes doI Store account balances, contract code and variables

I Execute smart contracts code on request

I Maintain a shared view of the global state


Contracts



Introduction




6/23

Ethereum security challenges

I Decentralized execution environment

I New software stack

I Very limited ability to patch contracts

I Anonymous financially motivated attackers

I Rapid pace of development

I Suboptimal high-level language


Contracts



Introduction




7/23

Outline

Introduction





Contracts



Introduction




8/23


I Security: directly lead to exploits

I Functional: violate the intended functionality1

I Operational: lead to run-time problems

I Developmental: make code hard to improve

1Though without a specification we only assume what the intendedfunctionality is.


Contracts



Introduction




9/23

Typical issues in Solidity code

Let us focus on three examples of code issues:

I Re-entrancy (security)

I Locked money (functional)

I Costly loop (operational)

SmartCheck detects 21 types of issues.


Contracts



Introduction




10/23

Example 1/3: Re-entrancy

I Contract maintains internal list of balances

I If a user withdraws funds; their balance is set to zero

I Adversary requests withdrawal via malicious contractwhich calls the victim back before their balance is set tozero, depleting the victim contract’s balance

I Real-world case: The DAO hack (June 2016): $50m lost


Contracts



Introduction




11/23

Example 2/3: Locked money

I Contracts that receive ether should have a way towithdraw it: call transfer, send, or call.value

I Otherwise money is be stuck in contract forever


Contracts



Introduction




12/23

Example 3/3: Costly loop

I Ethereum users pay for contract execution with gas

I Tx’s are atomic: if one step fails, whole tx fails

I Miners enforce a block gas limit(hence, a limit on computation in one tx)

I A costly function called inside a long enough loopexceeds block gas limit: tx is never confirmed

I Example: payouts for all winners in a game fail becauseof one (maliciously) failing payout


Contracts



Introduction




13/23

Outline

Introduction





Contracts



Introduction




14/23

Code analysis: dynamic vs static

Dynamic code analysis:

I black box

I no false positives

I some code execution paths are missed

Static code analysis:

I white box

I some false positives

I all the code is analyzed


Contracts



Introduction




15/23

Smart contracts code analysis

Smart contracts code compared to web applications code:

I immutable

I self-bug-bounty

I all the code is crucial

but

I less code (∼1,000 LOC vs ∼100,000 LOC)

Thus, static analysis is our choice.


Contracts



Introduction




16/23

Static code analysis

Static analysis usually includes three stages:

1. building an intermediate representation (IR)

2. enriching the IR with additional information

3. vulnerability detection


Contracts



Introduction




17/23

SmartCheck: static code analyser

SmartCheck uses:

I ANTLR parser generator

I custom Solidity grammar

I XPath queries


Contracts



Introduction




18/23

Example parse tree


Contracts



Introduction




19/23

Vulnerabilities in 4,600 real contracts


Contracts



Introduction




20/23

Outline

Introduction





Contracts



Introduction




21/23

Future work

I Improve the grammar

I Make patterns more precise

I Add new patterns

I Implement more sophisticated static analysis methods

I Add support for other languages


Contracts



Introduction




22/23

Current state of the project

I First version is open-sourced (GPL-3.0):github.com/smartdec/smartcheck

I Improved version is freely available as a service:tool.smartdec.net

I Currently 100 scans per day, 4212 scans in total

github.com/smartdec/smartcheck

tool.smartdec.net


Contracts



Introduction




23/23

Questions?

I github.com/smartdec/smartcheck

I tool.smartdec.net

I cryptolux.org

I s-tikhomirov.github.io

Documents

SmartCheck: Static Analysis of Ethereum Smart Contracts · SmartCheck: Static Analysis of Ethereum Smart Contracts Tikhomirov, Voskresenskaya, Ivanitskiy, Takhaviev, Marchenko, Alexandrov