echidna

Echidna is a weird creature that eats bugs and is highly electrosensitive (with apologies to Jacob Stanley)

More seriously, Echidna is a Haskell library designed for fuzzing/property-based testing of EVM code. It supports relatively sophisticated grammar-based fuzzing campaigns to falsify a variety of predicates.

Features

• Generates inputs tailored to your actual code
• Optional coverage guidance to find deeper bugs
• Automatic testcase minimization for quick triage
• Seamless integration into the development workflow
• Fast
• Powerful API for advanced usage
• Beautiful logo

Usage

Executing the test runner

The core Echidna functionality is an executable called echidna-test. echidna-test takes a contract and a list of invariants (properties that should always remain true) as input. For each invariant, it generates random sequences of calls to the contract and checks if the invariant holds. If it can find some way to falsify the invariant, it prints the call sequence that does so. If it can't, you have some assurance the contract is safe.

Writing invariants

Invariants are expressed as Solidity functions with names that begin with echidna_, have no arguments, and return a boolean. For example, if you have some balance variable that should never go below 20, you can write an extra function in your contract like this one:

function echidna_check_balance() { 
    return(balance >= 20); 
}

To check these invariants, run:

$ echidna-test myContract.sol

An example contract with tests can be found examples/solidity/basic/flags.sol. To run it, you should execute:

$ echidna-test examples/solidity/basic/flags.sol

Echidna should find a a call sequence that falisfies echidna_sometimesfalse and should be unable to find a falsifying input for echidna_alwaystrue.

Truffle integration

Echidna can be used to test contracts compiled with Truffle using crytic-compile. For instance, we can uncover an integer overflow in the Metacoin Truffle box using a contract with Echidna properties to test:

$ cd examples/solidity/truffle/metacoin
$ echidna-test . TEST
...
echidna_convert: failed!💥
  Call sequence:
    mint(57896044618658097711785492504343953926634992332820282019728792003956564819968)

Configuration options

Echidna's CLI can be used to choose the contract to test and load a configuration file.

$ echidna-test contract.sol TEST --config="config.yaml"

The configuration file allows users to choose EVM and test generation parameters. An example of a complete and annotated config file with the default options can be found at examples/solidity/basic/default.yaml. More detailed documentation on the configuration options is available in our wiki.

Advanced usage

Echidna exports an API to build powerful fuzzing systems, and has a multitude of configuration options. Unfortunately, these parts of the codebase change quickly and are thus poorly documented. The examples/api directory or Trail of Bits blog are excellent references, or use the references below to get in touch with us directly.

Installation

If you want to quickly test Echidna in Linux, we offer a statically linked binary release of v1.1.0.0 to download here.

Otherwise, to install the latest revision of Echidna, we recommend to use docker:

$ docker build -t echidna .

for example

$ docker run -t -v `pwd`:/src echidna echidna-test /src/examples/solidity/basic/flags.sol

If you'd prefer to build from source, use Stack. stack install should build and compile echidna-test in ~/.local/bin. You will need to link against libreadline and libsecp256k1 (built with recovery enabled), which should be installed with the package manager of your choosing. Additionally, you need to install the latest release of libff (you can take a look to this script used in our CI tests)

If you're getting errors building related to linking, try tinkering with --extra-include-dirs and --extra-lib-dirs.

Getting help

Feel free to stop by our #ethereum slack channel in Empire Hacking for help using or extending Echidna.

• Get started by reviewing these simple Echidna invariants

• Review the Solidity examples directory for more extensive Echidna use cases

• Considering emailing the Echidna development team directly for more detailed questions