State Cleaning

The primary bloat to the state have been generated from the following contracts.

1. Sequentially increasing
   • 0x6a0a0fc761c612c340a0e98d33b37a75e5268472
2. Non sequential (identical contracts)
   • 0x7c20218efc2e07c8fe2532ff860d4a5d8287cb31
   • 0x8a2e29e7d66569952ecffae4ba8acb49c1035b6f

0x6a0a0fc761c612c340a0e98d33b37a75e5268472

This one generated suicides into sequentially increasing addresses, from

	0x0000000000000000000000000000000000000001 -> 0x0000000000000000000000000000000000346b60

So the cleanup from that is pretty trivial.

0x7c20218efc2e07c8fe2532ff860d4a5d8287cb31

These are a bit more tricky, using two sources for seeding and generating destination addresses from these. See reverse_engineering.md for details.

In order to generate the same addresses, we need to two pieces of data from each original transcation:

• CALLDATA
• The hash of the previous block (which is not available on-chain any longer, since we've passed 256 blocks)

Also the exploit-contract worked like this:

1. 0x7c20218efc2e07c8fe2532ff860d4a5d8287cb31 created contract x.
2. It CALL:ed x 40 times with an address of a sucide beneficiary. Before each call, generate a new address. During each call, x performed suicide to the supplied address.
3. If we have more than 1800 gas, repeat step 2.

One more piece of data that we need is the number of suicides performed, in order to know when to stop our sweep.

Files in this repo

Contracts

This repository contains a solidity implementation of a Sweeper contract, with the following signature:

function asm_clean(uint s, uint i);

function sol_clean(uint256 s, uint i);

These should be equivalent, but with asm_clean requiring less gas. The first parameter s is the initial seed, and the i is the number of touches to perform.

Data files

The files in /data are:

• state_bloat_transactions_original.json - A file containing some basic data about all transactions into the two attack-contracts listed above.
  • blh the block hash of the preceding block
  • txhash the transaction hash
• state_bloat_transactions.json - Generated from state_bloat_transactions_original.json by using a web3 API to fetch some more data for each transaction:
  • input - the input to the transactoin
  • gasUsed - the gas used by the transaction
• mappings_gas_suicidecount.json - Generated from state_bloat_transactions_original.json, by using a web3 API to perform traces of transcations, and mapping gasUsed to number of suicides performed.
• final_data.json - Generated from state_bloat_transactions_original.json and mappings_gas_suicidecount.json. This calculates the seed and iter values to send into the solidity contract. The json file has the following data points:
  • seed - Seed value
  • num - Number of addresses to touch

The file state_bloat_transactions_original.json was generated from the Etherchain API, which has been hugely helpful in gathering data. The scripts to create this file is not included in this repository. This file is the only file required to generate the rest of the files.

Python

The preprocess_data.py generates all data based on the state_bloat_transactions_original.json. During execution, it saves results to files, and can be aborted/resumed. In this repo, the files are already generated and the script does not need to actually do much work.

If you want to regenerate the data based on state_bloat_transactions_original.json from scratch, you need to delete the other json-files and ensure that you have a http-api with debug available: geth --rpc --rpcapi "debug,eth"

Live contracts

The Sweeper.sol contract was deployed on the main net in 0xad4ceddc9e345ac9f3076bf657ee1e22e382b98de6d351d35c7f8e28e8398021, and lives on 0xa43ebd8939d8328f5858119a3fb65f65c864c6dd

var sweeperAbi = [{"constant":false,"inputs":[{"name":"s","type":"uint256"},{"name":"i","type":"uint256"}],"name":"sol_clean","outputs":[],"payable":false,"type":"function"},{"constant":false,"inputs":[{"name":"s","type":"uint256"},{"name":"i","type":"uint256"}],"name":"asm_clean","outputs":[],"payable":false,"type":"function"}];
var sweeperContract = web3.eth.contract(sweeperAbi).at("0xa43ebd8939d8328f5858119a3fb65f65c864c6dd");