System Contracts

System contracts are a set of pre-deployed smart contracts on Citrea that are responsible for the core functionalities. These contracts are embedded in the genesis state. They contain functions that can only be processed through a system transaction, in addition to regular functions that can be called by any address.

System contracts are also audited under Citrea and Clementine - you can find the reports at https://docs.citrea.xyz/security/audits-inquiries section.

Address	Name & Explorer Link
0x3100000000000000000000000000000000000001	Bitcoin Light Client Proxy
0x3100000000000000000000000000000000000002	Bridge Proxy
0x3100000000000000000000000000000000000003	Base Fee Vault Proxy
0x3100000000000000000000000000000000000004	L1 Fee Vault Proxy
0x3100000000000000000000000000000000000005	Priority Fee Vault Proxy
0x3100000000000000000000000000000000000006	WCBTC
0x3100000000000000000000000000000000000007	Failed Deposit Vault Proxy
0x3200000000000000000000000000000000000001	Bitcoin Light Client Implementation
0x3200000000000000000000000000000000000002	Bridge Implementation
0x3200000000000000000000000000000000000003	Base Fee Vault Implementation
0x3200000000000000000000000000000000000004	L1 Fee Vault Implementation
0x3200000000000000000000000000000000000005	Priority Fee Vault Implementation
0x3200000000000000000000000000000000000007	Failed Deposit Vault Implementation
0x31ffffffffffffffffffffffffffffffffffffff	Proxy Admin

In this section we're going over three main system smart contracts of Citrea:

• https://docs.citrea.xyz/developer-documentation/system-contracts/bitcoin-light-client

• https://docs.citrea.xyz/developer-documentation/system-contracts/bridge

• https://docs.citrea.xyz/developer-documentation/system-contracts/fee-vaults

System Transactions

System transactions originate from a hardcoded address with no private key:

address constant SYSTEM_CALLER = 0xdeaDDeADDEaDdeaDdEAddEADDEAdDeadDEADDEaD;

Finding the corresponding private key is a 1-in-2^160 problem, which is practically impossible within the lifetime of the universe.

The sequencer prepares the calls and injects them at the start of every block. They spend no balance from the sender, but their gas consumption still counts toward the block gas limit (which is 10 million).

Typical system transactions include the one-time bootstraps

lightClient.initializeBlockNumber(uint256 height);
bridge.initialize(bytes prefix, bytes suffix, uint256 depositAmount);

as well as the per-Bitcoin-block maintenance call

lightClient.setBlockInfo(bytes32 blockHash, bytes32 witnessRoot, uint256 coinbaseDepth);

and the bridge’s deposit handler:

bridge.deposit(Transaction moveTx, MerkleProof proof, bytes32 shaScriptPubkeys);

Because their inclusion is enforced, these transactions are deterministic and cannot be censored by external actors even though no private key signs them.