Protocol Canisters

Protocol canisters implement platform-level features on the Internet Computer. Unlike system canisters, which govern the network itself, protocol canisters provide infrastructure that applications build on: Bitcoin integration, Ethereum integration, chain-key tokens, and exchange rates. They are controlled by the NNS and run on dedicated system subnets.

For all chain-key token canister IDs (ledger, minter, index), see Chain-Key Token Canister IDs. For deposit, withdrawal, and transfer flows, see Chain-key tokens.

Bitcoin canisters

The Bitcoin integration canisters connect ICP to the Bitcoin network. They track the Bitcoin UTXO set and expose an API that other canisters use to read Bitcoin state and submit transactions.

Call the Bitcoin canisters directly using the canister IDs below for better performance and to avoid potential future changes to the management canister Bitcoin API.

Bitcoin mainnet

Field	Value
Canister ID	ghsi2-tqaaa-aaaan-aaaca-cai
Subnet	w4rem-dv5e3-widiz-wbpea-kbttk-mnzfm-tzrc7-svcj3-kbxyb-zamch-hqe
Specification	Bitcoin canister interface spec

Bitcoin testnet (v4)

Field	Value
Canister ID	g4xu7-jiaaa-aaaan-aaaaq-cai
Subnet	w4rem-dv5e3-widiz-wbpea-kbttk-mnzfm-tzrc7-svcj3-kbxyb-zamch-hqe
Specification	Bitcoin canister interface spec

Key endpoints

• bitcoin_get_utxos: returns UTXOs for a Bitcoin address
• bitcoin_get_balance: returns the balance of a Bitcoin address in satoshi
• bitcoin_send_transaction: submits a signed Bitcoin transaction
• bitcoin_get_current_fee_percentiles: returns fee percentiles in millisatoshi/vbyte
• bitcoin_get_block_headers: returns block headers for a range of heights

For integration patterns, see the Bitcoin guide.

ckBTC minter

The ckBTC minter holds real BTC in a threshold ECDSA-controlled wallet and mints or burns ckBTC tokens. It issues a unique Bitcoin deposit address per (owner, subaccount) account and handles withdrawal requests by submitting signed Bitcoin transactions.

For canister IDs, see Chain-Key Token Canister IDs: ckBTC.

Minter parameters

Parameter	Value	Description
retrieve_btc_min_amount	50,000 satoshi	Minimum amount for BTC withdrawal
max_time_in_queue_nanos	10 minutes	Maximum time a retrieval request waits
min_confirmations	4	Bitcoin confirmations required before minting
kyt_fee	100 satoshi	Fee for know-your-transaction (KYT) check

Minter endpoints

• get_btc_address(owner, subaccount): returns a unique Bitcoin deposit address for the given principal and subaccount
• update_balance(owner, subaccount): checks for newly confirmed UTXOs and mints ckBTC
• get_known_utxos(owner, subaccount): returns UTXOs already processed for the given account
• estimate_withdrawal_fee(amount): estimates the fee for retrieving a given BTC amount
• get_deposit_fee: returns the current fee charged when minting ckBTC (the KYT fee)
• retrieve_btc_with_approval(address, amount, from_subaccount): burns ckBTC via ICRC-2 approval and sends BTC to the given Bitcoin address
• retrieve_btc_status_v2(block_index): returns the status of a previous withdrawal request
• retrieve_btc_status_v2_by_account(account): returns statuses for all recent withdrawal requests from the given account
• get_minter_info: returns current minter parameters
• get_events(start, length): returns the minter’s internal event log

KYT checker

The ckBTC checker canister (oltsj-fqaaa-aaaar-qal5q-cai) performs know-your-transaction compliance checks on incoming Bitcoin UTXOs. It is called internally by the minter on deposit and is not part of the developer-facing API.

ckETH minter

The ckETH minter bridges ETH and all ERC-20 tokens between Ethereum and ICP. It monitors the ckETH helper contract on Ethereum via HTTPS outcalls to detect deposits, and submits signed Ethereum transactions for withdrawals using threshold ECDSA.

For canister IDs, see Chain-Key Token Canister IDs: ckETH.

Helper contract

The minter uses a helper smart contract on Ethereum to receive deposits for both ETH and ERC-20 tokens. Always verify the current address before constructing a deposit transaction:

icp canister call sv3dd-oaaaa-aaaar-qacoa-cai get_minter_info '()' -n ic

Check deposit_with_subaccount_helper_contract_address in the response.

Minter endpoints

• get_minter_info: returns current minter info including the helper contract address and supported_ckerc20_tokens
• withdraw_eth(address, amount): burns ckETH or ckERC20 and submits an Ethereum withdrawal transaction; used for both ETH and all ERC-20 withdrawals
• get_canister_status: returns the minter’s current status

ckERC20 ledgers

ckERC20 tokens share the ckETH minter. Each ERC-20 token has its own ICRC-1 ledger canister. New tokens are added via NNS governance proposals.

To get the authoritative current list of supported tokens and their ledger canister IDs at runtime:

icp canister call sv3dd-oaaaa-aaaar-qacoa-cai get_minter_info '()' -n ic

Check supported_ckerc20_tokens in the response. For a static reference table, see Chain-Key Token Canister IDs: ckERC20.

ckDOGE minter

The ckDOGE minter follows the same UTXO-based model as ckBTC. It holds real DOGE in a threshold ECDSA-controlled wallet and issues a unique Dogecoin deposit address per (owner, subaccount) account.

For canister IDs, see Chain-Key Token Canister IDs: ckDOGE.

Minter endpoints

• get_deposit_address(owner, subaccount): returns a unique Dogecoin deposit address for the given principal and subaccount
• update_balance(owner, subaccount): checks for newly confirmed UTXOs and mints ckDOGE
• retrieve_doge_with_approval(address, amount, from_subaccount): burns ckDOGE via ICRC-2 approval and sends DOGE to the given Dogecoin address
• get_minter_info: returns current minter parameters

Amounts are denominated in koinu (1 DOGE = 100,000,000 koinu).

Source: dfinity/ic rs/dogecoin/ckdoge

ckSOL minter

The ckSOL minter bridges SOL between Solana and ICP. It issues a unique Solana deposit address per (owner, subaccount) account and verifies deposits via the SOL RPC canister using threshold signatures (Ed25519).

For canister IDs, see Chain-Key Token Canister IDs: ckSOL.

Minter endpoints

• get_deposit_address(owner, subaccount): returns a unique Solana deposit address for the given principal and subaccount
• process_deposit(tx_signature, owner, subaccount): verifies a Solana deposit transaction and mints ckSOL; requires cycles to cover RPC verification
• withdraw(address, amount): burns ckSOL via ICRC-2 approval and signs a Solana transaction using threshold Ed25519
• withdrawal_status(burn_block_index): returns the status of a pending withdrawal

Amounts are denominated in lamports (1 SOL = 1,000,000,000 lamports).

Source: dfinity/cksol

EVM RPC canister

The EVM RPC canister proxies JSON-RPC calls to Ethereum and EVM-compatible chains via HTTPS outcalls. Your canister sends a request to the EVM RPC canister, which fans the request out to multiple RPC providers, compares responses for consensus, and returns the result. No API keys are required for the default providers.

Field	Value
Canister ID	7hfb6-caaaa-aaaar-qadga-cai
Subnet	34-node fiduciary subnet
Candid interface	evm_rpc.did

Supported chains

Chain	Chain ID
Ethereum Mainnet	1
Ethereum Sepolia	11155111
Arbitrum One	42161
Base Mainnet	8453
Optimism Mainnet	10
Custom EVM chain	any

Built-in RPC providers

The following providers are available without API keys:

Provider	Ethereum	Sepolia	Arbitrum	Base	Optimism
Alchemy	yes	yes	yes	yes	yes
Ankr	yes	-	yes	yes	yes
BlockPi	yes	yes	yes	yes	yes
Cloudflare	yes	-	-	-	-
LlamaNodes	yes	-	yes	yes	yes
PublicNode	yes	yes	yes	yes	yes

Cycle costs

Each call requires cycles attached. The cost formula is:

(5_912_000 + 60_000 * nodes + 2400 * request_bytes + 800 * max_response_bytes) * nodes * rpc_count

Where nodes = 34 (fiduciary subnet) and rpc_count = number of providers queried. For a practical starting budget, attach 10B cycles per call: unused cycles are refunded. Use the requestCost method to get an exact estimate before calling.

Consensus

By default, the canister requires all providers to agree (Equality consensus). For calls like eth_getBlockByNumber("latest") where providers may be 1-2 blocks apart, use threshold consensus instead: 2-of-3 agreement. Multi-provider results are returned as MultiRpcResult::Consistent(result) or MultiRpcResult::Inconsistent(results): always handle both variants.

For integration examples, see the Ethereum guide.

Exchange rate canister (XRC)

The exchange rate canister (XRC) uses HTTPS outcalls to fetch cryptocurrency and foreign exchange rates from major exchanges. It runs on the uzr34 system subnet and is used by the cycles minting canister (CMC) to convert ICP to cycles at a stable XDR-pegged price.

Field	Value
Canister ID	uf6dk-hyaaa-aaaaq-qaaaq-cai
Subnet	uzr34-akd3s-xrdag-3ql62-ocgoh-ld2ao-tamcv-54e7j-krwgb-2gm4z-oqe
Specification	XRC interface spec

Data sources

The XRC pulls from the following exchanges: Coinbase, Kucoin, OKX, Gate.io, MEXC, Poloniex, Crypto.com, Bitget, and DigiFinex.

For forex rates, it queries public APIs from foreign exchange data providers worldwide on a periodic basis.

Rate aggregation

The XRC calculates rates using candlestick chart data for specific one-minute intervals across exchanges. Rather than time-weighted or volume-weighted averages, it collects, combines, and filters rates from all sources and returns the median. This approach minimizes manipulation risk. The XRC can also derive rates for pairs not directly traded (e.g., A/B from A/C and B/C rates).

Interface

The XRC exposes a single endpoint:

get_exchange_rate : (GetExchangeRateRequest) -> (GetExchangeRateResult)

Request:

type GetExchangeRateRequest = record {
  base_asset  : Asset;
  quote_asset : Asset;
  timestamp   : opt nat64;
};

Asset is a record with a symbol (e.g., "BTC") and class (Cryptocurrency or FiatCurrency). Any combination of digital asset and fiat is supported (e.g., ICP/USD, BTC/ICP, USD/EUR). If timestamp is omitted, the current rate is returned.

Response:

type GetExchangeRateResult = variant {
  Ok  : ExchangeRate;
  Err : ExchangeRateError;
};

Cycle costs

Each request requires 1B cycles attached. If insufficient cycles are provided, the canister returns ExchangeRateError::NotEnoughCycles. The actual cost depends on the asset types and cache state:

Condition	Actual cost
Served from cache	20M cycles
Both assets are fiat currencies	20M cycles
One asset is fiat or USDT	260M cycles
Both assets are cryptocurrencies	500M cycles

Unused cycles are refunded. At least 1M cycles are charged even on error, to prevent denial-of-service attacks.

Example call

Calling the XRC requires attaching cycles, which is only possible from canister-to-canister calls. The CLI cannot attach cycles to direct calls. Call the XRC from a canister using the Candid interface: pass the required cycles in the ic_cdk::api::call::call_with_payment128 call or equivalent.

To query the current rate without attaching cycles (for inspection only, expect a NotEnoughCycles error on mainnet):

icp canister call uf6dk-hyaaa-aaaaq-qaaaq-cai get_exchange_rate \
  '(record {
    base_asset  = record { symbol = "BTC"; class = variant { Cryptocurrency } };
    quote_asset = record { symbol = "USD"; class = variant { FiatCurrency } };
  })' \
  -n ic

SNS-W canister

The SNS Wasm canister (SNS-W) manages the deployment and upgrade of Service Nervous System (SNS) instances. The NNS controls which SNS Wasm binaries are blessed for deployment.

Field	Value
Canister ID	qaa6y-5yaaa-aaaaa-aaafa-cai
Subnet	tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe (NNS subnet)

The SNS-W canister stores blessed SNS Wasm binaries, creates new SNS instances, and coordinates SNS upgrades. When the NNS passes an SNS upgrade proposal, it installs the new Wasms on each SNS canister via SNS-W.

For governance context, see the SNS documentation.

Quick reference

Canister	ID	Purpose
Bitcoin mainnet	ghsi2-tqaaa-aaaan-aaaca-cai	Bitcoin mainnet UTXO tracking
Bitcoin testnet (v4)	g4xu7-jiaaa-aaaan-aaaaq-cai	Bitcoin testnet UTXO tracking
ckBTC Minter	mqygn-kiaaa-aaaar-qaadq-cai	BTC ↔ ckBTC minting and burning
ckBTC KYT Checker	oltsj-fqaaa-aaaar-qal5q-cai	Know-your-transaction compliance
ckETH Minter	sv3dd-oaaaa-aaaar-qacoa-cai	ETH and ERC-20 ↔ ckETH/ckERC20 minting and burning
ckDOGE Minter	eqltq-xqaaa-aaaar-qb3vq-cai	DOGE ↔ ckDOGE minting and burning
ckSOL Minter	lh22c-kyaaa-aaaar-qb5nq-cai	SOL ↔ ckSOL minting and burning
EVM RPC	7hfb6-caaaa-aaaar-qadga-cai	Ethereum JSON-RPC proxy
Exchange Rate (XRC)	uf6dk-hyaaa-aaaaq-qaaaq-cai	Crypto and forex exchange rates
SNS-W	qaa6y-5yaaa-aaaaa-aaafa-cai	SNS deployment and upgrades

For ledger, index, and testnet canister IDs for all chain-key tokens, see Chain-Key Token Canister IDs.

Next steps

• Chain-Key Token Canister IDs: ledger, minter, and index IDs for all chain-key tokens
• Chain-key tokens: deposit, withdrawal, and transfer flows for all chain-key tokens
• Bitcoin guide: integrating Bitcoin in canisters using the Bitcoin canister and ckBTC
• Ethereum guide: integrating Ethereum in canisters using the EVM RPC canister and ckETH
• System canisters: NNS canisters, Internet Identity, ICP ledger, and other network-level canisters
• Management canister: the virtual canister for canister lifecycle, signing, and platform APIs