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System canisters

Intermediate
Concept

System canisters are canisters that provide a necessary function to the ICP network. They are controlled by the NNS and upgraded via NNS proposals. Each system canister is deployed on a system subnet. System subnets have special parameters, such as no cycles costs, to guarantee that the system functions without interruption. These canisters have static canister IDs that projects can make calls to. One common example of a system canister that is used by projects is the Internet Identity canister.

Bitcoin mainnet​

The Bitcoin mainnet system canister is used to facilitate connection from the ICP mainnet to the Bitcoin mainnet.

It has canister ID ghsi2-tqaaa-aaaan-aaaca-cai.

The Bitcoin mainnet canister is hosted on the system subnet w4rem-dv5e3-widiz-wbpea-kbttk-mnzfm-tzrc7-svcj3-kbxyb-zamch-hqe.

View the Bitcoin specification.

Bitcoin testnet​

The Bitcoin testnet system canister is used to facilitate connection from the ICP mainnet to the Bitcoin testnet.

It has canister ID g4xu7-jiaaa-aaaan-aaaaq-cai.

The Bitcoin mainnet canister is hosted on the system subnet w4rem-dv5e3-widiz-wbpea-kbttk-mnzfm-tzrc7-svcj3-kbxyb-zamch-hqe.

View the Bitcoin specification.

Cycles ledger​

The cycles ledger canister is used for cycles management and has been developed as an alternative to the cycles wallet. The cycles ledger allows principals to hold cycles directly rather than requiring a separate cycles wallet canister to be used.

It has canister ID um5iw-rqaaa-aaaaq-qaaba-cai.

The cycles ledger canister is hosted on the system subnet uzr34-akd3s-xrdag-3ql62-ocgoh-ld2ao-tamcv-54e7j-krwgb-2gm4z-oqe.

View the cycles ledger specification.

Cycles ledger index​

The cycles ledger index canister is the corresponding index canister for the cycles ledger.

It has canister ID ul4oc-4iaaa-aaaaq-qaabq-cai.

The cycles ledger canister is hosted on the system subnet uzr34-akd3s-xrdag-3ql62-ocgoh-ld2ao-tamcv-54e7j-krwgb-2gm4z-oqe.

View the cycles ledger specification.

Cycles minting​

Often referred to as the CMC (short for cycles minting canister).

The CMC converts ICP to cycles. Cycles are used up by canisters as they do work (simply storing data counts as doing work, even when no code in the canister is running). In this conversion, ICP is destroyed, and cycles are created. Thus, this operation is referred to as cycles "minting".

The CMC has canister ID rkp4c-7iaaa-aaaaa-aaaca-cai.

The CMC canister is hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

In general, you must do a couple things to use this canister:

  1. Send ICP to the CMC (by calling the ICP ledger canister).
  2. Tell the CMC about the ICP that was sent.

When minting cycles, the ICP transfer parameters must meet the following requirements:

  1. subaccount - Matches the recipient of the new cycles. More on this below.
  2. memo - Indicates what type of operation will be performed using the ICP.

The subaccount corresponding to a recipient principal is constructed as follows:

  1. Start with an arry of length 32 with all elements set to 0.
  2. The first byte is set to the length of the principal (as a blob, not in the string format).
  3. The principal bytes are copied into the remaining bytes of the subaccount.

For example, to send 4.2 ICP to CMC such that principal "mcj7w-qq3pa-zsxyt-fjs6f-4s7px-mrq3c-i6wmj-ciqw6-7q4aj-odhgc-4ae" will end up getting the newly created cycles, ICP could be sent to the CMC like this:

CYCLES_MINTING_CANISTER_ID=rkp4c-7iaaa-aaaaa-aaaca-cai
ICP_LEDGER_CANISTER_ID=ryjl3-tyaaa-aaaaa-aaaba-cai

dfx canister --ic call $ICP_LEDGER_CANSITER_ID icrc1_transfer "(record {
  to = record {
    owner = principal "${CYCLES_MINTING_CANISTER_ID}";

    // This corresponds to principal "mcj7w-qq3pa-zsxyt-fjs6f-4s7px-mrq3c-i6wmj-ciqw6-7q4aj-odhgc-4ae".
    subaccount = opt blob "\1d\1b\78\33\2b\e2\65\4c\bc\5e\4b\ef\bb\23\0d\89\1e\b3\12\24\42\de\fc\38\04\b8\67\30\b8\02\00\00";
  };

  // This matches what the CMC's notify_mint_cycles method requires.
  memo = opt blob "\4d\49\4e\54\00\00\00\00";

  // 4.2 ICP, denominated in 1/100_000_000ths of of an ICP, known as an e8.
  amount = 420_000_000 : nat;

  // Also in e8s. Transfers are very inexpensive in ICP :D
  fee = opt (10_000 : nat);
})"

This transaction will be recorded in a block whose index is printed by the above command. For example, suppose the block index is 123_456_789. This is used in step 2, which can be performed as follows:

dfx canister --ic call $CYCLES_MINTING_CANISTER_ID notify_mint_cycles '(record {
  block_index = 123_456_789 : nat64;
})'

After the above command, the destination principal has a higher cycles balance. To read the balance, the cycles ledger canister can be queried like so:

CYCLES_LEDGER_CANISTER_ID=um5iw-rqaaa-aaaaq-qaaba-cai

dfx canister --ic call $CYCLES_LEDGER icrc1_balance_of '(record {
    owner = principal "mcj7w-qq3pa-zsxyt-fjs6f-4s7px-mrq3c-i6wmj-ciqw6-7q4aj-odhgc-4ae";
})'

The exchange rate from ICP to cycles varies, depending on the price of ICP in XDR (see the exchange rate canister). The result is that the price of cycles in XRD is relatively stable.

Exchange rate​

The exchange rate canister (XRC) uses HTTPS outcalls to fetch data from major cryptocurrency exchanges by using the exchange's public API to retrieve real-time or historical cryptocurrency pricing information. The XRC also queries the public APIs for foreign exchange data providers around the world periodically in order to get rates.

It has canister ID uf6dk-hyaaa-aaaaq-qaaaq-cai.

The exchange rate canister is hosted on the system subnet uzr34-akd3s-xrdag-3ql62-ocgoh-ld2ao-tamcv-54e7j-krwgb-2gm4z-oqe.

Learn more about the exchange rate canister or view the exchange rate canister specification.

Genesis token​

The genesis token canister is used to query balance and account information regarding the genesis token.

It has canister ID renrk-eyaaa-aaaaa-aaada-cai.

The genesis token canister is hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

ICP index​

The ICP index canister is the corresponding index canister for the ICP ledger.

It has canister ID qhbym-qaaaa-aaaaa-aaafq-cai.

The ICP index canister is hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

ICP ledger​

The ICP ledger canister is used for sending and receiving ICP tokens on the mainnet. It can also be used to obtain account information, such as the account's current balance of ICP.

It has canister ID ryjl3-tyaaa-aaaaa-aaaba-cai.

The ICP ledger canister is hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

ICP ledger archive​

The ICP ledger archive canisters are used to store historic data about ICP token transactions. There are two ICP ledger archive canisters.

They have canister IDs qsgjb-riaaa-aaaaa-aaaga-cai and qjdve-lqaaa-aaaaa-aaaeq-cai.

The ICP ledger archive canisters are hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

Internet Identity​

The Internet Identity canister is used to provide an authentication method used across ICP applications, such as the NNS dapp.

It has canister ID rdmx6-jaaaa-aaaaa-aaadq-cai.

The Internet Identity canister is hosted on the system subnet  uzr34-akd3s-xrdag-3ql62-ocgoh-ld2ao-tamcv-54e7j-krwgb-2gm4z-oqe.

View the Internet Identity specification.

NNS canisters​

The NNS is comprised of the following canisters:

The NNS canisters are hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

SNS Wasm​

The SNS Wasm canister is used for deploying and updating SNSes.

It has canister ID qaa6y-5yaaa-aaaaa-aaafa-cai.

The SNS Wasm canister is hosted on the system subnet tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe.

Using system canisters​

Developers can use system canisters in their projects to integrate services into their dapp or enable functionality that requires data from a system canister.

For example, Internet Identity can be integrated into a dapp to provide user authentication service to the project. Internet Identity is commonly integrated into a dapp through the dfx deps command. dfx deps allows you to pull a system canister into your local project for testing.

For other projects, calls can be made to system canisters to obtain information, such as DeFi projects making calls to the ICP index to obtain information about ICP transactions or price.