The node_key.json file

The node ID, the host address and the P2P port together identify a node in a CometBFT network: nodeID@host:port.

The easiest way to get the nodeID is running the cometbft show-node-id command.

The node_key.json file resides at $CMTHOME/config/node_key.json. This can be overridden at the node_key_file parameter in the config.toml file.

The file contains a private key (in priv_key.value) to an asymmetric algorithm (in priv_key.type).

The node ID is calculated by hashing the public key with the SHA256 algorithm and taking the first 20 bytes of the result.

priv_key.type

The type of the key defined under priv_key.value.

Default example in context:

{
  "priv_key": {
    "type": "tendermint/PrivKeyEd25519",
    "value": "jxG2ywUkVPiF4XDW1Dwa5ZfcrC0rEa4iM1y4O5qCMpYxdiypykyf9yp7C81cJTZHKMOvrnGcZiqxlMfyQsaUUA=="
  }
}

The string values are derived from the asymmetric cryptographic implementations defined in the crypto package.

CometBFT will always generate an Ed25519 key-pair for node ID using the cometbft init or the cometbft gen-node-key commands. Other types of encryption keys have to be created manually. (See examples under priv_key.value.)

priv_key.value

Base64-encoded bytes, the private key of an asymmetric encryption algorithm. The type of encryption is defined in priv_key.type.

Default example in context:

{
  "priv_key": {
    "type": "tendermint/PrivKeyEd25519",
    "value": "jxG2ywUkVPiF4XDW1Dwa5ZfcrC0rEa4iM1y4O5qCMpYxdiypykyf9yp7C81cJTZHKMOvrnGcZiqxlMfyQsaUUA=="
  }
}

CometBFT will always generate an Ed25519 key-pair for node ID using the cometbft init or the cometbft gen-node-key command. Other types of encryption keys have to be created manually. (See examples below.)

The Ed25519 encryption implementation requires the public key concatenated in the value. The implementation ignores the private key and uses the stored public key to generate the node ID. In the below example, we zeroed out the private key, but the resultant concatenated bytes still produce a valid node ID. Other algorithms generate the public key from the private key.

Examples:

Ed25519:

{
  "priv_key": {
    "type": "tendermint/PrivKeyEd25519",
    "value": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAxdiypykyf9yp7C81cJTZHKMOvrnGcZiqxlMfyQsaUUA=="
  }
}

Secp256k1:

{
  "priv_key": {
    "type": "tendermint/PrivKeySecp256k1",
    "value": "2swJ5TwUhhqjJW+CvVbbSnTGxqpYmb2yvib+MHyDJIU="
  }
}