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Manage keys

The Snaps JSON-RPC API allows you to manage users' private keys with their approval.

important

Managing users' keys comes with great responsibility: Misplaced or stolen private keys can lead to a complete loss of funds for users of your snap.

Responsible key management​

It's critical to practice responsible key management. The general rule is: Don't create a situation where your users can lose assets.

examples of responsible key management:
  • Deriving private keys and/or storing them in Snaps persistent storage, without ever moving them out of the Snaps execution environment.
  • Ensuring arbitrary code execution can't access irreversible operations or private keys.
  • Asking the user for consent and informing them of what's going to happen before performing irreversible operations.
examples of irresponsible key management:
  • Allowing extraction of private keys outside the snap in any way, especially through RPC or network connections.
  • Executing arbitrary or untrusted code with access to private keys.
  • Not getting properly informed consent before performing irreversible operations.
  • Asking for consent but ignoring the decision.
  • Exposing key material in clear-text.
  • Producing a bug that leads to any of the above.

Derive keys​

To derive a user's private keys:

  1. Choose between the BIP-32 or BIP-44 specifications to derive the user's private keys. If the keys you want to derive conform to the BIP-44 structure, use snap_getBip44Entropy to derive them. Otherwise, use snap_getBip32Entropy.
  2. Add the required permission to your manifest file.
  3. Find out the derivation path to use. This is dependent on the application you're building.
  4. Use the @metamask/key-tree module to derive the keys. Any additional code, for example, to derive addresses from keys, is application-specific.

Dogecoin example​

For example, to derive Dogecoin keys:

  1. Dogecoin uses the BIP-44 scheme, so you'll use snap_getBip44Entropy.

  2. Dogecoin has coin type 3, so add the following to the manifest file:

    {
      "initialPermissions": {
        "snap_getBip44Entropy": [
          {
            "coinType": 3
          }
        ]
      }
    }

  3. Dogecoin uses the following derivation path:

    m/44'/3'/0'/0/{address_index}

    To get the second Dogecoin account, add the following code to your snap:

    import { getBIP44AddressKeyDeriver } from '@metamask/key-tree';

    // Get the Dogecoin node, corresponding to the path m/44'/3'.
    const dogecoinNode = await snap.request({
      method: 'snap_getBip44Entropy',
      params: {
        coinType: 3,
      },
    });

    /**
     * Create a function that takes an index and returns an extended private key for m/44'/3'/0'/0/address_index.
     * The second parameter to getBIP44AddressKeyDeriver isn't passed. This sets account and changes to 0.
     */
    const deriveDogecoinAddress = await getBIP44AddressKeyDeriver(dogecoinNode);

    // Derive the second Dogecoin address, which has index 1.
    const secondAccount = deriveDogecoinAddress(1);

Examples​

The following are examples of existing snaps that manage accounts and keys: