Create an account key

Motivation

In order for a user to have a MobileCoin wallet, they must have an account key. An AccountKey can be thought of as a username+password used to access an account on the MobileCoin blockchain.

Any application integrating MobileCoin must provide the functionality to allow users to either import an existing AccountKey or to create a new one.

Implementation

Using the MobileCoin Android SDK, there are a few different methods that can be used to create an AccountKey

Creating a new AccountKey

The simplest way to create a new AccountKey is to use the static createNew method of AccountKey

AccountKey newAccountKey = AccountKey.createNew(
        fogReportUri,
        fogReportId,
        fogAuthoritySpki
);

The fogReportUri should be a valid Fog report service URL.

The fogAuthoritySpki is the Fog authority public key. This will be provided by the Fog provider.

The fogReportId is important when the Fog provider operates multiple Fog Ingest enclaves. The value is used to select which ingest key should be used to create outputs. This usually isn't necessary. It is generally fine to use a fogReportId = "".

Importing an existing AccountKey

There are two methods that can be used to import an existing AccountKey

1. Importing form mnemonic phrase

2. Importing from Bip39 entropy

Importing from menmonic phrase

AccountKey newAccountKey = AccountKey.fromMnemonicPhrase(
        mnemonicPhrase,
        accountIndex
        fogReportUri,
        fogReportId,
        fogAuthoritySpki
);

There are two new fields here: the mnemonic phrase and the account index. The mnemonicPhrase is a space-separated String of the 24 words that make up the account's mnemonic phrase.

Each mnemonic phrase can be used to create multiple accounts. The accountIndex argument specifies which account index to create a key for. For most applications, only one AccountKey is needed. In such cases, it is fine to always use accountIndex = 0

Importing from Bip39 entropy

AccountKey newAccountKey = AccountKey.fromBip39Entropy(
        bip39Entropy,
        accountIndex
        fogReportUri,
        fogReportId,
        fogAuthoritySpki
);

This approach is similar to the mnemonic phrase method. The only difference is the first argument. Instead of using the 24 word bip49 mnemonic, the corresponding bip39 entropy is used.