// deriveCoinTypeKey derives the cointype key which can be used to derive the
// extended key for an account according to the hierarchy described by BIP0044
// given the coin type key.
//
// In particular this is the hierarchical deterministic extended key path:
// m/44'/<coin type>'
func deriveCoinTypeKey(masterNode *hdkeychain.ExtendedKey,
coinType uint32) (*hdkeychain.ExtendedKey, error) {
// Enforce maximum coin type.
if coinType > maxCoinType {
return nil, fmt.Errorf("bad coin type")
}
// The hierarchy described by BIP0043 is:
// m/<purpose>'/*
// This is further extended by BIP0044 to:
// m/44'/<coin type>'/<account>'/<branch>/<address index>
//
// The branch is 0 for external addresses and 1 for internal addresses.
// Derive the purpose key as a child of the master node.
purpose, err := masterNode.Child(44 + hdkeychain.HardenedKeyStart)
if err != nil {
return nil, err
}
// Derive the coin type key as a child of the purpose key.
coinTypeKey, err := purpose.Child(coinType + hdkeychain.HardenedKeyStart)
if err != nil {
return nil, err
}
return coinTypeKey, nil
}
// checkBranchKeys ensures deriving the extended keys for the internal and
// external branches given an account key does not result in an invalid child
// error which means the chosen seed is not usable. This conforms to the
// hierarchy described by BIP0044 so long as the account key is already derived
// accordingly.
//
// In particular this is the hierarchical deterministic extended key path:
// m/44'/<coin type>'/<account>'/<branch>
//
// The branch is 0 for external addresses and 1 for internal addresses.
func checkBranchKeys(acctKey *hdkeychain.ExtendedKey) error {
// Derive the external branch as the first child of the account key.
if _, err := acctKey.Child(ExternalBranch); err != nil {
return err
}
// Derive the external branch as the second child of the account key.
_, err := acctKey.Child(InternalBranch)
return err
}
// deriveAccountKey derives the extended key for an account according to the
// hierarchy described by BIP0044 given the master node.
//
// In particular this is the hierarchical deterministic extended key path:
// m/44'/<coin type>'/<account>'
func deriveAccountKey(coinTypeKey *hdkeychain.ExtendedKey,
account uint32) (*hdkeychain.ExtendedKey, error) {
// Enforce maximum account number.
if account > MaxAccountNum {
return nil, fmt.Errorf("account num too high")
}
// Derive the account key as a child of the coin type key.
return coinTypeKey.Child(account + hdkeychain.HardenedKeyStart)
}