code: func (ks *KeyStore) ImportECDSA(priv *ecdsa.PrivateKey, passphrase string) (accounts.Account, error) {
  	key := newKeyFromECDSA(priv)
  	if ks.cache.hasAddress(key.Address) {
  		return accounts.Account{}, fmt.Errorf("account already exists")
  	}
  	return ks.importKey(key, passphrase)
  }
docs: // ImportECDSA stores the given key into the key directory, encrypting it with the passphrase.