@Override
    public void setOldKey(final byte[] oldKey) {
        super.setOldKey(oldKey);
        oldIdentityKey = SecureUtils.calculateIdentityKey(oldKey);
        oldDerivatives = SecureUtils.calculateK2(oldKey, SecureUtils.K2_MASTER_INPUT);
    }
Returns the key refresh phase of the network key

@return int phase
mesh/src/main/java/no/nordicsemi/android/mesh/NetworkKey.java