@Override
        public byte[] getApplicationKey(final int aid) {
            for (ApplicationKey key : mMeshNetwork.getAppKeys()) {
                final byte[] k = key.getKey();
                if (aid == SecureUtils.calculateK4(k)) {
                    return key.getKey();
                }
            }
            return null;
        }
Updates the minimum security property of a Network Key. If the node was provisioned
insecurely, all network keys added to the node are marked as insecure.

@param node Provisioned mesh node.
mesh/src/main/java/no/nordicsemi/android/mesh/MeshManagerApi.java