Let’s suppose that the US is at war against another country, while trying to negotiate an armistice. What would happen if the US hacked the enemy’s government to make the adversary’s troops believe that a cease-fire has been signed?

Messengers in the Tapestry of Bayeux.

If successful, such a cyber attack could have devastating effects when combined with surprise kinetic strikes on vulnerable enemy troops. Can we say that this strategy would violate the cease-fire treaty? Not really, because no real cease-fire treaty was signed. However, such a behavior is forbidden by jus in bello rules (the legal norms governing war) applied to cyber operations.

In the Law of war manual (2015) issued by the US Department of Defense, section 16.5.4, one can read:

Under the law of war, certain signs may not be used improperly. These prohibitions may also be applicable during cyber operations. For example, it would not be permissible to conduct a cyber attack or to attempt to disable enemy internal communications by making use of communications that initiate non-hostile relations, such as prisoner exchanges or ceasefires. Similarly, it would be prohibited to fabricate messages from an enemy’s Head of State falsely informing that State’s forces that an armistice or cease-fire had been signed.

On the other hand, the restriction on the use of enemy flags, insignia, and uniforms only applies to concrete visual objects; it does not restrict the use of enemy codes, passwords, and countersigns. Thus, for example, it would not be prohibited to disguise network traffic as though it came from enemy computers or to use enemy codes during cyber operations.

In spite of the possibilities offered by cyber operations—hacking Donald Trump’s Twitter account to trigger a war, or creating a deepfake surrendering video of Kim-Jong Un—the traditional rules of war still apply.