Inside Cyber Warfare - Jeffrey Carr [34]
Self-defense responses must comply with international law. Just because an armed attack has occurred against a victim-state does not mean that the victim-state has a blank check to wage unlimited war against the aggressor. Self-defense responses must be necessary and proportional. Necessity means that self-defense is actually required under the circumstances because a reasonable settlement could not be attained through peaceful means. Proportionality requires self-defense actions to be limited to the amount of force necessary to defeat an ongoing attack or deter future aggression. This principle does not require the size and scope of defensive actions to be similar to those of the attack. A defensive action may need to employ significantly greater force than the attacker used to successfully repel the attacker. The key is to determine the amount of force needed to either defeat the current attack or deter future attacks. These two principles define the legal boundaries to self-defense responses.
A Subset of Self-Defense: Anticipatory Self-Defense
Anticipatory self-defense is a subset of self-defense and a longstanding tenet of international law. It allows states to defend themselves against imminent armed attacks, rather than forcing them to wait until their enemies cross their borders.
The legality of anticipatory self-defense rests on the imminency of an attack. Initially, imminency restricted anticipatory self-defense to situations immediately before an attack, where an attack was detected, but there was no time to deliberate about other ways to prevent the attack short of self-defense. The principle effectively balanced the victim-state’s right to ward off violence against its obligation to find peaceful means to resolve disputes. However, due to changes in the nature of warfare, imminency has evolved significantly.
Today, imminency allows states to legally employ force in advance of an attack, at the point when (1) evidence shows that an aggressor has committed itself to an armed attack and (2) delaying a response would hinder the defender’s ability to mount a meaningful defense. Thus, imminency is actually a relative concept, which operates as follows:
Weak States may lawfully act sooner than strong ones in the face of identical threats because they are at greater risk as time passes. In the same vein, it may be necessary to conduct defensive operations against a terrorist group long before a planned attack because there is unlikely to be another opportunity to target terrorists before they strike. ... In other words, each situation presents a case-specific window of opportunity within which a State can foil an impending attack.[5]
Finally, just because a single attack may be complete does not mean that future attacks are not imminent. When evidence suggests that an attack is part of an ongoing campaign against a state, such as the terrorist attacks against the United States on 9/11, future armed attacks will be considered imminent and anticipatory self-defense will be authorized.
An Alternate Basis for Using Active Defenses: Reprisals
Reprisals, also known as proportionate countermeasures, provide another way for states to address illegal uses of force against them. As discussed earlier, no consensus exists as to what constitutes an armed attack, meaning that a cyber attack could be seen as a use of force below the armed attack threshold. As a result, it is important to explore the rights that states have to react to illegal uses of force against them that fall short of an armed attack.
Reprisals are an exception to the general rule that states are required to solve their disputes peacefully. Reprisals allow victim-states to take normally unlawful actions against another state, when the other state is violating its international obligations with respect to the victim-state. Reprisals must