Digital forensics law matters
International legal framework
The Council of Europe Convention on Cybercrime (also known as the Budapest Convention) is, afaik, at present still the main international instrument on cybercrime. It aims to help its state parties harmonise their national laws, improve their investigative techniques and increase cooperation. In addition to most EU countries, the US, Japan, Australia, Canada and others have ratified the convention.
National legal systems
A national legal system in its pure form is an entity separate from rules on the international level. Individuals are subject to the rules of the legal system of the nation where they reside. The rules come from a parliament (legislative body, or lawmaker, in democratic societies). A nation state’s authority to create binding rules on its citizens is associated with sovereignty. Basically, the state may decide “the law of the land” (enact cybercrime legislation) without taking external considerations.
Every individual is entitled to enjoy the fundamental human rights and protections conferred by the rule of law. Contrary to conventions that are binding on nation states, these rules give rights to the individual regardless of whether they have been formally implemented in the national legal system or not.
It is widely held that fundamental rights and the rule of law flow from natural law. According to this perception, conventions are not necessary in order to create such rights, because those rights exist independently of any written legal framework or convention. That said (written), international legal instruments are at least helpful in describing the rights.
Transborder search and surveillance
As a note, global integration in terms of digital networks and services exposes individuals to invasive online investigation methods by law enforcement agencies of other states. Absent valid permission from the state in which the individual resides, transborder investigation amounts to a violation of sovereignty. A violation of sovereignty may give rise to a claim by the aggrieved nation state, but not by the individual. The individual is also barred from availing herself of the courts in her jurisdiction, because the interference was not caused by anyone working for law enforcement authorities in the state in which she resides.