Aim: The use of covert means is any information gathering intelligence operation (secret police activity) in which the authorised authorities of the State seek to obtain new knowledge in the course of administrative and criminal proceedings without the knowledge of the holder of the information, by limiting the right of self-determination. In dictatorships, this form of exercise of state power is also dominated by arbitrariness. Constitutional states place the use of secret means on a public law basis. This study aims to demonstrate that it is possible to regulate acts of public authority that are at the heart of secrecy by means of legal instruments whose core is publicity. Methodology: The objective outlined above can only be achieved if the dogmatic and moral characteristics of the legislation are harmonised with the specific characteristics of the secret police. The task is not easy. Legislation is always about the future and is always based on abstract prognosis; covert intelligence aims to discover the past, the present and the future, and the knowledge to be acquired is always unique and concrete. Finidings: The abstract nature of the regulation and the uniqueness of the intelligence operation resolve the contradiction between publicity and secrecy. What is public is the rule, what is secret is the application of the rule to a specific situation. However, legislation can become fully formalised when it no longer imposes limits on the operation of state power, but merely authorises it, opening the way to free discretion. In such a case, the guise of legality conceals an untrammelled power. Value: Law that serves humanity is an effective means of preserving social order. Secret data-collection requires a limitation of rights, yet it is indispensable to combat violations (principle of necessity), provided that it does not cause more serious harm than the threat against which it is used (principle of proportionality).