Your intuitution is right. At least in Germany it is not legal if not asked for permission first.

See also the German Criminal Code, starting with §202a "Data espionage":

Germany isnt a serious country though Decompilng code is illegal there

	▲	consumer451 30 minutes ago \| parent [-]
		It is no wonder there is an anarchist counterculture there. I find anarchism to be really disturbing in general, but in the context of Germany, it might make a lot more sense.