It's even a problem with allies as well as adversaries; countries can potentially get around their own legal limitations by agreeing to spy on one another, and

It's even a problem with allies as well as adversaries; countries can potentially get around their own legal limitations by agreeing to spy on one another, and where needed to build a case, covering their tracks via parallel construction. Whether officially or unofficially, any backdoor keys would leak almost immediately. https://en.wikipedia.org/wiki/Five_Eyes https://en.wikipedia.org/wiki/Five_Eyes https://en.wikipedia.org/wiki/Parallel_construction https://en.wikipedia.org/wiki/Parallel_construction