Do you really think its fair to blame US intelligence services for the backdoors? What you have to remember is they are authorized to basically do whatever they want. If they want a secure login to your phone, they can get it. If someone in the private sector developing software for phones makes that same secure login and then logs in to spy on customers, he can be found and convicted just on the basis that he had the password to get into his own backdoor. However If he "screws up" and makes a vulnerability "by mistake" anyone can exploit, who can tie it to him if "some hacker" happens to exploit that vulnerability to get in to spy on customers? It makes sense most of the backdoors are coming from this kind of corruption in the private sector, not the government.