Master keys for decrypting?
In theory, someone could do this, but in practice nobody really uses random, sketchy third party cryptography software. Most, if not all, of the commonly used cryptography functions are well understood and tested. Most of them also openly reveal precisely how they work so anyone can implement them. This means lots of people can analyse the algorithms for built in weaknesses like the one you described.

The case you described is a good reason to stay away from unknown and untrusted third party cryptography software.