No, breaking an encryption is all about knowing how it works, many cryptographers make their algorithm proprietary in hopes that an attacker will have a hard time figuring how it works, however they turn out to be weak, other encryption algorithms are developed in the open so that many people look at it and see the flaws
The key word is : weak The idea is not making a backdoor directly, the idea is making it flawed, it’s like securing a bank with steel doors with the exception of one door, that door is made out of wood and only you know where it’s located.