I'm not sure that BillC-51 itself deals with encryption, but I can certainly answer that question.
Think of encryption as being like a safe. You can put material into it and you can lock it, or you can open it and have the material accessible. When you talk about strong encryption, you are minimizing the ways in and out of that safe, as opposed to allowing for a different way of access or multiple different combinations. Every change that you make other than that one single way in or out weakens it by necessity.
The reason this is so important is that it's the same encryption standards that are guarding Gmail messages or instant messages that are going back and forth, that are taking care of government's messages, that are taking care of your bank integrity when you're online banking, that are taking care of personal information when you're on the Internet. For that reason, it's very difficult to design a system where.... If you undermine a particular type of encryption, if you undermine the encryption standards that are widely available, that are widely enforced, if you require them to have a back door into them, then that will necessarily weaken the encryption that everybody's using.