You are referring to a 'firewall' -- this is a standard computer term taken from actual physical walls in buildings that are specifically constructed to protect other parts of the building should a fire break out. In computers, it is software or hardware that protects your computer from specific types of 'hackers' and malware.
As you know, the Chinese government has put its own firewall on the internet in China. In English, it has been humorously called 'The Great Chinese Firewall', which a reference to the real Great Wall of China. If your friend knows what a firewall is, then you can say that you are using special software that allows you to 'get over the Great Chinese Firewall' -- as many Chinese netizens do. You could also say that you can 'get through the Chinese government firewall'. Again, the person you are talking to must have an understanding of what a firewall is on a computer system.