https://en.wikipedia.org/wiki/HTTP/2#Encryption Encryption[edit]
HTTP/2 is defined for both HTTP URIs (i.e. without encryption) and for HTTPS URIs (over TLS using ALPN extension[26] where TLS 1.2 or newer is required).[27]
Although the standard itself does not require usage of encryption,[28] most client implementations (Firefox,[29] Chrome, Safari, Opera, IE, Edge) have stated that they will only support HTTP/2 over TLS, which makes encryption de facto mandatory.[30]
浏览器只支持 TLS (也就是 https )的 HTTP/2,即使劫持了证书,你浏览器会红色警示你。但是恶意软件偷偷给你电脑安装私有证书,那么这就不安全了。