安全超文本传输协议（英语：Secure Hypertext Transfer Protocol，缩写：S-HTTP）是一个HTTPS URI scheme的可选方案，也是为互联网的HTTP加密通讯而设计。S-HTTP定义于RFC 2660。

浏览器通常利用HTTP协议与服务器通讯，收发信息未被加密。安全敏感的事务，如电子商务或在线财务账户等信息，浏览器与服务器必须加密。当时HTTPS: URI scheme与S-HTTP二者在1990年代中期均已被定义来满足这一需求。不过占据浏览器市场的网景及微软公司支持HTTPS远胜S-HTTP，使得HTTPS成为安全万维网通讯的事实标准。

Secure Hypertext Transfer Protocol (S-HTTP) is an obsolete alternative to the HTTPS protocol for encrypting web communications carried over HTTP. It was developed by Eric Rescorla and Allan M. Schiffman, and published in 1999 as RFC 2660.

Web browsers typically use HTTP to communicate with web servers, sending and receiving information without encrypting it. For sensitive transactions, such as Internet e-commerce or online access to financial accounts, the browser and server must encrypt this information. HTTPS and S-HTTP were both defined in the mid-1990s to address this need. S-HTTP was used by Spyglass's web server, while Netscape and Microsoft supported HTTPS rather than S-HTTP, leading to HTTPS becoming the de facto standard mechanism for securing web communications.