S-HTTP and HTTPS are both protocols designed for secure communication over computer networks, but they differ fundamentally in their security approaches.

Secure Hypertext Transfer Protocol (S-HTTP) focuses on securing individual messages by encrypting the data contained within them. This means that each message sent using S-HTTP is protected independently, applying security measures on a per-message basis. This can be advantageous in scenarios where only specific portions of the communication require security.

In contrast, HTTPS (Hypertext Transfer Protocol Secure) establishes a secure connection between the client and the server, ensuring that all data transmitted over this connection is encrypted. This is accomplished through the use of Transport Layer Security (TLS) or its predecessor, Secure Sockets Layer (SSL). Once a secure connection is established, every piece of data exchanged between the client and the server is encrypted, regardless of its content. This method offers a higher level of security, as it safeguards all communication rather than just selected messages.

Another significant distinction between these two protocols lies in their usage. HTTPS is extensively employed on the internet for secure communications, particularly for transactions involving sensitive information, such as credit card details. It is widely supported by all modern web browsers. Conversely, S-HTTP is less commonly adopted, primarily because it requires more computational resources to secure individual messages, making it less efficient than HTTPS for handling large volumes of data.

In summary, while both S-HTTP and HTTPS are intended for secure communication, they differ in their security methodologies. S-HTTP secures messages individually, making it suitable for scenarios where only certain parts of the communication need protection. In contrast, HTTPS encrypts all data transmitted over a secure connection, offering a broader level of security for all communications between the client and server.