In its popular deployment on the internet, HTTPS provides authentication of the web site and associated web server that one is communicating with, which protects against Man-in-the-middle attacks. Additionally, it provides bidirectional encryption of communications between a client and server, which protects against eavesdropping and tampering with and/or forging the contents of the communication.[1] In practice, this provides a reasonable guarantee that one is communicating with precisely the web site that one intended to communicate with (as opposed to an impostor), as well as ensuring that the contents of communications between the user and site cannot be read or forged by any third party.
Because HTTPS piggybacks HTTP entirely on top of TLS, the entirety of the underlying HTTP protocol can be encrypted. This includes the request URL (which particular web page was requested), query parameters, headers, and cookies (which often contain identity information about the user). However, because host (web site) addresses and port numbers are necessarily part of the underlying TCP/IP protocols, HTTPS cannot protect their disclosure. In practice this means that even on a correctly configured web server eavesdroppers can still infer the IP address and port number of the web server (sometimes even the domain name e.g. www.example.org, but not the rest of the URL) that one is communicating with as well as the amount (data transferred) and duration (length of session) of the communication, though not the content of the communication.[citation needed]
Historically, HTTPS connections were primarily used for payment transactions on the World Wide Web, e-mail and for sensitive transactions in corporate information systems. In the late 2000s and early 2010s, HTTPS began to see widespread use for protecting page authenticity on all types of websites, securing accounts and keeping user communications, identity and web browsing private.
HTTPS is especially important over unencrypted networks such as WiFi as anyone on the same local network can do packet sniffing and discover sensitive information. Additionally, many free to use and even paid for WLAN networks do packet injection for serving their own ads on webpages or just for pranks, however this can be exploited maliciously e.g. by injecting malware and spying on users.[2] Another example where HTTPS is important is connections over Tor (anonymity network), as malicious Tor nodes can damage or alter the contents passing through them in an insecure fashion and inject malware into the connection. This is one reason why the Electronic Frontier Foundation and Torproject started the development of HTTPS Everywhere, which is included in the Tor Browser Bundle.
A site must be completely hosted over HTTPS, without having some of its contents loaded over HTTP, or the user will be vulnerable to some attacks and surveillance. E.g. Having scripts etc. loaded insecurely on a HTTPS page makes the user vulnerable to attacks. Also having only a certain page that contains sensitive information (such as a log-in page) of a website loaded over HTTPS, while having the rest of the website loaded over plain HTTP will expose the user to attacks. E.g. if the user first accesses the front page of the website with HTTP where he only after that clicks an HTTPS link to the log-in page, the session has already been compromised. On a site that has sensitive information somewhere on it, every time that site is accessed with HTTP instead of HTTPS, the user and the session will get exposed. Similarly, cookies on a site served through HTTPS have to have the secure attribute enabled.[3]
A common misconception is that HTTPS is performance heavy and cannot be deployed on existing equipment. This isn't true; deploying HTTPS requires no additional equipment or special hardware.[1][3] Deploying HTTPS also allows the use of SPDY, which is designed to reduce page load times and latency.
It is recommended to use HTTP Strict Transport Security with HTTPS to protect users from man-in-the-middle attacks.[3][4]
As of 2012-06-22 only 12.3% of the Internet's 186821 most popular web sites have a secure implementation of HTTPS. This leaves 87.7% (163776) open to some attacks.[5] This survey is powered by Qualys' SSL Server Test, in which anyone can audit the HTTPS implementation of a specified web server.
HTTPS should not be confused with the little-used Secure HTTP (S-HTTP) specified in RFC 2660.
Difference from HTTP
HTTPS URLs begin with "https://" and use port 443 by default, whereas HTTP URLs begin with "http://" and use port 80 by default.
HTTP is insecure and is subject to man-in-the-middle and eavesdropping attacks, which can let attackers gain access to website accounts and sensitive information. HTTPS is designed to withstand such attacks and is considered secure against such attacks (with the exception of older deprecated versions of SSL).
