| HTTP |
| Persistence · Compression · HTTPS |
| Request methods |
| OPTIONS · GET · HEAD · POST · PUT · DELETE · TRACE · CONNECT |
| Header fields |
| Cookie · ETag · Location · Referer |
| DNT · X-Forwarded-For |
| Status codes |
| 301 Moved permanently |
| 302 Found |
| 303 See Other |
| 403 Forbidden |
| 404 Not Found |
Hypertext Transfer Protocol Secure (HTTPS) is a combination of Hypertext Transfer Protocol (HTTP) with SSL/TLS protocol. It provides encrypted communication and secure identification of a network web server. HTTPS connections are often used for payment transactions on the World Wide Web and for sensitive transactions in corporate information systems.
HTTPS should not be confused with the little-used Secure HTTP (S-HTTP) specified in RFC 2660.
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HTTPS is a URI scheme which has identical syntax to the standard HTTP scheme, aside from its scheme token. However, HTTPS signals the browser to use an added encryption layer of SSL/TLS to protect the traffic. SSL is especially suited for HTTP since it can provide some protection even if only one side of the communication is authenticated. This is the case with HTTP transactions over the Internet, where typically only the server is authenticated (by the client examining the server's certificate).
The main idea of HTTPS is to create a secure channel over an insecure network. This ensures reasonable protection from eavesdroppers and man-in-the-middle attacks, provided that adequate cipher suites are used and that the server certificate is verified and trusted.
Web browsers know how to trust HTTPS websites based on certificate authorities that come pre-installed in their software. Certificate authorities (e.g. VeriSign/Microsoft/etc.) are in this way being trusted by web browser creators to provide valid certificates. Logically, it follows that a user should trust an HTTPS connection to a website if and only if all of the following are true:
Most browsers display a warning if they receive an invalid certificate. Older browsers, when connecting to a site with an invalid certificate, would present the user with a dialog box asking if they wanted to continue. Newer browsers display a warning across the entire window. Newer browsers also prominently display the site's security information in the address bar. Extended validation certificates turn the address bar green in newer browsers. Most browsers also display a warning to the user when visiting a site that contains a mixture of encrypted and unencrypted content.
The Electronic Frontier Foundation, opining that "[i]n an ideal world, every web request could be defaulted to HTTPS", has provided an add-on called "HTTPS Everywhere" for Mozilla Firefox that enables HTTPS by default for several frequently used websites.[1][2]
HTTPS URLs begin with "https://" and use port 443 by default, where HTTP URLs begin with "http://" and use port 80 by default.
HTTP is unsecured 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).
HTTP operates at the highest layer of the OSI Model, the Application layer; but the security protocol operates at a lower sublayer, encrypting an HTTP message prior to transmission and decrypting a message upon arrival. Strictly speaking, HTTPS is not a separate protocol, but refers to use of ordinary HTTP over an encrypted SSL/TLS connection.
Everything in the HTTPS message is encrypted, including the headers, and the request/response load. With the exception of the possible CCA cryptographic attack described in limitations section below, the attacker can only know the fact that a connection is taking place between the two parties, already known to him, the domain name and IP addresses.
To prepare a web server to accept HTTPS connections, the administrator must create a public key certificate for the web server. This certificate must be signed by a trusted certificate authority for the web browser to accept it without warning. The authority certifies that the certificate holder is the operator of the web server that presents it. Web browsers are generally distributed with a list of signing certificates of major certificate authorities so that they can verify certificates signed by them.
Authoritatively signed certificates may be free[3][4] or cost between US$13[5] and $1,500[6] per year.
Organizations may also run their own certificate authority, particularly if they are responsible for setting up browsers to access their own sites (for example, sites on a company intranet, or major universities). They can easily add copies of their own signing certificate to the trusted certificates distributed with the browser.
There also exists a peer-to-peer certificate authority, CACert.
The system can also be used for client authentication in order to limit access to a web server to authorized users. To do this, the site administrator typically creates a certificate for each user, a certificate that is loaded into his/her browser. Normally, that contains the name and e-mail address of the authorized user and is automatically checked by the server on each reconnect to verify the user's identity, potentially without even entering a password.
A certificate may be revoked before it expires, for example because the secrecy of the private key has been compromised. Newer versions of popular browsers such as Google Chrome, Firefox,[7] Opera,[8] and Internet Explorer on Windows Vista[9] implement the Online Certificate Status Protocol (OCSP) to verify that this is not the case. The browser sends the certificate's serial number to the certificate authority or its delegate via OCSP and the authority responds, telling the browser whether or not the certificate is still valid.[10]
SSL comes in two options, simple and mutual.
The mutual version is more secure, but requires the user to install a personal certificate in their browser in order to authenticate themselves.
Whatever strategy is used (simple or mutual), the level of protection strongly depends on the correctness of the implementation of the web browser and the server software and the actual cryptographic algorithms supported.
SSL does not prevent the entire site from being indexed using a web crawler, and in some cases the URI of the encrypted resource can be inferred by knowing only the intercepted request/response size.[11] This allows an attacker to have access to the plaintext (the publicly-available static content), and the encrypted text (the encrypted version of the static content), permitting a cryptographic attack.
Because SSL operates below HTTP and has no knowledge of higher-level protocols, SSL servers can only strictly present one certificate for a particular IP/port combination.[12] This means that, in most cases, it is not feasible to use name-based virtual hosting with HTTPS. A solution called Server Name Indication (SNI) exists, which sends the hostname to the server before encrypting the connection, although many older browsers do not support this extension. Support for SNI is available since Firefox 2, Opera 8, Safari 2.1, Google Chrome 6, and Internet Explorer 7 on Windows Vista.[13][14][15]
If parental controls are enabled on Mac OS X, HTTPS sites must be explicitly allowed using the Always Allow list.[16]
From an architectural point of view:
A sophisticated type of man-in-the-middle attack was presented at the Blackhat Conference 2009. This type of attack defeats the security provided by HTTPS by changing the https: link into an http: link, taking advantage of the fact that few Internet users actually type "https" into their browser interface: they get to a secure site by clicking on a link, and thus are fooled into thinking that they are using HTTPS when in fact they are using HTTP. The attacker then communicates in clear with the client.[17]
In May, 2010, a research paper[18] by researchers from Microsoft Research and Indiana University discovered that detailed sensitive user data can be inferred from side channels such as packet sizes. More specifically, the researchers found that an eavesdropper can infer the illnesses/medications/surgeries of the user, her family income and investment secrets, despite HTTPS protection in several high-profile, top-of-the-line web applications in healthcare, taxation, investment and web search. This finding points out a unique challenge on information leaks that HTTPS faces on the era of web 2.0.
Netscape Communications created HTTPS in 1994 for its Netscape Navigator web browser.[19] Originally, HTTPS was used with SSL protocol. As SSL evolved into Transport Layer Security (TLS), the current version of HTTPS was formally specified by RFC 2818 in May 2000.
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