What is https in information security?

Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It uses encryption for secure communication over a computer network, and is widely used on the Internet.[1][2] In HTTPS, the communication protocol is encrypted using Transport Layer Security (TLS) or, formerly, Secure Sockets Layer (SSL). The protocol is therefore also referred to as HTTP over TLS,[3] or HTTP over SSL.

The principal motivations for HTTPS are authentication of the accessed website and protection of the privacy and integrity of the exchanged data while it is in transit. It protects against man-in-the-middle attacks, and the bidirectional block cipher encryption of communications between a client and server protects the communications against eavesdropping and tampering.[4][5] The authentication aspect of HTTPS requires a trusted third party to sign server-side digital certificates. This was historically an expensive operation, which meant fully authenticated HTTPS connections were usually found only on secured payment transaction services and other secured corporate information systems on the World Wide Web. In 2016, a campaign by the Electronic Frontier Foundation with the support of web browser developers led to the protocol becoming more prevalent.[6] HTTPS is now used more often by web users than the original, non-secure HTTP, primarily to protect page authenticity on all types of websites, secure accounts, and keep user communications, identity, and web browsing private.

The Uniform Resource Identifier (URI) scheme HTTPS has identical usage syntax to the HTTP scheme. However, HTTPS signals the browser to use an added encryption layer of SSL/TLS to protect the traffic. SSL/TLS 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).

HTTPS creates 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.

Because HTTPS piggybacks HTTP entirely on top of TLS, the entirety of the underlying HTTP protocol can be encrypted. This includes the request's URL, query parameters, headers, and cookies (which often contain identifying information about the user). However, because website 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 infer the IP address and port number of the web server, and sometimes even the domain name (e.g. www.example.org, but not the rest of the URL) that a user is communicating with, along with the amount of data transferred and the duration of the communication, though not the content of the communication.[4]

Web browsers know how to trust HTTPS websites based on certificate authorities that come pre-installed in their software. Certificate authorities are in this way being trusted by web browser creators to provide valid certificates. Therefore, a user should trust an HTTPS connection to a website if and only if all of the following are true:

HTTPS is especially important over insecure networks and networks that may be subject to tampering. Insecure networks, such as public Wi-Fi access points, allow anyone on the same local network to packet-sniff and discover sensitive information not protected by HTTPS. Additionally, some free-to-use and paid WLAN networks have been observed tampering with webpages by engaging in packet injection in order to serve their own ads on other websites. This practice can be exploited maliciously in many ways, such as by injecting malware onto webpages and stealing users' private information.[7]

HTTPS is also important for connections over the Tor network, as malicious Tor nodes could otherwise 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 the Tor Project started the development of HTTPS Everywhere,[4] which is included in Tor Browser.[8]

As more information is revealed about global mass surveillance and criminals stealing personal information, the use of HTTPS security on all websites is becoming increasingly important regardless of the type of Internet connection being used.[9][10] Even though metadata about individual pages that a user visits might not be considered sensitive, when aggregated it can reveal a lot about the user and compromise the user's privacy.[11][12][13]

Deploying HTTPS also allows the use of HTTP/2 and HTTP/3 (and their predecessors SPDY and QUIC), which are new HTTP versions designed to reduce page load times, size, and latency.

It is recommended to use HTTP Strict Transport Security (HSTS) with HTTPS to protect users from man-in-the-middle attacks, especially SSL stripping.[13][14]

HTTPS should not be confused with the seldom-used Secure HTTP (S-HTTP) specified in RFC 2660.

As of April 2018[update], 33.2% of Alexa top 1,000,000 websites use HTTPS as default,[15] 57.1% of the Internet's 137,971 most popular websites have a secure implementation of HTTPS,[16] and 70% of page loads (measured by Firefox Telemetry) use HTTPS.[17] However despite TLS 1.3’s release in 2018, adoption has been slow, with many still remain on the older TLS 1.2 protocol.[18]

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 whether 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 show the legal entity on the certificate information. Most browsers also display a warning to the user when visiting a site that contains a mixture of encrypted and unencrypted content. Additionally, many web filters return a security warning when visiting prohibited websites.

The Electronic Frontier Foundation, opining that "In an ideal world, every web request could be defaulted to HTTPS", has provided an add-on called HTTPS Everywhere for Mozilla Firefox, Google Chrome, Chromium, and Android, which enables HTTPS by default for hundreds of frequently used websites.[19][20]

Forcing a web browser to load only HTTPS content has been supported in Firefox starting in version 83.[21] Starting in version 94, Google Chrome is able to "always use secure connections" if toggled in the browser's settings.[22][23]

The security of HTTPS is that of the underlying TLS, which typically uses long-term public and private keys to generate a short-term session key, which is then used to encrypt the data flow between the client and the server. X.509 certificates are used to authenticate the server (and sometimes the client as well). As a consequence, certificate authorities and public key certificates are necessary to verify the relation between the certificate and its owner, as well as to generate, sign, and administer the validity of certificates. While this can be more beneficial than verifying the identities via a web of trust, the 2013 mass surveillance disclosures drew attention to certificate authorities as a potential weak point allowing man-in-the-middle attacks.[24][25] An important property in this context is forward secrecy, which ensures that encrypted communications recorded in the past cannot be retrieved and decrypted should long-term secret keys or passwords be compromised in the future. Not all web servers provide forward secrecy.[26][needs update]

For HTTPS to be effective, a site must be completely hosted over HTTPS. If some of the site's contents are loaded over HTTP (scripts or images, for example), or if only a certain page that contains sensitive information, such as a log-in page, is loaded over HTTPS while the rest of the site is loaded over plain HTTP, the user will be vulnerable to attacks and surveillance. Additionally, cookies on a site served through HTTPS must have the secure attribute enabled. On a site that has sensitive information on it, the user and the session will get exposed every time that site is accessed with HTTP instead of HTTPS.[13]

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 not encrypted and thus is vulnerable to man-in-the-middle and eavesdropping attacks, which can let attackers gain access to website accounts and sensitive information, and modify webpages to inject malware or advertisements. HTTPS is designed to withstand such attacks and is considered secure against them (with the exception of HTTPS implementations that use deprecated versions of SSL).

HTTP operates at the highest layer of the TCP/IP model—the application layer; as does the TLS security protocol (operating as a lower sublayer of the same layer), which encrypts an HTTP message prior to transmission and decrypts a message upon arrival. Strictly speaking, HTTPS is not a separate protocol, but refers to the use of ordinary HTTP over an encrypted SSL/TLS connection.

HTTPS encrypts all message contents, including the HTTP headers and the request/response data. With the exception of the possible CCA cryptographic attack described in the limitations section below, an attacker should at most be able to discover that a connection is taking place between two parties, along with their domain names 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.

A number of commercial certificate authorities exist, offering paid-for SSL/TLS certificates of a number of types, including Extended Validation Certificates.

Let's Encrypt, launched in April 2016,[27] provides free and automated service that delivers basic SSL/TLS certificates to websites.[28] According to the Electronic Frontier Foundation, Let's Encrypt will make switching from HTTP to HTTPS "as easy as issuing one command, or clicking one button."[29] The majority of web hosts and cloud providers now leverage Let's Encrypt, providing free certificates to their customers.

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, which the user loads into their browser. Normally, the certificate contains the name and e-mail address of the authorized user and is automatically checked by the server on each connection to verify the user's identity, potentially without even requiring a password.

An important property in this context is perfect forward secrecy (PFS). Possessing one of the long-term asymmetric secret keys used to establish an HTTPS session should not make it easier to derive the short-term session key to then decrypt the conversation, even at a later time. Diffie–Hellman key exchange (DHE) and Elliptic curve Diffie–Hellman key exchange (ECDHE) are in 2013 the only schemes known to have that property. In 2013, only 30% of Firefox, Opera, and Chromium Browser sessions used it, and nearly 0% of Apple's Safari and Microsoft Internet Explorer sessions.[26] TLS 1.3, published in August 2018, dropped support for ciphers without forward secrecy. As of February 2020[update], 96.6% of web servers surveyed support some form of forward secrecy, and 52.1% will use forward secrecy with most browsers.[30]

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 Firefox,[31] Opera,[32] and Internet Explorer on Windows Vista[33] 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 (Online Certificate Status Protocol) and the authority responds, telling the browser whether the certificate is still valid or not.[34] The CA may also issue a CRL to tell people that these certificates are revoked. CRLs are no longer required by the CA/Browser forum,[35] nevertheless, they are still widely used by the CAs. Most revocation statuses on the Internet disappear soon after the expiration of the certificates.[36]

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) encryption can be configured in two modes: simple and mutual. In simple mode, authentication is only performed by the server. The mutual version requires the user to install a personal client certificate in the web browser for user authentication.[37] In either case, the level of protection depends on the correctness of the implementation of the software and the cryptographic algorithms in use.

SSL/TLS does not prevent the indexing of the site by a web crawler, and in some cases the URI of the encrypted resource can be inferred by knowing only the intercepted request/response size.[38] 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 TLS operates at a protocol level below that of HTTP and has no knowledge of the higher-level protocols, TLS servers can only strictly present one certificate for a particular address and port combination.[39] In the past, this meant that it was 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 old browsers do not support this extension. Support for SNI is available since Firefox 2, Opera 8, Apple Safari 2.1, Google Chrome 6, and Internet Explorer 7 on Windows Vista.[40][41][42]

From an architectural point of view:

A sophisticated type of man-in-the-middle attack called SSL stripping was presented at the 2009 Blackhat Conference. 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.[43] This prompted the development of a countermeasure in HTTP called HTTP Strict Transport Security.

HTTPS has been shown to be vulnerable to a range of traffic analysis attacks. Traffic analysis attacks are a type of side-channel attack that relies on variations in the timing and size of traffic in order to infer properties about the encrypted traffic itself. Traffic analysis is possible because SSL/TLS encryption changes the contents of traffic, but has minimal impact on the size and timing of traffic. In May 2010, a research paper by researchers from Microsoft Research and Indiana University discovered that detailed sensitive user data can be inferred from side channels such as packet sizes. The researchers found that, despite HTTPS protection in several high-profile, top-of-the-line web applications in healthcare, taxation, investment, and web search, an eavesdropper could infer the illnesses/medications/surgeries of the user, his/her family income, and investment secrets.[44] Although this work demonstrated the vulnerability of HTTPS to traffic analysis, the approach presented by the authors required manual analysis and focused specifically on web applications protected by HTTPS.

The fact that most modern websites, including Google, Yahoo!, and Amazon, use HTTPS causes problems for many users trying to access public Wi-Fi hot spots, because a Wi-Fi hot spot login page fails to load if the user tries to open an HTTPS resource.[45] Several websites, such as neverssl.com, guarantee that they will always remain accessible by HTTP.[46]

Netscape Communications created HTTPS in 1994 for its Netscape Navigator web browser.[47] Originally, HTTPS was used with the SSL protocol. As SSL evolved into Transport Layer Security (TLS), HTTPS was formally specified by RFC 2818 in May 2000. Google announced in February 2018 that its Chrome browser would mark HTTP sites as "Not Secure" after July 2018.[48] This move was to encourage website owners to implement HTTPS, as an effort to make the World Wide Web more secure.

This encryption renders data undecipherable until a site owner unlocks it, allowing users to share sensitive data, such as passwords and other personal information, safely and securely over the Internet or a network.

HTTPS can only initiate an encrypted and secure connection after establishing trust between the browser and server. The importance of this trust is highlighted by the subsequent introduction of HTTP Strict Transport Security (HSTS), a web security policy mechanism that renders websites accessible only via secure connections.

HTTPS and HTTP are the same protocol. The main difference is that the HTTPS protocol has an added layer of encryption (SSL/TLS). HTTP sites change to HTTPS by gaining an SSL certificate (sometimes called a security or digital certificate). An SSL certificate is a small data file that protects the transfer of sensitive data between the web browser and the web server.

The SSL certificate encrypts this data by making it unreadable during the transmission process. It contains a public key that allows users to send sensitive information from their web browser securely. The domain owner has a private key that decrypts this information once it reaches the server. This public-private key pairing ensures a secure connection.

For a domain to become HTTPS-enabled, it must be issued with an SSL certificate from a trusted Certificate Authority (CA). When a web browser attempts to connect with a server through HTTPS, it checks that the SSL certificate matches the domain name the user is trying to enter through a process called an SSL/TLS handshake.

The certificate contains a digital signature from the CA to verify that the certificate was issued to the specified domain name. Once the web browser verifies the certificate’s signature to establish trust with the server, the connection becomes secure. All trusted CAs are automatically recognized by browsers.

However, HTTP connections are not secure, especially when made over public Wi-Fi networks. Anyone can easily intercept communications on the network using freely accessible software. As HTTP does not use SSL certificates, any information the web browser transmits to the web server is available in unencrypted plain text. HTTP also cannot verify a domain owner's authenticity as it does not have a validation process.

Learn more about the difference between HTTP vs HTTPS here.

HTTPS is now the preferred protocol for all activity on the Web, as it is the safest way for users to protect sensitive information.

HTTPS is not just crucial for websites that request user information. Aside from information sent directly from users, attackers can also track behavioral and identification data from unsecured connections.

HTTP has benefits to site owners other than data security, including improved web functionality and user experience.

HTTPS establishes trust from website users, allowing them to double-check the domain name against the SSL Certificate. As the protocol encrypts all client-server communications through SSL/TLS authentication, attackers cannot intercept data, meaning users can safely enter their personal information.

Gaining user trust is especially important for online businesses, such as e-commerce stores. Potential customers need assurance that their payment details will not be compromised. Website owners without HTTPS are not only risking their customers' privacy but also their own reputations. Attackers can easily access customer information through unsecured connections. Such a breach could deter users from future transactions with the business due to lost trust.

As HTTPS widely stands as the gold standard protocol, web browsers have been prompt to take note. For example, Google Chrome flags HTTP websites, and Mozilla Firefox now offers "HTTPS-only mode". Google's search engine algorithm also penalizes HTTP websites in its results in favor of HTTPS pages. Site owners can therefore improve their SEO by switching to HTTPS.

The release of HTTP/2 (a revision of the protocol) in 2015 saw browsers further prioritize HTTPS over HTTP. HTTP/2 allows for faster web browsing and improved user experience through a range of new features. Most browsers now only allow the use of HTTP/2 on web pages that use HTTPS. This update forces HTTP site owners to transition if they want to take advantage of these features.

With most browsers now promoting HTTPS connections, it is simple to distinguish between secure and unsecured websites. The easiest way to identify if a website uses HTTP or HTTPS is to check the browser's address bar. HTTP sites use http:// while HTTPS sites use https://.

You should also see a padlock icon to the left of the address bar on HTTPS websites, indicating that the website has a security certificate. Click on the padlock to view more certificate information, such as a confirmation message, the certificate issuer, and its expiration date.

Most major browsers, including Google Chrome, will alert users upon entering an HTTP page with a warning screen or pop-up message. You can also check if a website is secure by using anti-virus software as website security checks are often an included feature.

It is essential to secure your website using HTTPS if you ask for sensitive information from users. All reputable organizations understand the importance of website security; you will need to certify your website before linking it with third-party services.

For example, PayPal and other online payment platforms will ask you for a security certificate to use their services. Securing your website also improves credibility among users, as they can rest assured that their personal details will remain private.

To enable HTTPS on your website, you must obtain a security certificate from a Certificate Authority (CA). There are six different certificate types available for you to buy. Each option varies depending on the level of validation you need and the number of domains you have:

Once you purchase your chosen certificate from a CA, install it on your server to enable HTTPS. Your connection is now secure.

Below are some frequently asked questions and answers about HTTPS.

For an in-depth introduction (no technical background required), check out the DigitalGov University presentation, “An Introduction to HTTPS”, to learn what HTTPS is and how it protects web services and users.

When properly configured, an HTTPS connection guarantees three things:

A plain HTTP connection can be easily monitored, modified, and impersonated.

HTTPS encrypts nearly all information sent between a client and a web service.

For example, an unencrypted HTTP request reveals not just the body of the request, but the full URL, query string, and various HTTP headers about the client and request:

An encrypted HTTPS request protects most things:

This is the same for all HTTP methods (GET, POST, PUT, etc.). The URL path and query string parameters are encrypted, as are POST bodies.

While HTTPS encrypts the entire HTTP request and response, the DNS resolution and connection setup can reveal other information, such as the full domain or subdomain and the originating IP address, as shown above.

Additionally, attackers can still analyze encrypted HTTPS traffic for “side channel” information. This can include the time spent on site, or the relative size of user input.

HTTP/2 (finalized in 2015) is a backwards-compatible update to HTTP/1.1 (finalized in 1999) that is optimized for the modern web.

HTTP/2 includes many features that can drastically speed up website performance, and emerged from the advancements Google demonstrated with SPDY in 2009.

While HTTP/2 does not require the use of encryption in its formal spec, every major browser that has implemented HTTP/2 has only implemented support for encrypted connections, and no major browser is working on support for HTTP/2 over unencrypted connections.

This means that in practice, the major performance benefits of HTTP/2 first require the use of HTTPS.

For more information:

In general, migrating to HTTPS improves a website’s own SEO and analytics.

To make the migration as smooth as possible, and avoid taking a SEO hit:

By default, when a user is on an HTTPS website and clicks a link to an HTTP website, browsers will not send a Referer header to the HTTP website. This is defined in the HTTP 1.1 specification, and is designed to avoid exposing HTTPS URLs that would otherwise have remained protected by the guarantees of HTTPS.

However, this means that if a website migrates to HTTPS, any HTTP sites it links to will stop seeing referrer data from the HTTPS website. This can be a disincentive to migrate to HTTPS, as it deprives linked HTTP sites of analytics data, and means the HTTPS website won’t get “credit” for referring traffic to linked websites.

Website owners who wish to continue sending outbound referrer information to linked HTTP sites can use Referrer Policy to override browser default behavior, while retaining the privacy of HTTPS URLs.

To do this, websites should use the origin-when-cross-origin policy. This will allow supporting browsers to send only the origin as the Referer header. This limited referral information applies even if both sites use HTTPS.

For example, if a user is on https://agency.gov/help/aids.html and clicks a link to https://moreinformation.com, then if origin-when-cross-origin is set, the browser will make an HTTP request to https://moreinformation.com with a Referer header of https://agency.gov.

The simplest way to set this policy is by including a tag in the body of the HTTPS website:

The Referrer-Policy HTTP header may also be used as an alternate delivery mechanism, but this is not widely supported in web browsers (as of late 2016).

Websites should not use the unsafe-url policy, as this will cause HTTPS URLs to be exposed on the wire over an HTTP connection, which defeats one of the important privacy and security guarantees of HTTPS.

Attacks on HTTPS connections generally fall into 3 categories:

These are all possible, but for most attackers they are very difficult and require significant expense. Importantly, they are all targeted attacks, and are not feasible to execute against any user connecting to any website.

By contrast, plain HTTP connections can be easily intercepted and modified by anyone involved in the network connection, and so attacks can be carried out at large scale and at low cost.

This is primarily to support Server Name Indication (SNI), a TLS extension that allows multiple hostnames to be served over HTTPS from one IP address.

The SNI extension was introduced in 2003 to allow HTTPS deployment to scale more easily and cheaply, but it does mean that the hostname is sent by browsers to servers “in the clear” so that the receiving IP address knows which certificate to present to the client.

When a domain or a subdomain itself reveals sensitive information (e.g. ‘contraception.foo.gov’ or ‘suicide-help.foo.gov’), this can reveal that information to passive eavesdroppers.

From a network privacy perspective, DNS also “leaks” hostnames in the clear across the network today (even when DNSSEC is used). There are ongoing efforts in the network standards community to encrypt both the SNI hostname and DNS lookups, but as of late 2015, nothing has been deployed to support these goals.

Most clients support SNI today, and site owners are encouraged to evaluate the feasibility of requiring SNI support, to save money and resources. However, whether SNI support is required to access a specific website or not, a website’s owner should consider their hostnames to be unencrypted over HTTPS, and account for this when provisioning domains and subdomains.

DNSSEC attempts to guarantee that domain names are resolved to correct IP addresses.

However, DNS resolution is just one aspect of securely communicating on the internet. DNSSEC does not fully secure a domain:

HTTPS guarantees the confidentiality and integrity of communication between client and server, and web browsers have rigorous and evolving HTTPS enforcement policies.

In practice, HTTPS can protect communication with a domain even in the absence of DNSSEC support.

A valid HTTPS certificate shows that the server has demonstrated ownership over the domain to a trusted certificate authority at the time of certificate issuance.

To ensure that an attacker cannot use DNS spoofing to direct the user to a plain http:// connection where traffic can be intercepted, websites can use HTTP Strict Transport Security (HSTS) to instruct browsers to require an HTTPS connection for their domain at all times.

Hypertext Transfer Protocol Secure (https) is a combination of the Hypertext Transfer Protocol (HTTP) with the Secure Socket Layer (SSL)/Transport Layer Security (TLS) protocol. TLS is an authentication and security protocol widely implemented in browsers and Web servers.