Public-Key-Pins

The HTTP Public-Key-Pins response header associates a specific cryptographic public key with a certain web server to decrease the risk of MITM attacks with forged certificates. If one or several keys are pinned and none of them are used by the server, the browser will not accept the response as legitimate, and will not display it.

For more information, see the HTTP Public Key Pinning article.

Syntax

Public-Key-Pins: pin-sha256="<pin-value>"; 
                 max-age=<expire-time>; 
                 includeSubDomains; 
                 report-uri="<uri>"

Directives

pin-sha256="<pin-value>"

The quoted string is the Base64 encoded Subject Public Key Information (SPKI) fingerprint. It is possible to specify multiple pins for different public keys. Some browsers might allow other hashing algorithms than SHA-256 in the future.

max-age=<expire-time>

The time, in seconds, that the browser should remember that this site is only to be accessed using one of the defined keys.

includeSubDomains Optional

If this optional parameter is specified, this rule applies to all of the site's subdomains as well.

report-uri="<uri>" Optional

If this optional parameter is specified, pin validation failures are reported to the given URL.

Example

Public-Key-Pins: 
  pin-sha256="cUPcTAZWKaASuYWhhneDttWpY3oBAkE3h2+soZS7sWs="; 
  pin-sha256="M8HztCzM3elUxkcjR2S5P4hhyBNf6lHkmjAHKhpGPWE="; 
  max-age=5184000; includeSubDomains; 
  report-uri="https://www.example.org/hpkp-report"

In this example, pin-sha256="cUPcTAZWKaASuYWhhneDttWpY3oBAkE3h2+soZS7sWs=" pins the server's public key used in production. The second pin declaration pin-sha256="M8HztCzM3elUxkcjR2S5P4hhyBNf6lHkmjAHKhpGPWE=" also pins the backup key. max-age=5184000 tells the client to store this information for two months, which is a reasonable time limit according to the IETF RFC. This key pinning is also valid for all subdomains, which is told by the includeSubDomains declaration. Finally, report-uri="https://www.example.org/hpkp-report" explains where to report pin validation failures.

Specifications

Browser compatibility

See also

• Public-Key-Pins-Report-Only