Public-Key-Pins

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Note: The Public Key Pinning mechanism was deprecated in favor of Certificate Transparency and Expect-CT header.

The HTTP Public-Key-Pins response header used to associate a specific cryptographic public key with a certain web server to decrease the risk of MITM attacks with forged certificates. However, it has been removed from modern browsers and is no longer supported. Use Certificate Transparency and Expect-CT header instead.

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

Header type Response header
Forbidden header name no

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

Warning: HPKP has the potential to lock out users for a long time if used incorrectly! The use of backup certificates and/or pinning the CA certificate is recommended. 

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

Specification
Public Key Pinning Extension for HTTP
# section-2.1

Browser compatibility

BCD tables only load in the browser

See also