Secure website certificate

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A secure website certificate helps Firefox determine whether the site you are visiting is actually the site that it claims to be. This article explains how that works.

Certificate hierarchy

When you visit a website whose web address starts with https, your communication with the site is encrypted to help ensure your privacy. Before starting the encrypted communication, the website will present Firefox with a certificate to identify itself.

An https website is only secure to the extent that the website is operated by someone in contact with the person who registered the domain name, and the communication between you and the website is encrypted to prevent eavesdropping. No other surety is implied.

When you visit a secure website, Firefox will validate the website’s certificate by checking that the certificate that signed it is valid, and checking that the certificate that signed the parent certificate is valid and so forth up to a root certificate that is known to be valid. This chain of certificates is called the certificate hierarchy.

Certificate content

Secure website certificates contain the following information.

Serial Number: Uniquely identifies the certificate.

Subject: Identifies the certificate owner, such as the name of the organization owning the certificate.

Issuer: Identifies the entity that issued the certificate.

Subject Alt Name Extension: List of website addresses that the certificate can be used to identify.

Signature: Data that verifies that the certificate came from the Issuer.

Signature Algorithm: Algorithm used to create the Signature.

Valid-From: The date the certificate is first valid.

Valid-To: The expiration date.

Key-Usage and Extended Key Usage: Specifies how the certificate may be used, such as for confirming ownership of a website (Web Server Authentication).

Public Key: The public part of the data that comprises the public/private key pair. The public and private keys are mathematically linked, so the data encrypted with the public key can only be decrypted with the corresponding private key.

Public Key Algorithm: Algorithm used to create the Public Key.

Fingerprint: An abbreviated form of the Public Key.

Fingerprint Algorithm: Algorithm used to create the Fingerprint.

View a certificate

You can view certificate details from either the Firefox Page Info window or from your Firefox settings.

From the Firefox Page Info window

You can quickly view the certificate details for the website that you are currently viewing, from the Firefox Page Info window.

When you have browsed to a website whose web address starts with https, there will be a lock icon at the beginning of the address bar. Do the following to view a certificate:

  1. Click the Site Info Site Info button icon in the address bar.
  2. Click the right arrow in the Control Center drop-down panel.
  3. In the next panel, which will show who verified the certificate, click the More Information button.
    Fx60SecureSite-MoreInfo
  4. From the Security tab in the Page Info window that opens, click the View Certificate button.
    Fx60PageInfo-ViewCertificate

When you have browsed to a website whose web address starts with https, there will be a lock icon at the beginning of the address bar. Do the following to view a certificate:

  1. Click the lock Fx70GreyPadlock icon in the address bar.
  2. Click the right arrow in the Site Information drop-down panel.
  3. In the next panel, which will show who verified the certificate, click the More Information button.
    fx71 - View Certificate
  4. From the Security tab in the Page Info window that opens, click the View Certificate button.
    Fx70PageInfo-ViewCertificate

The Certificate Viewer tab that opens will display basic information about the certificate, such as issuer, period of validity and fingerprints. The Details tab will show the certificate hierarchy, certificate fields for the selected certificate on the hierarchy, and field value details for the selected field.

Problematic certificates

When you browse to a website whose web address starts with https and there is a problem with the secure website certificate, you will see an error page. Some common certificate errors are described in the What do the security warning codes mean? article.

To view the problematic certificate, follow these steps:

  1. On the Your connection is not secure warning page, click Advanced.
  2. Click the Add Exception… button.
    Add Cert Exception 44
  3. When the Add Security Exception dialog appears, click the View… button.
    The Certificate Viewer dialog displays.
  1. On the Warning: Potential Security Risk Ahead page, click Advanced. (On other error pages, click More Information.)
    Technical details about the error display.
  2. Beneath the Error code, click View Certificate.
    The Certificate Viewer dialog displays.
    Fx66ViewCertificate

Reporting certificate errors

Certificate error pages include an option to report the error to Mozilla. Sharing the address and site identification (the secure website certificate) for the site that was untrusted will help Mozilla identify and block malicious sites to keep you better protected.