Expect CT, or Certificate Transparency (CT), is a security mechanism used in the HTTPS protocol. Its main task is to increase transparency and trust in the process of issuing and managing SSL/TLS certificates. This mechanism was designed in response to incidents where certificate-issuing authorities improperly or erroneously issued certificates.

How Expect CT Works Expect CT requires servers to send the Expect-CT HTTP header. This header informs browsers that the server uses and expects all issued certificates to be logged in publicly accessible CT logs. If the browser detects that the server's certificate is not recorded in the CT log, it can alert the user or even block access to the website.

Setting Up Expect CT Configuring Expect CT involves adding the Expect-CT HTTP header with several parameters:

• enforce: When this parameter is set to 1, the browser actively prevents access to the page if the certificate is not in the CT log.
• max-age: This parameter specifies how long the browser should respect the Expect CT policy.
• report-uri: The URL where reports of Expect CT policy violations should be sent.

Example of Setting the Expect CT HTTP Header

Expect-CT: max-age=86400, enforce, report-uri="https://example.com/report"

In this example, the policy is set to be active for one day (86400 seconds), with mandatory enforcement and reporting to the specified URL.

The Importance of Expect CT for Security

Expect CT significantly contributes to HTTPS security by increasing the transparency of the certificate issuance process. By logging all certificates in public logs, it is easy to identify and address cases of certification authority abuse. This mechanism also allows webmasters to actively monitor and respond to potential security issues related to their SSL/TLS certificates.

Implementing Expect CT is an important step for securing web communication. It allows better control over the issuance and use of certificates and increases overall trust in the HTTPS ecosystem. Given the growing number of cyber attacks, this mechanism is essential for any website that wants to maintain a high level of security and trust with its users.