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Certificate Transparency Log Policy

To improve trust and security when communicating with secure services, Chromium-derived products, such as Google Chrome, will require certificates presented by servers to be publicly audited using Certificate Transparency. As specified by RFC 6962, Certificate Transparency includes a multi-party protocol for providing cryptographically-verifiable proofs to audit the issuance and security practices of Certificate Authorities.

To support such auditing, Chromium-derived products include a list of Logs that are recognized to be operating in the public interest. This Certificate Transparency Log Policy ("Policy") sets forth how a Certificate Transparency Log Operator may have its Log recognized within Chromium, ongoing expectations of Log Operators, and how Chromium developers may preserve the integrity of recognized Logs. This policy may be updated by Google from time to time.

When a Log is recognized, Signed Certificate Timestamps (SCT) issued by that Log will be granted special treatment within the Chromium user interfaces, such as by indicating that the associated certificate certified by the SCT has been publicly noted by the Log Operator.


To apply for a Log to be included within Chromium, the Log Operator must file a new bug on the Chromium Issue Tracker, and provide:

  • Contact Information for the Log Operator, including:
    • An email or e-mail alias that is continuously monitored by the Log Operator
    • A phone number
    • A list of person(s) authorized to represent the Log Operator
  • A public HTTP endpoint that responds to all Log Client Messages indicated in RFC 6962, Section 4
  • The Log's public key, attached as a binary file containing the DER encoding of the SubjectPublicKeyInfo ASN.1 structure
  • A description of the Log, including applicable policies or requirements for logging certificates
  • The Maximum Merge Delay (MMD) of the Log
  • All of the Accepted Root Certificates of the Log
  • Whether the Log will reject certificate logging requests based on any of the Permissible Logging Rejection Criteria and if so, which criteria will be used as a basis for rejection by this Log.

After acceptance, Google will monitor the Log, including random compliance testing, prior to its inclusion within Chromium. Such compliance testing will include, but is not limited to, verifying the Log’s conformance to RFC 6962, and confirming the Log's uptime meets the requirements of this Policy and confirming the Log is append-only and consistent from every point of view.

To enable monitoring, log operators are asked to include Google's "Merge Delay Monitor Root" in the set of Accepted Root Certificates of their logs.

Ongoing Requirements of Included Logs

To remain included within Chromium-derived projects, Log Operators must operate the Log in accordance with this Policy. Log Operators must:

  • Have no outage that exceeds an MMD of more than 24 hours. Outages include, but are not limited to: network level outages, expiration of the Log’s SSL certificate, a failure to accept new Certificates to be logged (with the exception of the Permissible Logging Rejection Criteria defined below), HTTP response status codes other than 200, or responses that include data that does not conform to RFC 6962.
  • Conform to RFC 6962, including the implementation of all API endpoints defined within Section 4 of RFC 6962
  • Not impose conditions on retrieving or sharing data from the Log
  • Have 99% uptime, with no outage lasting longer than the MMD (as measured by Google)
  • Not present two or more conflicting views of the Merkle Tree at different times and/or to different parties.
  • Incorporate a certificate for which an SCT has been issued by the Log within the MMD.
  • If requested, accept certificates issued by a test CA run by Google to enable Google to monitor the log’s compliance to these policies.
  • Be operated in good faith, including, but not limited to each Log Operator:
    • Verifiably logging all certificates within the Log for which SCTs have been issued within the MMD
    • Maintaining the append-only property of the of the Log by providing consistent views of the Merkle Tree at all times and to all parties.
  • Notify the Chromium developers of any and all changes to information gathered during the Log Inclusion by detailing such changes in an update to the bug on the Chromium Issue Tracker in which they requested Log Inclusion.

Google will notify Log Operators, via announcements to the Chromium CT Policy Group, of changes to these requirements. Log Operators that fail to meet these requirements will be in violation of the Log Inclusion Policy, which may result in removal of the Log from the Chromium projects.

Permissible Logging Rejection Criteria

Under certain circumstances, it is permissible for a Log to reject logging requests for certain classes of certificates. A logging rejection means that the Log will not incorporate a given certificate entry into the Merkle Tree even if the certificate chains to an Accepted Root Certificate. In accordance with this policy, rejected logging requests must not be issued an SCT by the Log.

If specified within the Log's Chromium Application, a Log may reject requests to log certificates that chain up to an Accepted Root Certificate based on one or more of the following bases:

  • Revocation Status: If the Log determines that a certificate has been revoked by the issuing CA, it may reject the logging request. If the Log is unable to determine revocation status, it must accept the logging request and incorporate the entry into the Merkle Tree within the Log's MMD.
  • Certificate Expired: If a logging request includes a certificate whose notAfter timestamp represents a point in time before the logging request is made, the Log may refuse to log the certificate entry.
  • Certificate Lifetime: In order to control the growth of a Log’s size, a Log Operator may specify a certificate expiry range for that Log, which must be included in the Log’s Chromium Application in the form of two dates: [rangeBegin, rangeEnd). The certificate expiry range allows a Log to reject logging requests for certificates whose notAfter timestamp falls outside of this range, thus partitioning the set of publicly-trusted certificates that the Log will accept. In the spirit of operating Logs in the public interest, Log Operators who take advantage of this limitation are strongly encouraged to operate multiple Logs with staggered certificate expiry ranges to allow for logging of all currently valid publicly-trusted certificates.

The primary purpose of the permissible rejection criteria is to provide Log Operators with greater control over the growth and operation of a given Log instance while still performing the core functions of a trusted CT Log. Additionally, these criteria allow logs to be shielded from certain types of Denial of Service such as being spammed with the corpus of all expired certificates and being unable to respond to legitimate logging requests.

Policy Violations

The Chromium developers include Logs at their sole discretion, to further public auditability of Certificate Authorities. Upon learning of a Log’s potential violation of this Policy, the Chromium Authors will review the information and may take corrective actions to preserve the integrity of its Log program. The Chromium Authors may remove Logs at any time, and for any reason.

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