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AddTrust External CA Root expiring on May 30, 2020 – what you need to know

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Sectigo at present offers the ability to cross-sign certificates with the AddTrust legacy root to increase support among very old systems and devices. This root is due to expire at the end of May, 2020. Any applications or installations that depend on this cross-signed root must be updated by May, 2020 or run the risk of outage or displayed error message. For the vast majority of use cases Sectigo’s standard root supplies the full required client support. For unusual cases, Sectigo offers a new cross signing option with its AAA root, which will does not expire until 2038.

Read this article for a full explanation of cross signing, the AddTrust root expiration, and potential alternatives beyond that expiration date.

What Is a Root Certificate?

Root certificates are self-signed certificates. This means the “Issuer” and ”Subject” are the same. A root certificate becomes a trusted root certificate (or trusted CA, or trust anchor) by virtue of being included by default in the trust store of a piece of software such as a browser or OS. These trust stores are updated by the browser software or OS frequently, often as part of security updates, but on older outdated platforms they were often updated only as part of a full software update – such as Windows Service Packs or optional Windows Update releases.

Certificates for your site are issued from a “chain” of issuing or “intermediate” CA that completes a path back to these trusted root certificates.

It is important to note that security updates are of paramount importance today. There may be devices which do not have updates to include modern roots – but as a consequence also do not support standards required by the modern internet. A good example is Android. While Android 2.3 Gingerbread does not have the modern roots installed and relies on AddTrust, it also does not support TLS 1.2 or 1.3, and is unsupported and labelled obsolete by the vendor. For more information view this article: Sectigo Chain Hierarchy and Intermediate Roots

What Is Cross-Signing?

 CAs often control multiple root certificates, and generally the older the root the more widely distributed it is on older platforms. In order to take advantage of this fact, CAs generate cross certificates to ensure that their certificates are as widely supported as possible. A cross certificate is where one root certificate is used to sign another.

The cross certificate uses the same public key and Subject as the root being signed.


Subject: COMODO RSA Certification Authority
Issuer: AddTrust External CA Root

Uses the same Subject and public key as the self-signed COMODO root certificate.

Browsers and clients will chain back to the “best” root certificate they trust.

AddTrust External CA Expiration

Sectigo controls a root certificate called the AddTrust External CA Root, which has been used to create cross-certificates to Sectigo’s modern root certificates, the COMODO RSA Certification Authority and USERTrust RSA Certification Authority (as well as the ECC versions of those roots). These roots don’t expire until 2038.

However, the AddTrust External CA Root expires on May 30th 2020. After this date, clients and browsers will chain back to the modern roots that the older AddTrust was used to cross sign. No errors will be displayed on any updated, newer device or platform which has had updates

Chain Diagram













A legacy browser or older device that does not have the modern “USERTRust” root would not trust it and so would look further up the chain to a root it does trust, the AddTrust External CA Root. A more modern browser would have the USERTrust root already installed and trust itwithout needing to rely on the older AddTrust root.

What You Need to Do

For most use cases, including certificates serving modern client or server systems, no action is required, whether or not you have issued certificates cross-chained to the AddTrust root.

For business processes that depend on very old systems, Sectigo has made available a new legacy root for cross-signing, the “AAA Certificate Services” root. However, please use extreme caution about any process that depends on very old legacy systems. Systems that have not received the updates necessary to support newer roots such as Sectigo’s COMODO root will inevitably be missing other essential security updates and should be considered insecure. If you would still like to cross-sign to the AAA Certificate Services root, please contact Sectigo directly.

FAQs to Root Certificates

Will my certificate still be trusted after May 30, 2020?

Yes. All modern clients and operating systems have the newer, modern COMODO and USERTrust roots which don’t expire until 2038.

On platforms where the trust stores have been artificially limited or cannot be updated (embedded devices, for example), you will need to update and install the newer Sectigo roots. Please ensure these devices also have the necessary security updates from the vendor.

Do I need to reissue or reinstall my certificate?

No. Your certificate will remain trusted until it’s natural expiry date and does not need reissuance or reinstallation. You can choose to stop installing the cross-certificate on your servers if you wish. Should you need legacy compatibility after the AddTrust expiry we have a replacement cross-certificate that you can install on your servers in place of the AddTrust cross-certificate. See below for more details.

Can I test or check that I won’t see any errors?

Yes. If you have a certificate valid into June 2020 and beyond, you can set the clock on your system forward to June 1st 2020, and test the site. Modern browsers will display no errors, and you can see that the certificate chains back to the COMODO or USERTrust root. (Note: some browsers such as Google Chrome, will detect that your clock is “wrong” and show a warning unrelated to the certificates as a result.)

Here is a test site you can use to evaluate your environment:

These links provide a valid certificate issued from specific chains. They can be used to test what clients support which roots. You can also adjust your system clock into June 2020 to see how clients function after the expiry of the AddTrust root and cross-certificates.

USERTrust RSA Certification Authority – (USERTrust ECC Certification Authority –

COMODO RSA Certification Authority – (COMODO ECC Certification Authority –


These roots were added to the following platforms since:


  • macOS Sierra 10.12.1 Public Beta 2
  • iOS 10


  • Windows XP (via Automatic Root Update; note that ECC wasn’t supported by Windows until Vista)
  • Windows Phone 7


  • Firefox 3.0.4 (COMODO ECC Certification Authority)
  • Firefox 36 (the other 3 roots)


  • Android 2.3 (COMODO ECC Certification Authority)
  • Android 5.1 (the other 3 roots)


  • Java JRE 8u51


  • [Browser release on December 2012]

360 Browser:

  • SE 10.1.1550.0 and Extreme browser 11.0.2031.0

The cross-certificates with AAA Certificate Services provide compatibility to older versions:

  • Apple iOS 3.
  • Apple macOS 4.
  • Google Android 2.3.
  • Mozilla Firefox 1.
  • Oracle Java JRE 1.5.0_08.
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