USERTrust RSA Certification Authority: the root, its cross-certificate and how to recognise it

USERTrust RSA Certification Authority is a root certificate run by Sectigo. Its subject and its issuer are the same name, so the certificate is self-issued, and Sectigo publishes the file for download. If an SSL certificate fails with a trust error and the chain ends at this name, this page tells you which of two certificates you are looking at. For roots in general, see what a root certificate is.

Name

USERTrust RSA Certification Authority, one of the four modern roots Sectigo lists

Operator

Sectigo, as owner in Mozilla's CA report

Key and signature

RSA with 4096 bits, signed with SHA-384

Serial number

01FD6D30FCA3CA51A81BBC640E35032D

Sibling root

USERTrust ECC Certification Authority, a separate root with an ECC key

Cross-certificate

signed by AAA Certificate Services, an older Sectigo root

Trust

decided by each trust store, not by this page

How to recognise the root

Two published sources describe the same root: the file on Sectigo's site and Mozilla's report of included CA certificates. The subject reads C=US, ST=New Jersey, L=Jersey City, O=The USERTRUST Network, CN=USERTrust RSA Certification Authority. The issuer line is identical: the certificate names itself as its issuer.

The ECC root sits next to it under the same organization, with its own key and serial number; the common name tells them apart.

Compare the SHA-256 fingerprint: Mozilla's report lists it without colons, openssl prints the same bytes with colons.

Two certificates carry this name

Sectigo says each of its four modern roots is cross-signed by an older Sectigo root, AAA Certificate Services. Sectigo describes a cross-certificate as built with the same public key and the same Subject Distinguished Name as the root being signed. So the name appears on two certificates: the root, issued by itself, and the cross-certificate, issued by AAA Certificate Services.

Sectigo publishes both as separate files. The root is USERTrustRSACertificationAuthority.crt; the cross-certificate is USERTrustRSAAAACA.crt. The reason for the second file, in Sectigo's words, is that it extends trust to legacy versions of software, and its list includes iOS 3, macOS 10.4, Android 2.3, Firefox 1 and Java JRE 1.5.0_08.

A name alone does not say which of the two you have; the issuer line does.

Check a file you hold

1. Print the names: openssl x509 -in root.crt -inform DER -noout -subject -issuer. Drop -inform DER if the file is PEM text.

2. Read the issuer of a certificate whose subject is USERTrust RSA Certification Authority. The same name means the self-issued root. AAA Certificate Services means the cross-certificate.

3. Print the fingerprint: openssl x509 -in root.crt -inform DER -noout -sha256 -fingerprint. The OpenSSL manual says -fingerprint hashes the whole DER-encoded certificate and that SHA-1 is used unless you name another digest, so the -sha256 matters. For the root, the output must equal the first row of the fingerprint table.

A match shows the file is the certificate Sectigo and Mozilla's report describe. It does not show that a given client trusts it; the trust store of that client decides. More checks on a live server are in OpenSSL commands to check a certificate.

Where the chain meets it

Sectigo's intermediate-certificates article says all its subscriber certificates are issued by an intermediate certificate. It adds that Sectigo sends the intermediates together with the subscriber certificate and recommends installing the intermediate on the server. The same article lists USERTrust RSA Certification Authority as a "SHA-2 Root" under its root certificates.

It also recommends importing one more cross-signed certificate into the chain, named "Sectigo Public Server Authentication Root R46 x USERTrust RSA CA", and offers it under "Cross Signed Root Certificates". The certificate chain guide shows how the pieces fit together.

Sectigo is one certificate authority among many; what such an authority does is set out on the certificate authority page.

Looking for a certificate for your own site? For CAs that issue certificates at no charge, see free public certificate authorities.

Where Sectigo says its roots were added

Sectigo, the certificate authority that runs this root, lists in its root certificates article the platforms its modern roots were added to. The table gives the entries that cover the RSA root; Firefox and Android are marked there as covering the three modern roots other than the one added in an earlier version. Which roots a product's trust store holds is that vendor's decision, not this page's.

This is Sectigo's own account of its root certificate, not a statement about any client's current behaviour.

Sources

1. Sectigo, Sectigo Root Certificates (knowledge base article).

2. Sectigo, SHA-2 Sectigo Intermediate Certificates - RSA (knowledge base article).

3. Mozilla CCADB, Included CA Certificate Report (CSV).

4. OpenSSL 3.0 manual page openssl-x509(1).

5. Our run: openssl x509 on the root file that Sectigo publishes; subject, issuer and fingerprint matched the report.