Can an offline root CA be used for more than one domain

Hello Experts,

Our organization has two separate Active Directory domains (separate forests):
1.      company.local
2.      youthed.local

We have recently implemented a PKI infrastructure using AD CS.  The infrastructure consists of an offline CA (named Company-RootCA).  This CA is not part of any domain or forest.  We have an intermediate CA in the company.local domain that is issuing certificates as expected in that domain.  We would like to implement a PKI solution in the youthed.local domain.  Can my offline CA be the root CA for both the company.local intermediate CA and a youthed.local intermediate CA?

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Jose Gabriel Ortega CastroCEOCommented:
I don't think so since they're different forest, so the forestA doesn't trust the forestB.

What you could try in this to make it possible is to do the testing after creating a full domain trust relationship.
David Johnson, CD, MVPOwnerCommented:
offline root ca I'd say no, online root CA yes on the root CA you  need a webserver to handle the crl and odsp duties. as you may want at sometime to revoke an issuing CA's Cert even if you don't you need some way of accessing it from anything that wants to check the certificate chain.

root CA's are generally not domain joined. be careful when you set the crl/odsp locations when you setup the root CA

normally when one sets a pki with root and issuing CA's on the root ca's crl/odsp you put in a web location that is part of the issuing CA's domain.  BTW, having issued certs, and revocation lists available on the WWW is not a security hole since none of these expose the private keys.

To set things up correctly I'd suggest hiring a PKI professional like Brian Komar (

You should also register your OID's and create your capolicy.inf's before installing the Certificate Authority.  You may be asked in the future by a PKI auditor about your policies and be able to prove to them that you actually are auditing what you say you are in the capolicy.inf.

Large companies commonly trust other companies CA's but may only trust a specific issuing CA

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