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The PKI RFC talks about revoking or suspending certificates. It also talks about revoking CA certs. However, I could not find anything about whether a CA or a Sub CA's certificates can be revoked or not in the RFC.

What is common practice. If a CA feels that a subCA is compromised, they may want to suspend the certificate till the time, they confirm that this is true.

Do any of the Commercial Certificate issuing Software allow this?

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This may see like a cop-out answer but it is not if you stay with me. PKI is just as much about the paperwork (policies and procedures) than it is about technical constraints. So if you have defined in your Certificate Practice Statement that your organization can and will suspend CA certificates as part of normal operations, then yes I do believe that the major CA software packages do maintain facilities for doing just that.

I would question if this is something that you would really want to do. If I saw that in your CPS, I would be slightly less likely to want to bridge with you, depending on the situation. If you think that a CA has been compromised, it is hard to make an argument against revocation and reissue. Especially if you have a 3-tier architecture and have isolated CAs by policy types in tier 2.

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If a Commercial CA believe they are compromised they will revoke the sub-CAs that they believe are affected. This does not mean that all software that trusts that CA will automatically distrust the compromised CA.

Browsers for example should check a certificate revocation list (CRL) before trusting a certificate chain. However, these checks are notoriously done incorrectly or don't exist at all. They do however generally update their trusted certificates store with an update to the browser. Other commercial software that trusts a certificate that is compromised must update their trusted stores as well. It's up to the software to keep up with known compromises of certificates and certificate authorities.

I'm not entirely sure what you mean by "Commercial Certificate Issuing software". But I'm sure that CAs like Symantec (Verisign), Comodo, and Go Daddy all provide some mechanism for revoking their certificates. However, it is up to the software that trusts the certificate to make sure that those certificate revocations get implemented in some way. Either by using up-to-date CRLs, or by providing updates to the software to remove un-trusted certificates.

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CA or a Sub CA

Anything apart from a Root CA may in principle be revoked using the regular ways. (CRL and/or OCSP)

[...] they may want to suspend the certificate till the time, they confirm that this is true.

Technically you should be able to do this by using reason code "certificateHold (6)" on your CRL. This is a temporary revocation and may be undone. BUT: I can't tell you if any clients implement this correctly. (But I wouldn't be too optimistic.)

Do any of the Commercial Certificate issuing Software allow this?

Sorry. No idea. Try to find out if your CRL allows you to give a reason code at all.

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If you think a downstream (subordinate) CA is compromised, you have a duty in your position of trust to revoke the suspected compromised CA to prevent them from eroding trust in you, the parent CA.

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