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EDIT: I have edited my question to not only consider SHA-1 deprecation, but more general the direct signing of subscriber certificates from root.

In case a legacy system still uses a setup whereby a self-signed, internal root CA directly issues server certificates, will these certificates still be accepted by end-user's browsers (e.g. employees)?

I am thinking about the impact of:

  • SHA-1 deprecation: if I have the SHA-1 root directly issue SHA-256 subscriber certs, is this allowed? I know that the signature on the root is not used, but directly issuing certificates from roots might be considered an illegal set-up.
  • Other measures that are taken by browsers: for example the document I was linked to by CryptoGuy mentioned "CAs MUST NOT issue Subscriber Certificates directly from Root CAs."

Please also provide links to credible sources, if available.

  • This is about an internal root CA that you install in all the browsers you use, correct? – Josef Jul 26 '16 at 14:58
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  • @Josef, I am particularly interested in the case where certificates are signed directly from the root. Although I can imagine that it does not matter whether or not you use an intermediate cert, I want to be sure. That question does not explicitly mention that. However, it's similar indeed. And yes, it's about an internal root CA. – Michael Jul 26 '16 at 15:04
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    @Josef, modified my question to focus more on the fact that it is about certs that are issued directly from root. – Michael Jul 26 '16 at 15:19
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Yes, your scenario is acceptable when CA itself has SHA1 certificate, while signing issued certificates with SHA2.

Refernces:

Internet PKI: CA Browser Forum (CAB Forum) baseline requirements, §6.1.5

Microsoft: Windows Enforcement of Authenticode Code Signing and Timestamping

Google: An update on SHA-1 certificates in Chrome

All these references from major vendors include explicit information that SHA1 root is acceptable, while non-root certificates MUST be SHA2.

Edit to reflect your second question.

CAB Forum requirements are designed for their members (public CAs). Although, it is not recommended practice to issue end entity certificates directly by root CA, it is acceptable from browser perspective. In fact, most badly designed private PKIs consist of single Enterprise Root CA which issues certificates to end entities. Although, it is completely acceptable, it is insecure.

Instead, I would recommend to implement a 2-tier PKI with offline (offline here should be treated literally. It MUST NOT be connected to any network) Root and online Subordinate Issuing CA which will issue certificate to end entities.

  • You say yes, but in the document you reference I read "CAs MUST NOT issue Subscriber Certificates directly from Root CAs."... Although this has nothing to do with SHA-1 / SHA-256, it seems this kind of certificates will not be accepted? – Michael Jul 26 '16 at 15:09
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    It is requirement for CAB Forum members only. Private CAs SHOULD follow these guidelines, but are not obligated. No browser will complain about SSL certificate issued directly by root. – Crypt32 Jul 26 '16 at 15:19

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