For the last few months, I have been using self signed certificates to provide ssl for a system that I have been building. We are now getting ready to start getting external users on the system, but this will require purchasing a certificate.

This system will be one of several others that will be running on a sub-domain, but may move to its own domain later on. There will also be several other secured systems running in a similar fashion.

We would also like to put our main site on ssl only too.

So, although I know I can use a wildcard certificate, could I purchase an ssl certificate for the main site, then create a signing request for the sub-domain, and sign it with the purchased certificate, and would that validate for visitors to the sub-domain?

  • I disagree that 18188 is a duplicate as it only talks about wildcards, but yes to 47267
    – topherg
    Commented Sep 29, 2014 at 11:16
  • You might want to read more than the first paragraph of 18188 before arguing that it is only about wildcards. Not only is the question similar to yours, also the answer is appropriate to your question. Just look at the all the other paragraphs of the response. Commented Sep 29, 2014 at 11:47
  • Apologies, speed reading took over. Started on wildcards, then moved to the Another Strategy section, and concluded non-relevance when the page didn't contain the word usage (but did extension)
    – topherg
    Commented Sep 29, 2014 at 13:54

1 Answer 1


No, the certificates you purchase for SSL are not valid for certificate signing. This is enacted via usage extensions.

It is possible to buy signing certificates which can be used for that purpose, but it is prohibitively expensive - the certificate authorities do not, after all, wish to put themselves out of business.

  • damn, thought it might be something along those lines. It would seem counter-intuitive from a business perspective to create such allowances :(
    – topherg
    Commented Sep 29, 2014 at 11:10
  • 1
    The genie's wish cannot be used to get more wishes.
    – gowenfawr
    Commented Sep 29, 2014 at 11:11

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