CSR with only public key

Kyle Hamilton aerowolf at gmail.com
Thu Sep 12 13:25:24 UTC 2019

If a CA signs a certificate without proof of possession of the private key,
the CA is enabling whoever does have that private key to look as though
they are the one who they sign the certificate for (i.e., impersonation).
The entire structure of PKI (the binding of the public half of a keypair to
some external identity) depends on this not happening.

More importantly, in the situation where the person submitting the unsigned
request can't prove possession, they know it is a situation where either
the private key is lost (and the certificate would be useless anyway) or
that impersonation is simply guaranteed.

There might be a scenario desired where the generation of the CSR isn't
done by the holder of the private key internal to a company (perhaps
because the holder of the private key is otherwise extremely busy), but
because there's no way to tell if that limited scenario is different from
the other scenarios based on available evidence, publicly trusted CAs are
required (by rules of the CABF) to reject non-proof-of-possession scenarios

To answer your question, yes the error is because the request wasn't signed
with the private key.  As such, it's not a complete request, and doesn't
match the expected ASN.1 structure.

-Kyle H

On Thu, Sep 12, 2019, 02:47 Bharathi Prasad <barati.j.prasad at gmail.com>

> Hi,
> I have the public key of the client but not the private key. I am required
> to generate a CSR with only public key. I understand private key is
> required
> for Proof of Possession. However, as per my requirement I am supposed to
> create CSR only with public key and my CA would create a certificate.
> I was able to create a CSR with CX509CertificateRequestCertificate and
> CX509Enrollment classes using the available public key. When I try to read
> the contents the of CSR in openssl (i used this command: openssl req -in
> client.csr -noout -text) i get "unable to load X509 request".
> Is this happening because the CSR does not contain the signature of private
> key or the CSR is faulty.
> Kindly help me.
> Regards,
> Bharathi
> --
> Sent from: http://openssl.6102.n7.nabble.com/OpenSSL-User-f3.html
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