TLS certificates for NFS-over-TLS floating client
rmacklem at uoguelph.ca
Thu Mar 19 02:09:14 UTC 2020
Miroslav Lachman wrote:
>Hiroki Sato wrote on 2020/03/04 05:35:
>> I do not think it is a good idea to use a certificate with an
>> embedded secret for authentication and/or authorization.
>> In the case that the client offers a certificate upon establishing a
>> TLS connection for authentication purpose, the authenticity will be
>> checked on the server usually by using the CA certificate which was
>> used to issue the client certificate. The CA cert must be put to
>> somewhere the NFS server can read.
>> The CA cert is secret. So if the NFS server can check the client
>> certificate by the CA certificate, it means the NFS server can
>> trust the client. I think no additional information is required.
>NFS (or any other server) should check list of revoked certificates too.
>Otherwise you will not be able to deny access to user which you no
>longer want to have an access.
Yes, good point.
I won't claim to understand this stuff, but from what I can see, all that is
done is the CRL is appended to the CAfile (the one with the CA certificates
are in being used for certificate verification via SSL__CTX_load_verify_locations().
shows a CAfile and CRLfile being concatenated and then used to verify a certificate.)
There is code in sendmail that loads a CRL file separately, but it seems to
just put it in the X509 store returned by SSL_CTX_get_cert_store(), which
is the one where the CAfile certificates are stored via SSL_CTX_load_verify_locations(),
(It just seems easier to append it to CAfile than do this. The sendmail code uses
poorly documented functions where the man page says
"SSL_CTX_load_verify_locations()" normally takes care of this.)
Does this sound right? rick
> Authorization such as which mount point can be mounted by using the
> client cert can be implemented by using the CN field or other X.509
> attributes, of course. It can be just a clear text.
> I think this is one of the most reliable and straightforward ways
> because in most cases both NFS servers and the clients are under the
> sysadmin's control.
> rm> Now, I'm not sure, but I don't think this certificate can be created via
> rm> a trust authority such that it would "verify". However, the server can
> rm> look for the "secret" in the certificate and allow the mount based on that.
> In the way described above, to use TLS client authentication, the NFS
> server admin has to have a certificate which allows to sign another
> certificate. This means that the admin must be a CA or trusted
> In practice, one can generate a self-signed certificate by using
> openssl(1) and use it as its CA certificate. He can issue
> certificates signed by it for the NFS clients, and put his CA
> certificate to somewhere the NFS server can read.
Take a look on easy-rsa
It is used for example by OpenVPN to create private CA and sign
certificates of clients. It is good starting point to understand what
and how can work.
> rm> Also, even if the NFS client/server have fixed IP addresses with well known
> rm> DNS names, it isn't obvious to me how signed certificates can be acquired
> rm> for them?
> rm> (Lets Encrypt expects the Acme protocol to work and that seems to be
> rm> web site/http specific?)
> TLS certificates do not always have (or do not need to have) a domain
> name as an attribute. Data in attributes are restricted depending on
> the purpose, so certificates issued by Let's Encrypt can have only
> domain names (CN or Subject Alternative Name), for example. An
> example which is not supported by Let's Encrypt is a certificate for
> S/MIME email encryption which has an email address.
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