[Ovmsdev] TLS CA question

Mark Webb-Johnson mark at webb-johnson.net
Thu Mar 4 10:38:45 HKT 2021


A thorny issue. Servers are _supposed_ to provide intermediate certificates, up to a trusted root. When you are issued a certificate, it includes a bundle of these intermediary certificates to be installed at the same time.  In practice, servers are often mis-configured so they do not. This is made worse by browsers silently detecting this, then downloading the missing intermediate certificates (the child certificate contains a URL to its parent’s cert).

For Open Vehicles, I don’t think we need to deal with this, and we certainly don’t need the complexity of automatically downloading intermediate certificates. I think if the user wants to access a server misconfigured in that way, he can simply import and trust the intermediate certificate directly.

I don’t think we should set WOLFSSL_ALT_CERT_CHAIN.

Regarding your question, in normal operation OVMS as a client must validate the server certificates it connect to. I don’t think OVMS currently supports client certificates, although if it did we would have to correctly provide those to the server on connection.

Regards, Mark.

> On 4 Mar 2021, at 9:00 AM, Stephen Casner <casner at acm.org> wrote:
> I find that I need to enable the following option in my testing of the
> possible replacement of MEDTLS with WolfSSL, otherwise I get an "ASN
> no signer to confirm" error:
>    WOLFSSL_ALT_CERT_CHAIN allows CA's to be presented by peer, but
>    not part of a valid chain. Default wolfSSL behavior is to require
>    validation of all presented peer certificates. This also allows
>    loading intermediate CA's as trusted and ignoring no signer
>    failures for CA's up the chain to root. The alternate certificate
>    chain mode only requires that the peer certificate validate to a
>    trusted CA.
> Is that expected for the trust arrangements we are using?
> A possibly related question: do we expect the server to validate
> clients, or only the clients to validate the server?
>                                                        -- Steve
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