Re: using TLS (>1.2) with more than one certificate

[Dirk-Willem van Gulik <dirkx@xxxxxxxxxxxxxx>]

On 25 May 2022, at 09:16, <Tobias.Wolf@xxxxxxxxxxxxx> <Tobias.Wolf@xxxxxxxxxxxxx> wrote:

I’ve a server application and need to support RSA and ECC clients at the same time.
I don’t know which certificate from my local keystore I have to send to the client, btw I have a rsa and a ecc certificate in my keystore already.
I don’t know with which certificate (rsa or ecc) a client comes during handshake of a tls connection.
How can this technically work?

On a protocol layer - have a look at the Client Hello which the client sent to the server prior to selection:

Have a look at ;

https://tls12.ulfheim.net. / The Illustrated TLS 1.2 Connection

To understand this. On coding level; in openssl - most of this `should’ simply work if you’ve set up OpenSSL correctly. The code behind s_server is a good start. Other good resources are

https://www.feistyduck.com/library/openssl-cookbook/online/

Dw.