[openssl-users] SSL_get_peer_certificate returns NULL in client_cert_cb after upgrade to openssl 1.1.1

[Matt Caswell]

I opened this issue to track this problem:

https://github.com/openssl/openssl/issues/7384

Matt


On 11/10/18 10:25, Matt Caswell wrote:
> 
> 
> On 10/10/18 23:04, Dave Wang wrote:
>> Hi there,
>>
>> I have a client can talk with server, where the client certificate is
>> loaded in client_cert_cb  based on matching the server side certificate.
>>
>> it works perfectly in openssl 1.1.0h, however it stops working after I
>> upgrade to openssl 1.1.1.
>>
>> In client_cert_cb , when I call SSL_get_peer_certificate, it returns
>> NULL, which is different from openssl 1.1.0h.
>>
>> I do set SSL_VERIFY_PEER on both sides. 
>>
>>
>> any thoughts on this?
> 
> I assume this only happens with a TLSv1.3 handshake?
> 
> From the documentation, the client_cert_cb is called: "when a client
> certificate is requested by a server". In practice this means when we
> have received the CertificateRequest message from the server.
> 
> In TLSv1.2 (and below) the server's first flight of messages for a
> client-auth full handshake in response to a ClientHello looks like this:
> 
> ServerHello
> Certificate
> ServerKeyExchange
> CertificateRequest
> ServerHelloDone
> 
> In TLSv1.3 it looks like this:
> 
> ServerHello
> EncryptedExtensions
> CertificateRequest
> Certificate
> CertificateVerify
> Finished
> 
> Note that in TLSv1.2 the CertificateRequest message comes *after* the
> server has sent the Certificate but in TLSv1.3 it comes *before*. That
> means of course that in TLSv1.3 the client_cert_cb gets called before we
> have processed the server's certificate and hence
> SSL_get_peer_certificate() returns NULL.
> 
> I'm wondering whether we should delay calling the client_cert_cb in
> TLSv1.3 until after the CertificateVerify has been processed.
> 
> Matt
>