What do I have to change so Google Chrome won't say that I am using an obsolete key exchange?

Obsolete Connection Settings

The connection to this site uses a strong protocol (TLS 1.2), an obsolete key exchange (RSA), and a stronc cipher (AES_128_GCM).

I am using Apache 2.4.18 and OpenSSL 1.0.2g. These are my settings:

SSLOpenSSLConfCmd DHParameters    /etc/ssl/certs/dhparam.pem
SSLOpenSSLConfCmd ECDHParameters  Automatic
SSLOpenSSLConfCmd Curves          secp521r1:secp384r1:prime256v1
SSLProtocol                       all -SSLv3 -TLSv1 -TLSv1.1 
SSLHonorCipherOrder               on  
SSLCompression                    off 
SSLSessionTickets                 off
SSLUseStapling                    on 
SSLStaplingResponderTimeout       5 
SSLStaplingReturnResponderErrors  off
SSLStaplingCache                  shmcb:/var/run/ocsp(128000)

These are the recommended modern settings from the Mozilla ssl-config-generator. Any ideas?

  • 1
    The config you show (only ECDHE key exchange) does not match the message (RSA key exchange). My guess is that the configuration you show is not the one which is in effect, maybe because you've failed to restart, have a different SSL configuration in some other config files or have a reverse proxy in front with different configuration. – Steffen Ullrich Dec 18 '16 at 12:41
  • Firefox is using the correct key exchange. So maybe I'll need to reset something in Google Chrome?? – EasyPeasy Dec 18 '16 at 14:32
  • How do you know that Firefox is using the expected key exchange? And no, there is nothing to reset in Chrome: which key exchange is used is determined by the ciphers suite which is ultimately chosen by the server. You might check your site agains SSLLabs for more information which configuration is seen from the internet and which cipher will be used with different browsers. – Steffen Ullrich Dec 18 '16 at 15:32
  • FYI OpenSSL 1.0.2 (and earlier) does not support CHACHA-POLY, only 1.1.0 does. However OpenSSL ignores unsupported items in a cipherlist with others, so setting it now does no harm and may save you a few seconds later. – dave_thompson_085 Dec 19 '16 at 3:13
  • 1
    @EasyPeasy: check the certificate you get, i.e. the full chain. There might be an SSL interception going on, for example by a local AV or by a corporate firewall. In this case you will see differences in the certificate (fingerprint does not match original fingerprint), in the chain and there might also be differences in TLS protocol and cipher since the connection from the browser is not to the original server but to some MITM with different TLS settings. – Steffen Ullrich Dec 19 '16 at 14:05

As Steffen Ullrich mentions in the comments, Google Chrome or Chromium basically lets you know there is no ECDHE ciphersuite used. This is no problem per se, but if you can permit it, use an EC key exchange.

The config you post is correct to the level that it will generate a certificate based on Elliptic Curves. However it seems like Apache is serving an RSA certificate.

  • Do you know what the problem could be? Firefox is using the correct key exchange – EasyPeasy Dec 18 '16 at 14:43
  • @EasyPeasy Firefox cannot use an ECDHE key exchange while Apache is doing an RSA. We have no info here so we can only guess. Try using OpenSSL s_client. – Yorick de Wid Dec 18 '16 at 14:50
  • OpenSSL s_client --> OpenSSL s_client: SSL-Session: Protocol : TLSv1.2 Cipher : ECDHE-RSA-AES256-GCM-SHA384 – EasyPeasy Dec 18 '16 at 15:03
  • @EasyPeasy oke, so the Kex is ECDHE, but the certificate was generated with an RSA keypair. You should generate a EC keypair (ecparam) then convert the CSR into a CRT via the CA and you're good to go with an ECDSA. – Yorick de Wid Dec 18 '16 at 15:05
  • 1
    @YorickdeWid: of course it is possible to combine ECDHE key exchange with RSA certificates. In fact this is probably the most common configuration for all sites which use PFS since ECDSA certificates are not that universally supported yet. While you need RSA certificate for RSA key exchange you can have ECDHE and DHE key exchanges with both RSA and ECDSA certificates. – Steffen Ullrich Dec 18 '16 at 15:31

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