Problem

Trying to configure and use an nginx server that uses intermediate certifcates, you get the error about values mismatch and nginx does not start

2020/09/23 09:49:38 [emerg] 20958#20958: SSL_CTX_use_PrivateKey("/etc/ssl/private/cakey.pem") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)

Solution

It seems that this is a common mistake and it is mentioned here: https://nginx.org/en/docs/http/configuring_https_servers.html. In order to fix this you will need to change/reverse the original order that you have concatenated the chain, as in:

cat certs/cacert.pem intermediate/certs/intermediate.cacert.pem > intermediate/certs/ca-chain-bundle.cert_new.pem