I'm also getting this error. I invoked the client simply with "letsencrypt", having the nginx plugin installed, and selected multiple domains. Then I get this error:

2015-12-03 23:25:45,174:ERROR:letsencrypt_nginx.configurator:Nginx Restart Failed!

2015/12/03 23:25:45 [emerg] 25958#0: SSL_CTX_use_PrivateKey_file("/var/lib/letsencrypt/snakeoil/0016_key.pem") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)

And after that:

Correct zName not found for TLS SNI challenge.

For a single domain, it also works for me.

i've seen this issue on an ubuntu server with openssl 1.0.1f but moving the cert and key to a parabola server with openssl 1.0.2d worked correctly

but i got the same error on ubuntu wily with openssl 1.0.2d

I'm using Arch Linux, and have tried openssl 1.0.2d and 1.0.2e.

well it may be a nginx error since the same cert loaded+worked fine with dovecot, postfix and prosody

fails in debian jessie with libssl 1.0.1k and both nginx 1.6 from debian and nginx 1.8 from phusion passenger...

@jsha these are not the snakeoil certs, could you edit the title?

@fauno: Could you explain more? You mean the problem is using a snakeoil key with a non-snakeoil cert?

Jacob Hoffman-Andrews notifications@github.com writes:

@fauno: Could you explain more? You mean the problem is using a
snakeoil key with a non-snakeoil cert?

you reported the issue for the snakeoil certs, but i'm having the same
error with the production certs.

have you solved it?

:>

Ah, now I get it. The issue is not regarding the staging certs ("happy hacker fake CA"), but regarding the self-signed (snakeoil) certs that the letsencrypt client creates locally to solve the TLS-SNI challenge.

the error i see is with the live certs:

nginx: [emerg] SSL_CTX_use_PrivateKey_file("/etc/letsencrypt/live/domain.com/privkey.pem") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)

http://librevpn.org.ar

That's a different problem, probably related to the configuration of your Nginx. Please post about it on https://community.letsencrypt.org/, including the relevant sections of your Nginx configuration.

done: https://community.letsencrypt.org/t/key-values-mismatch-error-using-live-certs-on-nginx/7029