Postfix cannot get RSA private key from file /etc/ssl/private/server.key: disabling TLS support

Question

I installed a postfix mail server. But it is wrong when I use thunderbird to login a user. This is configuration.

Postconf -n:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
broken_sasl_auth_clients = yes
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
debug_peer_level = 2
home_mailbox = Maildir/
html_directory = no
inet_interfaces = all
inet_protocols = all
mail_owner = postfix
mailbox_size_limit = 20000000000
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
message_size_limit = 200000000
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mydomain = stack.daolicloud.com
myhostname = mail.stack.daolicloud.com
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
myorigin = $mydomain
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.6.6/README_FILES
relay_domains = $mydestination
relayhost =
sample_directory = /usr/share/doc/postfix-2.6.6/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtp_tls_note_starttls_offer = yes
smtpd_helo_required = yes
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
smtpd_sasl_auth_enable = yes
smtpd_sasl_authenticated_header = yes
smtpd_sasl_local_domain = $myhostname
smtpd_sasl_path = private/auth
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_sender_restrictions = reject_unknown_sender_domain
smtpd_tls_CAfile = /etc/ssl/certs/cacert.pem
smtpd_tls_auth_only = no
smtpd_tls_cert_file = /etc/ssl/certs/cacert.pem
smtpd_tls_key_file = /etc/ssl/private/server.key
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
smtpd_use_tls = yes
tls_random_source = dev:/dev/urandom
unknown_local_recipient_reject_code = 550

dovecot -n:

# 2.0.9: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-431.1.2.0.1.el6.x86_64 x86_64 CentOS release 6.4 (Final) 
auth_mechanisms = plain login
mail_location = maildir:~/Maildir
mail_privileged_group = mail
mbox_write_locks = fcntl
passdb {
  driver = pam
}
protocols = imap pop3
service auth {
  unix_listener /var/spool/postfix/private/auth {
    mode = 0666
    user = postfix
  }
}
service imap-login {
  inet_listener imap {
    port = 143
    ssl = yes
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}
ssl_cert = </etc/ssl/certs/cacert.pem
ssl_key = </etc/ssl/private/server.key
userdb {
  driver = passwd
}

And this is log:

 dovecot: imap-login: Fatal: Can't load private ssl_key: Key is for a different cert than ssl_cert
dovecot: master: Error: service(imap-login): command startup failed, throttling
dovecot: pop3-login: Fatal: Can't load private ssl_key: Key is for a different cert than ssl_cert
dovecot: master: Error: service(pop3-login): command startup failed, throttling
postfix/smtpd[13891]: warning: cannot get RSA private key from file /etc/ssl/private/server.key: disabling TLS support
postfix/smtpd[13891]: warning: TLS library problem: 13891:error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch:x509_cmp.c:331:
postfix/smtpd[13893]: warning: cannot get RSA private key from file /etc/ssl/private/server.key: disabling TLS support
postfix/smtpd[13893]: warning: TLS library problem: 13893:error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch:x509_cmp.c:331:
postfix/smtpd[13894]: warning: cannot get RSA private key from file /etc/ssl/private/server.key: disabling TLS support
postfix/smtpd[13894]: warning: TLS library problem: 13894:error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch:x509_cmp.c:331:
postfix/smtpd[13895]: warning: cannot get RSA private key from file /etc/ssl/private/server.key: disabling TLS support
postfix/smtpd[13895]: warning: TLS library problem: 13895:error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch:x509_cmp.c:331:

I think the pem and key file were wrong. So I generate this files again followed by this link. But it still goes the same error. Any ideas? Could someone helps me? Thanks a lot!

Answer 1

In order to check if the cert and key match use this,

(openssl x509 -noout -modulus -in /etc/ssl/certs/cacert.pem | openssl md5 ;\
openssl rsa -noout -modulus -in /etc/ssl/private/server.key | openssl md5) | uniq

If you get more than one identifier, then you key and cert don't match.

Just create a new one;

openssl req -new -x509 -days 3650 -nodes -out /etc/ssl/certs/cacert.pem -keyout /etc/ssl/private/server.key

Cheers!

Answer 2

Building on @Ark74's answer from someone's blog, on ubuntu the check command for the snakeoil certificate is:

(openssl x509 -noout -modulus -in /etc/ssl/certs/ssl-cert-snakeoil.pem | openssl md5 ; openssl rsa -noout -modulus -in /etc/ssl/private/ssl-cert-snakeoil.key | openssl md5) | uniq

If you get two hashes, then the certificate needs to be regenrated:

make-ssl-cert generate-default-snakeoil --force-overwrite

Answer 3

For anyone seeing this error on Centos 8, Postfix 3.3.1 running SELinux I tried all the above and I knew my certs and chains were correct as apache was loading them correctly.

I was seeing the following error under the original error:

warning: TLS library problem: error:0200100D:system library:fopen:Permission denied

Turns out that the certs must be in the:

/etc/ssl/certs

directory - even though I had the right chcon on them. Thought this might help anyone else as it was very frustrating. I'm not sure why Postfix couldn't load them from the httpd directory.